Tape Project Forum

Tape Machines => Reel to Reel Tape Machines => Topic started by: Tubes n tapes on March 25, 2008, 10:36:35 AM

Title: How you can convert your Revox B77 or PR99 into a Tape Project machine.
Post by: Tubes n tapes on March 25, 2008, 10:36:35 AM
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.
Title: Re: How you can convert your Revox B77 or PR99 into a Tape Project machine.
Post by: docb on March 25, 2008, 11:02:06 AM
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...
Title: Re: How you can convert your Revox B77 or PR99 into a Tape Project machine.
Post by: classicrecordings on March 25, 2008, 11:28:19 AM
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
Title: Re: How you can convert your Revox B77 or PR99 into a Tape Project machine.
Post by: Danny Kaey on March 25, 2008, 08:21:18 PM
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

Title: Re: How you can convert your Revox B77 or PR99 into a Tape Project machine.
Post by: Tubes n tapes on March 25, 2008, 10:10:15 PM
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
Title: Re: How you can convert your Revox B77 or PR99 into a Tape Project machine.
Post by: mstcraig on March 26, 2008, 11:12:16 AM
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
Title: Re: How you can convert your Revox B77 or PR99 into a Tape Project machine.
Post by: Tubes n tapes on March 26, 2008, 01:44:32 PM
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.

Title: Re: How you can convert your Revox B77 or PR99 into a Tape Project machine.
Post by: Tubes n tapes on March 26, 2008, 01:52:50 PM


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.
Title: Re: How you can convert your Revox B77 or PR99 into a Tape Project machine.
Post by: Danny Kaey on March 26, 2008, 05:02:54 PM
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... :)
Title: Re: How you can convert your Revox B77 or PR99 into a Tape Project machine.
Post by: xcortes on March 26, 2008, 10:24:52 PM
If smomeone is in Texas:

http://cls.audiogon.com/cgi-bin/cls.pl?misccass&1211728206 (http://cls.audiogon.com/cgi-bin/cls.pl?misccass&1211728206)
Title: Re: How you can convert your Revox B77 or PR99 into a Tape Project machine.
Post by: ironbut 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.
Title: Re: How you can convert your Revox B77 or PR99 into a Tape Project machine.
Post by: Tubes n tapes 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. 
Title: Re: How you can convert your Revox B77 or PR99 into a Tape Project machine.
Post by: Tubes n tapes 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.
Title: Re: How you can convert your Revox B77 or PR99 into a Tape Project machine.
Post by: stellavox on May 13, 2008, 08:07:19 AM
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
Title: Re: How you can convert your Revox B77 or PR99 into a Tape Project machine.
Post by: docb on May 13, 2008, 08:30:40 AM
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.
Title: Re: How you can convert your Revox B77 or PR99 into a Tape Project machine.
Post by: TonyB on May 14, 2008, 10:18:31 AM
Hi Charles,

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

Which Cerafines did you use for coupling caps?

Regards,

TonyB
Title: Re: How you can convert your Revox B77 or PR99 into a Tape Project machine.
Post by: Tape Guy on October 13, 2008, 03:26:26 PM
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?


YES that would be absolutely fantastic! PLEASE do this :D
Title: Re: How you can convert your Revox B77 or PR99 into a Tape Project machine.
Post by: Ben on October 13, 2008, 03:39:11 PM
I think Cerfines are harder to get than Black Gates.
Michael Percy Audio, still has some Black Gates in stock,
and 'Last' tape cleaning products. The revox mods I have
seen pull parts off other cards. It would be nice to keep
record/play back if possible. Or have NO EQ out and that
done on the playback amp.

Title: Re: How you can convert your Revox B77 or PR99 into a Tape Project machine.
Post by: Tubes n tapes on October 22, 2008, 02:42:31 PM
Well, here is the problem with changing the EQ on the record side of the B77/PR99 or pretty much any other serious R2R. Doing so only makes sense if you have the possibility to do a full adjustment of your R2R.

The common method is first to adjust your playback frequency characteristic using a reference tape. For the B77/PR99, that is fixed and pretty accurate, so that makes a change from NAB to IEC fairly simple as described in the article.

On the recording side it is not that straight forward, because part of the recording EQ is adjustable. To adjust an R2R on the recording side, you first set the bias level (which cannot be done properly without some test and measurement equipment) and then you will adjust the EQ for flat response over the tape. As a final optimization you then tweak the bias level and the EQ simultaneously.

So changing the record electronics to match the IEC EQ circuit is easy, but it will be completely out of adjustment at that moment. So unless you have the possibility to adjust the R2R (or have it adjusted) afterwards, changing your record EQ will put you further away from your goal of being able to make decent recordings.

In that case it would be better to leave the EQs as they are on both the record side and the playback side and make only those changes on the playback side that improve the sound quality. You can then play IEC tapes with the new passive circuit I just posted on the LAOCAS website and you can still playback your own recordings with the NAB EQ from the machine itself.


PS. Keep in mind that IEC recordings at 15ips are only slightly better than NAB recordings at that speed. The difference only pays off with either live recordings or with extremely good source material. If you would record at 7.5ips, NAB is actually a better EQ for modern tape formulas than IEC is.

Title: How you can convert your Revox B77 or PR99 into a Tape Project machine.
Post by: Gcalo on April 03, 2010, 01:35:45 PM
Always amazes me the wizard that there are! Reminds me of what I find on the Ferrari web sites.

Great minds. Great article.

What's the detailed advice if one wants to retain the record functions at the modified speeds?

Many thanks in advance.

Update: maybe I don't fully understand:

This mod leaves the 7.5 ips record EQ alone but allows plays back at 15 ips w/o record? So if the EQ were altered to record at 15 ips it would no longer record at 7.5 ips properly?
Title: Re: How you can convert your Revox B77 or PR99 into a Tape Project machine.
Post by: Tubes n tapes on April 16, 2010, 10:18:53 PM

Thanks for the compliments on the article.

To retain the record function, one only needs to leave the components on the record boards and use new components for the modification described in the article.  The problem is that when the speed has been modified from 3.75/7.5ips to 7.5/15ips, the record adjustments and EQ are totally off, so you wouldn't be able to make any half decent recording with it anymore, even if the electronics are still in tact.

If the unit originally was a 7.5/15ips NAB machine, the record function at 7.5ips would still be valid. At 15ips you would record with an NAB EQ, but playback with IEC.
Title: Re: How you can convert your Revox B77 or PR99 into a Tape Project machine.
Post by: Gcalo on April 16, 2010, 10:55:49 PM
I got it.

Still a brilliant modification.

best regards
Title: Re: How you can convert your Revox B77 or PR99 into a Tape Project machine.
Post by: Thomas on April 17, 2020, 04:13:08 PM
Hello everybody,

I hope you are safe and your families as well
I am an analog music fanatic Living in Germany (although I am French) crazy about Hard Bop

I just ordered my first Tape Project tape, I have a B77HS 2T IEC (320nwb at the Moment) and my dream is to bypass the OnBoard pre-amp to improve my Sound Quality/my pleasure ;-)

I have tried to find Arian's amazing article but the link does not work anymore, I would really like to read it... Would Arian or another member of the Group be willing to share it again?

Any other advice for me to enjoy Tape Project tapes on my machine is very welcome! My intention is to get a tube pre amp from Dan/Bottlehead as an external "head" pre amp ;-)

Many thanks in advance and stay healthy and home with great music!
Cheers
Thomas