Source Manufacturing - C-Mark, Thomann and Audiohead Amps

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I'm reasonably familiar with these beasts if anyone needs to know anything specific!

Ok, here goes......

I have a 2.5K AH that I started this thread with, It was down on one channel and after some tinkering couldn't really see anything that was wrong, I'm not great at electronics but I know the basics. I managed to get hold of another 2.5K AH with a channel down and thought I would just swap the channels around, I did this and still had an issue, the fault light would stay on for a few seconds longer on one channel before it would go out. by chance I turned it on one day whilst looking inside and saw that one of the bridge rectifiers (left channel) on the power board was arc'ing across itself so off to the internet I went. I was able to find a data sheet for the original rectifier here

KBPC3510PW

The only rectifier I could find as a replacement was this one

GBPC3510W

After replacing with the above it seemed to work fine and I took it out for a few gigs and the only thing I noticed was that one channel was clipping quiet a bit sooner that the other (right channel), however the 2 channels sounded the same, the strange thing was that it was not the channel on which I had changed the rectifier.

Anyway, during a very small gig (it was a kids party so very low levels, just over background level) I started getting one channel playing up in that the volume level would greatly increase for a few seconds at a time and after a while i got a very strong smell from the amp and lost a channel (left channel).

Upon investigation, I have 2 resistors on the board that are totally black and the board is considerabley scorched along with another 2 resistors that are showing signs of overheated (not unusual on these amps i'm led to believe) and the legs are discoloured consistant with overheating (I can provide pics if needed).

Anyway, the other amp seems to be power supply related so I took the other channel out and put it in place of the dead channel, I dont get any fault lights when powered up but dont want to put any load on it in case I blow it again, would you suggest I change all the bridge rectifiers so they are all the same, after that what do you suggest?

Much appreciated

Nelix
 
hi Nelix,
just a very quick reply - firstly i would say the bridge rect you have chosen is correct.
3510 translates as 1000V / 35A, K means the case is made out of expoxy resin, GP means the case is glass re-inforced plastic as you've found in the data sheet.

as for the clip LED's in these amps, they are driven through a bridge rectifier from the same output that drives the power amp.
This means - that if correctly designed, the LED will give a true indication of when the output waveform is distorted when compared to the input.
There are a few floors in this system - firstly, on a high quality amp, the LED drive would be taken through a buffer chip so that the high quality drive amp did not see the nasty load that the LED presents (which, in theory, would actually create distortion).
secondly, if components in this LED circuit are tired or mis matched, you may see the LED on one side behaving differently to the other.
Thirdly (but not in your case), if the amp is continuously run at clipping, or goes DC, it can kill the clip LED, or the 1k resistor that is in series with it.

burned resistors:
this series of amps has a lot of power resitors that run hotter than i like.
the power resitors do various jobs:
1) to save the cost of an additional +/-15V supply for the chips, the HT rails are dropped through a pair big resistors in paralell (10k - 18K, depending on the model), then through a 15V zener(reverse biased) to ground, there is a small electrolytic across the zener to smooth the resultant supply.

http://www.wisc-online.com/objects/index_tj.asp?objID=SSE7005

these resistors run too hot in my opinion.

2) There are some snubber resistors across the rail switching FETs - as mentioned by kev. These are in serier with something like a 100nf / 1kV capacitor, and act exactly like switch suppressors.

3) There is a power resistor (10R/3W) in series with something like a 100nf / 1kV across the speaker output and ground (on the circuit board, but other manufacturers often fit them across the speaker terminals).
The purpose of this is to provide the amp with a load at high frequencies if it is driving an inductive load.
However, If (any) amp is driven at clipping.. the HF harmonics of the clipped waves end up being dissipated in this resistor, which can actually burn out. (remember, its a 3W resistor across a 1kW amp !).
I found in the AH 4000 that i was testing, that if i let it clip for more than 20 seconds, this resistor will smell, and start to smoke.

If you can get some pics, or more importantly, work out what is connected to each eand of the resistors in question, it would be useful.

