"The sole objective of the audio industry as a whole is to sell products..."
Stereo in my living room (05-2009)
Tube Pre Amplifier
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After 2 years is this project now finished.
The amp is more then 25 years old. I bought this peace on Ebay for nearly nothing
because he did not work.
The first thing i did was drawing the schematic.
Then i started to repair this amplifier, this was'nt a big problem (all capacitors,
2 resistors, 1 switch and 2 tubes).
All capacitors are now high quality caps, as the resistors.
I bought the two 12AU7 at www.tubeworld.com 2 years ago.
 
This two 12AU7 are old ( 1967 ) and shit expencive, $45 each! @*#$:-(#^*@!
Next step: replace the Alps with a 24 step attenuator...
- All inputs are switched by high quality relais (the 5 red blocks on the top side)
to keep signal path as short as possible.
- The 4 black Capacitors on the left side are for the hight voltage of the tubes.
The 2 capacitores above ( the orange and the black) are for the tube heating and
the relais.
- The coupling capacitors are high voltage Solen caps.
- I used a ALPS potentiometer (not the best solution, but for the moment it's ok)
Heater power is 24 Vdc because the heating of both tubes is in series. Normaly it
should be 25.2 Vdc but i think it is beter to use a lower voltage. It's about 4.75%
less.
For the high voltage i used 4 very fast diodes and a cascade resistors filters with
4 times 400uF. I also bypass each diode with a small capacitor.
Some measurements:
- Frequency response: 10Hz-86kHz(-1dB)
- Harmonic distortion: < 0.11% (1kHz)
- Signal-to-Noise Ratio: < 91dB (A)
Sound: good bass, mid-range vocals more pronounced, sweet highs
Schematic Amplifier - Schematic Power Supply
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TPR-1
Tube Pre Amplifier
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A lot of things on this PreAmplifier are modified:
some resistors and capacitors are replaced, the Cathodefollower is recalculated and modified
and the potentiometer has be changed with an Alps "Blue Beauty".
 
Also the negative feed back is recalculated and modified.
The Tubes 6N6 are still the same, because they are good.
Measurements
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TPR-1 Frequency Response, measured with RMAA
THD + Noise (at -3 dB FS), measured with RMAA
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The results are disappointing!
So i decided to rebuild the Pre-amplifier using different tubes (12AX7).
That will be my next project....
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A link to a german site about Dynavox TPR-1 tuning:
Dynavox TPR1 tuning...
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MC 767 RD
Tube Phono Pre Amplifier
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The MC input of this amplifier sucks!
The amplification of the cathode stage is to low to amplify the output voltage of a Moving Coil cartridge
( about 0.5mV ) to the needed level of min. 500mV or 60dB.
The schematic shows that only 2 components are readjusted, the 100 ohms resistor and the cathose bypass capacitor of the second stage.
Believe me, that's not enough to get 60dB amplification!
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Some data (after modifications):
- Vacuum Tube 1 x 12AX7, 1 x 5687, 1 x 6N6 for the PowerSupply
- 2 x 5670 (6N3) for amplification
- Output resistance 12 kohm
- MM input Level 2.5 mV 47 kohm / 100pf
- Output Level max. 2000mV
- RIAA accuracy: < 0.55dB, 20Hz - 20kHz
- Stereo Crosstalk (db): -65.0dB
- Total harmonic distortion (THD): 0.29%
The 6N6 (E182CC), 5687 and 12AX7 tubes are used in the power supply, where the 6N6 (E182CC) is responsible for rectification and the 5687 and 12AX7 are utilised for smoothing/stabilisation.
Perhaps i will change the 6N6 (E182CC) for the EZ81 tube...
The 5670 tube is very microphonic, so i replaced this tube with the 6N3P which is a realy good tube.
The 6N3P tubes are used for the signal and gain stages. Both tubes compliment each other very well and produce remarkable detail and vivid vocals.
