modify Studer A810 with vacuum tube

[tony ky ma]

CD 's DAC use vacuum tube in their analog out-put section can improve digital sound quality, to-day's supper hi end phono stage amp almost with tubes, reel to reel machine start with tubes built in, but in their golden age is the same time when solid state was replacing tubes, so most of the pro machine do not with tubes any more, and today people want this combination back again (bottle head's repro tube amp) in Studer's pro machine that you can find in market, C37 is the only one with tubes but rare and expensive A810 is the most easy model that you can find, but it look like a digital machine more than a analog one. it has a CPU to control the whole machine and full of ICs inside. it is impossible to change all of them into tubes, so I decide just change the out-put section and see, of cause a tube rectifier high voltage power supply has to be separated (no space for build in) , and I also install a switch can switch back to the original section for compare. result, this switch is a wast, it only work for showing the different to friends, I will never turn it back to the original section for listening
tony ma

 

[RogerD]

Hi Tony,

Looks like about $300 in parts, I want one.

 

[tony ky ma]

Hi Tony,

Looks like about $300 in parts, I want one.

Hi Roger
two 7119 (5687) in mu stage, two 47mf(250v) out put cap and a 296v 40ma power supply were the main cost I forgot how much for that because most parts in my junk box already, maybe less than $200 can do it, the only thing is to find out the in-put point of the out-put section on the PSB, cut and make a extension with wire to the tube amp, very simple
tony ma

 

[jcmusic]

Tony,
That's way too cool tell us more!!!

Jay

 

[Doc B.]

it is impossible to change all of them into tubes

Your mod looks very clean and neat! We have attached a Tube Repro directly to the repro head in an A810. Not impossible, but it does have to be outboard of the deck and it's definitely challenging to bypass the preamp that sits behind the head block.

 

[tony ky ma]

Your mod looks very clean and neat! We have attached a Tube Repro directly to the repro head in an A810. Not impossible, but it does have to be outboard of the deck and it's definitely challenging to bypass the preamp that sits behind the head block.

Hi Doc
What I mean impossible is the whole machine's ICs, I did this mod two years ago, also this is not my final step and mine is modification yours is useing A810's transport to a brand new repro amp, I believe yours will be much better sound and I will do the same thing too in the future, but now I am working on a A80's record amp, change two stages only into tube and keep the original EQ stage on , I am a DIYER and like to experience the sound difference in step by step, otherwise no fun
tony ma

 

[Ki Choi]

Hi Tony:

Your idea is very original and simple. I like it! Could you share the schematics for the preamp?
I'd be interested in your implementation for EQ selections and adjustabilities.

Thanks,
Ki

 

[tony ky ma]

Hi Tony:

Your idea is very original and simple. I like it! Could you share the schematics for the preamp?
I'd be interested in your implementation for EQ selections and adjustabilities.

Thanks,
Ki

Hi Ki
Do you own a unit too ? and do you have the service manual also ? the schematic is very simple , not too many parts, it connect direct from the repro amp's out-put ( resistor R40 ) with a selector switch, that can switch it back to the line amp broad's in-put, the tube amp is by passed the recorder's volume control so the gain is different and out-put is RCA, but the original out put is balance,maybe you need a adepter from balance to RCA for compare use, power supply is separated simple choke cap filter, I like tube rectifier better (6CA4) than silicon, don't forget raise the filament voltage 100v above ground, you need a test tape for adjustment, the manual has telling how to do it and it show in numbers, mark all down in tube 's and the original one, you have to put the right one on for the amp in use
have fun in modification
tony ma

 

[eugen_syd]

Hi Tony,

That looks so good. I have a unit too but on that area I have my VU-meters. Do I have to do it outside? Any chance you can sell a modification ready to install? How much that would be?

Regards,

Eugen

 

[yjwu]

Hi Tony:

Following your direction I just registered this forum. Very good one indeed.

Your modification looks impressive. I problbay modify mine in the near future.

I just got my A810 last month. It was a part machine. With the help from Ki and many other experts my A810 start working.
Although it would stop playing from time to time, I am pretty sure the fault was the poor EPROM IC10. Due to corrosion (near a Ni-Cd rechargable battery) some of the pins had very poor electrical conductivity, even broken off easily. I re-solder the broken pin to its trace of contact area. No wonder it was not reliable. I had registered total eight hours of playing without problem until last night.
So I gave it another try. Eventaully I should replace this troublesome 2764 when I can find a working one.

