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CAudio SR808

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Category: General
Forum Name: Amp Forum
Forum Description: The 'Stopping Jake Fielder moaning constantly' forum description...
URL: https://forum.speakerplans.com/forum_posts.asp?TID=104745
Printed Date: 28 March 2024 at 9:53am
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Topic: CAudio SR808
Posted By: midas
Subject: CAudio SR808
Date Posted: 24 January 2020 at 6:42pm
So....After many years of wanting one, I had given up. Until yesterday, picked (sort of) one up today. To say it's a bit rough is an understatement, but hey ho. Looks like  its had more fingers inside than Katie Price.

The seller said one channel is quieter than the other, so need to get it to someone who will service it and replace parts as required. I intend to get this back up and fully working. 

One thing. Would anyone have a photo of the back of one please, I just want to compare. 


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In bass no one can hear you scream!



Replies:
Posted By: jbl_man
Date Posted: 24 January 2020 at 8:50pm
Funnily enough i saw that advertised on FB, £150 i think. The usual rust,but they all have that. Think he said the fans are worn out too? Noisy bearings he means? But they should be quite easy to replace. Odd one channel is working but quieter, would be interesting to see photos of the inside?


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Be seeing you.


Posted By: midas
Date Posted: 24 January 2020 at 9:52pm
I did some research and from about 2 years ago there was an 808 with the same symptoms, although the lad I bought this off said it started over the last few weeks. Someone has deffo been in and done some work as there is some pretty awful soldering going on. One of the slides on the back looked o be in the wrong position, who knows. 

I have drilled out all the screws that wouldnt come out with a screwdriver and replaced them. I realised as I was screwing the lid back on that someone had swapped the lid for the base. 

Time for a proper engineer to service it I paid a low price for it. So let's get it running properly so I can have confidence in it. 

I had to laugh when I picked it up. I had to waddle to the van with it...


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In bass no one can hear you scream!


Posted By: APC321
Date Posted: 24 January 2020 at 10:24pm
A wheel board is a lovely thing.


Posted By: njw
Date Posted: 25 January 2020 at 10:38am
 Wow, an 808, you don't see many of those! I loved my old Xr3801's, the 'like a tank' build quality, the sound quality and the power, they just never seemed to run out of steam. What I didn't like was having to put them all in separate racks just so I could  move them. Any chance of some pics? Smile


Posted By: midas
Date Posted: 25 January 2020 at 8:45pm
Well. That was dramatic. Thought I would just plug it in and test it at least goes through the stages of waking up. 

Turned on, hummed and went bang....Bit of smoke and the house stinks...lol.

Took the top off as much to make sure it was not going to burst into flames (after pulling the plug obviously) and it looks like the resistor on the soft start has exploded. 


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In bass no one can hear you scream!


Posted By: midas
Date Posted: 25 January 2020 at 9:23pm


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In bass no one can hear you scream!


Posted By: njw
Date Posted: 25 January 2020 at 9:23pm
Originally posted by midas midas wrote:

Well. That was dramatic. Thought I would just plug it in and test it at least goes through the stages of waking up. 

Turned on, hummed and went bang....Bit of smoke and the house stinks...lol.

Took the top off as much to make sure it was not going to burst into flames (after pulling the plug obviously) and it looks like the resistor on the soft start has exploded. 
 
 Ah bugger, from my experience of C Audios that either means the soft start relay is stuck or more likely (and unfortunately) blown output transistors. 

 Are you going to repair it or take it back for a refund?


Posted By: midas
Date Posted: 25 January 2020 at 9:25pm


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In bass no one can hear you scream!


Posted By: midas
Date Posted: 25 January 2020 at 9:27pm
I fully intend to get it back on its feet and reliable.

If you look at the Gold resistor one end is missing with a strand of wire poking out. I assume that has protected things further into the main body of the amp.

I need to get it to someone who knows how to work through and fix it.

NOW....you say blown output transistors, that would suggest the seller was telling the truth about going quiet on one channel.

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In bass no one can hear you scream!


Posted By: simonp1100
Date Posted: 26 January 2020 at 7:15pm
Things to check on the SR808 are as follows:

1. The soft start resistor is a 47R 50 Watt Aluminium clad resistor.
2. The soft start protection fuse should be a 1.6A Quick Blow (THIS IS THE ONLY FUSE YOU USE & NO OTHER TYPE), if it blows, there is a fault and replace with the same type.
3. Check the soft start & channel protection relays are o.k. and not stuck etc and change over O.K.
4. Each driver PCB check R14 & R50 (were 24K 1/2 Watt now changed to 27K 1 Watt).
5. Measure across D18 & D19 (Aux power supply to supply the TL071 op-amps) this should be 18 Volts.
6. Looking at your pictures, there seems to be some wire messing around by the XLR inputs, check this.
7. The output MOSFET's are normally bomb proof so a MOSFET blown is a rare (but not impossible). You could measure each MOSFET rail PCB between the Source & Drain and if low ohms (near short) would indicate a faulty MOSFET on that PCB rail. To isolate which MOSFET is faulty, just de-solder each Drain on every MOSFET on that row and then again measure each MOSFET and this should show you which one is faulty.
8. The bridge rectifiers may also be faulty and would need checking with a meter (diode check).

