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Revox A77 vs A700 - Do they sound different?

I had a77 mkIV, have a b-77 MKII and had an A700. The B-77 had the flatest response of the three, but the A700 could put on take off more signal to and from tape than the other two with higher head room with out sounding soft or mushy. The B-77 seemed to give the best presentation and details from percussive instruments. All the machines were high speed 7 1/2 / 15, though the A-77 was quarter track and the B-77 2 track along with the A700. I preferred my Ampexs however. I had a 300-2 using 354 electronics, tubed, and I loved its forward very life like sound.(7 1/2 / 15) I didn't miss the response above 16,000 hz the Revoxes had and the Revoxs seemed to push the staging of the instruments back from the Ampexes . The Ampexs all had punchier bass.too. The AG440 C was the cleanest , had the most head room, best signal to noise, but the tube 354 was a very close second. The A-700 and B-77 couldn't handle the signal levels of the master tapes of the 300 or 440. Using 3% distortion as a +6 db reference level with Maxell UD tape the old Ampexes could place 3 to 5 db more signal on the tape at 700 hz. I used Ampex AME or NAB EQ for the Ampexs at 15 ips ands NAB at 7.5 ips. I also had a 4 channel 1/2 inch 300-4. Its was a duplicator master deck with belt drive to the capstan rather than idler drive with 351 tube electronics and a custom master SS bias oscillator running at 150khz as I remember. Using Dolby and DBX noise reduction was a revalation in the 70's. Sadly all the decks and tapes have been gone since 1984. Except for the B-77 and an Old Ampex Ag500-2 HS both now in storage. My old Ampex f-4460 (1964) is in a state of disrepair, but hope to get it going one of these days for my little museum.
 
twiiii said:
I had a77 mkIV, have a b-77 MKII and had an A700. The B-77 had the flatest response of the three, but the A700 could put on take off more signal to and from tape than the other two with higher head room with out sounding soft or mushy. The B-77 seemed to give the best presentation and details from percussive instruments. All the machines were high speed 7 1/2 / 15, though the A-77 was quarter track and the B-77 2 track along with the A700. I preferred my Ampexs however. I had a 300-2 using 354 electronics, tubed, and I loved its forward very life like sound.(7 1/2 / 15) I didn't miss the response above 16,000 hz the Revoxes had and the Revoxs seemed to push the staging of the instruments back from the Ampexes . The Ampexs all had punchier bass.too. The AG440 C was the cleanest , had the most head room, best signal to noise, but the tube 354 was a very close second. The A-700 and B-77 couldn't handle the signal levels of the master tapes of the 300 or 440. Using 3% distortion as a +6 db reference level with Maxell UD tape the old Ampexes could place 3 to 5 db more signal on the tape at 700 hz. I used Ampex AME or NAB EQ for the Ampexs at 15 ips ands NAB at 7.5 ips. I also had a 4 channel 1/2 inch 300-4. Its was a duplicator master deck with belt drive to the capstan rather than idler drive with 351 tube electronics and a custom master SS bias oscillator running at 150khz as I remember. Using Dolby and DBX noise reduction was a revalation in the 70's. Sadly all the decks and tapes have been gone since 1984. Except for the B-77 and an Old Ampex Ag500-2 HS both now in storage. My old Ampex f-4460 (1964) is in a state of disrepair, but hope to get it going one of these days for my little museum.
Click to expand...

Service the B-77 and play it :music: Great sounding consumer machine, sometimes it's a good thing NOT to have been around all the Pro equipment back then. I still like the sound of my A-77 Mk IV (I don't use the Dolby in it) I am 61 now and don't hear past 15,000( I use AGFA PER 528) so some of these more expensive machines are wasted on my old ears. I mostly play Blues/Rock and most of this music is below 16,000 on the highs. Blurays. I get caught up in the movie and don't notice. I think I hear what I see on most DVD/Bluray movies .
I am happy with all the vintage equipmentPop I collected thru the years shame we sold all the tubes(McIntosh) and other TT(Thorens) etc when CD and DVD hit we went SS and digital except for the Revox and I just had it completely restored, every "Cap" in it has been replaced. Pop is gone and I am relearning about analog again.sure is FUN. Next R2R I want is a Otari MX5050BIII-2 and have it restored and play with 1/2 track 15. I can't afford a Studer A-820 and up keep on it. Several local shops can work on the Otari but a Studer needs someone that like you knows what they are doing.
 
jan_stevns said:
TBA931 can benefit from being replaced with NE5532 etc.... :)
Click to expand...

There are cautionary tales about replacing the first op-amp in the playback chain... apparently choosing the 'wrong' one can make the A700 put clicks onto the tape at power on/off. There are several references to it around the www.
 
steerpike2 said:
There are cautionary tales about replacing the first op-amp in the playback chain... apparently choosing the 'wrong' one can make the A700 put clicks onto the tape at power on/off. There are several references to it around the www.
Click to expand...

True ! - But all had apparently ignored a service bulletin from STUDER, adressing this "problem".
(they don't do their homework......)

It is available on ftp.studer.ch


in essential - Studer selected opamps usable for +/- 18 volts, normal TBA931 would litterarely explode when operated above +/- 13 volt

Revox or Studer exploding items - hmmmm ... hehe.... Now, where have we heard that before ??
 
