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Using the Ampex 601 Mini-Mod

Avoiding confusion while using these units comes down to understanding the signal paths. These units have 2 primary "Modes." The following examples are intended to show the possibilities.

Mode 1: As a Mic / Line preamp

To put the 601 into this mode, turn the "Input / Tape" switch to the input position. In this mode the instrument input can't be used.

Mode 1 examples:

1) A low Z ribbon mic is plugged into the 601. The impedance switch is placed in the down position. The mic/line switch is placed in the mic position. The Cathode follower output is fed to a recorder input (audio card, mixer, some device for recording.) The Altec output is fed to a recorder input. The "Phones" output is fed to a recorder input. Turn up the mic/line master level to about 20, then bring up the "Mic Record Level" control and adjust the various levels to taste. One can record all 3, then experiment with blending, panning or whatever with the tracks.

With the output switch in the middle position, all these outputs are active and they all sound different. The "Phones" output (unbal Hi-Z) does not go through the output transformer, so it has a different sound than the 600 Ohm balanced output at the XLR. Have fun with the different flavors.

2) A CD or DVD player is plugged into the line inputs. The mic/line switch is set to line. The Altec and/or CF and/or Phones outputs are fed into a high quality stereo system (amplifier and speakers only is best.) Music is enjoyed.

3) The stereo sends from a mixer are fed into the 601 line inputs and the 601 outputs of choice are sent to the mixer returns as an effect loop. If the CF outputs are used, there is a wide variety of coloration that can be applied by adjusting the Line Rec Level and mic / line master level controls.

Note: The line input has enough gain for clean electric guitar or bass, and will provide another color for your instruments in addition to the Instrument input.

Mode 2: As an instrument preamp / DI box

To put the preamp into this mode, set the "Input / Tape" switch to the "Tape" position. In Mode 2, The Altec ouput is still available to the mic and line inputs.

1) Plug a guitar into the Instrument input. Select a tube with the "Tube selector switch." If you select the EF86 tube, set the EF86 drive level control. Plug the CF output into your recorder input. The Altec output is only available to the mic and line inputs. It doesn't work with the Instrument input. Also, the Instrument inputs only work in Mode 2. Turn up the Instrument level control and have fun.

2) The Instrument input is setup as described in #1. The output select switch is set to the Altec position. A mic is plugged into the 601 (or another instrument into the line input) and the Altec output fed into another record channel. This configuration allows one to use each unit to handle one mic and one instrument (or 2 instruments.) If one wanted to, up to 4 guitars (or 2 guitars and 2 mics) can be recorded on 4 separate channels with these 2 units.

 

 

 

More Ampex 600 series info:

Most of the Ampex 600 and 601 tape decks/preamps (with the mic transformer) work pretty well with dynamic mics like the classic shure sm-58 and also vintage ribbon mics. In fact, I have never heard a 58 sound as good as it does through the 9er-ized 601. Unmodified 601s still use the 4th amp stage which limits (IMHO) the 601 for general purpose recording. It does provide overdrive capability and is a worthwhile circuit. This stage adds a pot/voltage divider(can be used as an attenuator for overdriving) to lower the signal followed by an amplification stage to bring it back up then the cathode follower. This colors the sound and is less transparent than the Altec 15095 (or other transformer) tapped off after the mic preamp section.

If you Google for Ampex 601 you'll see people talking about using it for a special effect - distorted vocal or bass guitar preamp. You'll also find mention of how noisy they are. They can be noisy, but they can also be fairly quiet when they are setup well. The 601 tape decks were only rated at 40 - 15k frequency response. The preamps are a diamond in the rough however, since their circuitry is based on classic tube preamp design incorporating a pentode first stage, followed by a dual triode. In the 601, it has been compromised by size and cost restrictions, as well as the compromises due to the tape electronics. These are some of the reasons the unmodified 350 / 351 sells for 4 times as much as the 601. The 601 is a great candidate for mods and upgrades, though. The belt driven decks like the 601 aren't prized for their mechanical performance, so converting them isn't too frowned upon.