[LarBO]

I've got a PPA that I bought from a member here some time ago and I've been using it with some HD600 phones. Actually, not using it as much as I'd like for a variety of reasons, one of which was that it was a bit too forward/aggressive for my taste. After reading a bit here I learned that the AD8610s might be giving me too much 'detail' and that the OPA627s might be better. So I got ahold of some OPA627 op-amps and put them in. I prefer the sonics with the OPA627s. However, if I crank the volume up to even 11 o'clock (moderate-to-high listening level for me) there's a distinct distortion that worsens if the volume's increased. It's worse if the bass-boost is on. I don't recall this happening with the AD8610s. The distortion is there, but to a lesser degree at lower volumes.

Can anyone clue me in as to what might be wrong here? Are the OPA627s bad? Could the buffers (12 x HA-5002) be bad? I'm pretty ignorant of this stuff, but can easily swap these things as they're socketed, and can even make a solder joint to be proud of if needed.

I know the PPA wasn't necessarily designed for 'phones like the HD600s, but LOTS of people seem to pair these up without complaint so I figure something must have gone wrong with my amp. The phones are fine when used with other amps/sources.

Thanks in advance for the help/advice.

 

[MisterX]

What kind of power supply do you have?

 

[LarBO]

The amp was built by SubSonic, and this is what he had to say about the PS:

"In regards to the power supply, it's a variant of Tangent's STEPS which is
basically derived right from Linear's datasheet. I drew up the artwork and
etched and drilled the pcb myself. Also I use 8000uF of output capacitance
in addition to the 8x470uF Elna's in the PPA itself. The STEPS I believe
doesn't have output capacitance. Not to mention the 8x1000uF (total)
capacitors are all Nichicon KZ's which are the best Nichicon audio grade cap
they offer. The power supply is very quiet, with the gain set at 11x and
using low impedance headphones, only a small amount of fuzz is noticable
past 12o'clock. With higher impedence headphones it's silent even at max
volume."

Here's some specifics about the parts used:

* PCB mount Talema/Amveco Tranny
* 8x 1000uF Nichicon Muse KZ (4 input + 4 output)
* 2x 100uF/35v Elna Cerafines
* LT1086 Regulator

Is this helpful at all?

Thanks.

 

[MisterX]

Try putting the 8610s back in and see what you get.


Quote:

The amp was built by SubSonic

In that case you are in very good hands..... have you talked to him about this problem?

 

[LarBO]

I'll try the 8610s again and see. If they're fine (in terms of distortion) would that mean the OPA627s are bad and should be replaced? From what I've read they should be a drop-in replacement for the 8610s, yes? BTW, I put the OPA627s in all three slots (including the ground circuit).

I haven't written to SubSonic directly since it's been many months since I purchased the amp from him and didn't want to pester him. However, it'd probably be a good idea so I will.

Thanks for your help.

 

[dknightd]

Quote:

Originally Posted by LarBO * LT1086 Regulator

I'd check the output voltage of the power supply. I think the lt1086 is an adjustable, relatively low voltage (3-12) chip. To drive hd600 at loud volume needs at least 12v supply.