[00940]

All the needed schematics and even the pcb files are available at http://www.pmillett.addr.com/ha-4_headphone_amp.htm

Is this amp nothing special but for its look ?

A reminder :

 

[Voodoochile]

I'd like to build it... does that almost count?
I did build his low-voltage hybrid tube amp.
But that's not what this thread is about.

If I was to build the HA-4, I think I'd make a short body to hold up the 'head' amp. Maybe have the arms holding a CDP as though it were a butler's tray.

I think you should build it, 00940! I'm still building the Klaus Noll amp from the May AX.

 

[00940]

I'm seriously thinking about it. perhaps just the amplifier part to begin, i'd let aside the processing for later (till more cash come in). I just have to find how expensive it would be to get the pcb done.

 

[erix]

If you are going to have the PCB's manufactured in order to build this amp, you might have a hard time finding the OPA4132's or OPA4134's in PDIP package, I think they are only available in surface mount now.

You can sub in an OPA4228 but the OPA4228 isn't unity gain stable.

I *think* it isn't unity gain stable. However, I used it at unity gain and didn't have a problem in the Forehead amp, which, though named after a part of a head, does not in fact resemble any portion of a human body at all.

At least not mine.

I digress.

I'm anxious to hear that EQ myself. The amp portion is the pretty common (around here anyway) opamp-followed-by-buffers topology, not multi-loop but the buffers are in the feedback loop. You could build that portion of the amp pretty easily. Have a look at the Smoothster

What I'm most interested in in this project (funny you should bring it up) is the muting circuit. I'd like to integrate this into one of my amps.

If anybody knows of another soft-start or muting circuit, bring it on!

ok,
erix

 

[00940]

It's funny erix, i've spent a few hours last days searching parts for your smoosther. I'm ready to order.

It doesn't look too complicated or expensive (i've two buf634 laying around and an old 12V 1A dc transformer, for all other parts, i'm in the 30-40€ range with nice parts) and should be a quite easy start for testing my skills. I just plan to use the ad275 instead of the ad744 you use.

I'll get audyn polyprop, big pana ts-ha for caps, probably good nos philips metal film resistors, vishay are insanely expensive in europe, and an alps blue,

 

[Voodoochile]

Please make sure you do try the AD744 at some point, at least.
I have a pair in a META driving the buffers from the comp pins, and it is something to be experienced.

 

[00940]

Problem is that if i use the dual chip 275, i'll have problems later to swap in the single ad744. I've to think about it. It's just that I read somewhere that the 275 matched well with the buf634.

here's the parts list btw.

op2752.19€ (1)2.19€schuro850141
buf634p5.09€ (1)5.09€schuro850559
4 ic sockets dip8 ??local shop
2 pana tsha 10,000uf, 50v4.71€ (1)9.42€schuro852226
1 pana fc 10uf, 50V0.10€ (1)0.10€schuro852477
2 1uf bypass audyn polyprop caps1.56€ (1)3.02€diy
P1 alps blue 50k stereo log15.09€ (1)15.09€schuro850065
2 R 10K
2 r2 470k
2 r3 249
2 r4 1k
2 r5 47.5
2 r6 47.5 1/2wall resistor Beyschlag1€diy
power switchspst toggle?diy
1 1/4 stereo jack1.4€ (1)1.4€diy
2 rca jacks, gold plated, teflon2.14€ (1)4.28€schuro028376/028377
input dc jack ??local shop

total cost : about 50€


for bypass, I 'd like to try something else than wima. Since it's not a portable amp (I'll use it on my computer) I'm gonna use Audyn caps. It's not a big deal for 20cents for 2 caps. They're probably as big as the electrolytic

these ones :

 

[erix]

I don't know if I'd go for those big honkin' caps as bypass - part of the beneficial effects of bypassing come from the very small size of the cap and it's proximity to the supply pins.

If you can't get Wima I would suggest some of the metalized polyester Beyschlag equivalents. Digikey sells them 10 for $5 which makes them a pretty good alternative to the Wima MKS.

Now the Wima FKS, the new light green ones, Mmm mmm Good!

Also, If you are going to build the Smoothster, I would ditch the output resistors (the R6's) as they are not really needed - the BUF634's are stable without them.

I like Beyschlag resistors - glad Digikey sells them too!

ok,
erix

 

[00940]

well, i can get wima mkp-10 too, a bit cheaper.

Thanks erix