[jasonhanjk]

I just completed one PPA (OPA627) with a self built PSU. I manage to get some hum by:
1. Not grounding the 0V
2. Grounding the PPA casing
3. Not grounding the PPA casing and volume knob with signal ground

Now I sold the amp with a peace of mind as I look through my oscilloscope and NO change of any waveform when turning the knob...

 

[morsel]

Sorry for replying so late, I've been really busy this week. I left a message with PPL a few days ago to take a look at this. Here is a summary of suggestions for dealing with high sensitivity low impedance closed headphones that make sense to me:

Decrease amp gain
Increase local loop gain
Scale down resistor values
Use a better power supply than the Elpac
Use a battery board
Use proper grounding practices
Use different headphones

Raif, power conditioners are generally ineffective. Using different headphones is more of an avoidance than a solution, but in your case it is the sensible choice. Sovkiller is out of his depth, I suggest you not take him too seriously.

Finally, a word on proper grounding practices. I'm cutting and pasting this from http://elvencraft.com/ppa/:

Wiring Considerations

Signal ground is input ground, not output ground. Output ground is the output of the ground channel. It exists solely to drive headphones. It is not a true ground. Do not connect signal ground to output ground. This defeats the purpose of differential output and may cause amplifier instability. Do not use the headphone output as a line level output as this may short signal ground to output ground. Use signal ground instead of output ground for line level outputs.

Many sources tie signal ground to AC ground, either directly, or via another component in the system. The PPA ties signal ground to a vitual ground created halfway between the power supply rails, so an isolated power supply must be used. Do not use a power supply with an AC grounded output, as this will short one of the power rails to signal ground if the PPA is connected to an AC grounded source, possibly damaging the PPA.

Connect the case and pot housing to signal ground. This helps shield the PPA from hum and noise. Most cases are tied to signal ground and/or AC ground. Do not connect V+ or V- to the case instead of signal ground as it will short the rail if it touches another case, cable plug, or other grounded conductor. Do not connect AC ground to signal ground or the case. This may cause ground loop problems. For more information:

Rane Note 110 Sound System Interconnection
Rane Note 151 Grounding and Shielding Audio Devices
Sound Reinforcement Handbook classic treatises on basic connections and grounding
The Art of Electronics an excellent electronics textbook

If the bass boost circuit is not used, S2 must be jumpered to complete the global feedback loop, otherwise the amp will malfunction with excessive noise, distortion, and DC offset.

 

[Voodoochile]

I believe it is safe to say that you can have a PPA that is free from hiss, not only by utilizing a battery supply, but even with an AC power supply.

I'm not saying that someone has not heard hiss, or that hiss does not exist on some amplifiers, but rather that you can indeed have one that does not hiss.

Also, I do not believe that the PPA is any more susceptible to noise than many other amps, and in fact, might well be less susceptible. This is not intended to be a pitch for the PPA, but just an accounting of my experiences with several different amps, including cmoy, a47, meta42, millett lv tube, gilmore dynamic, pimeta, and the ppa. It does not speak for everyone or every situation, but is is a somewhat broad spectrum.

 

[Sovkiller]

Quote:

Originally posted by Voodoochile I believe it is safe to say that you can have a PPA that is free from hiss, not only by utilizing a battery supply, but even with an AC power supply. I'm not saying that someone has not heard hiss, or that hiss does not exist on some amplifiers, but rather that you can indeed have one that does not hiss. Also, I do not believe that the PPA is any more susceptible to noise than many other amps, and in fact, might well be less susceptible. This is not intended to be a pitch for the PPA, but just an accounting of my experiences with several different amps, including cmoy, a47, meta42, millett lv tube, gilmore dynamic, pimeta, and the ppa. It does not speak for everyone or every situation, but is is a somewhat broad spectrum.

Thanks voodoochile for that note....we need it, in order for some others to understand that....it seems that they are blaming the whole PPA design for this flaw, which is not true....

BTW morsel I now how to swim, so I will not drown in here, and in the last case, I was just supporting the design you partially work on, so I consider that I'm on your side, so I don't know why you complain, or have to be so arrogant....part of the human nature.

 

[raif]

Just in case anyone missed my last thread.

It is a hiss not a hum. There is no humming, I misinterpreted what hum meant in my first posting.

all these sound like great ideas, one problem though. What can I do? All of these fixes would require someone with alot more expertise than I possess.
I have already sent it back to jmt, he couldn't find anything wrong with it, and heard no hiss. Also morsel witnessed his wiring and was rather impressed if I recall corectly.(i remember the "straight up" line, about the bassboost switch wire though)

voodoochile, what power supply do you use? could I just buy one to try out or do you build something in to the casing?

sov, where do you put the volume knob when you listen to the amp?

 

[Sovkiller]

Quote:

Originally posted by raif Just in case anyone missed my last thread. It is a hiss not a hum. There is no humming, I misinterpreted what hum meant in my first posting. all these sound like great ideas, one problem though. What can I do? All of these fixes would require someone with alot more expertise than I possess. I have already sent it back to jmt, he couldn't find anything wrong with it, and heard no hiss. Also morsel witnessed his wiring and was rather impressed if I recall corectly.(i remember the "straight up" line, about the bassboost switch wire though) voodoochile, what power supply do you use? could I just buy one to try out or do you build something in to the casing? sov, where do you put the volume knob when you listen to the amp?

That depends of the recording, but I never had exceed the 11:00 point IIRC, from 9:00 to 10:00 mostly.....in some very low recordings go to 11:00 should be plenty....more is insane in my system...and less than nine is good, but for my taste pretty low...I can heard at 8:00 even less, but is not OK for me....too low

 

[jeffreyj]

Quote:

Originally posted by morsel Sorry for replying so late, I've been really busy this week. I left a message with PPL a few days ago to take a look at this. Here is a summary of suggestions for dealing with high sensitivity low impedance closed headphones that make sense to me: ... Increase local loop gain ...

It just occurred to me that perhaps the problem here is *excessive* inner loop gain... Higher inner loop gain will result in larger noise error voltages for the outer loop to correct. The outer loop, being composed of buffers which are used more for robustness, not precision, might only partially cancel the noise error votlage as a result. I must stress that this is an off-the-cuff analysis, but it feels right. The Jung multi-loop topology does deliver bandwidth benefits, but there ain't no such thing as a free lunch, so what's the cost, then?

 

[raif]

just got my hd650s this friday

ZERO HISS

Tried putting it in the worst of conditions, and could not get any sounds. Right now it is sitting between two computer monitors, in a room full of computers, radios, and cellphones. Dead silent.

Amp sounds incredible.

Sennheisers were my first audiophile headphones(hd525) and now it looks like they may be my last. If I had to describe the sennheisers in one sentence it would be that they are the cd3k's polite, easygoing cousin. I am now very happy with my setup.
(yah right, next step, send ns500v to sacdmods)

 

[Sovkiller]

BTW check the new thread about the Perreaux in the amps section.....guess what? good news.....!!!!!