From memory:
resistors connected to the +/- HT rails, with a zener to ground will be power supplies.
resistprs in series with a ~100nf should be snubbers or the output Z load.

Its always worth checking that the aux supplies in amps are ok... with an amp like this, where its difficult to get probes in, I often solder wires onto the board and connect the meter / scope to them....
I takes longer, but its a lot safer than waving metal probes around a live amp, and it makes you stop and think about what you're doing and the possible dangers.

Good Luck,
Jonathan

P.S. - Thanks Kev for the bias setting tip :)
 
Hi nelix,
I'm afraid the pics aren't much use to me - any chance you can find the value of the resistors by looking at the other board?

really, i'd need to know what is connected to each end of the resistors.
you need to carefully examine the board for burned tracks, and if any of the power devices have failed.

i can see some diodes nearby - are any attached to these resistors? does the other end go to the lower supply rail (~+/-70V) ?

now, i've just spent some time digging out photo's i took, and cct diags that i drew form the AH4000 that i was working on.

looking at the 'before' pics, i can see 2 badly burned resistors in a similar position on the board to the ones in your photo. I must stress, that these are different boards, but working on a total hunch.. I'm going to suggest that the burned resistors marked R67 and R68 are:

1) in paralell with each other
2) one end of the pair goes to a polyester capacitor ~2nf
4) there are 2 diodes (1n4004 or 1n4007) going from the junction of the resitors and the capacitor (they go off to the +15 and -15V supplies respectivley).
5) the other end of the resistor pair goes off the centre tap of the transformer (usually we'd call this "0V", but not in this grounded collector topology).
6) the other end of the 2nf cap should go to the common collector rail (L.S. -ve).

If these are correct, then the resistor pair are the ones i mentioned before which burn up if the amp clips for a long time.
on the AH4000 they were 1k8 / 3W and it wouldn't surprise me if they were the same value on this amp too.


good luck :)
jonathan
 
I can confirm that the resistors are 1K8 /3W, I'll have a look and let you know more regarding tracks etc as you described above.

The only thing that puzzles me is that when the channel went, It was only being used at low volume, I suppose that due to it being driven harder at previous gigs this was maybe the straw that broke the camels back.... so to speak.

More details to follow.

Thanks
 
Everything appears to be as you describe above.

I put the working channel from the other amp in the one i'm currently working on to rule out a problem on the board, I also changed ALL the bridge rectifiers. all seemed to be working fine and the clip lights were identical, however when I pushed it harder the 2 fuses on the board started glowing to the beat of the music then 'POP' one of them blew and the clip light is on constant.....as expected.

I'm begining to think I should just bin these amps, it's a shame and I dont really want to, kevvywevvywoo - if I was to send one to you how much would you charge to send it back working LOL.

Cheers
 
It was only being used at low volume

This suggests to me that the bias has been set too cool. At low volume, it can cause most of the output signal to be clipped though not always audible on a big speaker. This might also suggest why the RC networks have gone. Check the resistance of the snubber caps (the brown things next to the burnt resistors). They may be short! (they should be open). If a cap has gone short, it might also explain the glowing fuses since the poor series resistor would be the only thing limiting the current before the resistor fried as well. (And they dont always go dark..sometimes they just go open invisibly).

Most of these amps are tedious to work on, mainly because of the heavy varnish they're coated with. A short circuit rail switch (or bad drive) won't necesssarily cause audible problems but will stress the outputs till they fail usually on a gig. This may of course be another reason yours failed at low volume..the outputs may have been subject to full voltage at a low base drive.
 
good ideas kev.

i've been trying to think of reasons for the volume jumping "up".
all i can think of is possibly a dry joint in the input buffer around its feedback resistor.
another possibility is: if the level control was not set to max (quite common when doing a small gig with a big system), then if there was a dry joint in the ground connection to the level pot i guess it could cause the level to jump up.

i think if there was a dry joint in the power amps feedback this would cause the amp to latch up and fail rather than get louder.
maybe if the bias pot was faulty / oxidised this would cause the bias to drift randomly (i find this a lot in older amps, and often replace the bias preset as a matter of course).
although i don't think changes in bias would change the gain of the amp, low bias will increase harmonic distortion (2nd harmonic upwards). maybe the increased distortion would sound like and increase in overall volume ? - its not something i've experienced.

any ideas ?
jonathan
 
oh - i meant to say i agree with kev - these laquered boards are a total nightmare... you get false readings with probes, and if you press hard with a probe, you are likely to slip and short something out !
this is one of the reasons I solder wires to the point i wish to test even though its time consuming.
Also, the fumes from the laquer while soldering make me feel ill.

