Valve Itch phono

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merlin el mago

merlin el mago

Member
Joined 2009
Paid Member
Well Salas, I explaint you:

Before connected:
-Mains earth external PSU to chassis Itch box not the same where is connected the signal GND
-Tonearm GND only connected to other chassis GND and not connected to signal GND
-Itch signal GND connected to chassis trought a ground loop breaker (see Rod Elliot attached schematic) but not connected to the mains earth PSU.

Now:
-Mains earth external PSU to chassis Itch box sharing the same point as signal GND
-Tonearm GND connected to signal GND input RCA of Itch
-Signal GND connected to chassis trought ground loop breaker at the same point like mains earth PSU

Scope don't show any trace of ripple or any other strange, now time to listening if the buzz is gone:xfingers:
 

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Salas

Salas

diyAudio Chief Moderator
Joined 2002
Paid Member
Headphones listening is the most sensitive to buzz. Means its not coming from the Itch source anymore. If buzz will appear on loudspeakers then it will be interconnection ground loop or internal problem to be looked for in the other units. Best chance is there should be no more buzz.
 
L

le´flu

Member
Joined 2004
Hi Salas,

as announced in the njfet thread i´m about to go with the ValveItch.
Todays job was to search for all those parts in my boxes - nearly every-
thing is there exept for the IR-Diodes (will be ordered) and the 6sn7 tubes.
Are there alternative tubes for those? Maybe with noval socket?

Greetings
 
Salas

Salas

diyAudio Chief Moderator
Joined 2002
Paid Member
Unfortunately that's a system interfacing buzz problem that I can not positively guess from afar. Keep on trying different grounding policy until it will interface well (?) Also check the output capacitors in case they developed DC leak (?) because there is some pot scratch I also heard
 
Salas

Salas

diyAudio Chief Moderator
Joined 2002
Paid Member
V1 V2 valves (as named in V1.2 schematic) have their heaters connected directly to ground.

V3 V4 have them connected at the lifter between its two resistors. There's no hum by heater lifting. Its there not to allow higher than the tube's max spec for cathode to heater potential which would otherwise happen in the μ follower's top tubes if their heater was directly grounded.
 
merlin el mago

merlin el mago

Member
Joined 2009
Paid Member
Heaters GND valves V1 V2 aren't connected to signal ground were connected to chassis GND trought SLB so now corrected to:

1-Connected DC heaters valves V1 & V2 to signal GND trought Bus signal GND
2-Bus signal ground connected to chassis trought SLB at the output sockets RCA signal GND only one wire
3-Separate neutral AC mains earth
4-TT GND wire connected to chassis GND in other single point chassis and connected to input sockets RCA signal GND

Waiting to solve the issue:xfingers:

No buzz in headphones:):):):):), waiting tomorrow to connect the loudspeakers.
 
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