Please also be careful as there is high voltages around and the above MUST be done by a engineer or someone who knows about power amplifiers. Wink


Posted By: midas
Date Posted: 26 January 2020 at 11:57pm
Simon, thank you. Yes someone has been in there messing about by the looks of it. 

I do not intend to poke about any further. Happy to take the top off and have a look while keeping fingers out of the way, but but not willing to put said digits into electrical components. 


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In bass no one can hear you scream!


Posted By: kedwardsleisure
Date Posted: 26 January 2020 at 11:58pm
I think this should be in the vintage section....


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Kevin

North Staffordshire



Posted By: midas
Date Posted: 27 January 2020 at 12:00am
Kevin, I think it should be in your workshop...lol.

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In bass no one can hear you scream!


Posted By: kedwardsleisure
Date Posted: 27 January 2020 at 8:51am


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Kevin

North Staffordshire



Posted By: jbl_man
Date Posted: 09 February 2020 at 7:37pm
Any news on this overhaul yet Midas?

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Be seeing you.


Posted By: midas
Date Posted: 10 February 2020 at 5:51pm
No Ian, not yet. I was due to drop it off tomorrow, but not sure now with the weather as it is. 

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In bass no one can hear you scream!


Posted By: Xoc1
Date Posted: 10 February 2020 at 8:54pm
I used a a SR707 for years and it sits on the bench of shame at the moment having developed a small DC offset on one channel, big enough to put it into protection mode.
Schematics for the SR404 - 606 - 707 are easy to come by but I have never come across a schematic for the 808. Would anyone have the 808 schematics, or care to explain what the differences are to the 707?


Posted By: midas
Date Posted: 10 February 2020 at 9:08pm
The only obvious thing I can offer is the 808 has two power supplies, 4u and weighs a bloody tonne. 

To put it in perspective after shifting the 808, I could quite easily lift the 707 with one hand...lol. 


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In bass no one can hear you scream!


Posted By: jbl_man
Date Posted: 11 February 2020 at 9:16am
Originally posted by Xoc1 Xoc1 wrote:

Schematics for the SR404 - 606 - 707 are easy to come by but I have never come across a schematic for the 808. Would anyone have the 808 schematics, or care to explain what the differences are to the 707?


A quick visual look at an 808, there are 32 mosfets per channel, double the number in the 707....looking at the 120v smoothing capacitors,i assume it runs higher voltage rails too? But yes,a schematic would be good if anyone has one?


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Be seeing you.


Posted By: midas
Date Posted: 11 February 2020 at 3:48pm
Drop off to Kevin today, so will have a diagnosis when he has had a chance to look at it. 

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In bass no one can hear you scream!


Posted By: midas
Date Posted: 11 February 2020 at 3:52pm
Originally posted by jbl_man jbl_man wrote:

Originally posted by Xoc1 Xoc1 wrote:

Schematics for the SR404 - 606 - 707 are easy to come by but I have never come across a schematic for the 808. Would anyone have the 808 schematics, or care to explain what the differences are to the 707?


A quick visual look at an 808, there are 32 mosfets per channel, double the number in the 707....looking at the 120v smoothing capacitors,i assume it runs higher voltage rails too? But yes,a schematic would be good if anyone has one?

I am sure I recently read no one seems to have a schematic for this amp. 

I have seen some literature for a 909, has anyone seen one of those? It looked like it had the mk3 front.

#spelling.


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In bass no one can hear you scream!


Posted By: djeddie
Date Posted: 11 February 2020 at 10:00pm
Originally posted by midas midas wrote:

I have seen some literature for a 909...


I reckon they made it, but nobody could lift it to get it in the packing box.Wink


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Chas n Dave : it's like Drum and Bass but with beards.             E=mc² ±3dB


Posted By: kedwardsleisure
Date Posted: 12 February 2020 at 4:29pm
47kg



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Kevin

North Staffordshire



Posted By: Dub Specialist Sound
Date Posted: 12 February 2020 at 6:33pm
32 mosfets per channel, double the number in the 707??

so what theres 64 fets p/c ?


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Musical Roots Reggae Vibration is Life! for music is sound...sound is vibration...vibration is energy... and energy begets life. Therein lies my passion!...MUSIC IS LIFE...


