Speakerplans.com Homepage
Forum Home Forum Home > General > Amp Forum
  New Posts New Posts RSS Feed - Cloud VTX repair and restoration
  FAQ FAQ  Forum Search   Events   Register Register  Login Login

Cloud VTX repair and restoration

 Post Reply Post Reply Page  <123>
Author
Message
kipman725 View Drop Down
Registered User
Registered User


Joined: 02 September 2020
Location: Warrington
Status: Offline
Points: 231
Post Options Post Options   Thanks (0) Thanks(0)   Quote kipman725 Quote  Post ReplyReply Direct Link To This Post Posted: 01 November 2022 at 3:01pm
Its funny you mention the high air flow and then sand blasting. A couple of these I have fixed had not faults apart from a track worn away in the same place near the fan, when replaced with a wire they worked fine.  I suspect the airflow eroded the track.  Good amps if you don't care about the fan noise, I once ran one at full power for 45mins till the water of my test load boiled.
Back to Top
Randy Bohannon View Drop Down
Registered User
Registered User


Joined: 29 May 2022
Location: London
Status: Offline
Points: 107
Post Options Post Options   Thanks (0) Thanks(0)   Quote Randy Bohannon Quote  Post ReplyReply Direct Link To This Post Posted: 01 November 2022 at 8:14pm
I noticed a few corroded tracks, particularly at the front and rear of the bottom amplifier board.

In my case I think it was corrosion from the dust it trapped, that fan is an 11W, 160f^3/m beast compared to the average pair of 30f^3/m low voltage fans in the average amplifier and so I think it just sucks in more crap than most. this dust then holds moisture and corrodes the tracks through the solder mask.

Mine doesn't have a dust filter behind the front grille, incidentally, does yours?

I'm not surprised with your result, I couldn't get mine to overheat full power testing either, the load (1600w continuous in theory) however did... :D 

I'm setting it to the higher bias tonight for some critical listening tomorrow. 

Back to Top
kedwardsleisure View Drop Down
Old Croc
Old Croc


Joined: 20 January 2009
Location: Staffordshire
Status: Offline
Points: 4938
Post Options Post Options   Thanks (0) Thanks(0)   Quote kedwardsleisure Quote  Post ReplyReply Direct Link To This Post Posted: 02 November 2022 at 9:03am
probably overheat
Kevin

North Staffordshire

Back to Top
kipman725 View Drop Down
Registered User
Registered User


Joined: 02 September 2020
Location: Warrington
Status: Offline
Points: 231
Post Options Post Options   Thanks (0) Thanks(0)   Quote kipman725 Quote  Post ReplyReply Direct Link To This Post Posted: 02 November 2022 at 12:07pm
no filters in any of the VTX750 or VTX1000 I had
Back to Top
Randy Bohannon View Drop Down
Registered User
Registered User


Joined: 29 May 2022
Location: London
Status: Offline
Points: 107
Post Options Post Options   Thanks (0) Thanks(0)   Quote Randy Bohannon Quote  Post ReplyReply Direct Link To This Post Posted: 02 November 2022 at 4:31pm
Originally posted by kedwardsleisure kedwardsleisure wrote:

probably overheat

Nah, not this puppy...Big smile

It didn't overheat but it didn't sound any better that I could hear either. I've biased it back to factory spec and declared it finished. 

I did think about maybe fiddling with the opamps and making the input filter a little less severe but, as you say, it probably not worth it.
Back to Top
Randy Bohannon View Drop Down
Registered User
Registered User


Joined: 29 May 2022
Location: London
Status: Offline
Points: 107
Post Options Post Options   Thanks (0) Thanks(0)   Quote Randy Bohannon Quote  Post ReplyReply Direct Link To This Post Posted: 02 November 2022 at 4:32pm
Originally posted by kipman725 kipman725 wrote:

no filters in any of the VTX750 or VTX1000 I had

Cheers Kipman, I have some thin foam I will line the front vents with.
Back to Top
Randy Bohannon View Drop Down
Registered User
Registered User


Joined: 29 May 2022
Location: London
Status: Offline
Points: 107
Post Options Post Options   Thanks (0) Thanks(0)   Quote Randy Bohannon Quote  Post ReplyReply Direct Link To This Post Posted: 16 November 2022 at 7:51pm
The new pots arrived and I fitted them, together with a new LED for the buggered signal indication.

It seems that Cloud went out of their way to find low output LEDs for the front the panel and I appreciate their efforts as the new one is too bright, really. I hsvr found a special, not-as-bright LED and bought it, whilst cursing my OCD.

however the signal indication for channel B still doesn't work. I really don't feel like pulling the thing apart again but it seems the problem is with the channel B PCB...

I have to say though, new pots seem to have improved the sound more so than any other single thing I have done including recapping.


