[tdubl07]

Hi guys, I've got a slight issue when I first turn on the amp on. This happens with different tubes and tubes swapped from left to right as well. I have a very loud hiss at no volume in only the left channel. It doesn't change with volume or with input disconnected. I've exchanged quite a few emails with Tomb on this and just trying to see some others thoughts as well. The odd thing is, after the amps warmed up a bit the hiss is gone, or at least inaudible to my ears. This morning got it to disappear just by turning the volume pot up to about half volume. At that point the hiss ramped up louder (almost like a crashing wave or inrush of current) and then goes away completely. Once it's gone, I can completely turn the volume all the way back down and it's dead silent. I thought perhaps I overheated the front z switch desoldering it to get it to properly line up with the front panel (since only after I moved it and re-soldered it did I get the noise), so I removed the z switch altogether and added jumpers. That seemed to cure the problem at first attempt. But in the morning here at work the hiss was back. I should also add I trimmed the pot shaft (to get knob closer to amp) with my dremel at the same time I moved the switch. I've ordered new zeners, new switch and all new rectifiers, new led's, transistors and more from mouser just to have on hand to try and get rid of this. Probably be here by this weekend so I can do some troubleshooting. Any ideas gents? Also The amp sounds absolutely fantastic warmed up and with no hiss. I can listen all day and the hiss never returns. 

 

[dsavitsk]

That's a new one. Do all of the LEDs light up? What size resistors did you use for R10 and R11, and are C7 and C8 populated?

 

[tdubl07]

That's a new one. Do all of the LEDs light up? What size resistors did you use for R10 and R11, and are C7 and C8 populated?

Yes all led's light up, first the two, and then all 4 as they should. I got the full kit from beezar so R10 and 11 are 1M, and C7 and C8 are empty and unpopulated. An additon to my prior statement saying the hiss never returns.....it just came back strong in the left channel for a few seconds.....and is now gone again. The amp has been on since I got here to work this morning, so about 5 hrs. I basically reordered all components off of the BOM minus the capacitors to start troubleshooting. Is it possible I overheated the zeners desoldering them when I had them in backwards (or possibly harmed them by having them in reversed) and now one is acting up every so often causing the hiss? It's odd because it's only in the left channel. Dead silent in the right channel all the time. The zener's are gonna be the first thing I change when my mouser order comes in along with my z switch (although I've ruled that out with jumpers in place now). Thanks for the help guys, it's much appreciated. 

 

[dsavitsk]

Zener would definitely be the first thing I tried. Let us know.

 

[tdubl07]

Ok a little update. Got my mouser order in. Just put in the new z switch, and also swapped new zeners in, hoping for the best I fired it up and hiss is still there in left channel. All 4 LEDs light up fine, also checked Pl and PR voltages and got 97.2 and 97.9 so I'm guessing those check out fine. Ideas on next thing to swap? Got all new LEDs, all new resistors, transistors, and rectifiers from mouser so what's the most likely thing to be causing the hiss next in line? Forgot to add I do have an extra pot around, I'll probably try that as well. Thanks
Edit, just changed the pot out and so far so good. The hiss is always right when I turn on the amp and it's quiet as of now. It makes some sense to me it could be the pot since I trimmed the pot shaft (dremel), at the same time I moved the zeners and only after did the hiss start in. Fingers crossed that was it.

 

[tomb]

Ok a little update. Got my mouser order in. Just put in the new z switch, and also swapped new zeners in, hoping for the best I fired it up and hiss is still there in left channel. All 4 LEDs light up fine, also checked Pl and PR voltages and got 97.2 and 97.9 so I'm guessing those check out fine. Ideas on next thing to swap? Got all new LEDs, all new resistors, transistors, and rectifiers from mouser so what's the most likely thing to be causing the hiss next in line? Forgot to add I do have an extra pot around, I'll probably try that as well. Thanks
Edit, just changed the pot out and so far so good. The hiss is always right when I turn on the amp and it's quiet as of now. It makes some sense to me it could be the pot since I trimmed the pot shaft (dremel), at the same time I moved the zeners and only after did the hiss start in. Fingers crossed that was it.

I'm so sorry you're having trouble like this.  It's hard to see how the volume pot could cause something like this, but if things weren't completely sealed when trimming the shaft, it might have let some metal powder get inside the pot.  Maybe that could cause it.
 
Just an FYI, and it's my fault for not having this properly documented ... but I don't trim the pot shaft until the amp is built and completely assembled - endplates, all screws, everything - including the shaft washer and nut.  Then I put the amp in a small plastic garbage bag - pot shaft down at the bottom.  I cut a small slice in the bottom and then poke the shaft through (sometimes I cheat and just poke the shaft through the plastic - depends on how thick the bag).  Then I close the bag up in the back with a twist-tie.  A bit of tape on the bag plastic around the shaft threads/nut and things are completely sealed.  Then I dremel about 1/4" off with a cutoff disc(s).  I usually clean up with one of those tips that have a depressed center on top.  It fits right around the tip of the shaft and smooths off the edge.  Then I take the bag off, being careful to go backwards so no metal gets anywhere into the amp.

 

[tdubl07]

Thanks Tom. And no need to apologize, stuff like this happens. No big deal. That's exactly what I did when I trimmed it. I know I did the same thing on my mini max and it didn't cause an issue. Either way it's really the only thing that makes sense since the hissing started after my zener desolder and pot shaft trimmed. Good thing I ordered an extra pot from you a while ago and it's just been sitting in the closet waiting for a project haha. I'll keep u updated.

