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Old 10th July 2005, 11:33 AM   #1
Ila is offline Ila  Germany
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Default Phono for Bride of Zen

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.
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File Type: pdf riaa.pdf (37.5 KB, 1157 views)
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Old 10th July 2005, 09:13 PM   #2
steenoe is offline steenoe  Denmark
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Quote:
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

Steen
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Old 11th July 2005, 04:51 AM   #3
diy guy is offline diy guy  Singapore
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Default Phono gain

Hi,

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

as well?
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Old 11th July 2005, 09:52 AM   #4
Ila is offline Ila  Germany
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Default PCB, gain

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.
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File Type: pdf riaa_layout.pdf (45.6 KB, 498 views)
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Old 27th July 2005, 09:55 AM   #5
Ila is offline Ila  Germany
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Default Response

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
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Old 27th July 2005, 04:17 PM   #6
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A single resistor volume control? Presumably you mean a single series resistor...
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Old 27th July 2005, 10:11 PM   #7
lohk is offline lohk  Europe
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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)?
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Old 27th July 2005, 10:14 PM   #8
lohk is offline lohk  Europe
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I thought a pot is a single resistor with a tap, but you probably did not mean that..
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Old 27th July 2005, 10:27 PM   #9
Ila is offline Ila  Germany
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Default 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

LINNENBERG AUDIO
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Old 28th July 2005, 07:15 AM   #10
lohk is offline lohk  Europe
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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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