Back to Top
izzzzzz6 View Drop Down
Registered User
Registered User


Joined: 06 July 2012
Location: france
Status: Offline
Points: 45
Post Options Post Options   Thanks (0) Thanks(0)   Quote izzzzzz6 Quote  Post ReplyReply Direct Link To This Post Posted: 16 March 2023 at 10:20am
I think i have about every type of Cloud amp ever made. I had a question but i can't remember what it is now. Oh yea. Does anyone know what RV1 is for? RV2 is bias.
  What is the bias setting on the VTX is it correct that of the transistors are the Hitachi pair i set it to 100mA? So sometimes the main transistors are International Rectifier? I have the Hitachi in a CV1000 and Hitachi in VTX1200.
  Oh, i see VR1 is for offset it's marked on a CV1000. How do i set offset? is this for the speaker protection circuit to be balanced?
  In one of these amps someone has soldered fixed value resistors to the underside of VR1 so i wonder why they needed to do that.
  Fixed quite a few of these recently, one thing to note is never to touch both heatsinks at the same time as they are live, i got a shock and blew something on the amp.
  One repair was output transistors, several rotten tracks along the front of the board and one broken rotten track found under an audio cable that's soldered across the board on the cv1000.
  One repair was replacing the transistor that helps to regulate bias with temperature ZTX304 I'm going to swap with a BC639 but swap leg position, hope this works to do the same job.
  Another one had some strange resistances where someone had piggybacked some resistors along the speaker protection circuit somewhere. Putting those and one other resistor back to normal fixed that one.
  Would love to know where to set the offset. is that just done at the speaker output terminals?
Cloud amps i own and will sell many of them:
The 8ch with multizone mixer
The 6x 120W i think.
cv500
vtx750
cv1000
vtx1200
vtx1500

Petty decent, always ran very cool, need threadlock if you want to take them on the road. Bit heavy these days.

I noticed Old Croc mentioned noise on the older cv1000 etc due to an audio ic. I'm wondering if this is an issue i had on a cloud cv1000.
  I could sometimes hear scratchy random noise when the amps were on, not enough to hear over the music but annoying just the same. Assuming this was the same issue, does anyone know which IC tended to go noisy in-case i still have that amp somewhere.
  A Mr. Carlsons super probe would help here i imagine.


Just been checking bias on a vtx 1200 it was set around 25mA and max i could get was 60mA
Did you mean 100mV?
When i set bias to 100mV i have around 50mA across / between the + & - source legs of K414 and J119.
On the VTX1200 model i ended up setting bias to 25mA and offset to each speaker output to zero V. Couldn't find a service manual with the spec.
 


Edited by izzzzzz6 - 16 March 2023 at 1:58pm
Sound
Back to Top
kedwardsleisure View Drop Down
Old Croc
Old Croc


Joined: 20 January 2009
Location: Staffordshire
Status: Offline
Points: 4938
Post Options Post Options   Thanks (0) Thanks(0)   Quote kedwardsleisure Quote  Post ReplyReply Direct Link To This Post Posted: 17 March 2023 at 9:39am
Quote What is the bias setting on the VTX
In one of these amps someone has soldered fixed value resistors to the underside of VR1.
Would love to know where to set the offset.

noise on the older cv1000 etc due to an audio ic



Mosfet bias: Hitachi mosfets (old) are 100mA per device which equates to 33mV measured across an emitter resistor. Normally found in the older CV range (the predecessor of the VTX)
When the hitachis were discontinued they moved to IR devices which need 25mA per device which equates to 8.3mV across an emitter resistor. The IR devices are selected so they current-share properly. If you don't use selected devices, it's very possible the amp will fail; this is because the IR threshold voltages have a wide spread, even in the same batch and it's not enough to just change them all since a low threshold voltage on one fet can mean it does all the work and the others sit biased off. If in doubt, measure the bias across each emitter resistor and compare the relative currents at idle. Threshold voltages in a matched set are within 25mV of each other of V.thresh. (not bias).

Fixed resistors: This was a factory modification, and the resistors were incorporated into later revisions of the pcb. It is to limit the amount of bias adjustment particularly if the bias trimpot goes noisy. Without the mod, an open circuit pot can cause the amp to go into DC protect with possible speaker damage. An intermittent pot can sporadically blow speakers or melt the speaker relays if you don't realize what's happening. The contact distance of the protect relays is barely adequate which is why they have magnets (should have!) glued to the side of the relays at the side of the contacts, to help to quench the arc if the amp goes go DC.

Offset: Just measure across the speaker terminals with no input and adjust for minimum DC voltage.

Noise: The earlier CV range had a VCA chip to operate the limiter, this can do alsorts of weird and wonderful things, generate tones, squeals and rustles. It's no longer available AFAIK and was changed to a different system in the VTX.
But the biggest source of noise is probably failing bias and offset trim pots. The carbon tracks develop noise with old age and are easily replaced.

