[funch]

 
Quote:

Farnell only do business with companie's, they don't take credit card's. The only thing I could do is to order the parts through my school.


 


You don't have any PN4392's?

     No, sorry, just the 243/53.

 

[vgjako]

I managed to find both transistors on ebay, so now I am almost ready to start assembling my PPA V2.

 

[phishhead92]

how do i ground this in a wooden box? i do not have a drillpress (and i dont want to buy one just for this) for a metal case.
 
plus i have the perfect box for this project.
 
also do you guys just use standoffs and glue the standoffs to the base of the box? i never understood how you mount the finished project in there
 
EDIT: also i am a noob DIY'er, could anyone give me some tips on how to bias the opamps?

 

[tangent]

Quote:

how do i ground this in a wooden box?

 
You don't.
 
The panel components with ground connections get tied to something on the PPA amp board.  That's all.
 
The only potential problem with this is that it means you don't have an RF shield, but PPAs don't seem especially troubled by RF, so I wouldn't worry about it.
 

i do not have a drillpress (and i dont want to buy one just for this) for a metal case.

 
You don't need one.  I use a vise and a hand drill.  For very large holes, I use either a Greenlee panel punch or a step drill bit.  Everything else I shoot straight through.
 
I pad the panel from the vise jaws with a rectangle of denim cut from some old jeans.  One pair of jeans makes a lot of shop rags.
 
Quote:

also do you guys just use standoffs and glue the standoffs to the base of the box? i never understood how you mount the finished project in there

 
 
If the project won't be bounced around, you might get away with mounting the board only to the front panel by the pot shaft.
 
If the rear edge needs some support, yes, you can just glue some standoffs in there, but personally I'd use the kind that are threaded straight-thru and use screws from both sides: one affixes the PCB to the top end of the standoff, the other comes from the bottom outside the case to hold the standoff to the bottom of the case.  Use flat-head screws for the bottom-side ones so you can countersink them into the enclosure.
 
You can go ghetto here, too, if you'd like.  A couple balls of Blu-Tak would would give some of the benefit of a standoff with virtually no work.
 
It's DIY.  Work something out.
 
Quote:

EDIT: also i am a noob DIY'er, could anyone give me some tips on how to bias the opamps?

 
What's wrong with the instructions? (URL fixed; previously pointed to buffer biasing instructions.)

 

[phishhead92]

^^ wow thanks for all the info, i am not sure about the metal box tho, and i have the perfect wooden box atm (fits the TREAD board and the transformer in there perfectly)
 
and i think i will do the holes in the bottom and the double ended standoff, that sounds good and sturdy.
 
man i need to read closer i think i missed the article that went into detail.
 
anyways i hope to be getting said box ready soon, thanks for the help!

 

[vgjako]

I just finished building this amp yesterday, and I knew from various reviews that the amp would be good, but not this GOOD!
 
Listening Impressions:
The first thing I noticed was the separation of the instruments, I was listening to Telegraph Road by Dire Straits and heard many “new” sounds which I never had heard. The top and bottom is silky smooth, I have never heard such a good separation between bass and tremble. The sound is crystal clear and is a pleasure to listen to.
  
Here are the parts used:
- DACT CT-102 Audio Power supply (+/- 15 V)
- Burson Audio Single op-amp
- Elna Silmic II C1 and C4
- Wima MKP10 C2
- Wima MKS2 C5
- 10 pF Silver Mica C6
- Vishay 64W pots
- DACT CT2 50K
- Vishay Dale RN55 resistors
- Takman REY resistors
- 2N5484 Q1
- 2N5486 Q2
- PN4392 Q3, Q4
- 2N5087_J18Z Q-21-23
- 2N5088_J61Z Q31-33
- MJE243G Q24
- MJE253G Q34
- No TLE
 
Im running 20 mA through the output buffers, I have tried to ramp it up to 30 mA, but stangely the DC offset increased. At 20 mA the offset is under ten in all channels. However when I ramp it up to 30 mA the offset is 50 mV in the left channel, 39 in the rigth and 20 in the ground.
What could be causing this sudden increase of DC offset?
 
