IO1 head amp DIY

I’m pretty sure there are all sorts of reasons why this is a bad idea and SUTs are better etc.


I’m interested in a solid state active step up device to couple a IO1 to a Puresound P10. This below really interests me, although obviously wont work as is.

Parts List for the Common-Base Head Amplifier
R1 - 100 kohm
R2 - Select for a battery current of 0.125 mA, typically 330 kohm
R3, R4 - 1 Megohm
R5 - 2 kohm
C1 - 0.1 ufd
C2, C3, C8 - 100 pF
C4, C5, C6, C7 - 100 ufd
Q1 - 2N4401
Q2 - 2N4403

Any thoughts about getting the impedance and gain in the ball park with something like the above?

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What is it you like about the above?


I got to it via some convoluted drunken internet meandering. I’ve got a bit of a weird thing going for Jean Hiraga’s ideas, and it led here somehow.

I think too low gain and too high input impedance.

Also I keep on failing at grand diy attempts. I want a simple, cheap project to try that isn’t run of the mill.

I think coke and hookers :+1:


I’ve got the circuit for the Yves Cochet PP Un head amp somewhere. At the time I worked on it it belonged to Jake Mortlock but I understand @pmac bought it shortly before relocating and I’m not sure if it’s seen the light of day with him yet. It’s got slightly more gain than the Leach one (30dB I think) and a 20ohm Zin, although you could trivially lower that with a load resistor. The only reason I’m mentioning it is that I think Jake said he’d tried it with an Io and it had worked.

Active circuitry running at the microvolt levels out of an Io needs to be designed and built in such a way as to minimise noise. Leach’s use of a battery can be a big help with that. The PP Un had a mains supply and the bulk of its noise (not that there was much) was at 50Hz.

The circuit was more complex than the Leach one, but not ridiculously so. It can’t have been that tricky given that I was able to repair it !


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Richard Lee’s Ultra low Noise MC Head Amp
This thread is a good read, member Bonsai , his website has a good collection of circuits.

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That’s quite correct.

Although the music room is getting close to completion now, so maybe in a few weeks it could be getting dusted off/

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If it hasn’t yet, it won’t for another 7 months at least.

Leach’s notes said that the transistors were selected for their super low noise, and were actually 4db better s/n ratio than the ultra low noise audio ones he’d originally selected. That coupled with a battery might work, I’ve really no idea.

Low transistor noise is important. But it’s not the only type of noise. One way and another they all get on your nerves after a bit (including hum and hash pickup in SUTs). The trick is to get them comfortably below the surface noise on the record.


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