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Old 18th July 2007, 02:29 PM   #11
BillH is offline BillH  United States
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Hi, jarthel.

Here's a web page that explains the 'active ground' circuit.

It's the Szekeres VE headphone buffer. The author of the web page explains the operation of the circuit much better than I can, so I won't try.

I've built a headphone amplifier using the VE circuit, IRF510 mosfets, and LM317 constant current sources instead of the power resistors as shown. I think it sounds good. The only down side is the VE buffer provides no gain, so I had to add a gain stage to be able to drive my Sennheiser HD424 headphones.
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Old 18th July 2007, 03:15 PM   #12
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Quote:
Originally posted by jneutron


YOU!!!YOU!!YOU!!

What the H##L do you think you are doing, baiting me like that.


YOU KNOW...DON'T DENY IT....

I see that tube opamp...you knew I was refurbing a systron donner 3400, didn't ya.

Is that thing in your hands, or did you find the pic?

Cheers, John

I have that 'thing' in my hands... Paid 30 $ US, you think that's not too much ?

I have a standing order in with that guy in case he spots more. Maybe...

Jan Didden
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Old 18th July 2007, 03:19 PM   #13
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Quote:
Originally posted by jarthel



my apologies. I should have use the words "active ground" and it would return a lot of replies.

I'm searching for the thread that describe it but having no luck yet.

anyway, here's what a designer of headphone amps has to say:
===========
The designer (Ti Kan) of the Beta22 described it as follows:

A 3-channel "active ground" amplifier is the recommended configuration for standard 3-wire headphones. The ground channel amplifier sources or sinks the return current from the transducers, which would otherwise have been dumped into signal ground or power supply ground in a 2-channel amp. This shifts responsibility for the high current reactive load of the headphones from signal ground to the tightly regulated power supply rails, thus removing the primary source of signal ground contamination. The headphone transducer "sees" symmetrical output buffers with equal impedance and transfer characteristics on both sides, rather than an amplifier on one side and a capacitor bank of the power supply ground on the other. This results in lower output impedance, greater linearity and reduced stereo crosstalk.

=========================

in the design, you have PCBs for right/left channel. And then another PCB for the ground (same pcb as right/left channels except that the input is connected to signal ground).

the 1st image may give a better idea: http://www.amb.org/audio/epsilon22/
Sound like a great idea to up the price of your kit by 50% or so.

Why anyone would trade a perfectly low impedance star ground for the non-linear impedance from an amp output is a mystery to me. That is, IF I guessed correctly what this does. As is often the case with 'breakthroughs', any sensible overall system circuit diagram is carefully omitted.

Edit: I did find a circuit diagram. Incredible! A "ground follower" no less. So, either there is 'noise' on the ground, and the 'ground follower' carefully replicates that (after all, it's a follower), or there is no 'ground noise' and in that case that follower is just sitting there being ridiculous. Take your pick..

Jan Didden
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Old 18th July 2007, 03:27 PM   #14
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I was thinking the same thing Jan.
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Old 18th July 2007, 03:40 PM   #15
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Quote:
Originally posted by janneman
I have that 'thing' in my hands... Paid 30 $ US, you think that's not too much ?
Honestly, I don't know how much they go for. The analog computer I'm working on is a 10 channel widgit, so it has 10 vacuum tube opamps inside. I do not know if my unit is a big honkin board with lots of individual tubes, or if it uses 10 of the units you so callously dangle in front of my eyes..

I'll be cutting into the opamp chassis very shortly, to debug and repair that part. At the moment, I'm refurbishing the power supply and hold/compute relay sections. It is a bit difficult since I don't have a schematic, but have to create one by visual inspection...they tied the wires real neatly, and because they only have about 7 or 8 wire colors (always a stripe over white), figuring out where the other end of a wire is is time consuming.

So far, only one two-section cap and three resistors have bit the dust during the reforming sequence. Unfortunately, reforming only works if the dielectric paste is still good. Dried caps need not apply..

(refurbishing tip: when you do not have a schematic, take as many pictures of every component in the chassis, that way, when a part burns up and DESTROYS THE ******* COLOR CODE!!!, you have something to look back to to determine the value of the comp. I learned to do that after the first failure.) Duh...

Quote:
Originally posted by janneman

I have a standing order in with that guy in case he spots more. Maybe...Jan Didden
Why? Historical interest, or do you use em?

Andrew: I was having fun with Janneman, that avatar can certainly be cryptic if you've never seen one before.

ps...I'm rebuilding the worlds first video game.

Cheers, John
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Old 18th July 2007, 03:50 PM   #16
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Old 18th July 2007, 03:58 PM   #17
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Hey there Peter. How's it shakin?

What did you do with the triax I sent ya?

Cheers, John
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Old 18th July 2007, 04:05 PM   #18
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I'm still working on it.
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Old 18th July 2007, 04:36 PM   #19
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Quote:
Originally posted by Peter Daniel
I'm still working on it.
Wow, you've been working on it since april of 2006..

What's the story?

Cheers, John
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Old 18th July 2007, 04:53 PM   #20
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Quote:
Originally posted by jneutron
What's the story?
You know how hard it is to come up with properly controlled environment for serious comparisons...
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