Speakerplans.com Homepage
Forum Home Forum Home > General > 12v Powered Systems
  New Posts New Posts RSS Feed - Sure 2x100w distorting (overheating?)...
  FAQ FAQ  Forum Search   Events   Register Register  Login Login

Sure 2x100w distorting (overheating?)...

 Post Reply Post Reply
Author
Message
alphabetikal View Drop Down
Registered User
Registered User
Avatar

Joined: 20 May 2010
Location: UK
Status: Offline
Points: 217
Post Options Post Options   Thanks (0) Thanks(0)   Quote alphabetikal Quote  Post ReplyReply Direct Link To This Post Topic: Sure 2x100w distorting (overheating?)...
    Posted: 03 October 2011 at 3:48pm
Hi

We have had a hot week across Europe. Here in London I took my system out. It was used for voice and also playing some bass booming reggae.

The system is the one ive posted the DIY step on before - a 24V SLA, Sure 2x100 w amp, with crossover, single eminence tweeter and 12" driver (mono). It runs a mini mixer (9V) and a mp3 player.

After about 1 hour of playing in 30C temperature I started to notice some distortion in the sound. The bottom end (bass) was breaking up as well as the high freqs. (like in saxaphone etc).
The fan was spinning quite fast on the old Sure 2x100W amp.

I checked my battery (24v SLA) and that was full and also my mixer and mp3 player - full also. 

Could it be the amp over heating? Really only at 30C?!
Is distortion in the frequency range a characteristic of an overheating class D amp? anyone know?

I might consider adding some cooling. A 12v fan or heatsink or something. At the moment the amp is in a top box with the mixer and crossover, not the main cabinet. It can be modified. 
I did notice that after riding the system down the road back home (on a bike trailer) it seemed to sound okay again! maybe it cooled off... 

:(

Any help?

A

Back to Top
Saturnus View Drop Down
Old Croc
Old Croc


Joined: 13 July 2010
Location: Copenhagen
Status: Offline
Points: 2025
Post Options Post Options   Thanks (0) Thanks(0)   Quote Saturnus Quote  Post ReplyReply Direct Link To This Post Posted: 03 October 2011 at 3:55pm
I would try if I could measure the DC offset on the outputs. Distortion like you describe is typical for that. It may very well be that the sustained high temperature notched the DC offset tuning out of whack, and it needs to be recalibrated.
Back to Top
Hemisphere View Drop Down
Old Croc
Old Croc


Joined: 21 April 2008
Status: Offline
Points: 2272
Post Options Post Options   Thanks (0) Thanks(0)   Quote Hemisphere Quote  Post ReplyReply Direct Link To This Post Posted: 03 October 2011 at 3:56pm
If the heatsink and fan don't have cool air to disperse into or to fan onto the chip then they'll definitely be less effective - also you're driving one channel really hard which I guess is less than optimum for that board.

What's the case you're using made of? The lepai amps use an aluminium case that doubles as a heatsink extension, you could possibly do something similar with the Sure amp.


Back to Top
alphabetikal View Drop Down
Registered User
Registered User
Avatar

Joined: 20 May 2010
Location: UK
Status: Offline
Points: 217
Post Options Post Options   Thanks (0) Thanks(0)   Quote alphabetikal Quote  Post ReplyReply Direct Link To This Post Posted: 03 October 2011 at 3:58pm
holy shit that sounds serious. 
How can you measure it? How would you re-calibrate it??? I have no idea what DC offset is!!

Help!!

ahahahahah
no seriously.,,, help?

;D

a

Back to Top
Hemisphere View Drop Down
Old Croc
Old Croc


Joined: 21 April 2008
Status: Offline
Points: 2272
Post Options Post Options   Thanks (0) Thanks(0)   Quote Hemisphere Quote  Post ReplyReply Direct Link To This Post Posted: 03 October 2011 at 4:00pm
Saturnus: He said it got better on the bikeride home. If DC was knocked out of wack wouldn't it stay that way?
Back to Top
Saturnus View Drop Down
Old Croc
Old Croc


Joined: 13 July 2010
Location: Copenhagen
Status: Offline
Points: 2025
Post Options Post Options   Thanks (0) Thanks(0)   Quote Saturnus Quote  Post ReplyReply Direct Link To This Post Posted: 03 October 2011 at 4:13pm

No, you can just readjust it. It's just not as easy as it may sound, but not that complicated either.