I see the information on substituting the op-amp in the Studer A80 series, but that doesn't address the problem that arises in the A700.
The A700 has a condition where at power off, the positive and negative supply rails decay at different rates; this makes some species of op amp briefly draw excessive input bias current, which flows through the reproduce head, partially erasing the tape at the point where it rests on the head.
I think (no practical evidence though) FET input op-amps would be immune to this problem, otherwise a mod to the head amp power supply to kill both supplies at the same rate.
 
Hello R2R addicts :D


I am the proud owner of a B77 (7,5/15ips) PR99 (7,5/15ips) A77 (7,5/15ips) an A700 and a B67 as you will see 'em here on this page.

All of them are two tracks machines and have been thoroughly aligned, tweaked and optimized by me (some mods performed on the input and record amplifiers boards for the A700 and the B77) and I must say that they all sound very close to each othe and very, very good.

Of course the B67 because of it's butterfly heads allowing higher levels on the tape and it's electronics has less "sound" on it's own. It lets the music flow to your ears like if there was not any electronic circuitry between the tape and the speakers but they all really sound superb.

Making a Revox or Studer to sound superbly is mainly a matter of tape choice and proper alignment to this very tape, hence the necessity to stick to a brand (RMG Studio Master 911 for me) and use identical format machines for A/B comparisons, ie. 1/2 track on 0.25" tape.
Just my own experience.

Thierry
 
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Tinman said:
I have an A77, B77, PR99, A700, B67 and an A810. They all have their signature sound. While slight, there is a difference between machines that use IC's versus transistors. But I suspect most comes from alignment and the age of the components.

Having said that, I don't do A/B comparisons..... I like them just fine how they are.
But I was surprised by how good an A77 sounds, given it's age.
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Hi have. B77 and just got a A700 but from others it sounds like revox recorders generally do not suffer from the lift in the base regen like other makes do A worn head and a machine that is not optimised might have base lift and a reduced top end as in the hf starts to role off could this be the reason for different play back sound just a thought
Paul located in UK
 
jan_stevns said:
True ! - But all had apparently ignored a service bulletin from STUDER, adressing this "problem".
(they don't do their homework......)

It is available on ftp.studer.ch


in essential - Studer selected opamps usable for +/- 18 volts, normal TBA931 would litterarely explode when operated above +/- 13 volt

Revox or Studer exploding items - hmmmm ... hehe.... Now, where have we heard that before ??
Click to expand...
The revox A700 has +/- 12 volt supply for the TBA 931 so within supply limits for the TBA 931 unfortunately there is no crowbar to protect the ic’s in the event of a power supply fault
Can anyone please point me to the service builtin on using TBA931 replacements
 
Hi Guys,

with regard to the replacement of the TBA931 Op Amps. After a bit of Net Research, I settled on a surface mount package for an Analogue Devices AD8672. I wanted the small package so that I could mount it on a DIL Header 14 Pin. I did this mod back in 2007 and the 4 Track A700 has been running on them since then. All TBA931 chips were replaced with this conversion and has been running quite happily on them. There is the problem with the ticks which get written when you power it off but I always release the tension on the tape, due to the tensioners, and add a bit of slack. A backwards rotation of the RHS roller makes a loop which drops the tape from the heads. Here is a pic of the mod. It has a 0.1uF cap across the power pins as well.

AD8672 On DIL Header.JPG

I still have 4 spares as I have a 2 Track A700 as well but that machine is put on one side now as I have a 2 Track C270.

With regard to the clicks. From the C270 Service Manual, The Head Amp is a NE5532N. It has a transistor on the +ve power pin which is controlled by a Zener Diode which is across the power lines. When the power lines collapse the transistor isolates the +ve power pin before any damage is done.


Head Amp.jpg


Two resistors, a Transistor and a Zener could be fitted into the DIL Header with relative ease. If not practical they could be added to the back of the Pre Amp PCB. I am with Tinman on this one. When I can be bothered to get off my backside and do it. I am 63 now so enthusiasm and inclination (lack of) and "If it ain't broke, don't fix it" are getting the better of me. The C270 has just had ALL the PCBs removed and EVERY Electrolytic in it has been replaced. So other like projects are now low on the list. Listening to the C270 with a glass of wine and something to read does have me grinning on a regular basis. It was good before but now it sounds amazing!!

Hope this is of interest to you guys.

Cheers

GPS16
 
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Thank you for the Cct from the C 270 I am going to look at the manual and look into do a mod on the supply rails to prevent clicks on the tape
 
pqlia said:
Hey tape specialists!

I’m very pleased that this site helped me to revive an A700 a year or so ago and I have to say that I love it.
The guy who very kindly did the work also kindly loaned me an A77 whilst my A700 was being repaired. I seem to remember the A77 sounding slightly different: perhaps a little more flattering than the A700 coming off tape than going on. When my A700 was returned by the genius who repaired it I thought It sounded excellent but possibly even more 'accurate' (faithful to the source) and less flattering than the A77. unfortunately I didn’t have them at the same time to compare them though, so I keep wondering if I was making up the difference, was the difference simply psychological?

Every now and then, I keep searching online to see if anyone out there has done a side by side comparison but I’m unable to find anything. Maybe I’m just looking in the wrong places.

Would anyone know what the audible differences are, if any?

Thanks.
Click to expand...

go to an outboard tape head preamp and it will likely sound better than either.
 
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