Can you believe it? Tape Project is ten years old! Thanks to everyone who has supported us in introducing studio quality tape reproduction to the audiophile community!

Author Topic: Ampex ATR-700 Refurbishment  (Read 6047 times)

Offline tropicalcb

  • Newbie
  • *
  • Posts: 2
    • View Profile
Ampex ATR-700 Refurbishment
« on: April 18, 2010, 07:53:15 AM »
G'day TP forum comrades
... Another virgin poster ... so here goes the cherry!!
   I thought I'd do a quick summary of a mini project I started after discovering the Tape Project tapes a couple of months back. This might open up further the range of record/repro decks available to people thinking of jumping in & who have limited $$ & can do some basic refurbishment themselves. This won't get you a modded studer C-37 or Ampex ATR-100 or MR-70, but it will get you imho a better overall machine specifically for Tape Project tapes that will give the better consumer or prosumer decks mentioned a run for their money & the satisfaction of doing the work necessary to very noticeably improve the sonic flavor of the deck.
   I have a mid 60's tubed Crown 822 - 1/2 Track 15/7.5 IPS which I picked up cheap from an ol doctor bloke in NY somewhere, who spun me a yarn as to the shape the Crown was in - gross hyperbole!! ... but the sea freight ended up making the exercise a lot more expensive than I figured ... but thats the way it goes eh!  .. the real clanger was when I realised that its using ac reel motors & capstan & its 60hz !!  I have a giant step-down -1kva, so I wasn't worried about the line voltage .... anyway the short version is I've got to have a new set of pulleys done & although the heads are in VG condition there's a lot of work to do for another time.
   So; I started looking around & reading up on whats available ... didn't want anything I'd had in consumer types - X-2000, X-2000R, Akai, Tandberg etc .. and the Revox/Studers are way too expensive & generally bugga'd/flogged if out of a studio: although I like the PR-99 & had a G-36 years ago which I modded & changed to 7.5/15 & that was a very nice tubed unit ... came close with an 810 & a couple of others but found out at the last minute that what was being promised was not gonna be delivered!
     Also, I'm in a remote part of Cape York & its the wet, so only way out & in is by plane until may/june .. which means having a look/listen is out of the question. There was an Otari MTR-10 which was reasonably priced & a very nice looking studio job in VG condition if the seller was to be believed. Main issue would have been getting it up from Cairns to the Cape - 700km in the middle of monsoonal rain etc - not possible. And its way too big to get on a 6 seater charter.
  So I ended up getting an ATR-700 from a guy in the US - spare 1/2 track & 1/4 track new condition head stacks & all rebuilt, calibrated, grease & oil etc etc. .. it was the pick of a few he has.
   I have read references to these semi-pro units & suspect that the biggest beef die-hard ampex afficianados have is that it was made by Teac ... some say designed by Ampex ginger beers but I don't know about that.
  The 700 transport is good & the heads seem quite good & I would assume on a par with anything made in the 70's, except the Studers for the transport & heads - 70's pro, prosumer, consumer units that I have seen & heard, & I think its fairly well recognised, have not so crash-hot electronics ... probably designed by people who assumed that if it was new it was great, and like the 700, lots of pro bells & whistles for mixing 4 mics etc so overly complicated signal path. This was a disapointment with the teacs .. full of mediocre opamps from the mid 70's & never particularly renowned for sound quality. But great transport & heads... personal opinion here, lots of folks love em.
   The nice part of the 700 is its smooth operation & the easy access layout of the PCB's all in a row under the base. The Power Supply is quite well done & has a beautiful over-spec'd Dble-C-Core mains Tx, . I've never seen a C core in an R2R  It has universal AC & line frequency & both NAB & CCIR EQ. The cards are the old bakalite + print ... very similar to an Akai 330D I have;  & discrete transistors!  But easy to desolder & work on.   
    However, they have used a Toshiba TA7136P - 7 pin in line chip at the input to each channel on the Repro EQ amp... not a good audio chip!  This isn't a major issue because I've also got an Eros tape head pre I'm putting together to bypass the output electronics & take a feed straight of the small board behind the head-stack - just gotta figure out if I can parallel this output with whats there or incorporate a switch. It may load the circuit & I'll have issues.
  So I hooked the 700 straight into a power amp after I unpacked it - and making up some leads because its balanced out, which is another issue to be sorted - transformers??!!  is there such a thing as a good transformer!?  and do I really need balanced with short runs to a head amp & pre.
  Anyway, I put on the Jacqui Naylor TP tape which was the only one I had, and wondered what all the fuss was about. It sounded good but there were a number of sonic issues which I suspected were the electronics or related. You know how you get a gut feel about a component. It had a nice solid chunky feel to it, the controls were nice to touch, there was no clunking when going from rew to play etc. But the sonics were veiled & the bottom end "card-boardy"  ie: there was no overhang/sustain & no definition - was the PS deficient or was it the caps? ... The mids were veiled & instrument defintion lacking.... highs were recessed & not what I'm used to from a good CD or vinyl ... But I still had this gut feel that because it was in such good condition that more than likely it had all the original caps & this was a major factor in the short-sighted sound. Yep, and except for dust they were looking like they would've the day the machine was assembled.... and we all know how far caps have come in 30 years ( this is a 1980 build)
   I did the following component changes - replaced all the electros on the PS board with Elna Silmic 11 and Nichicon Fine Gold for the large reservoir caps - the Fine Golds are available reasonably priced from a guy on ebay ... and the Silmic 11 can be got from numerous places & they're way cheaper than BG's on a par with FC's & others
.... here's one bloke's neat test rig & sonics matrix to test the "sound" of various types of electros .. http://tech.juaneda.com/en/articles/electrolyticcapacitors.html   .... I had some BG's & Pana FC which I normally use in low voltage components like CDP's & other SS gear but I had to buy a bunch so I went with the Silmics after reading this guys work .....  I used a large 3300uf Silmic 50v for the main signal voltage rails in place of the old 2200uf.  I also replaced all the rectifier diodes on the PS board with fast/soft recovery diodes 1A & 3A 1kv ... cleaned all the connector pins with De-Oxit ... the layout & disassembly is relatively easy
  I then pulled each signal board out & replaced all electros & mylars(don't like em).... and subbed most low value electros like 1 & 2.2uf with 63 or 100v film caps - styrenes, polyprops, & rifa MKT ... these are all way better in this circuit than any electro incl BG's.
I also subbed the existing micas for styrenes.
  I didn't touch any of the 1/4w carbon film resistors but may replace the EQ resistors with 1% beyschlags or Kiwami in the future. The last thing I did was sub an 8 pin DIP single chip - BB OPA627 for the TA6136P .. I'm assuming it made a difference but shit, when you change over 140 caps & 14 diodes whats doing what to where??!! ... I like the 627 single & I figure it has to be better than the original, and its only a change to pin 2 & 3 & using cat5 wire to each pin & line them up by laying the 627 on its side. You could muck around with the offset & bypassing the supply pins to grnd etc but it will go striaght in as it is & its got internal compensation - a very forgiving opamp ... pin 8 on the 627 isn't connected anyway. If you have dual opamps in the output of ur CDEP they are probably cheap & nasties no matter what the price or they may be the OPA2604 duals or the 604 singles - the 627's are a better sounding opamp - very analogue & fast.
There's another 4 original 7136 right at the output  of the input selector board. Later!
   This refurbish is a time consuming process & involves a little creative placement on the underside of the boards especially with the 18 & 22n styrenes which are the stacked yellow 63v 1% telephony industry philips types rather than the usual axials. But it is definitely well worth the effort & surprised me with the improvement/change to the sonics.
  Everything I had aurally noted during the original listening session with the Jacqui Naylor tape was very noticeably improved & with about 3 hrs only for the much debated "burn-in" I'm sure it will crystalise into audio nirvana even further
... the bottom end has real definition & tone ... the constricted one-note bass has gone and it is particularly noticeable on this tape ... her voice was now attached to a body & projected into & from the soundfield ... the whole sonic spectrum has an added depth & openess & individual instruments are more individually recognisable one form another. The upper frequencies are now more clearly defined & part of this new clarity or "transparency".... to use a done to death image - veils have been lifted.
  These are all personal subjective impressions but it has maybe given food for thought for people who want a resonably well priced well made machine with most of the essentials on board - 15/7.5 IPS (there is a choice of models between 3.75/7.5 & 15/7.5), switchable EQ, variable voltage & interchangeable headstacks with minor adj't once set-up for 1/2 & 1/4 track ... the 1/2 track head-stack also has a spot for a 4th head for playback of 1/4 track tapes ...  the 700 has the potential to replay the TP tapes with comparable fidelity & facility to the preferred units mentioned as preferred machines. From what I'm told there are heaps of them sitting in churches, radio stations, libraries etc & they are way cheaper than the "name" consumer machines which seem to have reached ridiculous $$$ for what they are. The Ampex ATR-700 is a solid, well built machine that has had bad press ... don't ignore it for excellent value for money. ... at least until the Otari MTR-15 appears ... my choice over everything else for best deck, despite its opamps.
Did I say brief summary!!!???

