[Sycraft]

Wether idle or operational, my PPA draws 0.12 amps at 24 volts, according to my powersupply. I'm just wondering if it is supposed to draw that much, and if not what the problem could be.

I can't hear any sonic problems, the amp sounds just great, and there's almost no offset at the outputs, -1.5mv on one channel, 1mv on the other and that's fully connected to the mixer and soundcard, with both powered up (they also have slight offsets I'm sure).

The amp has 4x 5002 buffers on each channel and OP 637/627 opamps. It has all 12 Q3s filled and I made no attempt to match them. It does have the class A bias circutry, but it should be off (unless I'm confused which way to turn the varsistor).

So am I just worrying for no reason, and this is a normal draq for the amp, or is there likely a problem somewhere?

 

[tangent]

Quote:

it should be off (unless I'm confused which way to turn the varsistor).

Why guess?

a) Turn the pot the other way and see if your power supply's current meter shows a drop in current; or

b) measure volts across R10. Dropping voltage equals dropping bias current.

 

[morsel]

100mA 12x8.3mA HA5002 buffers
21mA 3x7mA OPA627 opamps
3mA 3x1mA TLE2426 rail splitters

124mA total Iq (quiescent current not including power indicator LED)

114mA total Iq with AD8610 opamps

 

[Sycraft]

Quote:

Why guess?

Two main reasons:

1) My friend stole my DMM, so I have no easy way to check right now.

2) I'm lazy

. I'm taking it to work tomorrow so I can hook it to a tone generator and a scope, so I can wait till then.


Thanks Morsel, so it is drawing what would be expected. I mean the draw didn't seem unreasonable, but hey, I worry. As I said, this is the first time I've messed with a precision analogue device. I probably should have started on something simpler but oh well. It seems to have worked pretty well. I just wanted to make sure I wasn't overlaoding something slowly.


So another question for you guys: What do you recommend in the way of caps for the PPA? I mean I wouldn't be happy with a working circut if I didn't try to break it as soon as everything was good. I'm using Cerafines on both the opamps and buffers. Other than Blackgates, which at this point I don't care to purchase, do you recommend any other caps to try in place of the Cerfines?

 

[morsel]

Both PPA sites have parts recommendations.

 

[Sycraft]

I know. I read both PPA site more or less completely. Hence the reason I picked Cerafine caps. I also noticed them used on a number of designs posted here. Then again, the slightly cheaper Panasonic FC caps are also speced on Tangent's site and I've heard some arguments that the lower impedance Nichon caps (UPW I think) are good.

I'm just curious on your personal opinon. You and tangent obviously have more than a bit of amp experience, I'm curious what you think. It's not like I'm going to take your opinons as holy writ, or get angry if I try caps you recommend and they aren't as good in my opinon, I'm just asking for your experience.

As I noted, this whole analogue scene, particularly precision analogue is new to me. So I'm curious what others think makes an amp sound good or not.

So please don't take this as I'm trying to ask for the "magic cap" that will make everything alright. I'm quite happy with the amp as it stands. I'm just intrested in advice from others that have built the amp. I don't pretend like there is a sinlge right way to do this.

 

[morsel]

My opinion is that uber electrolytic caps are a waste of money. Kurt and I compared a PPA with 2 1000µF Panasonic FC .vs. a PPA with 8 220µF Elna Cerafine and could not measure or hear a difference. Black Gates are a really colossal waste of money. If you search or read the old PPA threads you will find more detailed previous discussions about this.