We record music. I focus on tape recorders, such as reel to reel machines like the teac 40-4, and four track cassette recorders like the tascam 414 MkII. Microphone preamps, tube mic pres, Ribbon mics, Cassette tapes, Guitars and Vintage guitar amps, great sounding mics- these are things that I feel deserve attention in the world of digital audio and DAWs. Not obsolete, these recorders are more viable now than ever, and should be used! Vintage gear rules!
frank olson music
My Website!
Ampex 601 Schematic and Mic preamp Conversion
The Ampex 601 makes a fine tube microphone preamplifier, as built. Simply replacing most of the capacitors brings it new life for a new age in recording history.
I suggest replacing all of the electrolytic(if not now, you'll need to eventually), and whatever signal caps you like. If the preamp already sounds great- no need to mess with it really. In most cases, however, you'll need to replace some parts. See the video below for more:
So, I put together a revised schematic, showing exactly which parts are used, and which parts are in the audio path.
You can see that the tubes (valves) highlighted in yellow are the ones used directly in the audio circuit. Since most of the tubes are coupled to the circuit, I replace all the electrolytic caps in the entire unit. I also replace the enourmous 1000uf/6v and .5/600v caps, just to save space(and it only costs a dollar for those parts).
One can go as bananas as one likes, adding phantom power, phase switches and DI inputs, but there is real magic in this unit as it sits. Though the grounding is hectic, and the power supply dangerously close to everything else(possible hum), I was able to make this unit a surprisingly quiet.
Let me know if you have questions in the comments section, I'm always glad to lend a hand!
Just came across your site since I'm interested in modding two Ampex 601's into dedicated mic pre's. Comments and question....you leave all the tubes installed? Or do you remove the tubes not involved in the audio circuit? If you're removing the tubes, what do you do about the decreased load on the filament heater circuit? Any thoughts of using a DC supply for the heaters to decrease hum?
I leave the extra tubes installed to keep the circuit running at specification. My preference would be to put cheap but stable tubes in the unused(playback)portion of the circuit. People talk trash about the hum in these units, but if you sort out the possible ground errors(the one in the video was incredibly quiet) you shouldn't have any need for elevated heaters. Make sure your input is well grounded and your power supply caps are well grounded.
Just came across your site since I'm interested in modding two Ampex 601's into dedicated mic pre's. Comments and question....you leave all the tubes installed? Or do you remove the tubes not involved in the audio circuit? If you're removing the tubes, what do you do about the decreased load on the filament heater circuit? Any thoughts of using a DC supply for the heaters to decrease hum?
ReplyDeleteI leave the extra tubes installed to keep the circuit running at specification. My preference would be to put cheap but stable tubes in the unused(playback)portion of the circuit. People talk trash about the hum in these units, but if you sort out the possible ground errors(the one in the video was incredibly quiet) you shouldn't have any need for elevated heaters. Make sure your input is well grounded and your power supply caps are well grounded.
Delete