Y.-J. Wu

 

[tony ky ma]

Hi Tony:

Following your direction I just registered this forum. Very good one indeed.

Your modification looks impressive. I problbay modify mine in the near future.

I just got my A810 last month. It was a part machine. With the help from Ki and many other experts my A810 start working.
Although it would stop playing from time to time, I am pretty sure the fault was the poor EPROM IC10. Due to corrosion (near a Ni-Cd rechargable battery) some of the pins had very poor electrical conductivity, even broken off easily. I re-solder the broken pin to its trace of contact area. No wonder it was not reliable. I had registered total eight hours of playing without problem until last night.
So I gave it another try. Eventaully I should replace this troublesome 2764 when I can find a working one.

Y.-J. Wu

Hi Y J
Welcome to here, I don't have much knowledge of digital control , lucky my A810 don't have problem like your but battery dead, I just replaced it with a common one for wireless phone link by wire . also B62 is control by relays not by IC so I can fix the control problem, now I just did another mods with tube for A80 and B62 ( they are in same repro amp ) I will post it too later
cheers tony ma

 

[c1ferrari]

Hi Tony,

Have you modded the record side, too, with valves
How're the recordings coming along?

 

[tony ky ma]

Have you modded the record side, too, with valves
How're the recordings coming along?

Hi Sam
I already did for A80, we are not using A810 for recording, so far we have the best live recording than before because with tube and silver transformer, now by this A80 repro tube amp ( not yet with silver transformer because Electric Print Audio out of silver wire, just using a copper one instead still have a very big improving ) and we can start to make some copies . I will show a website for ordering tapes from us
tony ma

 

[c1ferrari]

Hi Sam
I already did for A80...so far we have the best live recording than before because with tube and silver transformer, now by this A80 repro tube amp ( not yet with silver transformer because Electric Print Audio out of silver wire, just using a copper one instead still have a very big improving ) and we can start to make some copies . I will show a website for ordering tapes from us
tony ma

That's excellent, Tony! I'm very excited about your project

 

[bblue]

Hi Ki
Do you own a unit too ? and do you have the service manual also ? the schematic is very simple , not too many parts, it connect direct from the repro amp's out-put ( resistor R40 ) with a selector switch, that can switch it back to the line amp broad's in-put, the tube amp is by passed the recorder's volume control so the gain is different and out-put is RCA, but the original out put is balance,maybe you need a adepter from balance to RCA for compare use, power supply is separated simple choke cap filter, I like tube rectifier better (6CA4) than silicon, don't forget raise the filament voltage 100v above ground, you need a test tape for adjustment, the manual has telling how to do it and it show in numbers, mark all down in tube 's and the original one, you have to put the right one on for the amp in use
have fun in modification

Tony, can you clue me on the best place to pick up the repro board output or line card input. I see the point on the Repro card itself (R40, point D), but not sure where to grab it on the main board.

Do you recall?

--Bill

 

[tony ky ma]

Hi Bill
Very easy there are two legs of R40, de-solder the leg which is to the board's out put keep the other leg connect with R41 in, the open leg connect to a selector switch, one to the tube amp the other back to the board's out put, everything will be connected back when you plug it back to the main board, maybe better add a gain adjust resistor in the in put of the tube amp to make sure with same gain with the original then you can easily compare with two of those
tony ma

 

[bblue]

Hi Bill
Very easy there are two legs of R40, de-solder the leg which is to the board's out put keep the other leg connect with R41 in, the open leg connect to a selector switch, one to the tube amp the other back to the board's out put, everything will be connected back when you plug it back to the main board, maybe better add a gain adjust resistor in the in put of the tube amp to make sure with same gain with the original then you can easily compare with two of those
tony ma

Thanks Tony.

So there is no clean way from the mainboard to accomplish this? My A810 is a HS VU so there is no place to put electronics except externally. It'd be nice if I could remote the outputs of repro out to a rear jack, and switch between them and the pass-through to standard output, via relays. I really would prefer not having the connections directly to a plug-in card.

Anything come to mind? I'm quite experienced with wiring and routing so that is not an issue.

--Bill

 

[tony ky ma]

Bill
If you want work on the mainboard, you can try by the socket of the repro amp on the mainboard no.10 point, you can cut from there too
tony ma

 

[bblue]

Thanks Tony.

--Bill