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Thread: Have I toasted my preamp by twiddling the headshell cables whilst it was switched on?

  1. #1
    Join Date: Nov 2011

    Location: United Kingdom

    Posts: 44
    I'm Wojtek.

    Default Have I toasted my preamp by twiddling the headshell cables whilst it was switched on?

    Hi everyone,

    As someone who is still an ingénue in the world of valves and turntables, I would very much value your opinion on what might have caused the following.:

    I recently bought a valve preamplifier with reputably an excellent MM phono stage ( a leben rs28cx). I bought it privately, it had been serviced in the past year, and played wonderfully well when I compared it with my graham slee phono stage. It was silent, with some hum from my speakers being from my papworth TVA 10 power amp, and no change on switching the pre amp on / off.

    Today I tried changing cartridges to an old Ortofon I had bought on another forum some months back. The headshell cables were a little stiff. I don’t really know what I’m doing yet, but I connected the new cartridge and screwed it in. On switching on the turntable, I initially had sound coming from one speaker only and perhaps a little noise. I thought to tweak the headshell cables, which I did whilst everything was switched on. This caused some noise ,but nothing that sounded damaging. It then played fine, and the cartridge sounded great.

    Howerver, on finishing the record, I now find the phono stage is quite noisy when selected, with occasional soft popping sounds and a bit of hum that sounds like when the ground is not connected. Disconnecting the phono cables helps, but not completely. More worryingly, there is now a bit of soft, steady noise audible through the speakers when the preamp is switched on. I’m pretty certain this was absent before, it's not audible when music is playing.

    Obviously I will need to go to an appropriate hifi dealer, but any thoughts as to what I might have damaged here? Thanks!

    p.s. since buying the preamp, a local dealer explained he had originally sold it to the seller, but that it had some noise/hum in the phono stage. This was definitely not the case when I first got it, so presumably it had been fixed by servicing.

  2. #2
    Join Date: Apr 2016

    Location: Gravesend and France

    Posts: 1,498
    I'm paul.

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    Quote Originally Posted by wojtek View Post
    Hi everyone,

    As someone who is still an ingénue in the world of valves and turntables, I would very much value your opinion on what might have caused the following.:

    I recently bought a valve preamplifier with reputably an excellent MM phono stage ( a leben rs28cx). I bought it privately, it had been serviced in the past year, and played wonderfully well when I compared it with my graham slee phono stage. It was silent, with some hum from my speakers being from my papworth TVA 10 power amp, and no change on switching the pre amp on / off.

    Today I tried changing cartridges to an old Ortofon I had bought on another forum some months back. The headshell cables were a little stiff. I don’t really know what I’m doing yet, but I connected the new cartridge and screwed it in. On switching on the turntable, I initially had sound coming from one speaker only and perhaps a little noise. I thought to tweak the headshell cables, which I did whilst everything was switched on. This caused some noise ,but nothing that sounded damaging. It then played fine, and the cartridge sounded great.

    Howerver, on finishing the record, I now find the phono stage is quite noisy when selected, with occasional soft popping sounds and a bit of hum that sounds like when the ground is not connected. Disconnecting the phono cables helps, but not completely. More worryingly, there is now a bit of soft, steady noise audible through the speakers when the preamp is switched on. I’m pretty certain this was absent before, it's not audible when music is playing.

    Obviously I will need to go to an appropriate hifi dealer, but any thoughts as to what I might have damaged here? Thanks!

    p.s. since buying the preamp, a local dealer explained he had originally sold it to the seller, but that it had some noise/hum in the phono stage. This was definitely not the case when I first got it, so presumably it had been fixed by servicing.
    Sounds to me it's old fault has returned and not what you have done. I wouldn't mention it to any repairer.
    Bakoon 13r Denon DP80 Stax UA-70 Shure Ultra 500 in a Martin Bastin body with jico stylus, project ds2 digital Rullit aero 8 field coils in tqwt speakers

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  3. #3
    Join Date: Dec 2015

    Location: Alicante. Spain.