Posted By: njw
Date Posted: 12 February 2020 at 7:21pm
Originally posted by djeddie djeddie wrote:

Originally posted by midas midas wrote:

I have seen some literature for a 909...


I reckon they made it, but nobody could lift it to get it in the packing box.Wink
  

 A 909?? 

 What mythical beast is this?!


Posted By: simonp1100
Date Posted: 12 February 2020 at 7:55pm
Originally posted by Dub Specialist Sound Dub Specialist Sound wrote:

32 mosfets per channel, double the number in the 707??

so what theres 64 fets p/c ?

The SR808 Has 15 MOSFETS per voltage rail, so each channel has a total of 30 MOSFETs (15 X 2SJ50 & 15 X 2SK135). So the total amount for both channels is 60 MOSFET's. ClapClap


Posted By: midas
Date Posted: 13 February 2020 at 2:47pm
Well.....

Prognosis is not good. 

It's knackered...lol. 

If anyone knows of someone with a transformer from a non working 808, please send them in my direction. 


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In bass no one can hear you scream!


Posted By: simonp1100
Date Posted: 13 February 2020 at 3:21pm
How do you know the transformer is not working ?, has Kevin had a look at it ?

If Kevin has had a look at it, does he know the spec of the transformer ?



Posted By: midas
Date Posted: 13 February 2020 at 4:53pm
Yes Kevin has looked at it. He knows the voltages but not the wire guage. 

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In bass no one can hear you scream!


Posted By: kedwardsleisure
Date Posted: 13 February 2020 at 6:05pm
I would estimate 1200VA from the physical size but I haven't taken it out as it's not a 5 minute job and I have more pressing stuff backing up.

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Kevin

North Staffordshire



Posted By: APC321
Date Posted: 14 February 2020 at 10:13am
https://ibb.co/thQ0bzQ" rel="nofollow - https://ibb.co/thQ0bzQ

Found this photo I took at Notting Hill Carnival in 2014.

In the right hand rack are six C-Audio SR-808. Must be the heaviest amp rack I have ever seen.

The sound system is listed as being provided by "CMC Matrix".

Maybe that is somebody on this forum. Possibly may still have spares.


Posted By: midas
Date Posted: 14 February 2020 at 10:39am
Thank you. 

I have sent them a message on Facebook. But if anyone does know them, please also see if they have any non working for spares.


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In bass no one can hear you scream!


Posted By: midas
Date Posted: 14 February 2020 at 11:21am
Would you pm me with likely cost please. 

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In bass no one can hear you scream!


Posted By: imageoven
Date Posted: 14 February 2020 at 11:39am
Originally posted by APC321 APC321 wrote:

https://ibb.co/thQ0bzQ" rel="nofollow - https://ibb.co/thQ0bzQ

Found this photo I took at Notting Hill Carnival in 2014.


Plenty of amplification there. looks like 56 amp channels.


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Keep pushing on, things are gonna get better.


Posted By: midas
Date Posted: 14 February 2020 at 12:01pm
Oof....

Looking at that lot, they should do a structural survey of that building next to it...


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In bass no one can hear you scream!


Posted By: midas
Date Posted: 14 February 2020 at 3:41pm
Well, the group who have 6 808's in a rack have read my message but not answered. :(

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In bass no one can hear you scream!


Posted By: midas
Date Posted: 14 February 2020 at 10:06pm
Another member has offered a possible lead. I will keep the thread informed. 

Fingers crossed.


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In bass no one can hear you scream!


Posted By: Andylaser
Date Posted: 14 February 2020 at 11:46pm
Originally posted by APC321 APC321 wrote:

https://ibb.co/thQ0bzQ" rel="nofollow - https://ibb.co/thQ0bzQ
The sound system is listed as being provided by "CMC Matrix".
Maybe that is somebody on this forum. Possibly may still have spares.


That rings a bell.
Run by a chap called Cecil IIRC. We used him to do some happy hardcore raves on Hastings pier back in the 90s. Absolutely banging system, JBL & 21" PD subs. C Audio amp racks. You could feel the pier vibrating with the bass, well interesting sensation when you were off yer tits. Tongue


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"music so loud, that if we move in next door to you; your lawn will die" - Lemmy


Posted By: midas
Date Posted: 15 February 2020 at 11:12am
Originally posted by midas midas wrote:

Another member has offered a possible lead. I will keep the thread informed. 

Fingers crossed.

Unfortunatly phone number is not recognised and a little digging shows no registered company...damn.


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In bass no one can hear you scream!


Posted By: service dept Steve
Date Posted: 15 February 2020 at 11:12am
Sorry I'm a bit late to the party. A customer gave me two of these a few weeks back in part ex for work. They are sitting in my workshop (on the floor obvs) waiting for a decision on what to do with them. Any ideas?
 

