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[Johnny B]

Although the following is posted on Steve's www.electrical.com website, I'd like to know more about how he (or others for that matter) might use something like an Ampex MX-10 or MX-35.

From www.electrical.com:

"Ampex MX-35
"Type: mic pre
"Quantity: 2

"We have two of these 4 channel 2-bus mic/line pres in Studio B. We built a control box for these which puts phantom power, phase reverse, and a -20dB pad before the mixer's input. They have a classic early 1960s sound reminiscent of early Motown and Beach Boys recordings. They don't have a lot of headroom, and the frequency response isn't perfect, but so what. When used with transformerless condenser microphones with low output impedance (less than 100 ohms) you may need to use the pad switch to properly terminate the input transformer and prevent distortion.
- Aug 09, 10:59"

[pg666]

from what Greg told me, they mostly keep 'em around for distortion purposes.

[electrical]

pg666 wrote on Tue, 24 January 2006 13:46

from what Greg told me, they mostly keep 'em around for distortion purposes.

I think Greg must have been pulling your leg.

I use these with ribbon mics all the time, and certain condenser mics sound fabulous through them. They don't have incredible headroom, but Greg has a plan to try fitting a couple channels with better input transformers than the little Beyer peanuts that are in there now.

I've always liked them, within their limits, and we're going to try to extend their limits a bit.

[Greg Norman]

I am not a big fan of these pre's so I'll use them for distortion, or other crazy sounds.  Sometimes for amped guitars where cleanliness is not the first priority.  

[rodabod]

electrical wrote on Tue, 24 January 2006 19:43

...better input transformers than the little Beyer peanuts that are in there now...

Does anyone have any opinions on these small Beyer mic transformers?

I have eight of them which I am planning to use for racking up some high gain mic preamps.

I have heard people complain that they don't have the best low end, but they were used in a lot of older equipment (Siemens desks, Klein & Hummel gear, etc.) so they can't be that bad, can they?

[Larrchild]

I put some Jensens in my MX10 and it sings.
Also I have a PR-10 tape electronics I turned into a mic pre and added a Jensen to. They are great for tubey sounding background vocals.

I have some of those small Beyer xfmrs on API 312 cards and they are not bad. Actually had some low end.

Not as good as a bigger xfmr, tho=)

[Johnny B]

electrical wrote on Tue, 24 January 2006 19:43

I use these with ribbon mics all the time, and certain condenser mics sound fabulous through them.

1. Which condersers sound fabulous through them?

2. What sources are you normally mic'ing with them?

3. When you get done with the mod, what kinds of things are you thinking of using it on in its new extended capacity?

4. Are parts easy to get for rehab, repair, and mods?

5. Yours looks really clean, did you get it that way? Or, did you have to spend time cleaning it up?

Thanks Steve.

[electrical]

Johnny B wrote on Wed, 25 January 2006 17:02

1. Which condersers sound fabulous through them?

Generally, those with high (+100Ohm) output impedance, and not a blistering output level. Cathode-output tube mics especially. Altec 175, AKG C60, 451, 414, Schoeps 221b, Lomos. We installed a box that Greg made with -20dB pads, polarity switches and phantom power ahead of the units. The -20dB pad works wonders for mics with either high output or low output impedance like later condenser mics or C12s, Neumann plate-output mics.

Quote:

2. What sources are you normally mic'ing with them?

Anything with a lot of HF detail. Piano, overheads, some vocals (especially with ribbon mics like RCA44, 77, etc), guitar cabinets. One combination I love is the Josephson C700 on a vocalist with a breathy or quiet delivery.

Quote:

3. When you get done with the mod, what kinds of things are you thinking of using it on in its new extended capacity?

Don't know yet. My hope is to make it less sensitive to source impedance, and maybe extend the low frequency headroom.

Quote:

4. Are parts easy to get for rehab, repair, and mods?

All the passive components except the pots, certainly. Tubes, pretty easy. Hardware (switches, sockets, etc.) can be cleaned and refurbished without replacing them.

Quote:

5. Yours looks really clean, did you get it that way? Or, did you have to spend time cleaning it up?

They were nice when we got them, though somebody dropped one and bent a corner of the faceplate. I don't remember who. Maybe it was me.

[Johnny B]

Thanks Steve.

Now can you tell us some of the details on the mod you are planning?

[Greg Norman]

I'm going to correspond with Jensen about how best to implement one of their transformers in place of the Beyer.  Nothing fancy at first.

[rodabod]

There's quite a few multi-tap trafos available now if you want to follow the trend of variable input impedance.

I'm going to be doing this with the next set of preamps which I am making, although I am slightly dubious about the amount of benefit gained.

[Greg Norman]

rodabod wrote on Thu, 26 January 2006 18:50

There's quite a few multi-tap trafos available now if you want to follow the trend of variable input impedance.

Nah.  I'm going to keep it simple, good.  
That seems more like a thing for a brand new box.  

[Larrchild]

So who makes a mini phantom-supply pc board that could be tucked into these old tube pre's?

[labcoat man]

I've been reading this old thread with interest as Ive been threatening to mod my Ampex mx10 for a while as much as I like it as is.

Ive got a question for Greg or anyone who has the time....

Greg, I noticed on your tech page at Electrical you considered changing the high impedance unbalanced outputs to transformer balanced at one point.... maybe to open up the sound a bit?

I just came across some Triad HS 52' output transformers with primaries of 20kohm or 5 kohm and secondaries of 600ohms ...so, for the technically challenged like me...

would they be about right to rig up in a box and put on the outputs as an optional balancing / impedance matching set up, or is it far more complicated than that and would I have to go in to the ampex and adjust its innards?

Any help from the tech savvy would be much appreciated!

Thanks

Tim