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Passively Equalized RIAA Tube Phono Preamp Based on ECC83 ECC82 & Fake NAGRA Chassis
Passively Equalized RIAA Tube Phono Preamp Based on ECC83 ECC82 & Fake NAGRA Chassis
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Old 13th May 2019, 04:11 PM   #1
bbp is offline bbp  China
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Default Passively Equalized RIAA Tube Phono Preamp Based on ECC83 ECC82 & Fake NAGRA Chassis

Almost one year working on this project, finally it comes out.

Fully tube amplification design based on ECC83 and ECC82 (follower), 2 gain stage, passively RC RIAA equalization, MM/MC input with step up trans, direct output from capacitor coupled RCA, balanced output through trans.

Separated power supply unit, connect to main unit via LEMO connectors, because I try to pretend to have a poor man's NAGRA

Fully hand wind MC step up transformer 1:11 , balanced output transformer 1:0.5+0.5, hand made magnetic shield case... that transformers cost a lot of time and patient.

MM Gain 52dB
MC1 Gain 72dB (with step up transformer)
MC2 Gain 52dB (for external step up transformer use, like 1:40 ratio etc.)

Yet it would be far away from NAGRA's electrical specification and sound standard, but I am quite satisfy with this phono preamp now



* All contents on this post are not for commercial use.
Attached Images
File Type: jpg IN3.jpg (205.4 KB, 454 views)
File Type: jpg IN4.jpg (77.7 KB, 442 views)
File Type: jpg IN2.jpg (200.8 KB, 445 views)
File Type: jpg IN1.jpg (166.6 KB, 433 views)
File Type: jpg FRONT1.jpg (117.0 KB, 420 views)
File Type: png MM GAIN.png (373.4 KB, 177 views)
File Type: png MC GAIN.png (368.8 KB, 137 views)
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Last edited by bbp; 13th May 2019 at 04:21 PM.
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Old 14th May 2019, 02:15 AM   #2
bbp is offline bbp  China
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Default SCH

1st gain stage+follower provides ~36dB voltage gain, a passively RIAA equalization cuts 20dB off, 2nd gain stage+follower provides another 36dB voltage gain, so, for MM input there's ~52dB gain. Here a pair of TFK ECC83 and a pair of MULLARD M8136/CV4003 are used.

It seems that hardly no commerical Phono Preamp on the market features in non-loop feedback design. Because matching tubes are too difficult? or too expensive?


I made the four transfomers by myself. Because I found no commercial transformers can match my requirement, unless special order??


Most of the resistors are VISHAY MMB0207, they are pretty good looking and very reliable (AECQ for automotive).
Attached Images
File Type: png SCH.png (233.6 KB, 250 views)
Attached Files
File Type: pdf Tube Phono.pdf (112.0 KB, 52 views)
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Old 14th May 2019, 03:01 AM   #3
rayma is offline rayma  United States
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Quote:
Originally Posted by bbp View Post
It seems that hardly no commerical Phono Preamp on the market features in
non-loop feedback design. Because matching tubes are too difficult? or too expensive?
This one is from 1959.
https://www.quadesl.com/schematics/hkcit1_sch.gif

Also see page 702 here.
http://www.tubebooks.org/tubedata/RC30.pdf

Last edited by rayma; 14th May 2019 at 03:12 AM.
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Old 14th May 2019, 05:51 AM   #4
bbp is offline bbp  China
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Thanks for the info. Especially RC30 document, really useful.

QUADESL_hkcit1 is a loop feedback design, circuit in page 702 RC30 is not.
BTW, QUADESL_hkcit1 is a commercial product, but the circuit in RC30 is not
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Last edited by bbp; 14th May 2019 at 05:54 AM.
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Old 14th May 2019, 07:04 AM   #5
analog_sa is online now analog_sa  Europe
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Passively Equalized RIAA Tube Phono Preamp Based on ECC83 ECC82 & Fake NAGRA Chassis
Quote:
Originally Posted by bbp View Post
It seems that hardly no commerical Phono Preamp on the market features in non-loop feedback design.