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We are not "They", We are "The others" http://www.servicedept.co.uk" rel="nofollow - http://www.servicedept.co.uk -


Posted By: midas
Date Posted: 15 February 2020 at 11:14am
Oh wow. Can I have some spares please.....

Actually, you do not mention not working..lol. so yours may be fully working.
 




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In bass no one can hear you scream!


Posted By: service dept Steve
Date Posted: 15 February 2020 at 11:52am
One is working but the other is of an unknown status because of it's general condition, It too has been in clumsy hands and is also rusty and a bit bashed up. I could easily get it to work but given these amps are not worth that much these days I might not bother. These amps do owe me money though so I might use one for spare parts.


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We are not "They", We are "The others" http://www.servicedept.co.uk" rel="nofollow - http://www.servicedept.co.uk -


Posted By: midas
Date Posted: 15 February 2020 at 12:25pm
In which case would you sell me the main transformer from the non working one please.

Just replied to PM. 

Thank you and I will await the discussion between yourself and Kevin. 


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In bass no one can hear you scream!


Posted By: njw
Date Posted: 15 February 2020 at 6:18pm
Originally posted by Andylaser Andylaser wrote:

Originally posted by APC321 APC321 wrote:

https://ibb.co/thQ0bzQ" rel="nofollow - https://ibb.co/thQ0bzQ
The sound system is listed as being provided by "CMC Matrix".
Maybe that is somebody on this forum. Possibly may still have spares.


That rings a bell.
Run by a chap called Cecil IIRC. We used him to do some happy hardcore raves on Hastings pier back in the 90s. Absolutely banging system, JBL & 21" PD subs. C Audio amp racks. You could feel the pier vibrating with the bass, well interesting sensation when you were off yer tits. Tongue
  

 Wasn't Hastings pier on the verge of being demolished at one point due to serious structural issues? ShockedLOL  

 And sounds like good news for the 808 too, speakerplans to the rescue!Smile


Posted By: midas
Date Posted: 15 February 2020 at 6:35pm
Cecil has replied to. He had a chat and at one carnival he has 30 CAudio amps in racks with 12 808's...lol. 


And a very big thank you to all concerned with helping to find a solution. 


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In bass no one can hear you scream!


Posted By: midas
Date Posted: 17 February 2020 at 3:44pm
Good news.

Thanks to Service dept Steve we now have a new transformer on it's way.. 


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In bass no one can hear you scream!


Posted By: simonp1100
Date Posted: 17 February 2020 at 4:12pm
I'm glad you got one. I did go back to the original company who made all the C-Audio transformers and they quoted over £300 (1200Kva). Cry


Posted By: kedwardsleisure
Date Posted: 17 February 2020 at 4:16pm
Quote they quoted over £300 (1200Kva)


that's cheap for a 1.2MW transformer! Maybe they could do a 1.21 jiggawatt transformer for this old delorean I'm trying to fix

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Kevin

North Staffordshire



Posted By: simonp1100
Date Posted: 17 February 2020 at 4:22pm
LOLLOLLOL


Posted By: Monitech
Date Posted: 17 February 2020 at 7:11pm
St ives windings haven't been about for at  15 years, must have been a very good phone line 

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phoenix out of the ashes


Posted By: simonp1100
Date Posted: 17 February 2020 at 9:32pm
Originally posted by Monitech Monitech wrote:

St ives windings haven't been about for at  15 years, must have been a very good phone line 

It was a very good phone line (cheers Martin), i think you been out of the loop for 15 years. Please check your facts before you post a comment and check there website. St Ives windings was there old name and have now changed & also now have two - three sites in England and are still going strong.


SEE BELOW:-----ConfusedConfusedConfusedConfusedConfusedConfusedConfusedConfusedConfusedConfusedConfusedLOLLOLLOLLOLLOLLOLLOLLOLLOLLOL

Classic Audio Transformers and Inductors

Our classic range of audio transformers and Inductors are world renowned and integral to many prominent professional pre-amp and mixer manufacturers.

These continue to be hand-built at our St. Ives site, which was formerly St. Ives Windings.

Featured types include balanced input and output transformers for maximum noise rejection at low signal levels, high level output transformers, impedance matching audio input transformers and tapped audio inductors.

As well as the classic range we also work alongside our customers to develop variations of these products for other applications.

Smaller quantities of these parts are available from our specialist distributor.



Posted By: kedwardsleisure
Date Posted: 17 February 2020 at 11:43pm
I believe they're part of Carnhill Transformers now. I do repairs for them from time to time on their equipment.