The earliest CV amps had really nice bargraph VU meters which were pretty. LEDs were still 'bling' in those days, easy to forget.







Edited by kedwardsleisure - 17 March 2023 at 9:48am
Kevin

North Staffordshire

Back to Top
izzzzzz6 View Drop Down
Registered User
Registered User


Joined: 06 July 2012
Location: france
Status: Offline
Points: 45
Post Options Post Options   Thanks (0) Thanks(0)   Quote izzzzzz6 Quote  Post ReplyReply Direct Link To This Post Posted: 21 March 2023 at 11:17am
Hi Kevin. Thanks for the details.
  It almost seems they don't want anyone biasing these amps. I blew 2 fuses in my multimeter just slipping off of the small resistor and into the heatsink that also comes off of the same leg because it's not easy to get to the underside of the main balance resistors perhaps i should try to clip directly to the transistors leg.
  The VTX 1200 I have been working on has Hitachi fets.
One thing i found is that 2sJ119 and 2sk414 are quite expensive and a cheaper pair is available, the 2sJ118 and 2sk413 seem to be same spec except a lower voltage rating. Wondering if they are still within spec.
 Next time i will try to measure across each resistor at a time rather than going across both of them from fet to fet. One thing i noticed was that bias ran slightly lower at one end of the amp and slightly higher at the other end. I wondered if this could be tweaked by changing resistances but it seemed fairly insignificant.
  Yes, i had to glue a few of those relay magnets back on and the "rustling" sound was in one of the cv 1000's might even be one of the ones i'm fixing.
  Makes sense to have (backup resistors) on the offset, annoying when those pots go bad.
  I have so many amps to fix right now. Some of them are:
2x Cloud
2x Lab 6400
2x large QSC amps around 4k and 5k size
2x peavey 2600
2x harrisons (can't remember the model but fairy chunky ones for their age)

Recently sold a crest something 900, built like a bomb, had those cool bar led's.

Got another rare touring crest can't find any data on it but it's very powerful.

Lots of issues with DSP's have a broken 2x4 sabine which sends random tones out to random channels.

Still wondering why the BSS fds355 shuts down when brightness is adjusted and why all of the screens across my 3x units all have different tints / colours but at least they work if you leave them alone.

so many repairs lurking around here and also piled up at my dads in the UK. Hopefully will make some progress this year on some of those amps. Also lots of digital amps from powered speakers. Getting there slowly.

James

PS. 
    I currently have a good price on used Toshiba 2SA1302 ans 2SC3281.
Bigger transistors but same leg spacing, mounting holes are higher up, but other than tapping a new mounting hole on the heatsink I'm wondering if they could run in the cloud amps given a different gate / base resistor setup.
 

 


Edited by izzzzzz6 - 21 March 2023 at 1:42pm
Sound
Back to Top
kedwardsleisure View Drop Down
Old Croc
Old Croc


Joined: 20 January 2009
Location: Staffordshire
Status: Offline
Points: 4938
Post Options Post Options   Thanks (0) Thanks(0)   Quote kedwardsleisure Quote  Post ReplyReply Direct Link To This Post Posted: 21 March 2023 at 2:05pm
from one of my previous posts:

Quote Use those j-hook test leads rather than multimeter probes, just to avoid an explosive slip of the probes


then


Quote It almost seems they don't want anyone biasing these amps. I blew 2 fuses in my multimeter just slipping off of the small resistor and into the heatsink that also comes off of the same leg because it's not easy to get to the underside of the main balance resistors perhaps i should try to clip directly to the transistors leg.



Lucky it didn't take out all those expensive fets!


Quote I'm wondering if they could run in the cloud amps

no









Edited by kedwardsleisure - 21 March 2023 at 2:07pm
Kevin

North Staffordshire

Back to Top
izzzzzz6 View Drop Down
Registered User
Registered User


Joined: 06 July 2012
Location: france
Status: Offline
Points: 45
Post Options Post Options   Thanks (0) Thanks(0)   Quote izzzzzz6 Quote  Post ReplyReply Direct Link To This Post Posted: 22 March 2023 at 10:13pm
I have 3 different types of clip on connectors but the ones that work the best i only have some hooked up to a component tester right now. Need to make some more leads up i have a bag of them somewhere.
  Those other fets share the same data sheet, how high could voltages get? Or am I missing something else. Rails are at +-~72V i believe.
 
Sound
Back to Top
 Post Reply Post Reply Page  <123>

Forum Jump Forum Permissions View Drop Down

Forum Software by Web Wiz Forums® version 12.06
Copyright ©2001-2023 Web Wiz Ltd.

This page was generated in 0.094 seconds.