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Old 10th January 2015, 10:59 AM   #1
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Default JLH "Liniac" RIAA

Hello everyone!

I intend to make a correction RIAA preamp transistor for a friend but I would like to have your opinion on the following diagram.
I also have a question about the capacitor 250uF is it related to the RIAA is correct or that a 220uF capacitor is suitable?
The link to the original scheme is on the website of Paul Kemble (A Paul Kemble web page - John Linsley Hood preamp designs.).

Thank you!
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File Type: png RIAA.png (42.2 KB, 445 views)
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Old 10th January 2015, 11:15 AM   #2
AndrewT is offline AndrewT  Scotland
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the 250uF has an F-3dB inside the audio passband.
It will "colour" the sound output.
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Old 10th January 2015, 11:59 AM   #3
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AndrewT thank you for that answer!

For the quality of the components of RIAA filter, it is necessary to use special capacitors (styroflex, mica, etc ...) or standard (MKT MKT, Ceramics) may agree?

Regards!
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Old 10th January 2015, 12:09 PM   #4
forr is offline forr  France
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A while after the liniac, Linsley-Hood created the super-liniac, where the input bipolar was cascoded by a FET. The open loop gain was said to be very high.
The first circuit using the super-liniac was called "RIAA reference standard" by the author and had a CFP push pull output stage.
The second version has a single ended output stage, it was part of an integrated 2 * 30 W amplifier.
I built this second version, but with a 10 kOhm input for a Grado cartridge requiring this load, and suppressed the electrolytic cap which has not the AndrewT's agreement.
There was no annoying noise but it was very sensible to a RFI of an FM emitter which was about 100 m from where I lived.
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Old 15th January 2015, 09:57 PM   #5
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I don't want to be a Negative Nancy but that design looks like it'll be quite noisy as you have a 47K resistance in series with the input which you are then amplifying by a considerable amount.

You'd probably do a lot better to use the two transistor non inverting amplifier topology for this. There are plenty of better circuits out there and you could build yourself something with fairly good performance with 3 transistors per channel.
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Old 15th January 2015, 11:34 PM   #6
rayma is offline rayma  United States
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Quote:
Originally Posted by monty78pig View Post
that design looks like it'll be quite noisy as you have a 47K resistance in series with the input which you are then amplifying by a considerable amount.
This JLH topology does have about 14dB worse s/n for a 47k load mm cartridge, although a head amp can mitigate this.
However, there are reasons of sound quality that this circuit remains well regarded.
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Old 16th January 2015, 12:07 AM   #7
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Well you only have about 3 volts of headroom either way, or even less, so you can't boost the signal upstream or you'll end up with overload.

This just looks like an on-the-cheap type job that you'd find in low quality equipment in the early 80's.

If you want a good discrete phono preamp use a single supply of 24V and a 3 transistor non inverting topology. If you want to use a low supply voltage then use a rail to rail op-amp. But this circuit will have a very low signal to noise ratio when compared to other offerings.
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Old 16th January 2015, 12:49 AM   #8
rayma is offline rayma  United States
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Originally Posted by monty78pig View Post
This just looks like an on-the-cheap type job that you'd find in low quality equipment in the early 80's.
Not at all, it's a well known, highly regarded circuit by an expert from the BBC.
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Old 16th January 2015, 01:03 AM   #9
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Here's something to look at/try:

Jfet-Mosfet Gain Cell
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Old 16th January 2015, 01:10 AM   #10
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Which expert?

The distortion performance may be adequate but the headroom is pitiful and the noise is a good 10dB higher than conventional offerings.
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