To measure it you just run the amp at high power level for 10-15 minutes in order for components to reach working temperature.

Then short inputs to ground and simply measure the voltage across the outputs. Should be less than 50mV, + or - doesn't matter.

To adjust it there's some really small pots on the Sure board. Unfortunately they're under the heat sink so you have to take the heat sink off. Adjust the pot, reattach heatsink, measure again. Rinse and repeat until you get lucky. Remember to let it run for a little while measuring as it will jump up and down a bit after you adjust it until it settles.

The pots and resistor network used for DC adjust on the Sure amp is horrible. You get huge changes almost without touching the pot so it's very likely that this happens to a lot of people.

Back to Top
alphabetikal View Drop Down
Registered User
Registered User
Avatar

Joined: 20 May 2010
Location: UK
Status: Offline
Points: 217
Post Options Post Options   Thanks (0) Thanks(0)   Quote alphabetikal Quote  Post ReplyReply Direct Link To This Post Posted: 03 October 2011 at 4:37pm
me thats shit

i hope it was the heat. if it happens again im going to have to throw this shit in the bin. haha. but seriously, thats rubbish!

thanks for explaining tho, very nice of y'all.

ill let you know what happens next time its hot.
Back to Top
alphabetikal View Drop Down
Registered User
Registered User
Avatar

Joined: 20 May 2010
Location: UK
Status: Offline
Points: 217
Post Options Post Options   Thanks (0) Thanks(0)   Quote alphabetikal Quote  Post ReplyReply Direct Link To This Post Posted: 03 October 2011 at 4:38pm
Hemisphere - good idea about the heat sink bro - im going to look into that. ive heard about mods using CPU fans and bigger heat sinks, which ill try too as i have some spare at home

a


Edited by alphabetikal - 03 October 2011 at 4:39pm
Back to Top
infrasound View Drop Down
Old Croc
Old Croc


Joined: 13 May 2011
Location: Brizzle
Status: Offline
Points: 2276
Post Options Post Options   Thanks (0) Thanks(0)   Quote infrasound Quote  Post ReplyReply Direct Link To This Post Posted: 03 October 2011 at 5:21pm
I successfully modded several Sure TK2050 with the Zallman ZM-NB47J heatsink.

It stops overheating. Period. Also costs a fiver.


Operating temperatures dropped from warm / very hot to  cold / slightly warm. You don't need a fan! Just this passive heatsink and access to open air.
Back to Top
infrasound View Drop Down
Old Croc
Old Croc


Joined: 13 May 2011
Location: Brizzle
Status: Offline
Points: 2276
Post Options Post Options   Thanks (0) Thanks(0)   Quote infrasound Quote  Post ReplyReply Direct Link To This Post Posted: 03 October 2011 at 5:23pm
Let me know if you do want to remove the heatsink, I'll find some old instructions on how to do it - it's all too easy to fry the chip or twist it off the board.
Back to Top
alphabetikal View Drop Down
Registered User
Registered User
Avatar

Joined: 20 May 2010
Location: UK
Status: Offline
Points: 217
Post Options Post Options   Thanks (0) Thanks(0)   Quote alphabetikal Quote  Post ReplyReply Direct Link To This Post Posted: 06 October 2011 at 11:54am
Bro if you could post those instructions to remove the naughty old heat sink that would be great and i can buy a  Zalman on amazon for £8 or so

Cheers!
a

Back to Top
infrasound View Drop Down
Old Croc
Old Croc


Joined: 13 May 2011
Location: Brizzle
Status: Offline
Points: 2276
Post Options Post Options   Thanks (0) Thanks(0)   Quote infrasound Quote  Post ReplyReply Direct Link To This Post Posted: 06 October 2011 at 12:02pm
Quote
re: removing the heatsink - it must be done carefully / slowly



howto:

1. remove the nylon fastners

2. get a heatgun / hairdryer and SLOWLY heat up the heatsink

3. as you heat it up, gently twist it from side to side untill it comes off. its important that you take your time as too hot means you'll fry the chips, too cold and you risk pulling them off the board. theres a 50 degree heat window, so take your time!

4. scrape off the old (crap) silicone adhesive

5. follow the heatsink instructions provided with the new sink


whole process should take about 15/20 mins, with a bit of practice I got it down to about 5 :)

NB. The zalmann thermal paste IS CONDUCTIVE. do not get it on the IC legs or bad things will happen Ouch


enjoy!

Back to Top
 Post Reply Post Reply

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.