 

[tdubl07]

OK, well I am absolutely clueless. I did not here a hiss at turn on as usual, and now 10 minutes after my amp has been on, it has made it's unpleasant return. SO I have now changed the pot, changed the zeners, and changed the z switch. What shall I start changing next guys? Like I said I've got all parts in hand except for the capacitors and choke. Is it possible I could have a bad choke? I really am clueless where to start as all my soldering looks great. Transistors next? This is driving me nuts not being able to pin this down! The worst part is how random the hiss is. It still remains only in the left channel. And when it's hissing it's loud enough to hear over the music. The upside to all of this is I'm getting very good at desoldering 

 

[dsavitsk]

Weird. I guess I'd do transistors next, and then LEDs.

One thing to think about is that as things heat up, due to expansion, once sound connections can become unsound. So it might be worth re-applying heat to all the joints first.

Choke is probably the least likely candidate on the board.

 

[tdubl07]

 

Weird. I guess I'd do transistors next, and then LEDs.

One thing to think about is that as things heat up, due to expansion, once sound connections can become unsound. So it might be worth re-applying heat to all the joints first.

Choke is probably the least likely candidate on the board.

OK thanks Doug. I would assume I should only be changing left channel stuff now. I have actually reflowed all joints that look even a little odd but they all look really good. Could this possibly be a bad decoupling/output cap? I have the solen's in right now. If I'm reading the schematic correctly looks like D10,D12 (already changed),D13, Q1,Q3,Q5 will be the next candidates. Also do you guys think it's possible that this could be a bad output transformer on the left channel or highly doubtful?
Thanks Trav

 

[tomb]

   

Weird. I guess I'd do transistors next, and then LEDs.

One thing to think about is that as things heat up, due to expansion, once sound connections can become unsound. So it might be worth re-applying heat to all the joints first.

Choke is probably the least likely candidate on the board.

OK thanks Doug. I would assume I should only be changing left channel stuff now. I have actually reflowed all joints that look even a little odd but they all look really good. Could this possibly be a bad decoupling/output cap? I have the solen's in right now. If I'm reading the schematic correctly looks like D10,D12 (already changed),D13, Q1,Q3,Q5 will be the next candidates. Also do you guys think it's possible that this could be a bad output transformer on the left channel or highly doubtful?
Thanks Trav

You've replaced so many parts to no effect, I kind of agree with Dsavitsk: the fact that you didn't notice it until you trimmed the pot shaft may just be a coincidence.  Or, the stress of trimming the shaft may have knocked something loose.
 
Again, I'm sorry you're going through this, but I would tend to focus on other things besides replacing the parts at this point.  Check all of your resistors - see if you can measure good resistance values by measuring from adjacent pads/traces, not the leads directly.  This can confirm good connections or not.  Also, you might take a close look at the tube sockets - especially on the left side.  I would've said this was a tube thing, but you said you switched them and it stayed in the left channel.  If that's the case, then maybe there's something wrong with the socket on that side and only allows intermittent connectivity with one or more of the pins.
 
Just some guesses ...

 

[tdubl07]

I am definitely going to have a long hard look at the left tube socket. As you said something might be odd with it. I did manage to break my telefunken in the left tube socket yesterday (cracked it around the pins). Think it was just a coincidence since I have no trouble getting tubes in or out of that socket. Then I shall be off to swapping more parts. Really the only things I've changed so far are the zeners, the pot, and the z switch. It's just been an ongoing battle so it seems like I've changed more. LOL. It's ok, I will get to the bottom of this, just a bit frustrating since I think it's fixed only to come back again. I'll get it fixed guys! There's really not too much to this circuit so not too many parts to go thru. One a time and we'll get to the bottom of it. I will rewet all my joints on the left channel, hopefully tonight, and try again. Thanks

 

[tomb]

  I am definitely going to have a long hard look at the left tube socket. As you said something might be odd with it. I did manage to break my telefunken in the left tube socket yesterday (cracked it around the pins). Think it was just a coincidence since I have no trouble getting tubes in or out of that socket. Then I shall be off to swapping more parts. Really the only things I've changed so far are the zeners, the pot, and the z switch. It's just been an ongoing battle so it seems like I've changed more. LOL. It's ok, I will get to the bottom of this, just a bit frustrating since I think it's fixed only to come back again. I'll get it fixed guys! There's really not too much to this circuit so not too many parts to go thru. One a time and we'll get to the bottom of it. (There something wrong with measuring directly to resistor leads Tom?) I know you can't touch the leads with your hands. Just the probes.

Measuring resistance at the resistor leads does nothing to check whether they're soldered firmly into the circuit board.  Also, when you're measuring resistance and circuit continuity, all power is OFF and the plug is not in the wall socket.

 
 
You can do the same thing with the tube socket - stick a probe in each of the holes, then use the other probe to connect to a part/trace somewhere removed from the socket (but supposed to be connected to that pin in the circuit).  If you get zero resistance, then the connection is good.  If not, either you measured the wrong thing or there's a problem.

 

 

[lithium1085]

Hi everyone,
 
I have been a lurker on this thread a long time. Do you guys think that someone with no DIY experience (like me) can successfully build this amp? I am very interested in this amp and hopefully can try it soon. Also, what do you guys think about the power output ?

 

[tomb]

  Hi everyone,
 
I have been a lurker on this thread a long time. Do you guys think that someone with no DIY experience (like me) can successfully build this amp? I am very interested in this amp and hopefully can try it soon. Also, what do you guys think about the power output ?

As Dsavitsk has confirmed recently, power is on the order of 250mW.  Considering the output transformer ability to switch impedances between high and low, that still works out to enough voltage and current for almost any dynamic headphone - K701/702/712's included.
 
There are built versions of the Torpedo available at Beezar.  No offense, but I suggest one of those rather than recommending a kit of this amp to someone who has no DIY experience.