cheers ... cb

Apologies .. I just read Dan's request to sign off with a real name --- chris Blayney ... Tropical North Queensland, Australia
« Last Edit: April 18, 2010, 07:57:02 AM by tropicalcb »

Offline ironbut

  • Global Moderator
  • leader in spreading disinformation
  • *****
  • Posts: 2503
  • rs1500>repro amp#1
    • View Profile
Re: Ampex ATR-700 Refurbishment
« Reply #1 on: April 18, 2010, 12:59:44 PM »
Wow Chris,.. talk about a great first post!
Thanks for sharing all that leg work. I have a 700 waiting in the wings and your post has moved it closer to the front of the queue.

I certainly agree with you that there are several machines out there that have yet to be explored for use by Tape Project members. I've come close to buying an MTR-10 a couple of times. They come up for sale quite often as do several other fine Otari studio models but the 10 can often be found for ridiculously low prices.
If you keep your eyes open, an MTR-15/20 will find it's way to you. One nice thing about those two machines, it should cost a fraction of the shipping rates for one of the "big machines. I can't even imagine what it costs to ship machines from the US to you.

Welcome to the forum.
steve koto
 Sony scd 777es(R. Kern mods)> Vpi Aires>Dynavector XX-2mkll>Bent mu>CAT ultimate>CJ premeir 140>Magnepan 1.6qr(Jensen xover)Headphone Eddie Current Zana Deux>AT ad2000,HD800 ,Metric Halo ULN-2 (battery powered),
 HE Audio Jades