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Help with T&R HEAD [message #24911]

Sun, 17 April 2016 12:44

bproctor
Messages: 11
Registered: December 2015
Location: BOSTON

Junior Member

Hello,
I am hoping for some help in diagnosing issues with my vintage blue tuck and roll head.
I believe this is an early head, which has a bright switch, and separate inputs for low and high.
The model number is 3-15J-1 and is marked 'Kustom by Ross, inc.'

For starters,
When i plug into the low inputs, I get a machine / hum modulation. This is with no sound coming through the quarter inch jack into the unit. It sounds a bit like an engine idle.

Any feedback on where i should start troubleshooting the amp would be appreciated.
I did switch over to a grounded cord and replaced the death cap.

Thanks,
Brian

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Re: Help with T&R HEAD [message #24912 is a reply to message #24911]

Sun, 17 April 2016 12:55

bproctor
Messages: 11
Registered: December 2015
Location: BOSTON

Junior Member

The hum / modulation seems largely due to feedback being fed back into the turntable.
When i power down the mixer and turntable, i still get a noticeable hum, but it is much less than before

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Re: Help with T&R HEAD [message #24915 is a reply to message #24912]

Sun, 17 April 2016 13:16

pleat
Messages: 1454
Registered: June 2004
Location: Belding, Mi

Senior Member

I'm not exactly sure what your trying to amplify. A turntable? My turntable has a separate ground wire to ground the turntable to my tuner. Does the amp react the same if you plug in a guitar or bass?

You wont get great results using a turntable in a guitar amp since there is a RIAA curve that is standard in the record industry to EQ back in the low end.
pleat

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Re: Help with T&R HEAD [message #24916 is a reply to message #24915]

Sun, 17 April 2016 13:55

bproctor
Messages: 11
Registered: December 2015
Location: BOSTON

Junior Member

Good call on checking the amp without the turntable.

My turntable is connected via a mixer (grounded to mixer) and then outputted to amp.

I tried my guitar and it sounded great. I tried my P bass, and it sounded OK, but I could hear 'radio static' at high volumes.
I have a T&R PA head as well.

My PA head had no static for the bass and handles the turntables quite well.

I was hoping to create a setup where a cross over was able to split up the frequencies between amps that powered speaker that were matched to the frequencies of the crossover.

Perhaps I should trade the blue amp for another K200?

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Re: Help with T&R HEAD [message #24917 is a reply to message #24916]

Sun, 17 April 2016 20:45

pleat
Messages: 1454
Registered: June 2004
Location: Belding, Mi

Senior Member

It is difficult to trouble shoot without knowing exactly which model Kustom amps you are referring to. The 315J-1 should be the K200A-1 model without any effects. Your PA head? What is it? If it's a Kustom with 4 channels with each channel having a reverb control that would be a dash 5 and can either be the K200A that would also say By Ross below the input jacks, If the amp has )))200((( below the Kustom logo then it would be a K200B model.

One thing you might try is break loose the nut on the input jack and then retighten. In the Technical tab on this site there is some info on modifications made to the K200 series amp. You may have an early model and the modifications never happened for whatever reason. They do talk about grounding issues of the boards.

I'm sure one of the techs will have some idea, but if they know exactly what amps you have.

pleat

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Re: Help with T&R HEAD [message #24918 is a reply to message #24911]

Mon, 18 April 2016 06:26

stevem
Messages: 4773
Registered: June 2004
Location: NY

Senior Member

Early Kustoms could have a problem with radio interference and there is a factory fix for it that involves placing a resistor and small value cap in series after each input jack.

Your hum issue sounds like a ground loop and is caused by having two grounds.

If both the mixer and the Kustom have a grounded power cable you need to get a ground lift adapter and place it on one of the power cables, and even further than this the wide tang of the adapter may need to get cut back so you can pivot it around the other way in the outlet.

Another source of your hum could be due to having the mixer and or turn table stacked up on top of the Kustom which can make for one units 60 HZ hum from its power transformer radiating out and getting into the preamp circuit of the other unit or into the turn tables Mag cartridge, or its RCA cables which are all too many times crappy cables to start with.

[Updated on: Mon, 18 April 2016 06:28]

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Re: Help with T&R HEAD [message #24920 is a reply to message #24911]

Tue, 19 April 2016 14:40

stevem
Messages: 4773
Registered: June 2004
Location: NY

Senior Member

The radio interference can be blocked by placing a .005 cap feeding a 47k resistor to ground off of the hot terminal of a input jack.

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