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Hiss

Home Theatre Systems

soundbuff

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Dec 26, 2015
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Hello tech-wise,
I plugged in my Bottle head foreplay preamp 3 (bought used) into the direct in-put of my SS amplifier. The sound is really nice and full-bodied, however there is a loud hiss in one channel. There are three tubes, only one is marked (6cg7eh) russian the others are un-marked. Its american voltage so there is an adapter. The power amplifier is brand new and works silently as an integrated.

Would I need to change the tubes or could it be something else. I am pretty clueless on the technical aspects.

Thanks
 

skdas

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Sep 5, 2012
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If its pre amp tube related issue, i think Mr.Arun may help you out.Bellow is his address , earlier we had many tube related communication & purchase.

Arun Amarnath

#17, Muddamma Garden,
3rd Cross, Benson Town Post,
Bangalore-560046

Ph: 9611125012


Regards,
 

Fantastic

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Third Rock
There are two tubes from the pictures I see. Some have three ( one in the middle) where the third one is for regulating the power supply voltage.
You can exchange the two extreme tubes ( if there are 3 ) and see if the hiss goes from one channel to the other channel. If so the tube is the problem. If not, it could be a passive part on the problem channel which seems unlikely.
The circuit is so simple it should be fairly easy to trouble shoot.
 

soundbuff

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Tried switching the tubes across. No change, hiss continues in the same channel. There is also some kind of 'whoosh' and short crackling a little while after I have started the power amp. Suppose I will have to take it to someone better qualified than I.

BTW the sound quality is actually quite good, with instruments sounding fuller, fatter and even more dynamic than when running as an integrated.

Thanks for the suggestions.
 

Fantastic

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Remove the tubes and spray the sockets with a good contact cleaner like Deoxit. NOT WD40 ! Other contact cleaners are also available. Also use 3M green kitchen cleaner pad with some alcohol to run on the pins of the tube to clean them .
Plug the tubes in and out carefully three four times. This is to ensure you don't have any contact problems. Good thing to do with any old amp. Often crackling can be due to poor contact of the pins.

Check the input sockets to ensure they are not loose and loosing proper ground contact. If your preamp amp has separate components in the power supply ( like separate regulators !) they should be checked. Nowadays it's usually unlikely but bad input resistors at the gate could also cause noise. If the amp is very old , you could replace them ( usually 1 meg ohm I'd guess). No guarantee that the hiss will disappear. Do they use input capacitors ?
Do you have a circuit diagram ?
 

soundbuff

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Location
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Sure,
I will clean the contact pins. The crckling is probably because it been lying unused for a while. I don't have circuit plan but it is available for USD 10 on line.
Even though the amp is not very old (5-6 years) I need to take a bigger call on whether to keep it or put my money elsewhere. Have contacted the gent listed above and plan to take it for a physical inspection. If I had not liked the sound I would not have bothered with even that. Its been a modest outlay thus far, would not want it to become bigger unless its going to stay a while.
 

skdas

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Sir, although off topic, still just a quarry,
is the SQ significantly improved/different between your new Integrated SS amp vs tube pre- in direct new SS amp ?
 

soundbuff

Active Member
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Messages
287
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Location
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I think yes, but I would need to hear some more. As of now because of the tube rush and crackle I don't want to risk my speakers. Basically the preamp needs servicing and only then would I really know. While the integrated is wonderful, the tube pre seems to add some fullness to the harmonics; OTH it could just be distortion and my imagination.
 
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