Perhaps 30 years ago this was true. Today there are dozens if not hundreds of nfb-free phono stages on the market. In fact the majority of high-end valve phono stages use passive correction and no global nfb.
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Old 14th May 2019, 12:01 PM   #6
bbp is offline bbp  China
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Quote:
Originally Posted by analog_sa View Post
Perhaps 30 years ago this was true. Today there are dozens if not hundreds of nfb-free phono stages on the market. In fact the majority of high-end valve phono stages use passive correction and no global nfb.
Perhaps I am too young & too naive
The only website I can search is stereophile equipment reviews, from where I can know the equipment design, sound style, measurement result, etc..

So, please give an example for non-loop feedback design based on passively RIAA equalization, especially use ECC83/12AX7 as amplification tube.

Klimo Merlin, they may use passively RIAA with ECC88/ECC808? No 3rd party measurement can be found.
Ypsilon VPS-100? Ultra-expensive one, C3g tube, but no measurement result.

Just for this DIY project, I made the measurement on noise, both non-weighting and A-weighting result, 10Hz to 90kHz bandwidth. Input shorted, but ground connect to Audio Precision APX-525, just like a real vinyl system ground loop.

Gain MM=52.5dB
MM L/R 1.4mV/888uV ~ 63.6dB/67.6dB SNR @ 5mV REF. input voltage
MM L/R 270uV/150uV ~ 78dB/83dB SNR @ 5mV REF, A-weighted

Gain MC=72dB
MM L/R 1.8mV/981uV ~ 60.9dB/66.2dB SNR @ 500uV REF. input voltage
MM L/R 280uV/160uV ~ 77dB/81.9dB SNR @ 500uV REF, A-weighted
Attached Images
File Type: png MM NOISE.png (369.6 KB, 202 views)
File Type: png MM NOISE A-W.png (382.7 KB, 20 views)
File Type: png MC NOISE.png (380.5 KB, 11 views)
File Type: png MC NOISE A-W.png (390.1 KB, 8 views)
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Last edited by bbp; 14th May 2019 at 12:22 PM.
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Old 14th May 2019, 02:01 PM   #7
bbp is offline bbp  China
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THD+N vs. Vout
10K load, 10Hz to 90kHz bandwidth, no weighting.
When AP source is in the signal loop, noise performance degrades due to residual noise of AP signal source.

ref. to 500uV MC input signal, the output is 2V, ~0.1% THD+N.\
Minimum THD+N ~0.05%, strongly related to the ECC83 tubes.
Maximum output close to 40Vrms @ 1% THD.
In this project, a pair of TELEFUNKEN ECC83 are used for amplification.

SIEMENS ECC83 (made by EI) provides best noise performance ~600uV to 800uV, and ultra-high gain 54dB.
MULLARD ECC83 short plate, 1mV to 3mV, tested on 3 samples.

Next step MULLARD M8137 or TESLA E83CC?
Attached Images
File Type: png THD VOUT.png (107.1 KB, 34 views)
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Old 14th May 2019, 02:40 PM   #8
Zung is offline Zung  Switzerland
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Good job!
Keep the measurements coming.
Thanks.
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Old 14th May 2019, 02:45 PM   #9
Bonsai is offline Bonsai  Europe
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Beautiful build Paul! Congratulations!
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Old 15th May 2019, 08:19 AM   #10
bbp is offline bbp  China
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Quote:
Originally Posted by Zung View Post
Good job!
Keep the measurements coming.
Thanks.
RIAA error

MM/MC with 10R&20R signal source resistance
Attached Images
File Type: png FR MM.png (91.2 KB, 51 views)
File Type: png FR 10R.png (86.5 KB, 46 views)
File Type: png FR 20R.png (80.0 KB, 31 views)
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