    Posts: 1,885
    I'm Adrian.

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    Have you tried putting the other cart in? Have you switched everything off for a good 5 minutes?
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  4. #4
    Join Date: Nov 2011

    Location: United Kingdom

    Posts: 44
    I'm Wojtek.

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    Thanks both. Yes sadly did wait and turn it on again. Other inputs still sound great. I’ll check the old cartridge again. What sort of thing goes wrong with valve stages in this way? Many thanks again.

  5. #5
    RothwellAudio Guest

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    It would be pretty difficult to damage a valve phonostage whatever you plugged into it - I wouldn't worry that you have done any harm.
    The way to test how quiet it is is to put a pair of shorting plugs into the phono inputs. That will be as quiet as it gets and you can be sure any noise is due to the phonostage rather than the cartridge or tonearm wiring. If you want to eliminate any power amp noise from your investigations, plug a pair of shorting plugs into the power amp inputs and listen to how much noise you have - that will be the base level noise floor of your system. Then try the shorting plugs into the phono inputs of the preamp - that will show you how much additional noise is coming from the preamp. Finally, reconnect the turntable and see how much extra noise there is. That will be due to the turntable/cartridge/tonearm wiring.

  6. #6
    Join Date: Nov 2011

    Location: United Kingdom

    Posts: 44
    I'm Wojtek.

    Default

    Thank you!

    The good news is that I am just a bit of an idiot: swapped headshells ( to the one I had been using, which has new cables), and lo and behold no noise. Oddly, the noisy one made lots of noise when the tonearm was resting on its rest, even when the turntable wasn't switched on. I've ordered some new leads and will try that.

    Listened to some Grieg tonight in the dark once the kids were asleep: glorious. I also experimented with the speaker taps for my 6ohm speakers - I had been using 4 ohm taps, but the 8 ohm taps seem to work better.

    I'll try some shorting plugs - thank you that's invaluable advice, I'll work through it. Also reassuring to know I haven't damaged the amp!

  7. #7
    Join Date: Apr 2009

    Location: Near Saffron Walden, Essex

    Posts: 7,087
    I'm Dave.

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    Try cleaning the contact pips on the end of the headshell and also the contacts in the end of the arm.

  8. #8
    Join Date: Nov 2011

    Location: United Kingdom

    Posts: 44
    I'm Wojtek.

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    Quote Originally Posted by hifi_dave View Post
    Try cleaning the contact pips on the end of the headshell and also the contacts in the end of the arm.
    Thanks Dave -

    Is that with alcohol and a cotton swab, or anything else in particular?

    Wojtek

  9. #9
    Join Date: Apr 2009

    Location: Near Saffron Walden, Essex

    Posts: 7,087
    I'm Dave.

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    Yes, that is what I would use and push in the contact pins inside the arm, a few times. These are spring loaded and sometimes get stuck, so that they make poor contact.

  10. #10
    Join Date: Aug 2012

    Location: Hartlepool UK

    Posts: 1,640
    I'm Alan.

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    Have you got the wiring colour code correct, Ortofon carts are not in the same order the same as others so double check that you definitely have signal and ground to the correct pins.
    Try also twisting the leads of each channel together

    Alan
    Turntable - Garrard 401/Jelco 750L/Ortofon Kontrapunkt B, Pioneer PLC 590, Micro Sieki MA505 , Denon DL103R - DIY Paradise Phono stage - Reel 2 Reel Studer A810, Otari MX55,Tascam BR20, Revox A77, B77, PR99, TEAC X1000 & 3440, Digital HTPC / Young Dac - Preamp - DIY B4, 821, Power Amp's DIY Avondale NCC300 Mono Block, Speakers Wilmslow Kit Volt BM220.8 / Scanspeak D2905/9500

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