AMPEX 351 INPUT TRANSFORMER MOD
So why not just mod one of these, and be done? Well, it turns out that there are a number of good reasons.
AMPEX 351 INPUT TRANSFORMER HOW TO
In fact, there’s a fair amount of documentation online (especially at the Electric Audio forum, courtesy of Greg Norman), describing how to mod one of these units into a preamp. One of the preferred platforms for the mod community has been the amplifier from Ampex 351 reel-to-reel player, as shown above.
AMPEX 351 INPUT TRANSFORMER FULL
As a tube aficionado, this makes perfect sense to me - in a world now flooded with sterile-sounding ultra-low distortion preamp choices, more and more musicians are realizing that a bit of distortion, of the right kind, can be just the ticket for producing a warm, full sound. In any case, Andrew is a big fan of tube microphone preamps based on modification of old Ampex reel-to-reel players. However, with Thursday currently on hiatus, Andrew has moved on to audio engineering, and is currently located in Auckland, New Zealand, where is an audio engineer working directly with Neil Finn (of Crowded House fame) at Neil’s well-known Roundhead Studios. This mic preamp was commissioned by Andrew Everding, perhaps best known as the keyboard player for the band Thursday. However, I’m working on a new microphone preamplifier project that I’m really excited about, and I hope to document a fairly complete build log here. But details of these just haven’t made it to the blog for want of time. Nevertheless, I have been working on some interesting projects, including a cool custom amp that was recently completed and a solid state equalizer. I realized today that it’s been nearly a year since this blog has been updated, but that doesn’t mean that Wombat Amps hasn’t been busy! On the contrary, we’ve now launched an improved web site, I’ve established a formal Wombat Amps workspace in a building that also houses dozens of bands – as a consequence I’ve been doing a fair amount of repair work – more than I had really intended actually. So if you’re thinking of buying one of these vintage tube pres for recording ask if there is a microphone input transformer before you make an offer, and remember that you’re going to be spending close to an extra $100 if there’s not one.
It won’t work well with microphones you are likely to own now though. This was cheaper and worked fine with the high impedance microphones designed to work with this sort of input back in the day. Since transformers are so expensive most of these Ampex 600 and 601 tape decks shipped with no input transformer. This is a simple dummy plug inserted into the transformer socket. If you can’t make out the windings, don’t be concerned. Here I’ve popped off the metal shield so you can see the transformer windings: The base looks just like an octal power tube and it plugs in in the same way. Here’s the base of the part that came in this Ampex: That’s how the input transformer plugs into the socket. Here’s what the socket looked like in this unit when it came to me: If this socket is empty, think of spending just shy of $100 to put a transformer in there. Good quality input transformers don’t come cheap. Ampex 96134-01 Bridging Input Transformer Ampex Mx10/35 10 Available-vintage. Ampex Atr-100 Atr-102 Extender Input Output Io Card New Rare. I Shrouded: TRANSFORMERS FOR VINTAGE MICROPHONE. Internal electrostatic shield See also input type 8540, output type 9900 and choke type CB24. Input and interstage: 1:1+1: 0: 410 Ohms +30 Dbu: K Style options: Buy: 9905: Federal AM864/U Compressor WW Primary 120,110 V Twin winding 50/60 Hz. The Ampex 351 is a classic American tape recorder from the 1958.
The input transformer was made for Ampex by several companies. It uses miniature noval tubes like the venerable 12AX7, printed circuit boards and lots of negative feedback. The Ampex 351 is also highly thought of for use as a mic preamp. Here’s the empty socket from an Ampex 601 that came in for a recapping job: In vintage tube mic pres this transformer frequently plugs into an octal socket like the ones used for large power tubes. A tube mic pre requires an input transformer to work well with modern low impedance microphones. Not a bad idea, but you do need to be pay attention to what you’re actually getting for the money. So they’re being bought as a way to get a real tube microphone preamp for not much dough. Not many people have a use for a mono tape deck these days, but these units have both a mic and a line input jacks and a line out. The Ampex 600’s and 601’s were mono reel to reel decks with tube electronics common to many units of the time.
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