Ampex electronics for the best possible sound

RogerD

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The further I delve into my Ampex projects the more I realise that their electronics are capable of superb sound.

My current project is a pair of 350 electronics that are awaiting a AG440C transport to be finished. The 350 preamps use octal tubes and are point to point wired. With a little TLC and recapping I now use these for my tube preamps, when playing CD's.

Next is a pair of Ampex MR70 nuvistor based preamps that feature 4 seperate equilisations,the only tape electronics to have this feature. The MR70 transport needs to be brought up to specs but I am sure that the sound from this deck will be exceptional.

I am still tweaking the 350's but right now the sound is far better than my big Studer, a very pleasent surprise.

Although the early Ampex transport are not as refined as the Studers,the electronics provide a solid foundation for great sound.

I think this hobby is alot of fun and keeps me busy. The only problem is finding knowledgeable people to work on these decks. So far so good. I just thought I would post this, I know MEP has a pair of 350's also.




MR70 Electronics and transport
 
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Andy

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Jun 22, 2010
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Neat! Roger do you know what ampex transports are compatible with the 350 preamps? I guess I was wondering if the 440 transport heads you have are stock and compatible as is with the 350's?
 

RogerD

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Neat! Roger do you know what ampex transports are compatible with the 350 preamps? I guess I was wondering if the 440 transport heads you have are stock and compatible as is with the 350's?

Andy,

Actually I am using 440 heads 2TR,PB,4TPB, my 350's are unusual as they have the ability to use high and low impedance heads. I chose the 440C transport as it is much better than the 350 transport. The 440C has a logic module that you can go from either FF or REW to play without coming to a stop. The 440 series also has a 4 head headstack available so 4T playback is possible.

I have only seen 4 pair of these type 350 electronics, I am told they are very rare.

Can you convert other 350's to the 440 transport? If you plan on doing this conversion pm me and I will give you a name to contact.

Cheers,
Roger
 

Andy

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Jun 22, 2010
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Thanks Roger, I know someday I will pick up a pair of 350's and will want to use them direct from heads, I might have to settle for a 350 era transport and heads.
 
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RogerD

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Thanks Roger, I know someday I will pick up a pair of 350's and will want to use them direct from heads, I might have to settle for a 350 era transport and heads.

Andy,

I went back and found some emails when I was researching this project. There are two problems to overcome when mating a 440 transport with the 350 electronics. Number #1 is the impedence difference with the heads. This was not a problem for me as my 350's have a 3rd transformer mounted for the heads. But you could still mount 350 heads in the 440 headstack and that would work.

The 2nd obstacle is getting the record function to work properly. This can be done by building a seperate relay box with a power supply.

I chose to build this deck as a play only. That,for me makes it a pretty simple conversion. I already have a working 350 transport so I can always use that transport if I choose to record.

Here's the emails I found on this subject.

"It is possible, but difficult given that the 440 erase and record head are lower impedance that what the 350 needs. The play head is low-impedance as well, but as you have special 350 electronics with a head transformer, you can use 440 play heads (the head I installed in your headstack is a low-impedance play head too)."

Well, it's two heads to mount instead of 3. Erase will probably work in position #2, record and play in pos. 3 and 4, this is using the heads from the 350 transport in a 440.
>
> There is still the problem of interfacing the record interlock, which is basically building an extra box with a relay and a power supply to run the record relays in the electronics.
>
> Obviously play-only is solved, just plug the 440 play head cables into the 350 electronics

I wanted the option of 2 and 4 track playback,so the record option wasn't that important to me.

The original 350 transport is not that bad of a option. Some of the best music ever put to tape was done on Ampex machines. Having a 350 deck is worth the trouble as the sound is really "magical" plus the ability to play recordings with the same electronics that they were originaly done with is exciting.

Good luck
 
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Andy

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Jun 22, 2010
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Thanks for the information Roger. I understand about the impedance mismatch with the older heads. I had read some remarks on the tape project forum about someone using moving coil phono step up transformers to match some heads on a tascam br-20 with the eros tape head preamp...noted another remark by doc that he hadn't had much luck with using phono step up transformers for impedance matching, in any case that approach doesn't seem to have been popular from the few remarks I have read. But your 350's have a transformer so some sort of step up for impedance matching? Not sure how to remark as this is beyond my diy experience but somewhat perplexed that these older quality playback electronics are not modified to match current high impedance heads? It would seem that the cost of the various current external head preamps would make it worth the effort (or is it too difficult?)

How about the mr70 electronics in terms of impedance matching?

Andy
 

RogerD

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Andy,

The Ampex 350 preamps were mostly if not all custom ordered, some came with a low impedance transformer. This feature allows the use of 440 type heads, which some feel are better than the earlier 350 type. Now about matching a 350 to a different transport with high impedance heads,I think mep(mark) uses his with his Otari deck. You might try sending him a PM or email John French at JRF magnetics,if anybody knows John does. You can always contact Dave Dintenfass at Full Track productions in your Seattle area. Dave wrote the book on 350 Ampexes.

As far as the MR70 goes, I just haven't researched them enough yet. John French is going to build me a set of flux heads as the deck currently has a set of Nortronics. The Nortronics are OK but not in the same class as the original Ampex heads or the flux for that matter.

Dave or John are wonderful and both can answer any questions you might have.


Cheers,
Roger
 

Andy

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Jun 22, 2010
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Thanks Roger, I think I had the imedance backwards in my above post. In any case it is very interesting and exciting to hear about your project and will be curious to read about your results.
 

