[rds]

Just finished building this amp and power supply.

I knew from the topology that it would be good, but I was not expecting it to be THIS good.
If any of you guys are considering this project I highly recommend you go for it. I would be very surprised if someone was disappointed with the end result (assuming you build it correctly).

PPA Parts:
opa627s (biased to class A)
bc components mkt/mkp film caps
Nichicon Muse KZ electrolytics
bourns pots
Alps Blue pot
dale 1/8 W resistors
2N5484 Q1
2N5486 Q2
2N5087RLRAOSCT Q21-23
BD139OS Q24
2N5088BU Q31-33
BD140OS Q34
TI 296-1994 TLE

(22 mA through the output buffers)

...and STEPS with everything (line filter and all caps)

Pictures:

 

[FallenAngel]

Bias the output to 30mA

What is the STEPS set at? Raise it to 30V

Yeah, it's a fantastic amp, my favorite thus far, and I've had many.

 

[rds]

I tried 30 mA and Q1 and Q2 were getting quite hot. I'm not sure if it's a good idea to run them that hot with heat sinks. I imagine it's probably fine.
Right now I'm running the STEPS at 25V. I'll try 30V. Did you actually hear an improvement with that voltage?
Thanks for the input.

Oh yeah, my gain is 3 (r4 is 2k).

 

[FallenAngel]

If your STEPS transformer is 2x15V, definitely crank it up to 32V, why waste it

30mA shouldn't be a problem, the case top might get a little warm, no big deal.

You're not likely to hear almost (if at all) any improvement at 24V vs 30V with almost all headphones, but why not feel good about having that voltage swing

 

[rds]

Someone showed me how to use this camera, so I've updated the pictures

 

[tangent]

Quote:

Originally Posted by rds /img/forum/go_quote.gif I tried 30 mA and Q1 and Q2 were getting quite hot.

If you have some way of measuring the temperature, take them to 60C. That's safe for semiconductors.

Quote:

I'm not sure if it's a good idea to run them that hot with heat sinks.

We purposely didn't sweat making room around the transistors for heat sinks. You can add them if you want, but it shouldn't be required.

 

[Eokboy]

I just populated one too!

I used Sanyo 2SC2344/2SA1011 instead (from tomb, great seller

). The MJEs are too sterile for my taste. I think it is possible to heat sink the TO-220s. Easiest is to fabricate a strip for 3 transistors facing the same way, but needs insulation though.

3760uF total Pana FMs and I purposely got the 50V ones so they fill the 12.5mm. Yea I'm vain...

But its only fed with a 24V TREAD.

 

[d-cee]

yay! PPAv2 love

mine uses the same case (diff colour), rocker switch and umbilical as yours!



my STEPS is running at 33v and my output transistors are 2SA1930 and 2SC5171, opamps are the LME49710

edit: ok, umbilical's a little different

 

[rds]

Those look really nice.
My STEPS is now at 30 volts. I should do 31 for the love of prime numbers. 627s are class A biased with 1.2 mA. Output transistors have 30 mA and actually don't heat up much (definitely far below 60C).

Eokboy
Although I like the look of having all the cap spots filled I think you're going pretty far overboard on rail capacitance. Around 2000 uF would probably give you better results. Maybe someone else can weigh in on this. Looks great though.
Also, what brand and model are the yellow output resistors?

 

[FallenAngel]

Those aren't output resistors, they're film caps

 

[rds]

haha oh yeah...
Still what are those output resistors? (the blue ones

).
I used vishay 5% 1 W as I couldn't find any 1% 1W at 2.2 ohms.

 

[rds]

damn browser

 

[FallenAngel]

Why go for 2R2, you can easily use 3R3 or 4R7. Those look like metal film resistors, but most use the much easier to find metal oxide.

 

[rds]

I wonder if the tighter tolerances of a larger resistor would be worthwhile. Lower resistance will cause less distortion, but so will closer matching.
I have a feeling this is a moot point (also I don't want to have to remove those resistors)

 

[FallenAngel]

I never noticed a difference in those and I've switched out 2R2 metal oxide to 3R3 metal film, 4R7 metal oxide and 4R7 metal film, couldn't tell a difference at all actually, nothing at all, just better stability with with 4R7 (lower current draw and more accuratele).