[Hottuna_]

Looking at oneplustwo's drawing, a question popped into my mind.
For single ended outputs from a 4 channel 2 sigma22 build where one sigma powers L+,L- and the other R+,R-.

Where does the sleeve of the TRS connector get connected to? Does it connect to whichever sigma22 or do the two sigmas need to be shorted at ground?

Or do the sigma22s have to be configured to power L+,R+ and L-,R- respecitvely and the sleeve of the TRS connector connected to the associated sigma's ground.

 

[ShinyFalcon]

It shouldn't matter which σ22 you use for TRS's ground.

 

[Beefy]

Quote:

Originally Posted by ShinyFalcon /img/forum/go_quote.gif It shouldn't matter which σ22 you use for TRS's ground.

I think it would if they are powered from separate transformers?

 

[amb]

It shouldn't matter. The grounds come together at the input jacks (and interconnect cable) anyway. As long as you don't let the higher current ground return from the headphones "ride" on the signal ground reference wires from the boards to the PSU, then all should be well.

 

[amb]

Quote:

Originally Posted by oneplustwo /img/forum/go_quote.gif Well, I tried it with the Grados and it works fine! Might be because one of the board's DC offset was only able to be reduced to 5mV and that in combination with my in ear phones (Ety's in my sig) made it oscillate?

It probably has nothing to do with DC offset. As I said, some headphones (and its cable) present enough impedance complexities that may cause the amp to oscillate, so add the zobel network.

Quote:

For the TRS jacks, what would be the proper way to maintain phase? + from right and - from left for both combo jacks? I'll probably leave it as I'm not a stickler for phase correctness per se, but I would like to know so I can do it right the next time.

No. L+ -> tip, R+ -> ring on both TRS jacks will give you correct phase.

 

[Beefy]

Quote:

Originally Posted by amb /img/forum/go_quote.gif It shouldn't matter. The grounds come together at the input jacks (and interconnect cable) anyway. As long as you don't let the higher current ground return from the headphones "ride" on the signal ground reference wires from the boards to the PSU, then all should be well.

Ah, gotcha.

 

[tintin47]

So the 100uF and 470uF caps for my sigma 22 are 50V instead of 63V. Is that going to be a problem or will the PS run normally?

 

[amb]

It's fine for +/-30V output.

 

[tintin47]

Wow. That was fast. Thanks very much.

 

[oneplustwo]

My joshua tree attenuator is being fed with 30V from the sigma. It's only supposed to take 7-24 but I've been doing it for short stints as I test out the amp. What's the easiest way to dial the voltage down to the acceptable range? Can I just put a resistor in line with the wiring? Or is a zener diode a better idea?

 

[Beefy]

Quote:

Originally Posted by oneplustwo /img/forum/go_quote.gif It's only supposed to take 7-24 but I've been doing it for short stints as I test out the amp.

The JT is meant to take 7-24VAC. Do it properly and get a separate transformer.

 

[ShinyFalcon]

If the relay board is anything like the TREAD the relay board should accept DC as well; the bridge and cap won't be doing much. If you have parts lying around I suppose lots of diodes in series (σ22 -> diodes -> Tree AC input) will work fine, but a nicer solution will indeed be a separate σ24. Remember that the tree only needs 5VDC to work.

 

[oneplustwo]

Yes, I know... someone else had asked the TPA guys and they said it wouldn't matter. So instead of adding another trafo and another umbilical, I figured this would work fine.

 

[Beefy]

Quote:

Originally Posted by ShinyFalcon /img/forum/go_quote.gif If the relay board is anything like the TREAD the relay board should accept DC as well; the bridge and cap won't be doing much. If you have parts lying around I suppose lots of diodes in series (σ22 -> diodes -> Tree AC input) will work fine, but a nicer solution will indeed be a separate σ24. Remember that the tree only needs 5VDC to work.

Yeah, I appreciate that, but to use the 30VDC would unnecessarily increase current draw on one rail of the S22 and cause unnecessary heat production on the JT regulator. It is a poor solution.

Quote:

Originally Posted by oneplustwo /img/forum/go_quote.gif Yes, I know... someone else had asked the TPA guys and they said it wouldn't matter. So instead of adding another trafo and another umbilical, I figured this would work fine.

There's a big difference between something working 'fine' and doing something properly.

 

[oneplustwo]

Point taken. I can't seem to find any little toroidal trafos. I guess I'll just do the sigma24 thing unless someone has a small cheap chassis mount option that would work.

UPDATE: I figured out the problem. Turns out one of the joshua tree attenuator boards was not working because the ribbon cable was not pierced all the way through at the connector. Finally listening to my Senns at their "full" potential.

Now that I'm going to go ahead and get the little trafo added and need the "spare" wires in the umbilical, I think I'm just going to not use SE headphones with it for the time being. Besides... why use my single ended grado SR80s when I can use my balanced Senn HD650s!