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Author Topic: How you can convert your Revox B77 or PR99 into a Tape Project machine.  (Read 29760 times)

Offline Tubes n tapes

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For those who are interested, I've published an article on the web site of the Los Angeles & Orange County Audio Society (LAOCAS) about how you can convert a standard Revox B77 or PR99 to a really nice performing Tape Project machine.

You can find the article under the following link: http://laocaudiosociety.net/tech.html

The mods can be carried out by anyone who has some soldering skills.
Arian Jansen.

SonoruS Audio.
VP of technology of the Los Angeles and Orange County Audio Society (LAOCAS).
ESL/OTL builder and modest Studer/ReVox collector.

Offline docb

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Wow, Arian, beautifully documented. I have a hunch I will be finding the PR99 at the studio sitting on the back porch of the lab as soon as Paul reads this...
Dan "Doc B." Schmalle
President for Life, Bottlehead Corp.
Managing Director - retired, The Tape Project

Offline classicrecordings

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Excellent article! It must be very well written; because even I can understand it ;-))

You wrote: "A very similar modification can also be done on the ReVox A77 mkIV, but not on the earlier revisions. Details for that modification will not be discussed here."

I have a High Speed version of a ReVox A77 mkIV, which I have been considering selling. Could you possibly post information for updating that unit in a similar way?

David
« Last Edit: March 25, 2008, 11:36:54 AM by classicrecordings »
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Offline Danny Kaey

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I have heard Arian's Studer's and ReVox's and have to say I am most impressed... the rest of his self-designed and built system is truly first rate as well... Arian knows his stuff!!!

now all I need is a clean 810 to add to my collection........ ha!

cheers,

Danny

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Offline Tubes n tapes

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David,

I'm glad you liked the article. I'll look into the details for modifying the A77 mkIV. That may take a couple of weeks. First I'll have to dig up my A77HS which should be sitting at the bottom of a pile of some other old equipment.

Are there any other people interested in modifying an A77 mkIV?


Excellent article! It must be very well written; because even I can understand it ;-))

You wrote: "A very similar modification can also be done on the ReVox A77 mkIV, but not on the earlier revisions. Details for that modification will not be discussed here."

I have a High Speed version of a ReVox A77 mkIV, which I have been considering selling. Could you possibly post information for updating that unit in a similar way?

David
Arian Jansen.

SonoruS Audio.
VP of technology of the Los Angeles and Orange County Audio Society (LAOCAS).
ESL/OTL builder and modest Studer/ReVox collector.

Offline mstcraig

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A very timely article Arian. I own a B-77II and was just looking into a Seduction preamp, still am actually. Any chance a companion piece on modifying the record side to IEC is coming to complete the set? What would be really great is for somebody to design a standalone unit to do both-Record and playback to IEC specs as an outboard unit to use with anything. Anyone interested? Craig
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Offline Tubes n tapes

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Craig,

Changing the record EQ to IEC is not a big deal. I didn't go there in this article because, well designed as the reproduce section of the B77 is, the record section has a significant design flaw. So it is an easy modification to make the B77 a real good sounding playback machine, but to clean up the record section requires quite a bit more.

Anyone else interested in the record modification?

Concerning a standalone Record/Playback unit, that is not as obvious as it looks. Record and playback electronics have to be carefully matched to the heads that will be used. So generic circuits don't exist. For example a circuit designed for the Revox B77 heads will already show deviations of more than 3dB when used on Studer heads. That's actually worse than the difference between NAB and IEC. And those heads are still of substantially the same pedigree. Imagine what happens if you would use Japanese heads that have significantly different constructions.

Arian Jansen.

SonoruS Audio.
VP of technology of the Los Angeles and Orange County Audio Society (LAOCAS).
ESL/OTL builder and modest Studer/ReVox collector.

Offline Tubes n tapes

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I didn't mention it clearly in this thread, but the modification article describes how you can convert a dead standard 3 3/4ips & 7 1/2ips NAB B77 or PR99 into a significantly better sounding 7 1/2ips NAB & 15ips IEC playback machine.

If you don't need the record function, this modification can be done without buying any new components.

It plays both your TP tapes as well as your standard 7 1/2ips NAB tapes.
Arian Jansen.

SonoruS Audio.
VP of technology of the Los Angeles and Orange County Audio Society (LAOCAS).
ESL/OTL builder and modest Studer/ReVox collector.