Original Schematic MC 767 RD of the old version (which sounds better then the new MC 767 RD)
A lot of things on this PreAmplifier are modified:
some resistors and capacitors are replaced, the Ouput Stage and RIAA Network is recalculated and modified.
| Here the orginal RIAA network plot: |
RIAA accuracy: > 3.0dB, 20Hz - 20kHz
- +1.1dB at 1kHz (in place of 0.0dB)
- -1.3dB at 2kHz (in place of -2.6dB)
- -5.9dB at 5kHz (in place of -8.2dB)
- -11.2dB at 10kHz (in place of -13.6dB)
- -16.9dB at 20kHz (in place of -20dB)
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The yellow line is the output-voltage of the Pre-Amplifier.
On this plot you can clearly see that this filter is not working as it should.
The red line shows the network funktion...
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Simulation is done with B2 Spice A/D v4.2 Lite
Here you can download B2 Spice A/D v4.2 Lite
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(image before modifications)
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Tube Buffer Amplifier |
My Tube Buffer Amplifier with the EF95
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| Features
- High input impedance - Does not offer any loading to the source CD player and as
a result it gives its best possible performance.
- Low output impedance - Drives any amplifier easily and ensures virtually perfect
linearity.
- Uses 2 EF95 tubes. Excellent technical performance, incredible longevity - great
sound.
- Low noise, low distortion, huge overload margin and wide bandwidth - Extremely clean
sound with huge dynamic range.
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| This Tube Buffer Amplifier is now used between the Tube-Phono-Preamplifier (MC 767) and the Tube-Preamplifier (TPR-1).
It's a simple Cathode Follower with high Input Impendance and low Output Impedance.
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- Tube: EF95
- Amplification: none
- Output impedance: 300ohms
- Frequency response: 10Hz-90kHz(-3dB)
- Noise Level (dBA): < 75.6dB (A)
- Total harmonic distortion (THD): < 0.015% (1kHz)
- Stereo Crosstalk (dB): -71.5dB
- Length 250mm x Depth 185mm x Height 210mm
- Weight: 3.2 kg
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Accuphase E204 |
One of the best...
I bought this amplifier secondhand, 5 years ago. It's still one of the best for the money.
But i was alltime interessted in Tube amplifiers, so i bought a secondhand Dynavox VR 70-E.
Shure you can't compare Dynavox with Accuphase....
But the possibility to modify my amplifier is for me very important and there is nothing to modify on a Accuphase
but a lot on the VR 70E (made in China for no money...)
| Power output: |
90 Watt per channel RMS at 4 ohms
65 Watt per channel RMS at 8 ohms |
| Distortion: |
both channels driven 20-20kHz
0,02% at 4 ohms
0,01% at 8 ohms |
| Damping Factor: |
80, 8 ohm load at 50 Hz |
| Output load impedance: |
4 - 16 ohms |
| Frequency response: |
20 Hz to 20.000 Hz: +0; -0,2 dB
1 Hz to 300.000 Hz: +0; - 3.0 dB |
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Dynavox VR 70-E
I switched....
From Transssssistor to Tubes.
I know, it's not the best tube amplifier, but i have a limited budget and i like
to modify my equipment.
The VR 70-E is ideal to upgrade (tubes, capacitor, resistors..)
The design is straight and even for starters not to difficult to understand :-)
Some measurements: RightMark Audio Analyzer test report VR70-E
Schematics:
Schematic (Amplifier)
Schematic (Power supply orginal)
Schematic (Power supply optimized)
Detail images:
Image before modification
Image after modification
All important capacitors are changed to high quality capacitors
( Black Gate & Clarity Caps ).
The input capacitor ( 0.1uF ) is gone, because it's not necessary.
The original Potentiometer is now disconnected, it's useless with a Preamplifier..
The recifier diodes are changed to Fast Recoery diodes.
I also changed the input tubes ( 6F2 ) against the NOS ECF82 and the
China Pentodes
against JJ EL34 tubes.
Last update ( september 2007 )
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My System
