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Tape monitor as Mono switch using y-cables

Discussion in 'audio' started by Nagraboy, Jan 12, 2019.

  1. Nagraboy

    Nagraboy pfm Member

    My Leben integrated has a tape monitor switch. I’ve heard I could possibly use y-cables to turn it into a mono switch for when I play mono vinyl.

    I have the cables here now. One has two RCAs to one RCA socket, the other has two RCAs to one RCA plug, so they would fit together and go between the Recording out and the Tape input. Turning the output into mono which could be heard by switching to Tape monitor.

    My concern is whether this might cause a shorting of my Leben’s output and possible damage. Can I try it to see if it works, or is it too risky? I really have no idea either way.

    Just need some advice from someone in the know. Thanks
  2. Nagraboy

    Nagraboy pfm Member

    I’ve now used the y-cables from my Croft RIAA output into the Leben and it works. Still not sure about the tape monitor idea though.
  3. Arkless Electronics

    Arkless Electronics Trade: Amp design and repairs.

    It should work fine and there is no risk.
    Nagraboy likes this.
  4. Nagraboy

    Nagraboy pfm Member

    Thank you! I read that I might need to solder some resisters in the plugs to stop it shorting. Makes no sense to me, but then I don’t know anything about DIY electrics.

    I’ll wire it up now and give it a try...
  5. Nagraboy

    Nagraboy pfm Member

    Yep, all works fine and sounds good. Thanks for the advice :)
  6. Arkless Electronics

    Arkless Electronics Trade: Amp design and repairs.

    Ideally add resistors of about 1K in line with each tape out but not really necessary and often included internally to the amp anyway.
  7. Nagraboy

    Nagraboy pfm Member

    Ah, I see. Well, glad I asked and thanks again ^
  8. Nagraboy

    Nagraboy pfm Member

    Found something strange happening with the y-cables in place. My digital source plays in Mono from a Stereo track, regardless of whether the Tape monitor switch is On or Off. Pulled the cables out and it’s back to Stereo, but the music stops when I switch the Tape monitor back on. It’s as if the Mono switch is always engaged when the y-cables are in place. Seems very strange.
  9. Jim Audiomisc

    Jim Audiomisc pfm Member

    I'd say your Y-connection is simply shorting the two channels together. I'd expect this if the tape out is taken direct from the channels and the 'tape monitor' just switches what follows from that to the tape inputs. By leaving the Y in place you're forcing mono all the time.

    Put some resistors in the leads from tape out to the Y-connection. I'd suggest more like 10k for caution's sake TBH, but I'm old fashioned. :)

    FWIW I've only just seen this thread. Personally I'd have put some few-kOhm resistors in the outputs from the start. I don't know the amp design but would have assumed it wouldn't like the channels shorted together. Assumes internal resistors. They should be there, but may not, or be too small.
  10. Arkless Electronics

    Arkless Electronics Trade: Amp design and repairs.

    Yes it would be permanently in mono.... I thought that was obvious... Adding the resistors will still mean reduced separation depending on the source impedance. Most amps do have resistors in series with the tape out... I guess there will be the odd exception though.
  11. Nagraboy

    Nagraboy pfm Member

    What surprises me is that the Tape monitor switch on the front panel of the amplifier has no effect when the cables are in place - it’s as if it becomes bypassed. I would’ve thought that when switched to OFF there wouldn’t be any way for the Mono signal to get into the amp’s inputs.

    I don’t have a soldering iron and wouldn’t know where to put the resistors anyway, but thanks for the tip. Why are they needed anyway?

    Think I’ll just get a phono stage with a Mono switch next time.
  12. Arkless Electronics

    Arkless Electronics Trade: Amp design and repairs.

    Hmm yes in effect the "monitor" and "source" positions are receiving exactly the same signals hence the tape monitor appearing to do nothing! This suggests, if there is no difference whatsoever between monitor and source, that your amp probably doesn't have the resistors... the difference could be very subtle anyway.

    The resistors avoid the two channels of the source being shorted together, which is very unlikely to cause any damage or anything but does mean that if there are no resistors in your tape out that it permanently puts everything in mono whilst the Y plugs are plugged into tape out. Adding the resistors puts separation between the two channels of the source whilst still summing them to mono at the output of the Y cable. The degree of separation will depend a lot on the impedance of the source. I would expect good results from external solid state sources but some degradation in crosstalk with the amps phono stage (it will likely have a fairly high output impedance).

    You just need to solder a resistor, 10K will indeed do fine, between the centre pin and centre conductor of the coax of each of the two phono plugs that go into tape out.
  13. Jim Audiomisc

    Jim Audiomisc pfm Member

    The output meant to go to the tape recorder is a couple of wires taken from the outputs of the L and R channels at a point in the preamp.

    The tape monitor switch normally connects the following parts of your amp to those, but changes to connect to the 'tape in' sockets when you select tape monitor. That doesn't disconnect the wires from the amp to its tape outputs.

    Your Y-lead clamps together the tape outputs - which are wired to the L and R channels. Thus you clamp together the two channels at that point in the amp - regardless of what you do with the tape monitor switch.

    By having series resistors you can avoid this as they get in between the Y-connection and the relevant points in the amp.

    If the amp had 'protection' resistors in those internal wires already you might not have got the problem. Some amps have these, but others may not. Or have values so small as to not help. When present they are there usually to stop the amp being damaged by a short circuit on the tape out sockets. (Which in effect your Y-lead will produce when the L and R signals differ!)

    So personally, I'd have used series resistors anyway as - without knowing about the internals of the amp - I'd asssume potential (pun) problems if you don't!
  14. Nagraboy

    Nagraboy pfm Member

    @Jim Audiomisc

    Right, I see. Well, Arkless said it would be ok so I thought it’d be ok to try it out. The amp sounds fine so no damage afaik.

    My next phono stage may well have a Mono switch, or I might get a true Mono cartridge to switch over when necessary.
  15. Jim Audiomisc

    Jim Audiomisc pfm Member

    It's not likely to cause the amp any permanant damage. But it may do something like increase the levels of distortion or alter the frequency response when you are playing non-mono material. Impossible to say more without knowing the details of the amp design.
  16. Arkless Electronics

    Arkless Electronics Trade: Amp design and repairs.

    I stick by what I said.
  17. Nagraboy

    Nagraboy pfm Member

    And the amp seems fine, so must’ve been sound advice :)

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