"transparent" ABY w/ headphones

[firemedic]

Hi again all, I posted this thread in the effects group but nobody's answering the phone.
I have a little chassis and PT I can use for an ABY box, with stereo headphones out as well. I have never built a headphone amp & will need guidance on that; I plan on using a Morgan Jones style White CF.

Any ideas on a good, somewhat transparent ABY circuit? Will an active effects loop circuit do the job?

I'll probably have enough heater current to do a Hotbox-style switchable distortion too, but I'd like to nail down these other issues first.

[RicharD]

What is an ABY?  I keep thinking of Young Frankenstein, "Abby somebody."

Attached is the headphone amp I built.  It hangs off my PC's sound interface.  The plate followers on the left drive the control room power amp and of course the circuitry on the right is the headphone amp.  I was gonna make a DC filament supply but never got around to it because it's unnecessary. 

[FYL]

ABY = external channel/input switcher, sometimes also with summing and/or buffering functions.

[RicharD]

DOH!

Add a DPDT switch to the input of my circuit.

[kagliostro]

I have never built a headphone amp & will need guidance on that

I too

so look here

http://www.pmillett.com/Jonokuchi.htm

http://www.pmillett.com/ecc99_srpp_headphone_amp.htm

here you can find other headphone stuff

http://www.pmillett.com/

hope this can be of some interest

Kagliostro

[RicharD]

Here's a link to the circuit I plagiarized. 

http://gilmore2.chem.northwestern.edu/projects/cmoy5_prj.htm

The beauty of the Morgan Jones circuit is no output transformers.  That saves you $100.00 right from the get go.

[RicharD]

I been toying around with the WCF this evening.  You could build an ear splitter using 6AS7's.  8 watts into 600 ohms.  Unfortunately that cost you 100mA @ 300V..... per channel.  I figure the 6DJ8 circuit is delivering about .15 watts into 600 ohms drawing only 9mA @ 220V per channel.   1/8th watt is plenty for for any set of ear mittens.

[DummyLoad]

1/8th watt is plenty for for any set of ear mittens.

not to some folks... i have a bankers box full of 6080 just for the purpose.... someday.

i'd be shooting for about 2W, yes i like headroom.

[RicharD]

You talking output or total watts?  A 6080 should be able to do a lot more than 2 watts.

[DummyLoad]

You talking output or total watts?  A 6080 should be able to do a lot more than 2 watts.

output - just for headphones - 6080 is loafing.

[DummyLoad]

> 472mW, I believe enough to drive low impedance headphones

Enough to blow your brains out your butt.
As a rough guide, headphones need 1/1000 of the power of speakers.
So 472mW in phones is like a 400+Watt speaker amp (in home use).

6080 is a really tame lame audio tube. Drive is insanely high, linearity is poor (and varies depending on factory and vintage). It was made as a pass-tube, though I think it isn't as good for that as it could have been. It has also been reported that the matching between sides is not good enough to trust a common cathode resistor (in fact RCA sais this when it was introduced).

i quote the master from another forum.,..  i guess that ends that. anyone need some 6080s? 

[RicharD]

I did a lot of searching on this last night.  I did even more 2 years ago.  I'm going to continue to stand by the 6DJ8 circuit as far as transformerless headphone amp circuits go.  There are a few other pure tube circuits but most of them have OPT's.  I did see a 6AS7 single ended cathode follower headphone amp, but I found it's output impedance to be about 150 ohms.  That's too high if you need to drive 2 or 3 sets of cans.  Most of the circuits floating around have a 12A*7 front end with a MOSFET output.  1 last design I toyed with was a 12AU7 WCF using parallel triodes.  I was able to get Zout down in the neighborhood of 60 ohms but as I have noted is typical, current is pretty high, about 35mA per side.

[firemedic]

As I suspected I think buttery has already dialed it in. I'll most likely use that plan for the H/Ps.
My headphones are a 32 ohm, not expensive not audiophile model. I can't see spending $100+ on headphones. That may impact my output values.
Looks like I need to order some 6DJ8s.

But I really could use some advice on a somewhat transparent active A/B/Y circuit. That's all I would have built, but the chassis & tranny are too large to leave it at that. Once I have some info on the ABY I can start drawing pretty shapes on pieces of paper.