modification with tubes of Studer A80's record amp

It just finished the prototype and test run last night, may be not too many reel to reel owner will have interesting of this post because most of them only use as a play back machine, We do live recording, modify repro amp can catch up in any time later but miss a good preform in recording will no more chance to get it again, so I do this one first,the prototype with tubes has a switch option back to the original circuit, we used two A80 in tape to tape copy, only one try my partner and I got the answer no need to repeat again, he said the texture was completely different whit tubes although it has not break in yet,sound more closer to the original tape which he did in live recording, I only adjusted it to the same sensitive level to the original no measurement of distortion, noise level or frequency respond, because those numbers will not give me the idea of sound's texture, I am sure the tube one has higher distortion than the original A80's one, but it sound more live like less down grade from the original tape, two sets of silver transformers had been ordered for replacement of the cooper one in the prototype, expect more improvement in future and can make more good copies of good recordings
tony ma

Cyranodb said:

Tony,

Is this design of any use in revox PR99 machines? Revox prosumer machines share the same recording PCB and oscylator board. Internal audio level is 80mV on rec input board but bias generator is only 150kHz. The heads may not be the same too.

Andrew

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Hi Andrew
Record amp is not like the repro amp that direct connect from the head to another out built repro amp, I had to use the original oscillation and I believe the original EQ section is good for the head too, so actually it is a hybrid mods, not all tube, only the in put and out put section change to tube with transformer coupling, and there a switch can switch back to the original too, last night we test the difference between of them but I can't use my pool English to common the detail but for sure will never go back again. coming Saturday will use in a piano solo concert and will post some pictures later, because of partly change of the circuit is not for all models
cheers
tony ma

flez007 said:

Tony Ma - My EAR/Technics RtR does have recording capabilities, and has all TdP mods in it for that purpose as well. I have not recorded anything live, but made some experiments copying some recorded material with great success, copies are almost identycal, minimum hiss and preserving the same "magic" of tape reproduction.

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Hi Flez
We did use two Studer A80 to copy from a master tape, has quality reduce in each copying but the tube one has less reduction than the original one. we plant to produce high quality classical music tapes in future that is why we try our best in recording
regard
tony ma

Cyranodb said:

I will look into A80 /rec/EQ/Osc/ schematics to better understand. Hovewer from what you are writing my understanding is that the additional circuitry you have developed injects tube/iron sound b/c NAB/IEC EQ stage and driver stage stay as they are. Some kind of follower to better match impedancies and ease the load with flat pass band.

If that's the case A80 developed mods would fit at least on the driver stage for revox too under one condition 'assuming that it sits just in front of the head and it is fully passing signal modulated Bias". That would be great as the recording head is wired for easy access. If the recording heads are the same its load freq. responce will be the same b/c the driver output responce has to be matched to the head therefor your inter stage will properly load the driver stage. Is it the case? Does the iron is custom made?

Andrew

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Hi Andrew
I think you already got the schematic (A80RC MKII) in hand, first stage of the in put is a 1 to 1 in put transformer and follow by a low pass filter, two resistors split the signal to half, right now I still keep this section in, next a emitter follower and out to the control of calibration and select switches and coming back to another emitter follower to drive two 5K level adjusting VR. this is the first part I change to use a half of 6900 (5687) and a step down transformer to directly drive that two VR. by pass all the control and switches, next stage is EQ also keep it in but replaced two coupling caps to a big size Solen, the load for the EQ section is 3.3 K, this one has to be exactly can not change. next driver stage's load ( head and filter combined) is around 1K so another half of 6900 and step down transformer to march same gain of original with 3.3K in put and 1 K out put,this is all I did in this mods I hope you can understand, in the first built I use 7119 and copper transformer, after checked everything is OK, now changed to 6900 and silver transformer too, in future I will bring the in put transformer out and switch to silver too make the sound path shorter and less contact points all transformer are custom made from Electric Print Audio in Las Vegas
cheers
tony ma