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Old 30th January 2004, 10:26 PM   #21
Electrons are yellow and more is better!
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Quote:
Originally posted by jewilson
That is just too much capacitance for this poor little diff amp to slew.
This is not a problem (I think) because the amp has no global feedback. The RIAA network is passive, sort of speaking.
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Old 30th January 2004, 10:40 PM   #22
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peranders

When one side of the diff amp goes positive, the other side swings the opposite direction. Therefore, you still having to charge and discharge the caps. It's kind of like having your own built in Miller effect. I would be interesting to see how much voltage in could really swing and how it would react at 10-20 KHz.
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Old 31st January 2004, 05:53 AM   #23
Electrons are yellow and more is better!
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I think this will be no problem. You can convince yourself if you transform the collector resistors and RIAA-network to D->Y Then you will have only collector load. This is homework, the conversion. Delta-Y conversion can be very handy when things get too complicated.

The design lacks maybe of sufficient common rejection (the pickup will pick up hum) but it may work.
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Old 1st February 2004, 12:07 AM   #24
Aiace is offline Aiace  Italy
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1) Yes Perenders, It pick some noise from pick up: if I short the input it has no noise. Have you any advice to me?

2) For my system 46.6 dB of gain is really too low. I have to raise it. I've tried to c.c. the emitter resistor of BJT but it is low yet. I don't want to use another stage.....I'll think about it.

3) What is d->conversion?



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Old 1st February 2004, 07:02 AM   #25
Electrons are yellow and more is better!
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Somebody may give you a good reference but this is know for those who have read theory about electrical circuits.

You have tre elements connected in a triangle. You can convet this to a Y instead. This can be very neat when you want to see the real ciruit. I should say that this is essential in electronics but you don't use it every day.

If not anybody can help you here in a day or two send me a message and I can dig up some material.
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Old 1st February 2004, 08:50 AM   #26
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This is a lot like Morrison's 'Siren Song' implemented with SS. Quite impressive, elegant, I like it.

Comments:

1. The emitter follower series power supply with FET CCS/Zener voltage reference is very nice. I've tried them and they work extremely well. Of course, this circuit really needs a good supply since the PSRR is low.

2. Is it possible to put equal emitter resistors on the input diff pair? This will give equal gain to each phase to reduce H2 to the minimum. Offset control is not a problem on this amp, and it could be trimmed to balance quite adequately by selecting input devices for the same beta and Vbe. I've found a small tip in the diff pair balance is not too damaging on the sound quality.

3. More gain could be extracted by using a bipolar input stage. I'd suggest using 2N4401/3 devices, cheap, very low noise. While this necessitates use of a quality input cap to protect the cartridge, a low voltage RTX or PPMX is fine in this role.

4. The slew issue alerted by JE Wilson looks bad to me too. Per-Anders' solution using a Y connection to ground looks good, but it may also be possible to split the RIAA, with the LF compensation in the second diff pair.

I like the elegance and simplicity, but I suspect device matching will be important. Generally I don't favor FETs for CCS, preferring bipolars with good voltage references (1.2 or 2.5 volt) or even a LED. The output caps could be Black Gate or Nichicon Muse; you can buy 25V versions in 10uF which would be ideal.

Congratulations! Nice circuit......

Cheers,

Hugh
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Old 1st February 2004, 04:21 PM   #27
Electrons are yellow and more is better!
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Here is Y-D transformation... only in swedish but I think you can have use for it.
http://www.tfe.umu.se/courses/elektr...sformation.pdf

Anybody who knows some cool Java calculator for this?
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Old 1st February 2004, 09:23 PM   #28
Aiace is offline Aiace  Italy
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1) Thank you Peranders, I already knew D->Y transfom but in Italy it's called Star->Triangle

2) Slew rate.... Thr slew rate is the time that you need to charge the capacitors. You can use large capacitance and low resistors or small capacitance and big resistors but the time costants are always those of the RIAA.

3) AKSA, I love you! thanks for yours compliment.
I also thought to use BJT at the input, but I have to re-design the RIAA equalitation

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Old 1st February 2004, 09:34 PM   #29
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Quote:
Originally posted by Aiace
1) Thank you Peranders, I already knew D->Y transfom but in Italy it's called Star->Triangle
Actually, I think the most common terms in swedish (after translation)
are either Star/Triangle or Star/Delta. The document P-A linked to
uses the latter of these two. D/Y is also use, where the D presumably
is an abbreviation for Delta and the Y simply reflects the actual
visual topology.
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Old 1st February 2004, 09:45 PM   #30
Electrons are yellow and more is better!
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Quote:
Originally posted by Aiace
2) Slew rate.... Thr slew rate is the time that you need to charge the capacitors. You can use large capacitance and low resistors or small capacitance and big resistors but the time costants are always those of the RIAA.
I think you can forget about slewing problems. This is only interesting when you have feedback.

About the noise, a pickup generates noise and you can't get more than 60-70 dB S/N out of a record.
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