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Kevin

North Staffordshire



Posted By: simonp1100
Date Posted: 18 February 2020 at 7:11am
Yes Kevin you are correct.

We get all our works transformers from them (about 700 a year) as well as a few C-Audio ones every now and then. Had a few RA3001's, RA4001's, XR3801's & SR707's transformers from them over the past few years, well made and as always perfect.

Say hello to Martin for me. Big smile


Posted By: midas
Date Posted: 21 February 2020 at 2:00pm
Parts on the way, courtesy of service dept Steve... Thank you very much. A life saver. Well SR808 saver.

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In bass no one can hear you scream!


Posted By: midas
Date Posted: 12 March 2020 at 4:00pm
Had a quick message from Kevin this afternoon for those interested in the 808. She is on the road to recovery. The parts Steve posted for me have been fitted, not a simple task by all accounts. Just waiting on the arrival of some new parts to be able to test properly and she will be ready. 

Thank you to all involved, my ears cant wait, but my back is not overly impressed at the thought. 


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In bass no one can hear you scream!


Posted By: pscstudio54
Date Posted: 15 March 2020 at 8:52am
Hi,I bought the working sr808 off of service dept Steve and it is in exceptional condition. A very tidy unit and quiet fans too. The question I have which after trawling through all the old questions that have been asked again and again is, does anyone have a spec/service/user manual or is this a thing of secret!! I would like to know what to do in respect to the I/P side requirements voltage/sensitivity to set up correctly. I got this to power two fane Xb scoop bins so it will have an easy life. My other amplifiers are all old Harrison xi 1000's which take very little I/P to give quite fast gain on the o/p. At the moment the sr808 is set on stereo.,would there be more benefit to run in bridge mode? So many questions...


Posted By: jbl_man
Date Posted: 15 March 2020 at 10:13am
"The question I have which after trawling through all the old questions that have been asked again and again is, does anyone have a spec/service/user manual or is this a thing of secret"

The fact that you have just purchased it from service dept Steve,surely that question should be directed at him? He must have one he could photocopy for you?


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Be seeing you.


Posted By: pscstudio54
Date Posted: 15 March 2020 at 11:01am
I agree about asking Steve , I'm hopefully meeting up with him soon but I couldn't pm him directly as I've had to start speakerplans from scratch again as well as e.mail and bank accounts due to as sky say...somethings happened! I did go through every post I could find on the 808 but couldn't find the answer. I did e.mail Steve to say I'd asked on Midas's post about it. I would have posted this on newbie if there wasn't a post about the 808 here. thanks anyway.


Posted By: simonp1100
Date Posted: 15 March 2020 at 11:39am
To my knowledge there is no circuit diagram for the SR808 & the circuit for the SR707 is the nearest you will get to this. 

The SR808 uses the same circuit as the SR707 with just more output devices and a higher transformer voltage everything else is the same (physicaly different relays and caps but electronically the same).

Hope this helps. Clap


Posted By: pscstudio54
Date Posted: 15 March 2020 at 12:23pm
That's everything I need to know. Thank you. I have to admit it, it does sound really good. Smile



Posted By: APC321
Date Posted: 15 March 2020 at 4:20pm
Found this information:

https://ibb.co/P9zGDsk" rel="nofollow - https://ibb.co/P9zGDsk


Posted By: simonp1100
Date Posted: 15 March 2020 at 4:54pm
That looks like it's from the Avitec catalogue as i have an original one still in very good condition. Clap


Posted By: APC321
Date Posted: 15 March 2020 at 5:24pm
Yes 1986. Well spotted Simon!


Posted By: simonp1100
Date Posted: 15 March 2020 at 5:31pm
My catalogue is the 1989 version and has the Beta Pro amplifiers  (220,500 & the 800) which were also built by C-Audio. Happy days.  Wink


Posted By: kedwardsleisure
Date Posted: 15 March 2020 at 6:18pm
1986 was a notable year in many ways. C-Audio launched the SR808, Peugeot launched the 309, Fergie and Prince Andrew got married and the Space Shuttle blew up shortly after launch.

Oh and I left school that year.


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Kevin

North Staffordshire



Posted By: studio45
Date Posted: 16 March 2020 at 5:00pm
There are white versions? OOOOOH never seen one in the wild!

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Studio45 - Repairs & Building Commotion Soundsystem -Mobile PA


Posted By: kedwardsleisure
Date Posted: 17 March 2020 at 10:55am
That's the load testing done, just a slight problem with one channel which was clipping assymetrically, caused by one of the VI clamp diodes being cut out of circuit for some reason.

I always like to do an audio test with music contemporary to the amp in question. In this case, I'm playing Whitney Houston.   