RogerD

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MR70 Restoration

I finally had my MR70 transports shipped to a tech for restoration. I have been busy finding parts for this rarest of Ampexes. I located a manufacturer of multi section capacitors in Iowa and he says he can provide all the caps and they are the latest spec. So far so good and the next step after rebuilding the 24v power supply is getting the relays up to speed. Then taking the motors off to get them rebuilt.

John French at JRF will provide the flex heads. Maybe by late spring I will have the original console refinished and this machine running. I'll post some pics when available. I don't know what would be more exciting rebuilding a MR70 or a Studer C37,I don't have a C37 yet. Steve Puntolillo at Sonicraft has been really helpful also.
 
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RogerD

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I got a call from my tech that he had finished one of my 350's. Fred Thompson has replaced most of the electrolytics with film caps and also replaced the carbon type resistors with metal film. I wanted to share a picture because I think Fred has done a beautiful job. I can't wait to get the slave and master units back and use them for my tube preamp.

Full size picture at this link,below
http://twitpic.com/47ycag



 
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tony ky ma

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Aug 21, 2010
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I am still tweaking the 350's but right now the sound is far better than my big Studer, a very pleasent surprise.

Although the early Ampex transport are not as refined as the Studers,the electronics provide a solid foundation for great sound.

Hi Roger
the main reason why your Ampex with 350 can beat Studer because the tube circuit vs SS circuit, if Studer's transport with a tube amp, you will never know the result, ( I got experience from modified the Studer's electronic circuit from SS to tube for both record and repro amp ) but I can feel like that Ampex is good for rock or jazz and Studer is good for classical music, even just look at the making of the transport will have that kind of feeling
cheers
tony ma
 

DonH50

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Jun 22, 2010
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I have built, rebuilt, and owned both in the past. The Studer is a much better machine in terms of build and performance, but there's just something about those old Ampex tubies that sounds nice even when I know the specs aren't as good... I'll bet you like the rebuild; upgrading caps and some bias tweaks really helps reduce the noise floor in the Ampex units.
 

RogerD

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I have built, rebuilt, and owned both in the past. The Studer is a much better machine in terms of build and performance, but there's just something about those old Ampex tubies that sounds nice even when I know the specs aren't as good... I'll bet you like the rebuild; upgrading caps and some bias tweaks really helps reduce the noise floor in the Ampex units.

Don,

I have had the noise floor lowered and they do sound beautiful. It will be interesting to see how the Mundorf caps sound,a mixture of M's,supremes,silver oil and gold silvers. As for the Studer vs the Ampex, I think it's the same as tube vs SS. I hope that with my Mundorf 350's I get world class bass and the overall sound should be stunning. I'm a great beleiver in circuit design and the Ampex circuit is one of the best.

Tony,

I hear ya, after I finish my Ampex project the A820 is next.
 

tony ky ma

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Aug 21, 2010
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I got a call from my Tech that he had finished one of my 350's. Fred Thompson has replaced all the electrolytics with film caps and also replaced the carbon type resistors with metal film. I wanted to share a picture because I think Fred has done a beautiful job. I can't wait to get the slave and master units back and use them for my tube preamp.

May I provide some suggestions in your 350's project, change volume control to a step type, change the in put and out put socket to better new one, all wire in sound path change to silver or at least silver cost or better copper wire
cheers
tony again
 

RogerD

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May 23, 2010
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I got a call from my Tech that he had finished one of my 350's. Fred Thompson has replaced all the electrolytics with film caps and also replaced the carbon type resistors with metal film. I wanted to share a picture because I think Fred has done a beautiful job. I can't wait to get the slave and master units back and use them for my tube preamp.

May I provide some suggestions in your 350's project, change volume control to a step type, change the in put and out put socket to better new one, all wire in sound path change to silver or at least silver cost or better copper wire
cheers
tony again

Tony,

Yes that would be good idea. My tech checked and replaced faulty wire with silver, but I'll check to make sure. Thanks
 

RogerD

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I just noticed looking at the full size picture,that these were made in March 1956. That's pretty cool as these are stereo units.
 

RogerD

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RogerD

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May 23, 2010
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BiggestLittleCity
I got a call from my tech that he had finished one of my 350's. Fred Thompson has replaced most of the electrolytics with film caps and also replaced the carbon type resistors with metal film. I wanted to share a picture because I think Fred has done a beautiful job. I can't wait to get the slave and master units back and use them for my tube preamp.

Full size picture at this link,below
http://twitpic.com/47ycag




I dropped by to see Fred(my tech) today to drop off some caps for the slave unit. We started talking about the project and he mentioned the Ampex design in the 350 uses "tree towers" ,that's the connector that the capacitors connect to for each tube circuit. Fred mentioned that it's rare and he has only seen the Ampex with that topology.

Being a Vac owner I happened to visit the VAC website and Kevin has posted a picture of his new flagship amps,the 450's. I noticed the point to point wiring and a smilar design to tree towers. Although not exactly like it given the age of the Ampex and 60+ years later,I thought the basic design was similar. I won't even mention the price point of the Vac's,but knowing Kevin and his cost no object philosphy,they should be stunning. I hope my Ampex preamps sound half as good.

 

tony ky ma

Industry Expert
Aug 21, 2010
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Whitby Ontario Canada
Roger - the project is not done yet ?, one more suggestion, the DC filament power supply should be re-build to use a adjustable regulator LT350 or LT338 and flesh diode rectifier and new cap too, this will let your tubes last longer
cheers
tony ma
 

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