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Author Topic: How you can convert your Revox B77 or PR99 into a Tape Project machine.  (Read 29888 times)

Offline TonyB

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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

Offline Tape Guy

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Re: How you can convert your Revox B77 or PR99 into a Tape Project machine.
« Reply #16 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

Offline Ben

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Re: How you can convert your Revox B77 or PR99 into a Tape Project machine.
« Reply #17 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.

« Last Edit: October 13, 2008, 03:42:16 PM by Ben »
Set 45,Open baffle speakers,Otari 5050,,Pioneer DV-79AVi DVD/CD/SCAD player

Offline Tubes n tapes

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Re: How you can convert your Revox B77 or PR99 into a Tape Project machine.
« Reply #18 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.

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 Gcalo

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How you can convert your Revox B77 or PR99 into a Tape Project machine.
« Reply #19 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?
« Last Edit: April 03, 2010, 03:24:10 PM by Gcalo »

Offline Tubes n tapes

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Re: How you can convert your Revox B77 or PR99 into a Tape Project machine.
« Reply #20 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.
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 Gcalo

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Re: How you can convert your Revox B77 or PR99 into a Tape Project machine.
« Reply #21 on: April 16, 2010, 10:55:49 PM »
I got it.

Still a brilliant modification.

best regards

Offline Thomas

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Re: How you can convert your Revox B77 or PR99 into a Tape Project machine.
« Reply #22 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       
Crazy about Hard bop Jazz, Soul, Ska, Otis, Nina, Janis, Jim & Marin Marais (Baroque)

Revox PR99 stock (not B77 HS as planned) for the moment dreaming of connecting my pair of LEAK to tape head pre amp and improving Transport as much as possible