A simple tube circuit for Studer A80's repro amp modification

[tony ky ma]

Finally A80 got a tube out-put stage in play back, I keep the first stage for EQ and second stage for calibrate of the original, just make a very simple tube circuit each channel with only one single tube, one transformer for out-put, one 2.4v rechargeable battery for bias and one resistor in gird to ground, that is all. simple is the best, I choose WE437A my favor tube for here because of similar gain to the original out-put stage, also a volume control for dubbing tape use and a mercury selector switch for back to the original stage for easy ABX test, there are three coupling tantalum cap ( from picture small color in blue) in the first two stages replaced by big Solen in black color,because of the size has to be link from out side. two power supply in separate case, choke in-put with 6CA4 Mullard and DC regulated voltage for filament. I connect to the Studer B62 for test drive because both B62 and A80 are the same amp in use.
result ? I will never back to the original stage again but the total parts costed almost same as you can get a working A80 from Ebay!
tony ma

 

[Gary D]

Wow! Tony,

I can visualise and upgrade,but my hat's off to you and others that can design from scratch. This must sound wonderful,so be sure to post some impressions if you can. I just go ape when I see somebody take a cost no object approach.

Great job!

 

[Gary D]

Wow! Tony,

I can visualise and upgrade,but my hat's off to you and others that can design from scratch. This must sound wonderful,so be sure to post some impressions if you can. I just go ape when I see somebody take a cost no object approach.

Great job!

Tony it's me Roger. Gary was logged on to my computer.....I can see the problems already.....Ok is this really you Roger? Lol.

 

[tony ky ma]

Tony it's me Roger. Gary was logged on to my computer.....I can see the problems already.....Ok is this really you Roger? Lol.

Roger - not yet, still from your brother, I am no good in telling impression by words, but it is more clear and more clean in low end too, sharper image, will find instrument's sound (violin) like in different level of sound ( anti Stri vs common cheap item) and feel the stock amp sound muddy, images are too close between two instruments that I never felt before and thought they already the best ! we are going to use it for making copies from our live recording master tape, so try to use the best components for this project, when our copy is ready, I will show our website for ordering, try some to know how the quality is.
tony ma

 

[microstrip]

Tony,

Impressive. The transformers we see in the amplification box are input or output transformers?

 

[tony ky ma]

That is a out-put 4.5K 30ma with a step down ratio 4 to 1, drive by WE437A and load with 1 K resistor (same load value in stock amp) can provide similar gain of the stock section, in-put gain control is 10K, same value of A80's uncalibrate control. we looking for a silver wound transformer but Electric Print Audio my transformer supplier out of silver wire, so using a copper one to instead first
tony ma

 

[stellavox]

Hearty Congratulations Tony

Charles

 

[tony ky ma]

Hearty Congratulations Tony

Charles

Thanks Charles, next project is going give a big modification on the B62 but first to fix those mecahanical problems and try to make it can be a portable one for recording
tony ma