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Ila 10th July 2005 11:33 AM

Phono for Bride of Zen
2 Attachment(s)
I would like to present a tricky phono preamp. Like the Bride of Zen it employs single-stage amplification. A common-source mosfet-stage will not have sufficient gain at low frequencies, so I used a compound gain-stage ( think of a complementary Darlington). The mosfet is ( of course ) completely voltage driven, contrary to the PNP-output-transistor, which is purely current driven, giving both their optimum performances. Loadind of the stage is passive with the 560 ohm resistor (R112).

The circuit works well, e.g. you will not encounter any noise problems you might think of when using a mosfet as input. RIAA equalisation accuracy is quite good and measures to within +/-0.1dB.

This amp is a real foot traper and you will have lots of fun with it.

As it is a "Pass like" circuit, feel free to experiment with it. No doubt there is room for some minor improvements.

steenoe 10th July 2005 09:13 PM


The circuit works well, e.g. you will not encounter any noise problems you might think of when using a mosfet as input. RIAA equalisation accuracy is quite good and measures to within +/-0.1dB.
Quite interesting layout! No noise?? It doesnt look like an Eagle sch. Any chance you could post the Eagle files, or a PDF of the board? IRF610 for the major amplification in a Grammo amp, Is not excactly common thing;) Toshiba JFet's, is more like it:) Nonetheless, it looks simple enough to be appealing:)


diy guy 11th July 2005 04:51 AM

Phono gain

What is the gain of the your design. Can it accomodate MC

as well?

Ila 11th July 2005 09:52 AM

PCB, gain
2 Attachment(s)
This phono preamp is a straight forward design (single stage). For this reason the PCB is simple. Attached is the layout in pdf-format (2:1).

It is possible to use J-FETs like 2SK170. You have to put at least 2 devices in parallel in order to maintain the transconductance. I must admit, that I havenīt tried that. As input devices I used IRF610, IRFP 240, BUZ900, 2SK76. Interestingly noise figure for verticals is just about the same as for laterals (BUZ900, 2K76).

Circuit gain is 37dB (1kHz). For MC you have to put in a step up transformer. In this case donīt need the 1uF Cap (C105), instead connect the transformer (sec.) in parallel to the 100k resistor.

Ila 27th July 2005 09:55 AM

It seems that a truly minimalist phono-amp is not your particular interest to work on. Never mind...
Perhaps I throw some different projects in the ring (e.g. a single resistor volume control)

Best regards

Ivo Linnenberg

Ian Macmillan 27th July 2005 04:17 PM

A single resistor volume control? Presumably you mean a single series resistor...

lohk 27th July 2005 10:11 PM

I find it very interesting, although I do not really understand why it is singlestage.. Particularly the very common values for the riaa feedback loop caps will make it easy to build.
In what kind of surrounding have you already tried this circuit (pickup and pre/amp)?

lohk 27th July 2005 10:14 PM

I thought a pot is a single resistor with a tap, but you probably did not mean that..

Ila 27th July 2005 10:27 PM

Single stage yes or no
The input mosfet and the bipolar transistor form a compound stage. It has the formal structure of an N-channel IGBT. The CCS is used to bias the mosfet properly ( in contrast to a real IGBT)

Best regards

Ivo Linnenberg


lohk 28th July 2005 07:15 AM

Ivo, please do not stop posting interesting circuits here - I started several threats here with a response smaller than anticipated.
I would like to here more experience detail (measurements etc.) and comparisons maybe about your very unusual phonostage.
Another idea: Following the experiences of single Jfet MC-prestages (ala L'Audiophile and Thosten Loesch), there could be - say - a single (or some in parallel) Fet as a MC stage followed by your Phono stage.
I made several phonos with different opamps in the last years, time to make another one without.

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