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Kevin

North Staffordshire



Posted By: totalAudio
Date Posted: 19 April 2020 at 10:52am
you guys seem like you might be able to help me out :D

I have three sr707 currently and one of them just started giving me major troubles :S

the peak limiter lights are coming on very quickly with little signal or gain

im guessing (with limited knowledge) that a power cap or two may have started to run dry given the age and unknown service history on these

can anyone suggest a way of getting to the root of the issue? willing to put my hand to it myself with some guidance

cheers for any help guys


Posted By: simonp1100
Date Posted: 19 April 2020 at 11:08am
"im guessing (with limited knowledge) that a power cap or two may have started to run dry given the age and unknown service history on these"

I doubt that the power caps are running dry.

Check the below first:--

1. Each driver PCB board check R14 & R50 (were 24K 1/2 Watt now changed to 27K 1 Watt), these tend to go open / high resistance if the value in your amplifiers are 24K (Maybe change these in ALL yor amplifiers)
2. Are BOTH peak lights doing this on both channels or just one channel ?.

Please also be careful as there is high voltages around and the above MUST be done by a engineer or someone who knows about power amplifiers. Wink


https://forum.speakerplans.com/caudio-sr808_topic104745_page1.html#top" rel="nofollow">Back to Top



Posted By: totalAudio
Date Posted: 19 April 2020 at 12:00pm
I will check this out ill get one opened up today

and it is both channels that are doing this one slightly more so then the other id say but that could just be the difference in the peak light, both channels are about the same audibly

thanks simon


Posted By: simonp1100
Date Posted: 19 April 2020 at 12:33pm
Hi, Each amplifier driver board controls ONE channel and has the following circuits on it---.

1. Amplifier driver stage.
2. Peak light driver circuit.
3. Balanced input op-amp driver.
4. Protection circuit (but this is normally only used on ONE board).

So if BOTH channels are doing then it could be one of the following---.

1. Check input connections (i.e. are you using balanced or unbalanced connections).
2. Resistors as montioned in previous reply could be faulty on BOTH channel PCB boards. This would need checking and also updating on any other SR amplifiers you have (24K To 27K 1 Watt)
3. The soft start relays is stuck and amplifier is still in "Soft Start Mode" i.e. the 50 ohm soft start resistor has'nt been shorted out by the relay and this in turn will give you a 50 ohm resistor in series with the main power transformer and will reduce power output. Clap


Posted By: totalAudio
Date Posted: 19 April 2020 at 12:40pm
Originally posted by simonp1100 simonp1100 wrote:

"im guessing (with limited knowledge) that a power cap or two may have started to run dry given the age and unknown service history on these"

I doubt that the power caps are running dry.

Check the below first:--

1. <span style=": rgb251, 251, 253;">Each driver PCB board check R14 & R50 (were 24K 1/2 Watt now changed to 27K 1 Watt), these tend to go open / high resistance if the value in your amplifiers are 24K (Maybe change these in ALL yor amplifiers)</span>
<span style=": rgb251, 251, 253;">2. Are BOTH peak lights doing this on both channels or just one channel ?.</span>
<span style=": rgb251, 251, 253;">
</span>
<span style=": rgb251, 251, 253;">Please also be careful as there is high voltages around and the above MUST be done by a engineer or someone who knows about power amplifiers. </span>Wink

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I have checked over the amp in question and it has the 24k 1/2w resistor so this must be part if not all the trouble I will have to have a good look at the others and see if I need to get an order list together then :)

thanks simon ill keep you updated with my journey


Posted By: totalAudio
Date Posted: 20 April 2020 at 12:13pm
Originally posted by simonp1100 simonp1100 wrote:

Hi, Each amplifier driver board controls ONE channel and has the following circuits on it---.

1. Amplifier driver stage.
2. Peak light driver circuit.
3. Balanced input op-amp driver.
4. Protection circuit (but this is normally only used on ONE board).

So if BOTH channels are doing then it could be one of the following---.

1. Check input connections (i.e. are you using balanced or unbalanced connections).
2. Resistors as montioned in previous reply could be faulty on BOTH channel PCB boards. This would need checking and also updating on any other SR amplifiers you have (24K To 27K 1 Watt)
3. The soft start relays is stuck and amplifier is still in "Soft Start Mode" i.e. the 50 ohm soft start resistor has'nt been shorted out by the relay and this in turn will give you a 50 ohm resistor in series with the main power transformer and will reduce power output. Clap

hey simon im just looking at my options and just to clarify I need the standard 27k 1 watt and not the 10% ? cheers again


Posted By: service dept Steve
Date Posted: 20 April 2020 at 12:42pm
Originally posted by totalAudio totalAudio wrote:



I have checked over the amp in question and it has the 24k 1/2w resistor so this must be part if not all the trouble
 


Well, Only if they are open circuit otherwise it is just maintenance.