Link to Pictures (Photobucket):
http://s789.photobucket.com/albums/yy179/vgjako/PPA%20V2/

 

[tangent]

Thanks for the review!
 
 
Quote:

What could be causing this sudden increase of DC offset?

 
Your amp may be marginally stable.  I'd try two things:
 
First, measure supply current to the whole amp while you're adjusting the bias.  If current draw goes up nonlinearly with respect to current setting, it's likely oscillating, which you could verify with an oscilloscope.
 
Second, try a "normal" op-amp, one known to work well in the PPA.

 

[vgjako]

 
Quote:

Thanks for the review!
 
 
 
Your amp may be marginally stable.  I'd try two things:
 
First, measure supply current to the whole amp while you're adjusting the bias.  If current draw goes up nonlinearly with respect to current setting, it's likely oscillating, which you could verify with an oscilloscope.
 
Second, try a "normal" op-amp, one known to work well in the PPA.

 
OK, I'll try measuring the current through the amp.
 

 

[vgjako]

OK, so I have a problem. I turned on the amp today, and I measured 15 V at the left- and ground channel, luckily I didn't plug my headphones in

. I suspected that the Q3's were fried, and so it turned out. I simply replaced them and everything was ok. I measured under 10 mV at each channel.
 
A few hours later the Q3's (PN 4392) fried again, and I don't have any more left. Is there a substitute for Q3 which I can easily get here in Europe/Norway. I use to order parts from https://www.elfa.se/elfa3~no_no/elfa/init.do?init=1&shop=ELFA_NO-NO
 
The PN 4392's have a minimun Idss of 25 mA, the burson op-amps draws 19 mA, and I have a class-A bias of 1,5 mA. This would add up to 20,5 mA which should work just fine. I don't have a clue why this happens, any here who does?
 
Thanks
vgjako

 

[Avro_Arrow]

A devices full power rating is only available with proper heat sinking.
Maybe you just exceeded the temperature rating.
 
Maybe a TO-92 heat sink will help the issue.
 
 
Quote:

OK, so I have a problem. I turned on the amp today, and I measured 15 V at the left- and ground channel, luckily I didn't plug my headphones in

. I suspected that the Q3's were fried, and so it turned out. I simply replaced them and everything was ok. I measured under 10 mV at each channel.
 
A few hours later the Q3's (PN 4392) fried again, and I don't have any more left. Is there a substitute for Q3 which I can easily get here in Europe/Norway. I use to order parts from https://www.elfa.se/elfa3~no_no/elfa/init.do?init=1&shop=ELFA_NO-NO
 
The PN 4392's have a minimun Idss of 25 mA, the burson op-amps draws 19 mA, and I have a class-A bias of 1,5 mA. This would add up to 20,5 mA which should work just fine. I don't have a clue why this happens, any here who does?
 
Thanks
vgjako

 

[vgjako]

Well, they didn't get hot, just sligthly warm.

 

[Koen]

Hi, back again but now with some not-so-good news.
 
It seems I have fried my PPA while trying to power it off of an SLA (battery). Turned out the wires in the DC connector to the PPA were shorted inside. I did not yet have a fuse in the battery wiring to the PPA, nor any kind of current limiting (if that would have helped...).
 
This resulted in
1) A lot of smoke and smell from the plastic burning from the - connection (so - terminal on the battery to V- in the PPA).
2) A PPA which has bad sound in the left channel and no sound in the right channel at all. 'Bad' in the left channel as in quieter than normal and when turning up the volume distorted sound.
 
So somehow the battery short damaged my PPA And I have really fallen in love with it over the last few months...
 
