ZAPpulse and S&B TX102 = smoke, help!

Tenson · 19th August 2006, 10:05 PM

Hi,

I just put together my LC Audio ZAPpulse 2.3SE amp and it works great from my soundcards output however when I connect it to my main system I get some nasty behaviour and I am stumped!

My main source is a Behringer DEQ2496 where I have bypassed the output stage and go direct to a pair of S&B TX102 attenuation transformers. The DAC chip had 2.6V DC on its like but when wired balanced to the transformers it becomes common mode so I wouldn't think this is the issue....

Anyway when I connected it at a low volume setting I get a fair but of hum and noise. I thought maybe it was an impedance issue as the LC Audio modules are only 17K Ohms input impedance. I switched to only a small amount of attenuation so the DAC sees nearly the full 17K but like this the modules started glowing red hot and smoking! I pulled the plug in time to save them though it did blow the tweeters on my test speakers.

It was as though the input earth was connected to the heatsink of the modules (output transistors connect to the heatsink, maybe the adjust pin? Why don't they use mica pads?)

I am lucky they still seem in perfect condition but I can't use them if I can't make it work with my set-up!

Please help!

Tenson · 19th August 2006, 11:06 PM

Okay well I checked to see if I had been sent a low noise version or something which has only a 2K input impedance which after the transformers my DAC wouldn't like much but I don't have that! So it has a 17K input impedance which I think should be fine... I am completely clueless why they like to smoke so much lol! They are addicted!

ghemink · 20th August 2006, 01:20 PM

Quote:

Originally posted by Tenson
Okay well I checked to see if I had been sent a low noise version or something which has only a 2K input impedance which after the transformers my DAC wouldn't like much but I don't have that! So it has a 17K input impedance which I think should be fine... I am completely clueless why they like to smoke so much lol! They are addicted!

What was the part that was smoking? I have had the 2.3SE and I got them smoking as well. The part that can easily be smoked is the resistor in the zobel network. If you get the amp to oscillate at a high frequency (which was not so tough with the 2.3SE in an experimental setup) then that resistor has to burn a lot of power, I have seen smoke from that resistor and I have also blown up one. This may also explain why your tweeters were fried (too much HF power).

I do not have a solution for you. Probably you have to look into earthing etc, to prevent that the thing oscillates. If you want an amp that behaves well, just use an Hypex UcD180 or 400 (as I do now), these amps are very low noise, do not have any HF oscillation issues and do not have a zobel filter, so one less part to blow up :-)

Best regards

Gertjan

Tenson · 20th August 2006, 04:06 PM

Thanks Gertjan!

I think the first time it smoked with this set-up was a fluke, I must have had something shorted as I have not got it to smoke that badly again (visibly glowing hot in less than 5 seconds).

However, I do still get smoking, and it is from the resistor in the zobel.

I did a bit more experimentation…

1. Using the attenuation transformers driven from my soundcard (which worked fine direct) also works fine, so it is not the transformers causing the problems.

2. I then tried the modded output from my DAC with the transformers, but I put in a pair of 2.2uF caps to block any DC. It now makes some very loud low frequency hum! Odd, as it should do the opposite! It also still gets hot so it is not DC on the line causing the problem.

3. I connected it up as I did when it went red hot last time with the modded DAC output and the transformers, no DC blocking caps as the DC should be common mode (like I said I think I had a short last time) and now, the left channel works fine (though still noisy) and the right channel gets very hot.

I looked over the right channel very carefully and I found a hair-crack in the orange cap on the input. I had bent it back a little bit to make soldering the input easier, obviously it didn't like it and cracked!

I think maybe this blocked high frequencies on the input and now its broken the right channel is oscillating.

Does this sound like the reason to you? Does anybody know the value of that cap so I can replace it?

I won't know what all the noise is until I solder up the transformers nicely instead of using crock-clips I just hope it is not an impedance issue as the noise is reduced with more attenuation (lower level) which does result in a higher input impedance and a lower output impedance on the transformer. However, I don’t see it should be an issue when the amp has a 17K input.

Cheers,

Tenson · 20th August 2006, 05:37 PM

Okay so I obviously need to replace that cap even if it is not the full problem.

Its a 'BC128 47uF 6V3' Google says it is a solid aluminium.

Where can I get a replacement? I looked on RS but I don't see any 'solid aluminium' section!

This is the one-

How about replacing it with a 47uF 6.3V Tantalum?
Or maybe a SMT aluminium electrolytic?

t. · 20th August 2006, 05:59 PM

Hi Tenson,

Don't use Tants mate, they won't sound as good as the BC128's

You can get both the 6.3v and 10v 47uf BC128 from Farnell, order code is 1166620 for the 10v

Good luck with sorting out your problem, I'm afraid I've never had any experiance with the ZAP modules so can't really help

Regards,

Leo

Granholm · 20th August 2006, 07:17 PM

Have you any possibility to check your DAC with a scope to see if any HF is getting out this way?

Rgds

Tenson · 20th August 2006, 07:26 PM

Usually the output is as clean as something very clean but I can hear noise all over it so I know there is HF noise on the line. Why, is another matter. I think it is likely to be not using any shielded cables, though it has not been a problem in the past. The amp runs fine from my soundcards output via shielded cables so I will build the transformers and DAC into a nice case with short shielded wires and see where we are then.

Thanks for the help and I will keep you updated.

Granholm · 20th August 2006, 08:38 PM

Maybe ask Lars Clausen if he know of a good replacement. He have had some problems on his new module (NCD) where a cap failed. Read here for details: New Module by Lars Clausen

And aparently he will replace it so he might be able to sugest a new one even if he is not involved in LC Audio any more. www.newclassd.com is his new site.