If both channels are misbehaving at the same time then I would be looking at the soft start circuit as previously mentioned. Can you hear the relays click after a short start up period? Does the 50 ohm resistor get hot during use?


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Posted By: totalAudio
Date Posted: 20 April 2020 at 12:49pm
Originally posted by service dept Steve service dept Steve wrote:

Originally posted by totalAudio totalAudio wrote:



I have checked over the amp in question and it has the 24k 1/2w resistor so this must be part if not all the trouble
 


Well, Only if they are open circuit otherwise it is just maintenance.

If both channels are misbehaving at the same time then I would be looking at the soft start circuit as previously mentioned. Can you hear the relays click after a short start up period? Does the 50 ohm resistor get hot during use?

yeh it clicks after a little while after startup so I will change the r14 & r50 and if I still have issues then ill have to move on with the fault finding cheers bud


Posted By: simonp1100
Date Posted: 20 April 2020 at 1:03pm
Hi, The circuit diagram says change the following on EACH driver PCB board from 24K 1/2 Watt to 27K 1 Watt 5%.

R24, R34 & R50. Hope this helps.

Again if both channels are doing this then it must be down to whats feeding both channels which is the power supply or soft start circuitry, and so i would also double check these parts of the amplifier.

Can you measure the DC voltages on the power supply capacitors and let me know what they are.

Clap


Posted By: midas
Date Posted: 24 June 2020 at 8:09pm
Well, it does look like this crazy time is quietening down. Hopefully I will soon be able to collect the 808, dump it round my mates on a pair of X1's.

I may put the 707 on the community tops as well...

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In bass no one can hear you scream!


Posted By: midas
Date Posted: 30 June 2020 at 3:49pm
And........she is home...

I wonder how many people would consider the CAudio sr707 as a lightweight amplifier. Me either, but let me say that compared to the 808 it is. 

Something else that's surprising it wasnt old age that took the old girl out either. It was some NUMPTY with an electric drill. Correct, really yes.  It looks like someone has drilled one of the pannels and the tip of the drill has taken out a few of the outer strands, which in turn has taken out the secondary winding. 




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In bass no one can hear you scream!


Posted By: Sergio B
Date Posted: 29 May 2022 at 1:31pm
Hello everybody

I'm new. Interesting this post because I also have a C-Audio SR808 with problems with a Driver board so much that I have to completely redesign the PCB,
the driver board is badly damaged, copper traces burnt, so I had to completely redesign the PCB.
Following yours messages but sorry I didn't understand anything. In the first part we talk about the replacement of the R14 and R50 resistors,
then it is said to update R24, R34 and R50, I think the latter is correct or am I wrong.

Thank you
Excellent discussion
congratulations.




Posted By: Sergio B
Date Posted: 29 May 2022 at 1:54pm





Posted By: Sergio B
Date Posted: 29 May 2022 at 2:02pm



Posted By: simonp1100
Date Posted: 29 May 2022 at 2:05pm
I did the same thing as you for the C-Audio SR Series. I used Proteus CAD & done two versions,  the original PCB & an updated version with all the mod's (protection circuity, better legends where the wires go & bigger pads sizes around the zener diodes & wirewound resistors etc). WinkWinkWinkWink

You need to update the resistors R24, R34 & R50 to 27K 1 Watt resistors (pretty sure these were originally 22K)




Posted By: Sergio B
Date Posted: 29 May 2022 at 2:14pm
great! WinkWinkWink

I also did the same thing, I used Eagle as my design software, I would say that one is as good as the other.

I saw you mentioned the protection circuit, what did you specifically do if I may know


Posted By: Sergio B
Date Posted: 29 May 2022 at 2:25pm
as for the R24 R34 R50 resistors, I confirm that they are originally 22k 1/4 watt

therefore the three must be replaced with 27k 1w




Posted By: simonp1100
Date Posted: 29 May 2022 at 2:30pm
Here is an updated version of the soft / start PCB







Posted By: simonp1100
Date Posted: 29 May 2022 at 2:32pm
Here is the updated protection circuitry.





Posted By: simonp1100
Date Posted: 29 May 2022 at 2:35pm
Here is my version of the updated driver card.




Posted By: simonp1100
Date Posted: 29 May 2022 at 2:42pm
The soft start PCB has updated components, including allowing you to use two versions of the 47R resistor (clad or PCB solder type) and added NTC's as well.

Also have the originals & updated versions of the following as well.

RA Series (1001-3001 T03 & Plastic FET's PCB board, including all mods & re-entrant circuit added to main board & a few other tweeks).
GB602 (just original main board & input PCB).
ST1000 (just original main board & all other PCB's).

