Ampex tape preamps

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Cathode_Ray

Member
Joined
Mar 1, 2007
Messages
10
Location
Atlanta
Are the electronics of 50/60's AMPEX recorders worth using as mic pre's? Can they be enhanced - easily.
And what's the difference 'tween these(mdl 601/602) and hi quality tube preamps.
They're trans coupled on front end. tubes :EF86+12AU7 or 12AX7 + 6DJ8.
 
tons of people use them; mainly because they look cool IMO. i don't like the idea of hacking up a tape machine to get one. there's a lot of redundant stuff you don't need in one.
 
After much discussion on the Ampex listserv the consensus seems to be that the mic inputs on Ampex record electronics were never intended for serious use. On the 350/351 recorders, 99% of the time users would run mics through an external preamp, and usually they'd bypass the input circuit on the electronics. (On the 351, at least, this padded the line-level signal down, then ran it through the not-particularly-good mic preamp.) The mic preamps were basically for emergencies, cue mics, etc..

So what are they? In the case of a 351, a 1:10 (I think) transformer connected to a 12AX7. Too much gain for most condenser mics, too much noise for dynamics and ribbons.

One of these days I'll dig the 351 electronics out of the basement and give them a workout on the bench and in the world, but not with a whole lot of hope attached.

They sure do look pretty, though.

Peace,
Paul
 
Can you give me a link to : "After much discussion on the Ampex listserv"?
Maybe contacting them could be beneficial to both of us...
Thanx
 
601 uses EF86 front end and 12AY7+12AU7 in the mic side.
602 uses 12AX7, triode half of 6AW8A then 6DJ8.
Both have transformer inputs.

If one of these isn't suitable as potential preamp I'll try different course.

I have a RODE K2 and a set(3) of Nakamichi 300's. Also 57's/58's etc.

Also does a mic with hi output such as a K2 benefit from a preamp? I feed a TASCAM US122 interface at present.
 
I like my 601, but I'm finally working on recapping and possibly modding it. I know there are other threads on this subject, but this is the most recent so I thought it be the best one to bump.

This is my first tube based project, but I'm working with my bud Jeff who repairs (among other things) tube gear for a living.

Anyway, I found this website recently and have been pondering a few things:

http://fixthatmix.com/ampex601.php

One thing we're still working on is the output transformer upgrade, can anyone suggest an alternative to the 15095 suggested in the link above?

Also, any idea where you might attach the 15095 (or substitute) to the circuit without loading the cathode follower ouput?

The link I posted suggests that it's possible to use both in paralell but we haven't figured it out.

Or, is the cathode follower output potentially going to benefit from improved iron? The stock output transformer is pretty small and cheesy looking. We can always experiment, but if anyone has any thoughts on the subject I'd love to hear them.

Here's the 601 schemo:

http://recordist.com/ampex/schematics/601man/601schem.gif
 
I've been doing the electrical audio build on the 351, and, man, it's a ton of work.

http://www.electrical.com/phpBB2/viewtopic.php?t=498&postdays=0&postorder=asc&start=0

I'm sure the pre will sound nice when done, but I can't imagine it will justify the time and money I've put into it. The pre (as in single channel) is 4 rack units high. It's cool looking, but it would have to sound insane for me to keep it.

Steve
 
I got a bunch of them I'm not sure I want to work on.

I may get rid of them to finance a U-47...

rackpe2.jpg
 
I loved the sound of my 601. Some of the best classical recordings ever were done on location with these little guys. Mine had noise issues I was to lazy to track down. Sold it.

I have a couple incomplete 351's that I wanted to do the Electrical Audio mods on. As mentioned previously, a ton of work. I have used Electrical's pre's on a couple occasions and will testify to the quality of their sound. I'd shell out good money for one of theirs. But screw modding them myself.
 
We have two 351's, but they don't see a ton of use. I think it's partly because they're a bit less convenient to use, they don't have 48v, and they aren't connected to the patchbay like all the other stuff.

I'm going to email cinemag and see if they have a suggestion for the output.
 
[quote author="nielsk"]the 351's make a great sounding line driver, I use a pair on the mix buss often to nasty it up[/quote]

I like to use our 2-610 for this, usually set fairly clean with a little bit of high shelf.

Back to the 601...

I think I'm looking for a 15k:600 ohms transformer, but I'm not sure what the cathode follower requires spec wise-- gapped core? DC Blocking cap?
 
[quote author="rattleyour"][quote author="nielsk"]the 351's make a great sounding line driver, I use a pair on the mix buss often to nasty it up[/quote]

I like to use our 2-610 for this, usually set fairly clean with a little bit of high shelf.

Back to the 601...

I think I'm looking for a 15k:600 ohms transformer, but I'm not sure what the cathode follower requires spec wise-- gapped core? DC Blocking cap?[/quote]

I'm looking at this one now:

http://www.edcorusa.com/products/transformers/xsm/xsm15k-600.html

Still not sure about DC blocking-- I noticed that when people have used Edcors with the G9 they do use a DC blocking cap, so I'm guessing I'd need to do that here as well.
 
One of Rein Narma's first audio projects was to replace the entire electronics in the Ampex 350 series for Les Paul.
Way too much distortion.
So be careful what you try to rebuild, it may be that you are restoring a lemon.
That happens a lot with vintage audio, the famous Acrosound Transformer that people pay a bundle for on evilbay, when it has a ring so bad that Heathkit had to install a "Tweeter Saver" circuit to overcome thew deficient xfmr.
But if you do not have this inside info, then you are forced to repeat history, mistakes and all. \

I should have asked Rein what he did to mod the 351 amps.
 
I feel ya CJ-- that's an eye (ear?) opener.

I'm working on a 601 though-- just to clarify.

I've been emailing with this gent a bit:

http://fixthatmix.com/ampex601.php

He really seems to think the stock output transformer is worth upgrading and has been really cool about letting me pick his brain--

The 601 output is pretty small compared to say API style iron etc. less than 1/2 size.

The pre isn't bad as is-- but I'm guessing it's worth recapping, diode rectifying, and then maybe changing the transformer.

That Edcor sure is affordable...
 
darn, i tossed one of those in the can.
the transport was an earlier model, but it was a portable from Andy's garage.
he thru it in the back seat as a gatuity for loading up.
it had that vu meter that reads Low/High.
I was going to put in on the dash.
Is that a tube model?
I believe so.
I just grabbed the tubes and the transformers out of it .

does yours have a bunch of bailing wire hanging out the back?
 
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