Marsh headphone amp from Linear Audio

[jackinnj]

Originally Posted by Telstar

Who sells the pcb, Jan?

I am selling the pcb's at cost -- actually a little below cost as I made a mistake in the price estimate before i sent the Gerber files out. I don't believe it's equitable to profit off Marsh's intellectual property. This way a lot of folks will build his device.

Benefit to me is that my cost for a board is only a few dollars, instead of $60 if i sent it out. I did the same thing with two of SY's designs.

[RNMarsh]

Just dropped by to say Hi to this forum. Got questions?

[RNMarsh]

This or any subject - whys and what and wherefores et al.

[RNMarsh]

Not bad considering you didnt match the devices. Anyone doing the ear eq tests, yet?

[jackinnj]

Originally Posted by RNMarsh

Just dropped by to say Hi to this forum. Got questions?

What did you use as the source resistors - R3,4 - 47 ohms seemed best to me. I ran the amp for 5 hours and offset changed by only a couple mV.

I only had a dozen or so of the MJE200/210 so rushed to solder it up without matching the output devices, and the results were really excellent for my "pro forma" sennheiser hd-650 impedance of 300 ohms.

[RNMarsh]

51.1 Ohms. The excellent thermal drift is due to the topology.... something i dont think most people appreciate and few of the circuits seen here can match without a dc servo (A concept I introduced to the world). You'll get sota distortion numbers if you match all devices. I hope others will buy the issue from LinearAudio for the explanations of this deceptively simple and cheap circuit. It's all in the topology as I think John Curl has said.

[RNMarsh]

As this buffer shown in the article is one of the derivatives in the article moving towards the final circuit and not intended for diy building - note it will probably smoke the Q1/Q2 unless you put series resistors in their emittters.

[Telstar]

Originally Posted by RNMarsh

Just dropped by to say Hi to this forum. Got questions?

Hello! I still love your article about capacitors!

[Yarpen]

Hi

Is it possible to paste a schematic of this amplifier?

[RNMarsh]

Originally Posted by Telstar

Hello! I still love your article about capacitors!

That developed out of listening tests done first by my friend Peter Moncrief of IAR which got me to wondering-- what is it about a capacitor that could make them sound the way he described? The research i did first came out in bits and pieces in TAS LTE until Walt Jung contacted me to do a article on the whole subject.