Would like to do the RA4001 as well at some point.

SmileSmile


Posted By: Sergio B
Date Posted: 29 May 2022 at 2:43pm
great job, congratulations Smile

you can put the wiring diagram with the parts list and values ​​if you don't mind


Posted By: Sergio B
Date Posted: 30 May 2022 at 2:03pm
Hello
today i mounted the driver board but i noticed that the volume is lower and that the transistors
of the channel give strange values ​​compared to the other channel. disconnecting power and audio i / o and checking with the multimeter
I noticed that one pin of all transistors does not give any value between pin and GND. it would be a nice "blow" to the wallet
15 pairs of transistors to replace and who knows where to find them. someone gives me some info where to buy them. thank you


Posted By: jbl_man
Date Posted: 30 May 2022 at 2:43pm
The SR808 Has 15 MOSFETS per voltage rail, so each channel has a total of 30 MOSFETs (15 X  Hitachi 2SJ50 & 15 X  Hitachi 2SK135.

You could try Ebay for good used ones. Beware of anything from China or any reporting to be "new", as doubtless there are fake ones around.


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Be seeing you.


Posted By: Earplug
Date Posted: 30 May 2022 at 3:47pm
Originally posted by jbl_man jbl_man wrote:

The SR808 Has 15 MOSFETS per voltage rail, so each channel has a total of 30 MOSFETs (15 X  Hitachi 2SJ50 & 15 X  Hitachi 2SK135.

You could try Ebay for good used ones. Beware of anything from China or any reporting to be "new", as doubtless there are fake ones around.


Getting that quantity of those is nigh impossibe these days. And yes - watch out for the fakes.  Dead

You might be able to find enough of the Exicon 10N/P16 or 10N/P20. They should be ok as a replacement.








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Earplugs Are For Wimps!


Posted By: service dept Steve
Date Posted: 30 May 2022 at 4:11pm
I wonder what a pulled, used but tested j50 or k135 is worth these days, us old boys have lots of strange stock tucked away


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We are not "They", We are "The others" http://www.servicedept.co.uk" rel="nofollow - http://www.servicedept.co.uk -


Posted By: jbl_man
Date Posted: 30 May 2022 at 4:21pm
About £10 each going by this Steve.

https://www.ebay.co.uk/itm/374096911833?hash=item5719e9ddd9:g:NNgAAOSw7wVfFsyd" rel="nofollow - https://www.ebay.co.uk/itm/374096911833?hash=item5719e9ddd9:g:NNgAAOSw7wVfFsyd




-------------
Be seeing you.


Posted By: Randy Bohannon
Date Posted: 30 May 2022 at 5:03pm
Cricklewood electronics reckon theirs's are real and they want £30 for them  

https://www.cricklewoodelectronics.com/2SJ50.html

The Batwing ones are where the money is:  

https://www.cricklewoodelectronics.com/2SJ83.html

Makes me want to sell the two pairs I have in the working bank of a random 80s DIY amplifier I have and replace them with Exicons at a profit! Confused

(sorry, can't get hyperlinks to work...)


Posted By: Earplug
Date Posted: 30 May 2022 at 5:12pm
Originally posted by service dept Steve service dept Steve wrote:

I wonder what a pulled, used but tested j50 or k135 is worth these days, us old boys have lots of strange stock tucked away


Haha, yes. I just sold a load of old (rescued) Crown devices to a guy here. C4751, C6492 as well as some rescued MJ15015/16 and MJ15022/23. The guy said that he prefered using old, used transistors to the new stuff that risked being fake.




-------------
Earplugs Are For Wimps!


Posted By: service dept Steve
Date Posted: 30 May 2022 at 6:01pm
Originally posted by Earplug Earplug wrote:

Originally posted by service dept Steve service dept Steve wrote:

I wonder what a pulled, used but tested j50 or k135 is worth these days, us old boys have lots of strange stock tucked away


Haha, yes. I just sold a load of old (rescued) Crown devices to a guy here. C4751, C6492 as well as some rescued MJ15015/16 and MJ15022/23. The guy said that he prefered using old, used transistors to the new stuff that risked being fake.


Sad but true, I pay more for used transistors than for new ones for that very reason. I'm not sure that the crown ones were great in period but certainly 22/23/24/25s are always in my wish list


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We are not "They", We are "The others" http://www.servicedept.co.uk" rel="nofollow - http://www.servicedept.co.uk -


Posted By: Sergio B
Date Posted: 30 May 2022 at 8:43pm
sorry, .. but at this point it is worth changing the configuration of the amplifiers with the new 2SJ162 2SK1058 and modifying the PCBs with side connection


Posted By: Sergio B
Date Posted: 30 May 2022 at 9:08pm
Example: 2sj50




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