Voice Of Music 1428 Stereo Tube Amp - Input Levels

[misterc57]

Trying to find a schematic please. Voice Of Music 1428 Stereo Tube Amp. V-M 1428

This is a stereo dual 6BQ5 output on each channel. Has phono and record inputs as well as tuner, tape and AUX.

A friend would like his V-M 1428 input levels (tuner, tape and AUX) to all have the same response as the AUX input. The tuner and tape inputs are not as loud as the AUX.

Could really use a schematic to guide me. I noticed at the inputs that the tape inputs each channel has a approx. 240K resistor right at the input RCA jacks. The AUX has no resistors. I think the tuner has resistors farther down the line.

I am considering just jumping these resistors.

Any thoughts on this?

Thank you

[Chuck H]

I think I got lucky finding this one in only five minutes.

[Mick Bailey]

I don't see the 240K series resistors on the tape inputs. Do they look original, and does the rest of the schematic match your amp? When looking at signal levels it's worth looking where there's a voltage divider where the signal is reduced and working out what the new ratio needs to be. You can try jumping resistors - no harm done other than the possibility of running into distortion if the level is excessive.

[misterc57]

Thank you all. Somehow I missed that schematic on the AK site. Well, I just realized it is the wrong schematic (in the case I have identified the wrong amp). I thought this was a 1428.

The amp I have Looks identical but has 7 tubes instead of 9 tubes. There are no 12AX7. All tubes are 6EU7 and EL84. Turns out to be a model 1448.

Can anyone explain the voltage divider which I guess is only on the tuner input?

Schematic attached.

[misterc57]

Also on the tape input, was the purpose of the 220K resistors having something to do with "record output"?

What is the "record output"?

Thank you

[Mick Bailey]

My take is;

The 'Record Output' is to connect the amp to a tape recorder input so you can record off phono, tuner or aux whilst listening (in effect using the amp as a monitor amp). The Record Outs disconnect when using the tape input (as you wouldn't play a tape and record onto it at the same time) The series resistors on the tuner and tape inputs form a voltage divider with the 1M volume control, which reduces the input level. The tuner input already has a divider 680k/330K on each input.

The other purpose of the resistors is that the inputs are shorted to ground when deselected, so the resistance offers some protection to the source outputs. Not required with the phono input, as these will happily run into a short.

[misterc57]

The other purpose of the resistors is that the inputs are shorted to ground when deselected, so the resistance offers some protection to the source outputs. Not required with the phono input, as these will happily run into a short.

So protecting a tape player or cd player? What kind of harm can happen? The AUX had no resistors to offer protection and I have jumped the tape series resistors so the levels will match AUX.

[Mick Bailey]

I didn't know whether it was intended to use the amp with vintage equipment. At the time the amp was sold, there were tape machines that had a speaker output, though fairly low level, but no separate line out. This could be run into an amplifier for more volume, but there was a minimum load impedance specified due to limitations in the output stage design. Running into a short could be problematic, especially with Ge drivers.

[misterc57]

He will be using the matching FM tube tuner. Turntable (which he will have to use a phono preamp) into either the tape or aux input jacks. CD player into either the tape or aux input jacks.