So, basically, I have just one question:

• Would somebody be so nice to help me troubleshoot and fix this? I have taken the following measurements, all with respect to V- (unless noted otherwise)

1. V+/V- = 13.4 (low, I know, but as designed; has been working fine on this voltage until now)
2. Q3R+ = Q3G+ = Q3L+ = 13.4
3. Q3R- = 11.7 || Q3G- = 12.3 || Q3L- = 2,6
4. DC Vout left channel (respect to out ground): -0,3 V
5. DC Vout right channel (respect to out ground): 0,09 V
6. VopampLv+v- = 10.8V
7. VopampGv+v- = 1.1V
8. VopampRv+v- = 1.6V
9. I stopped measuring after this because I don't know yet what exaclty I am looking for...

 
Possibly the following bits of information help:
 

• Opamps are AD8610
• There's no visbile damage to the PCB nor any of the components.
• If it helps, I do have access to a scope.
• (Academic-type-question) how/why did the 'infinite' current @ ~ 13 V between the battery terminals (and thus the V- and V+ pads?) damage the PPA? 

 

[tangent]

Quote:

how/why did the 'infinite' current @ ~ 13 V between the battery terminals (and thus the V- and V+ pads?) damage the PPA? 

I don't see how it did.  The fact that your + and - rail measurements don't add up to the + to - rail value is also suspect.
 
I'd look farther up the chain.  I'd replace the DC input jack for one thing.  If it melted, even a little bit, it could now be permanently shorted, or near-shorted.  That can cause all sorts of havoc.

 

[Koen]

Quote:

I'd look farther up the chain.  I'd replace the DC input jack for one thing.  If it melted, even a little bit, it could now be permanently shorted, or near-shorted.  That can cause all sorts of havoc.

Removed the jack (and switch) completely and took the board out of the case to make sure there's no ground loops there. Power supply is OK, nice flat 13.4 as indicated before. I did some additional measurements:
 
(these are the output resistor pairs, 2.2Ohms, there used to be 44mV across each single resistor, + probe always closest to output pad)
R24R -23,1mV
R34R 42,1mV
R24G -25.9mV
R34G 11,1mV
R24L -13.9mV
R23R 8.9mV
 
??? So there's not a single 'normal' channel, as these should all be at ~44mV..? Considering also there is no single pair showing the same drop across both resistors, would the Q24/Q34s be the next parts to check? If so, how do I check them??..
 
 
Also checked in/output of the L/R opamps:
* Both get the correct input-waveform (verified with scope)
* The R-opamp is outputting nothing (that's why I am hearing nothing in that channel, I guess)
* The L-opamp is outputting correct waveform, but is clipping (that's why I am hearing distorted sound in that channel). Clipping is on the top-side of the waveform, bottom side seems not to clip. Clipping occurs at around +140mV
 
I will be adding more troubleshoot data as I investigate further.

 

[Koen]

OK, some additonal troubleshooting info:

1. Removed the TLE for the (dead) right channel from the circuit to verify it's working: nicely splits 14V in half. So I guess that rules out the TLE as the source of the problem.
2. Also removed the opamp for the right channel from the socket to rule this part out as the culprit. Still seeing the same odd voltages at the pads for V+ and V-:
3.     measuring 1.56V from the opamp V- pad to opamp V+ (I expect this to be around DC nput V+/V-, so around 14V in my case)
4.     0.93V from V+ pad to signal ground (no source connected)
5.     -0.6V from V- pad to signal ground
6.     these nicely add up to ~1.56V difference...., but I guess not what I should be seeing here.
7. Q3 transistors nicely pass the V+/V- from the input, so I don't think these are the issues either.

 
Does anybody know what voltages I should be seeing here (feeding 14V from TREAD supply)?
 
Reading this on vritual grounds I should be seeing ~7 V between signal ground and input V-, but I am seeing ~12.4V??
 
Also swapped opamps, symptoms stay the same. I definately think there's something wrong with the part of the amp powering the opamps. Amp is drawing only 50mA (inluding a dimly lit green LED). I'll continue studying Tangent's troubleshooting guide.
 
In the mean time, any advice on where to look next much appreciated.