I'm currently using an AH4000 as a handy door stop :-D

j
 
To be fair they sound pretty good when they're working properly...but thank QSC for that one!

You get what you pay for, and no more. You sometimes get less. These amps are cheap...so work it out! The manufacturers, importers and stockists aren't philanthropists...they all make their mark-up before it gets to you!
 
is ta1400 and ta2400 the same amp

Hi,

Is TA1400 and 2400 the same amp. A friend asked me to wire back up the brigerecafire board (the board with the cap on it). He took the board out of a dead TA2400 and his TA1400 is working but it needs some capasitors replaced and he decided to do it himself but he forgot how the board was wired I have seen some pics of the TA2400 on the net and was going to wire up the TA1400 by the order of the colour on the wires.

I was looking for the schematic of the amps on the net but have not found any.
 
the brigerecafire board
bridge rectifier board maybe?


These psu boards will be the same basic pcb, but the component values may be different or some components not fitted on the smaller amp, I cant remember. Some are class B, some are class H, the former have 2 bridge-rectifiers and 4 capacitors, the latter have 4 bridge rectifiers and 8 capacitors. Some of the larger amps have the pcb tracks reinforced by fuse wire soldered all along the tracks.

It's best not to swap boards from dissimilar amps unless you're 100% certain they are identical.

If you want the schematic then pm me with a suitable email address.
 
bridge rectifier board maybe?


These psu boards will be the same basic pcb, but the component values may be different or some components not fitted on the smaller amp, I cant remember. Some are class B, some are class H, the former have 2 bridge-rectifiers and 4 capacitors, the latter have 4 bridge rectifiers and 8 capacitors. Some of the larger amps have the pcb tracks reinforced by fuse wire soldered all along the tracks.

It's best not to swap boards from dissimilar amps unless you're 100% certain they are identical.

If you want the schematic then pm me with a suitable email address.

Hi Kevin,

Thank you for the schematic.

yes both boards are the same as in having the same comopants but the output connectors in a diffrent order but the wires are in color are going to the same connectors on the amp boards in both amps as in colour.

The only diffrents I can see between the amp boards are there is one less power transistor on TA1400.
 
Well I have tryed power up the amp and it works well one side does and the other side has noise. Now all I have to do is find the noise and kill it and get some audio comming out of that channel.

Thank you keven for your help and there is just one more thing I need it the schematic for the amp board itself and the control board at the front of the amp (TA1400)
 
New mail address

Hi guys,

sorry I never changed my contact details when I finally caved in and went with Sky for my broadband and satellite.

Living in a small remote village means we'll never be cabled and BT has a strangle-hold on the boradband connection whether you use them as an ISP or not...

On a good day I get around 1mbps and at times it's as slow as dial-up.

Anyhow -

If I can help anyone just mail me at grahamprie@sky.com and I'll do my best.

Graham.
 
Good to see this thread is still active! I still have mine to sort out, put it to one side all those years ago intending to try and re-engineer the bias circuitry so it doesn't easily self destruct, but things get in the way -wife, kids, beer, not necessarily in that order. Perhaps I'll finally get around to it after Christmas. :)
 
If anyone's in london and wants to take away an audiohead 4000 for free... its in my way.
99% repaired them i mis-read my scope and killed the output devs.
needs:
Full set of o/p devs
probably a few of the switching fets
Current Limiting Setting (what i was doing when i killed it)
Bias Setting.

After that you'll have an amp !
 
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