BUZZ huge , upgrade version Smash preamp

[DAVORSMASH]

I bought second hand Smash preamp... over the net and no trying was possible.
Preamp has huuuge buzz and goes up with volume turn up. Michrophony is little present but that is minimal compare to buzz. I have some electronic skills but without schematic it is hard. Buzz is present only when it is turned on. No gnd loops sign. No buzz when iec cable is plugged in.
I checked...rcas are isolated correctly to gnd.
Buzz is still present when i put 6sn7 out and turn it on.
Buzz dissapeard when i put 4p1l out.
I found some voltage points at this forum and seems they are ok. All 8 leds are on ...maybe 2 pars of leds are little less glowing then other 2.
Thank you for any help.

 

[fullheadofnothing]

If the noise is affected by the changing of the volume control, it has to be coming in before the volume control. So it is either your source component, the cabling to the preamp, the wiring from the jack to the selector switch, or the selector switch to the volume control. Is this on all inputs? What is plugged into the input?

Removing the tube removes the amplification, so it's not that the noise has gone away, it's that you've disabled the ability of the circuit to function.

 

[Doc B]

The first thing that pops into my head is, have you talked to the seller? Was he aware of the issue? If not, it probably happened in shipping and that would tend to indicate that a connection has come loose.

 

[DAVORSMASH]

For make an complaint to seller is now too late...i think we will fix that problem.
Input source is not a problem because it buzz if no input cable is pluged in or if it is pluged in. it is no ordinary 50hz gnd hum but *tunel* sounded buzz...heard with bad tubes or when sometimes where wrong tube pins are accidentally attached and make contact. I think it is heather problem common known problem... any pictures of ccs board and heather connection... is heather connected with gnd just on c4s board across lm431? What is heather voltage ..4,2V?or better 3.9..4V to minimize michrphony as Bartola suggested? I tried to connect 6sn7 heather to DC 6,3v not AC but no help. Thank you.

 

[vetmed]

You keep talking about 6sn7 tube but as far as I can see from Bottlehead's product description there are two 4p1l and a 0D3 regulator tube. If you bought an unmodified Smash there should nowhere that you can plug in the 6sn7, unless there is some factory approved modification that I am unaware of.

 

[vetmed]

Sorry just noticed the shunt regulator kit ???

 

[Doc B]

I will suggest you contact Eileen at queen@bottlehead.com and purchase a manual for the Smash and for the Smashup upgrade. Go through the assembly instructions and make sure it has been assembled correctly, and do the resistance and voltage checks. Once that has been done we will have a better idea of where to look for the cause of the problem. Right now we don't really know enough to be able to offer a suggestion beyond the obvious ones - that a ground connection is bad somewhere or there is a miswire.

 

[DAVORSMASH]

Thank you. I want to use this forum to share ideas and find the solution. I will try first to buy 2 new tubes. It cost me less than you want to charge me for manuals. Thank you anyway. Maybe some member had similar problem and can share some ideas.

 

[Paul Birkeland]

What is heather voltage ..4,2V?or better 3.9..4V to minimize michrphony as Bartola suggested? I tried to connect 6sn7 heather to DC 6,3v not AC but no help. Thank you.

If you'd like to modify the circuit, that is certainly up to you.  Do keep in mind that it will make diagnosing your initial problem severely more difficult than leaving the amp stock and determining where the actual issue is.

If you hook up the 6SN7 to the DC supply for the 4P1L's, you can expect the extra load on that DC supply to blow out the heater diodes and cause more problems.

 

[DAVORSMASH]

I have soldered ordinary bridge to isolate it from heather regulator if maybe here were the problem.so no worry...not solved the problem...but at the end i find mistake... badly made job from maker. That design is good but still place for mods. Microphony is the main problem. I will do another dht preamp and try to fix that. At the end very good sound. I also made Materpiece pream for my friend. Hard to tell which i like more. Maybe M. more dynamic and Smash more refine. Thank you anyway.