PA-202
2011/04/03 created
2021/11/25 updated
Stereo Tube Preamplifier
High-class preamp with CR-NF type phone equalizer and Lux type tone control
| Features | Vacuum tube: 12AX7/ECC83 x6. Circuit type: CR-NF type phono EQ, P-K looped flat stage, Lux type tone control Separate power supply unit |
|---|---|
| Outline Specifications | Functions: selector, tape monitor, volume contorl, balance control, tone
control. Inputs: PHONO (MM) x2, LINE x2, MONITOR x1. Outputs: REC x1, PRE OUT x2. EQ spec: Gain: +36.5dB. Input impedance: 50kohm. Max input: 300mV. |
| Dimension | Amp unit: 400(W) x 124(H) x 200(D) mm (not including protrusions). Weight:
?kg. PSU: 200(W) x ?(H) x 100(D)mm. Weight: ?kg. |
| Cost | aprrox. 40,000 JPY |
| History | Built in 1974. Discarded in 1980. |
The following contents were copied from the page of PA-202 on my previous homepage 'Tonochi's Audio Room', and edited to fit in the new format.
Concept
High-end preamplifier superior to Marantz model 7.
This preamplifier was built on condition that it would be paired with the
power amplifier MA-201.
Design
High-end preamplifier superior to Marantz model 7.
This preamplifier was built on condition that it would be paired with the
power amplifier MA-201.
Circuit Design
I copied Yoshiro Uesugi's design (introduced in his book published in 1973; reference-3, pp.33-43) with some customization. I modified the power supply circuit. In the original design, Lux's mains transformer was used. It was not affordable to me. Instead of it, I used the cheapest mains transformer in Tango's product line. And I decided to place the power supply circuit in another enclosure. The power supply unit (PSU) was connected to the amp unit via a 6-core cable.
FYI: Yoshiro Uesugi is the founder of Uesugi Lab (known for U-BROS amplifiers). He was the president of the company until he died in 2010.
Since the original schematic has been lost, I restored the schematic based
on Uesugi's one and my recollection. The PSU is integral to the amp unit
in the schematic, as opposed to the real circuit.
[Schematic (PA-202_Schematic.pdf)]
Mechanical Design
The mechanical design was based on Uesugi's idea. Two simple aluminum chassis
were combined to form the enclosure. This construction offers separate
compartments for the L/R channels, and results in good channel separation.
I have repeatedly used this construction for later NOBODY amplifiers.
The difference from Uesugi's design was, as mentioned above, the PSU was
implemented in the separate case.
Building
I was very careful in soldering, as in MA-201.
Self-evaluation
E (Worst)!!
Every kind of noise could be heard including microphonic noise. Particularly,
Click noises caused by power on/off of other electrical appliances were
the most serious. Moreover, PA-202 picked up a radio wave emitted by a
nearby ham radio station as noise. The RF noise was demodulated somehow
in the amplifier and voice could be heard so clearly that I could catch
what they spoke.
This project resulted in a total failure as opposed to the catch copy "High-end
preamplifier superior to Marantz model 7." By the way, the catch copy
was not mine but Uesugi's.
Through this project, my overconfidence was shattered. I realized I had to learn a lot more to build high quality amplifiers.