Offline Danny Kaey

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Arian, I just bought a 7 track Miele dishwasher... I'd like to be able to play pre-recorded Derrick tapes on that... any chance you can work your magic?

.......

hehehehe... :)
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Offline xcortes

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Offline ironbut

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Re: How you can convert your Revox B77 or PR99 into a Tape Project machine.
« Reply #10 on: March 26, 2008, 11:18:56 PM »
I just got a chance to read your pdf tonight Arian. You wouldn't happen to be a technical writer would you? That was just fantastic! I used to have an A77 and I know the attraction to Revox very well and you've single handedly opened that option for fellow members. I've heard with users of the A77 that the boards get brittle. I've never heard of a B77 or A700 owner with this problem. I'd hoped it was a problem with just some of the A77's. Did you have any experience with this? And before someone else asks, are the electronics of the 700 similar to the B77 or Pr99?
Once again, amazing job! I just wish you'd written the service manual for the Technics machines.
steve koto
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Offline Tubes n tapes

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Re: How you can convert your Revox B77 or PR99 into a Tape Project machine.
« Reply #11 on: March 27, 2008, 10:21:49 AM »
The PCB material in the early 70's was more brittle than the material used in the early 80's, which is pretty much still used today. PCB material kind of matured by the end of the 70's. The biggest issue with the boards in the A77 is that you may have to use some excessive force to pull them out after being in place for decades. The B77 doesn't use PCB edge connectors like the A77 does, so the PCB won't see as much stress if you pull them.

The A700 is another story. A rather sad one, unfortunately. When the A700 was developed in the very early 70's (together with the Studer A67) the engineers at Studer had an attack of modernism and designed something that was 10 years ahead of it's time. The result was an unprecedented transport using a large (and disgustingly expensive in that time) custom IC that handles all the transport functions. A bit like a microprocessor, but with a fixed programming. That transport can hold it's own against everything that has been developed since. After that the attack of modernism on the Studer side stopped and the A67/B67 were populated with rather conservative but well performing electronics similar in philosophy to the Studer A80. On the Revox side, however, they went over the top and designed all the A700 electronics with opamps. Certainly not a good plan in 1972, when opamps were not very good and sounded even worse.

So the A700 is a bit like the RS1500. Very nice transport, but the stock electronics sound so bad that they are beyond salvation. The only option you have is to disconnect the stock electronics and use external circuitry. 
Arian Jansen.

SonoruS Audio.
VP of technology of the Los Angeles and Orange County Audio Society (LAOCAS).
ESL/OTL builder and modest Studer/ReVox collector.

Offline Tubes n tapes

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Re: How you can convert your Revox B77 or PR99 into a Tape Project machine.
« Reply #12 on: April 01, 2008, 12:48:50 AM »
Important correction !!

I just realized that some of the PR99 mkII and all of the PR99 mkIII machines are using another reproduce amplifier board than the one I describe in my article on http://laocaudiosociety.net/tech.html .

For now I will pull back any reference to the PR99 mkII or mkIII. I'm planning to publish an update for these versions within a few weeks.
Arian Jansen.

SonoruS Audio.
VP of technology of the Los Angeles and Orange County Audio Society (LAOCAS).
ESL/OTL builder and modest Studer/ReVox collector.

Offline stellavox

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EXCELLENT article Arian - thank You!

Couple of points.  Looks like the variable trimmer potentiometers used on the B77/PR99 are the same as those in the A77.  If so they have a significant potential aging problem.  Seems the spring tension on the wiper arm loosens up and the slightest readjustment "twist" can cause it to go at best loose, at worst intermittent (try tracking THAT problem down). I  suggest replacing ALL the trimmers with the Piher PT15LH06 series available from Mouser (531-PT15B-value) - they fit in the same holes.  Of course this means readjusting everything so maybe I should modify the previous sentence by saying only replace the pots you plan on tweaking.

Didn't read your article closely but do also suggest replacing ALL coupling caps - I've had VERY good experience with Elna Cerafines.

Charles

Offline docb

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Good idea, Charles. I'll suggest one tip that may save a little time:

Assuming the old pot is still functional and measurable - measure what resistance it is set at and preset the new pot to the same value before you install it. That should get you in the ballpark when you are ready to do the fine adjustment.
Dan "Doc B." Schmalle
President for Life, Bottlehead Corp.
Managing Director - retired, The Tape Project