Rgds.

bambadoo · 20th August 2006, 08:57 PM

In the zappulse 2.2se these caps were black gate n..

And the bigger caps were black gate fk I think.
I have blown a couple of 2.2ohm resistors in the zobel network all right..

19th August 2006, 10:05 PM	#1
Tenson diyAudio Member Join Date: Feb 2006 Location: Kent	ZAPpulse and S&B TX102 = smoke, help! Hi, I just put together my LC Audio ZAPpulse 2.3SE amp and it works great from my soundcards output however when I connect it to my main system I get some nasty behaviour and I am stumped! My main source is a Behringer DEQ2496 where I have bypassed the output stage and go direct to a pair of S&B TX102 attenuation transformers. The DAC chip had 2.6V DC on its like but when wired balanced to the transformers it becomes common mode so I wouldn't think this is the issue.... Anyway when I connected it at a low volume setting I get a fair but of hum and noise. I thought maybe it was an impedance issue as the LC Audio modules are only 17K Ohms input impedance. I switched to only a small amount of attenuation so the DAC sees nearly the full 17K but like this the modules started glowing red hot and smoking! I pulled the plug in time to save them though it did blow the tweeters on my test speakers. It was as though the input earth was connected to the heatsink of the modules (output transistors connect to the heatsink, maybe the adjust pin? Why don't they use mica pads?) I am lucky they still seem in perfect condition but I can't use them if I can't make it work with my set-up! Please help!

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19th August 2006, 11:06 PM	#2
Tenson diyAudio Member Join Date: Feb 2006 Location: Kent	Okay well I checked to see if I had been sent a low noise version or something which has only a 2K input impedance which after the transformers my DAC wouldn't like much but I don't have that! So it has a 17K input impedance which I think should be fine... I am completely clueless why they like to smoke so much lol! They are addicted!

20th August 2006, 04:06 PM	#4
Tenson diyAudio Member Join Date: Feb 2006 Location: Kent	Thanks Gertjan! I think the first time it smoked with this set-up was a fluke, I must have had something shorted as I have not got it to smoke that badly again (visibly glowing hot in less than 5 seconds). However, I do still get smoking, and it is from the resistor in the zobel. I did a bit more experimentation… 1. Using the attenuation transformers driven from my soundcard (which worked fine direct) also works fine, so it is not the transformers causing the problems. 2. I then tried the modded output from my DAC with the transformers, but I put in a pair of 2.2uF caps to block any DC. It now makes some very loud low frequency hum! Odd, as it should do the opposite! It also still gets hot so it is not DC on the line causing the problem. 3. I connected it up as I did when it went red hot last time with the modded DAC output and the transformers, no DC blocking caps as the DC should be common mode (like I said I think I had a short last time) and now, the left channel works fine (though still noisy) and the right channel gets very hot. I looked over the right channel very carefully and I found a hair-crack in the orange cap on the input. I had bent it back a little bit to make soldering the input easier, obviously it didn't like it and cracked! I think maybe this blocked high frequencies on the input and now its broken the right channel is oscillating. Does this sound like the reason to you? Does anybody know the value of that cap so I can replace it? I won't know what all the noise is until I solder up the transformers nicely instead of using crock-clips I just hope it is not an impedance issue as the noise is reduced with more attenuation (lower level) which does result in a higher input impedance and a lower output impedance on the transformer. However, I don’t see it should be an issue when the amp has a 17K input. Cheers,

20th August 2006, 05:37 PM	#5
Tenson diyAudio Member Join Date: Feb 2006 Location: Kent	Okay so I obviously need to replace that cap even if it is not the full problem. Its a 'BC128 47uF 6V3' Google says it is a solid aluminium. Where can I get a replacement? I looked on RS but I don't see any 'solid aluminium' section! This is the one- How about replacing it with a 47uF 6.3V Tantalum? Or maybe a SMT aluminium electrolytic?

20th August 2006, 05:59 PM	#6
t. diyAudio Member Join Date: May 2003 Location: notts	Hi Tenson, Don't use Tants mate, they won't sound as good as the BC128's You can get both the 6.3v and 10v 47uf BC128 from Farnell, order code is 1166620 for the 10v Good luck with sorting out your problem, I'm afraid I've never had any experiance with the ZAP modules so can't really help Regards, Leo

20th August 2006, 07:17 PM	#7
Granholm diyAudio Member Join Date: Feb 2006 Location: Copenhagen	Have you any possibility to check your DAC with a scope to see if any HF is getting out this way? Rgds

20th August 2006, 07:26 PM	#8
Tenson diyAudio Member Join Date: Feb 2006 Location: Kent	Usually the output is as clean as something very clean but I can hear noise all over it so I know there is HF noise on the line. Why, is another matter. I think it is likely to be not using any shielded cables, though it has not been a problem in the past. The amp runs fine from my soundcards output via shielded cables so I will build the transformers and DAC into a nice case with short shielded wires and see where we are then. Thanks for the help and I will keep you updated.

20th August 2006, 08:38 PM	#9
Granholm diyAudio Member Join Date: Feb 2006 Location: Copenhagen	Maybe ask Lars Clausen if he know of a good replacement. He have had some problems on his new module (NCD) where a cap failed. Read here for details: New Module by Lars Clausen And aparently he will replace it so he might be able to sugest a new one even if he is not involved in LC Audio any more. www.newclassd.com is his new site. Rgds.

20th August 2006, 08:57 PM	#10
bambadoo diyAudio Member Join Date: Feb 2003 Location: West Coast of Norway	In the zappulse 2.2se these caps were black gate n.. And the bigger caps were black gate fk I think. I have blown a couple of 2.2ohm resistors in the zobel network all right..

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