[Sathimas]

Hi together,
 
I am currently building the "Transistoramp V4.0" amp designed by Andreas Rauenbuehler.
 
You can find the layout, partslist and circuit on the website high-amp.de
(scroll down on the left for English version)
 
 
Now my problem is that the power supply is not working correctly.
 
The cicruit has an integrated protection for each the +400V and -400V section.
 
Now the +400V section works fine, but the -400V section goes into
protected state after turning on most of the time - until now it did not for 2 times
and the outputs were stable at 400V.
 
Does anybody here have experience with this circuit or can help my anyway
to track down the mistake?

 

[duncan1]

If you provided a direct link to the circuit diagram then I could help you.?
 

 

[Sathimas]

http://high-amp.de/html/reg_pws_v4_schematic.html
 
This is the circuit.
 
The problem is solved since yesterday anyway, I exchanged the diodes D507 and D407
with some other ones that are 500mW types (had 1200mW before).
 
No the supply works perfectly stable.
 
 
But I have the next problem already - connected one amp board and after 
about 5 or 10 seconds it gave a loud boom - now T07b and R59 are blown.
 
http://high-amp.de/html/trans_amp_v4_schematic.html
 
 
This thing is drivning me crazy, never had a build that gave me so much trouble.

 

[duncan1]

It is not a good idea to replace the 1.2W Zenners with 0.5W types. Especially as they control the Gate voltage of the mos-fets. When under slight load maybe okay but can blow when under full load putting a large voltage on the Mos-fet Gate blowing it and taking other components along with it

To8B/R59 blowing means a greater than 3 Amp current flowing through TO8B -check D56-18V Zenner and the capacitor that is across it for S/C also C55 and RD   R11B as well as To8A If not check voltage feed in. Its a lot harder giving more precise opinions when the Equipment is not in front of me. Your amp and power supply are of very good quality and are worth fixing.Get back to me.

 

[Sathimas]

Small update: R59 is just damaged on the outside,
I'll replace it anyway. All other resistors are ok.

Still have to check the caps.

I'll post a pic tomorrow.


Thanks for your help up to now, I'll give more information tomorrow.

 

[Sathimas]

concerning the "smaller" diodes:
 
The developer himself is using diodes of that type and I was told that
there are only 0,0001A flowing through it.
 
That part of the circuit is a protection circuit and not part of the
"real" power supply (see the explanation on the website for that,
I do not know enough to explain it to you)
 
 
concerning blown components:
 
- T07b - not T08b is broken
 
- D56 seems to be broken indeed
 
- caps are showing correct values,
but I can only measure 3nF across C54 - but I also get only 3nF across C53.
which should be 100nF (But I also only get those 3nF across the other caps of
that type (in the power supply for example) - Might be because my DMM is 
not very accourate.
 
 
 
Quote:

S/C also C55 and RD   R11B as well as To8A If not check voltage feed in.

 
I did not understand that completely (maybe because I'm no native Englisch-speaker).
 
1. "S/C" short and capacity?
2. RD?
3. R11b is ok
4. other transistors (apart from T07b) are all ok
5. "If not check voltage feed in." 
I don't understand that sentence
 
 
 
Here's the picture I promised:
 
http://www.bilder-hochladen.net/files/4bhv-59-6cdd-jpg-rc.html
 
 
There is another thing I did not mention yet:
While dismounting the board and the transistors from the heatsink
I recognized that the isloation pad on T07b was a little too short and
a small part of the bare metal was open to the heatsink. 
(Should not have had contact, though)
 
May that have caused the problem?
 
Here's also a picture of the entire amps interior:
 
http://bilder.hifi-forum.de/max/183387/transistoramp-v4-innereien_271891.jpg
 
The damaged board is the one on the right.

 

[duncan1]

Hello Sathimas.You mentioned your capacitor test meter might not be correct . If it is part of an multi-meter then right it is wrong. C53 should be 100NF but C54?C55 should be 10uf[microfarad] .C55 is in parallel with the Zenner Diode[18Volts] .If the diode is blown so will C55 be as it is rated at only 25Volts-change BOTH.As you say its TO7B thats blown my mistake there but it doesnt change    s   what I said. You could be right if a heat-sink attached to a bare metal rear of the TO7B it must not come into contact with any other electrical source or earth . But if thats not the case then yes if the heat-sink only covers 0.75% of the transistor then it could overheat.

 The reason I mentioned the voltage feed-in-meaning the supply voltage to that transistor in case it is over voltage in that case if you replaced the components they will blow again. Its a safety check.S/C means =Short circuit sorry for the scientific jargon I sometimes forget that not everybody knows electronics.So to sum up- Change TO7B/C55/D56[zenner diode-18Volts] and if supply voltage is okay then it should work --If not then you will have to send it for repair.Oh and get yourself a decent capacitor tester a dedicated one that can measure resistance and inductance too. They arent that dear.  They are called LCR Meters.                        /

 

[Sathimas]

I'll check all supply voltages again.
 
I also desoldered C54 and measured it - it's ok.
I just can't measure it properly in the circuit.
 
Have to order a new one anyway since I can't get the old one back in.
 
 
Seems I was really lucky.

 

[duncan1]

Sathimas. I didnt know you were testing the capacitors "in circuit" there is specialised equipment on the market that can do this but expensive. Any other capacitor testor MUST be tested out of circuit and make sure there is no voltage across the electrolytics when doing so or "goodbye" tester.Again dearer testers can overcome this but they cost.
AS I said before dont give up on this as going by your circuit diagrams and partsThese are Very good designs well worth repairing.Best of luck.
 

 

[Sathimas]

I'm about to get the parts to replace this week.
 
I'll post again.

 

[Sathimas]

Well, after producing another short circuit by accident the amp now finally lives!
 
I'm currently monitoring the offsets but everything is stable.
Seems I'll be testing with my Lambda Pros in an hour or so :-D

 

[duncan1]

Glad to hear that it is up and working! I like helping people built -in to me.This is a very good amp design and you should be happy with it for years. Glad you checked the off-set right thing to do. Wish you well for the future.

 

[Sathimas]

This is a very good amp design and you should be happy with it for years.

 
Unfortunately, I have not built it for myself
 
But I can keep it for testing for about 6 weeks before the real owner gets it.
 
 
I'm very curiuos if I'll hear some difference to my exstata.

 

[duncan1]

I have no information on the exstata but if you could post a link to the full circuit diagram I could at least tell you the quality of the circuit.But I am sure there will be many here who can tell you the difference between them  

 

[Sathimas]

http://www.cavalliaudio.com/diy/exstata/main.php?page=overview
 
There you can find everything about it.
 
I built the tube hybrid version.
 
 
It's kind of a "poor mans" electrostatic amp, and has been discussed a lot
here in the forum at the time. (Even more (and more critical) in other spaces)