TR120B hissing

Tube and solidstate amplifiers made by Rickenbacker

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TR120B hissing

Postby (vdtoorn) » Thu May 12, 2016 9:59 am

Dear Forum,

I've acquired a nice TR120B amplifier for a decent price, the only thing is: it's hissing like crazy! I'm no electronics wizard, but I'm not hesitant to do some soldering. Could you help me out where to start looking for the problems in the circuits?
I've noticed the hissing is filtered by the eq, so I'm suspecting somewhere around the pre-amp or the power supply.

I hope you have some ideas!

Thanks, Henk
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Re: TR120B hissing

Postby (jps) » Thu May 12, 2016 7:29 pm

Is it hiss or buzzing (60Hz, 120Hz, etc., probably more like 50Hz or 100Hz in your case :mrgreen: )?
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Re: TR120B hissing

Postby (vdtoorn) » Fri May 13, 2016 7:54 am

Hi, thanks for your response, I really appreciate it. You're right, that would be 50 Hz :), I'm in Yurp. :lol:

It's more of a white noise. There is some hum, but it's very much in the background and only if you crank it up very loud, so I don't consider that a problem. The hiss increases if you switch on the tweeters, and can influenced with the eq.
I know it's difficult to diagnose from thousands of miles away, so I'm hoping for some general hints on where to start looking. After a lot of googling I'm tempted to check the resistors around the transistors, and maybe replacing them (film resistors are supposed to generate less noise, if I understood correctly)

If someone knows a place for the schematics, that would be a great starting point. I found a schematic that resembles the configuration of this amp on the Rickenbacker site: the TR35B. Could anyone confirm that it's similar, if not the same (at least in the preamp and power supply parts?)

Thanks!
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Re: TR120B hissing

Postby (jps) » Fri May 13, 2016 7:03 pm

Transistors can get noisy, too. I had an old Walter Woods MI-100-8 that was noisy (hiss, like your amp); Walter sent me some transistors and I changed out the ones in the preamp and it was then nice and silent.
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Re: TR120B hissing

Postby (vdtoorn) » Fri May 13, 2016 8:57 pm

Thanks! I'll try to see if changing the transistors might help.

I've looked up the models that are there and they appear to be 'Darlington' transistors, so two transistors in a single package, amplifying around 10.000 times, I would say made for negative feedback designs. Maybe these are the culprits. I'll have a look if the local electronics store carries these.

It's great that you were able to have the Walter Woods amp fixed (I've had to look them up, they look superb! I also play the double bass, apparently those amps are superior... anyway, digressing).

I'll keep track of my progress (maybe slow) because it may help others.

Henk
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Re: TR120B hissing

Postby (jps) » Fri May 13, 2016 10:03 pm

I don't play upright, outside of a year or so that I had a NS Design CR4M, maybe when I get old and grey and loose my hair I will get an acoustic double bass to learn to play. :wink:

I have had three different WW amps, all were great; Walter was THE forerunner of micro amps, going back to the mid '70s.

Hopefully, you will get more advice on possible troubleshooting of your amp before you start swapping out components. 8)

Cross post this in the general amplifier section:

viewforum.php?f=19
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Re: TR120B hissing

Postby (vdtoorn) » Sat May 14, 2016 2:06 pm

I'll do that, if that's not a problem on these forums.
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Re: TR120B hissing

Postby (jps) » Sat May 14, 2016 3:39 pm

No problem! 8)
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Re: TR120B hissing

Postby (AndyM) » Sat Feb 04, 2017 9:48 am

Speaking from experience with amps of this vintage (but not your model), I immediately thought of transistors as the culprit. Furthermore, I would suspect the preamp stages, not the Darlingtons (power output amplification).
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