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RIAA Phono Amp Design
RIAA Phono Amp Design
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Old 29th March 2007, 03:32 AM   #51
Sheldon is offline Sheldon  United States
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Join Date: Dec 2003
Location: San Diego
I did a little crude testing of the preamp section too. Removed (per SY's suggestion in another thread) the caps bypassing the LED. No increase in noise detectable, and if there is a difference in sound, it's a very subtle one, so I left them out.

As the power supply is very quiet, I tried disconnecting the noise canceling bits. No measured or audible increase in residual noise. So the circuit could be simplified as follows, if used with a quiet supply (as below).

I went ahead and left the Broskie Aikido inspired elements in, as they added no noise and may also cancel any load induced noise at the plates.
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File Type: gif bench riaa led bias wo noise cancellation.gif (19.4 KB, 1530 views)
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Old 24th December 2007, 06:45 PM   #52
Bruce Anderson is offline Bruce Anderson  United States
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Join Date: Jun 2005
Location: Tempe, AZ
I love sheldon's schematic. Very innovative and I bet it sounds great. I went a little different direction but am very pleased with my results also. My input stage is similar to his output. ECC85, two halfs in parallel for low noise with resister loading for increased gain versus totem pole style. 6DJ8 cathode follower to easily drive low resistance RIAA and Russian teflon caps (Play with the RIAA calculator on the KAB site.) I tried 6N1P and 6DJ8 input. ECC85 has more gain, lower noise, less tendancy to oscillate and sounds good. The back end is the standard Aikido w/6SL7 input for high gain. I used 6SN7 for the final cathode follower. Very low noise. Will drive most any power amp direct. I like it. By the way, do not skimp on the power supply just because it is Aikido. Big improvement when I upgraded from a good quality heavy duty standard power supply.
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Old 18th August 2019, 01:48 PM   #53
kissabout2002 is offline kissabout2002  Italy
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Sheldon I really like your innovative approach and I want build it, the only thing I don't want use the input transformer, really out of budget for me, can you suggest some other way to get a good result without transformer, my pickup is a 47k Audio Technica....all the best...Acky
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Old 18th August 2019, 04:40 PM   #54
Sheldon is offline Sheldon  United States
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Typical Moving Magnet (or Moving Iron) cartridges will have high enough output so that the step-up transformer is not needed. Some high-output MC cartridges may also work OK. I can't tell from your description what kind of cartridge you have, but if the 47k refers to the input load, it would be typical for a MM or MI cartridge.

Sheldon
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Old 18th August 2019, 04:49 PM   #55
kissabout2002 is offline kissabout2002  Italy
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Thanks Sheldon for the fast reply, my cartridge is the Audio-Technica AT95E... all the best...Acky
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Old 18th August 2019, 05:08 PM   #56
rayma is offline rayma  United States
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Quote:
Originally Posted by kissabout2002 View Post
my cartridge is the Audio-Technica AT95E...
That has a standard output level, 3.5mV @ 5cm/sec. No step-up needed.
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Old 19th August 2019, 01:18 PM   #57
kissabout2002 is offline kissabout2002  Italy
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Thank you very much....all the best
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Old 25th August 2019, 08:06 PM   #58
hpeter is offline hpeter  Slovakia
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Quote:
Originally Posted by Sheldon View Post
I did a little crude testing of the preamp section too. Removed (per SY's suggestion in another thread) the caps bypassing the LED. No increase in noise detectable, and if there is a difference in sound, it's a very subtle one, so I left them out.

As the power supply is very quiet, I tried disconnecting the noise canceling bits. No measured or audible increase in residual noise. So the circuit could be simplified as follows, if used with a quiet supply (as below).

I went ahead and left the Broskie Aikido inspired elements in, as they added no noise and may also cancel any load induced noise at the plates.
ecc 88=>oscilator galore.
next question.., what the hell is r3, r22,r23 ???
running framegrids at such small currents, i just wonder the negative effects, noise.
literally 3x ecc88 should be replaced by low capacitance fets.
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Old 26th August 2019, 03:07 PM   #59
Sheldon is offline Sheldon  United States
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Original design here:

Steve's Tube Pages
http://diyaudioprojects.com/mirror/m...amps/RIAA5.gif
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