Preamplifier with 6H30 in SRPP mode.

 

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My brother and I have build a preamplifier with 6H30 double triode in SRPP mode. We have chosen the paeng design design we also used in our tuner as we like the sound of this amplifier. We have made the volume control with 6 relays (61 steps) as made by Dutch engineer: Jos Vaneijndhoven.
 We have experienced some 100Hz hum problems, especially with volume step > 32, this is caused by a change in the impedance the amplifier is experiencing, we have thus reduced all the resistors in the attenuator by 10 and placed a fixed voltage divider before the tube preamplifier. This has solved the problem 95%, but has reduced the max gain to approx 2dB and we had to skip 3 volume step thus we ended up with 61 volume steps.
New! To get rid of the remaining hum, we have tried a doublesided in/output pcb encapsulated in a little box made of bare pcb, but the hum was still present. We probably should have made the box of material  containing iron!
Finally we decided to ditch the relay volume control and replace it with an Alps motor potentiometer, and this has solved the problems with hum. Below you can see the old version with relay volume control and the new version with Alps motor potentiometer.
Note that you have to use a Sony compatible remote control with the preamplifier.

Concept design drawing of the whole preamplifier.
Concept design drawing of the front and back of the preamplifier.
The top of the preamplifier with cooling holes.
Pcbs placed on the concept drawing.
Picture of the first test.
The finished amplifier taken from the back.
The finished amplifier taken from the front.
The new version finished amplifier with Alps motor potentiometer. New version!
The finished amplifier front.
The finished amplifier back.
In/output pcb with 61 step relay volumecontrol.
Mounted in/output pcb with 61 step relay volumecontrol. Pcb file updated 2007.02.20.
The new in/output pcb with Alps motor potentiometer. New version!
The new mounted in/output pcb with Alps motor potentiometer. Pcb file updated 2008.02.12
pdf file showing the attenuator damping as  function of the relay steps.

pdf file showing the attenuator Rin/Rout as  function of the relay steps (before).

pdf file showing the attenuator Rin/Rout as  function of the relay steps (after).

The 6H30 SRPP preamplifier pcb.
Mounted 6H30 SRPP preamplifier pcb. Pcb file updated 2008.02.12.
The display pcb.
Mounted display pcb. Pcb file updated 2007.02.20.
The button front pcb.
Picture of mounted button front pcb. Pcb file updated 2007.02.20.
Picture of 18F452 pic control pcb.
Picture of mounted 18F452 pic control pcb. Pcb file updated 2007.02.20.
Menustructure of the 6H30 SRPP preamplifier.
 

 
The new motor driver pcb mounted on top of the control pcb.
Updated to the newest firmware!		 Program file updated 2009.05.09
The new motor driver pcb. New!
The mounted new motor driver pcb. Pcb file updated 2008.02.12
Back side of the new motor driver pcb with elevate connectors. New!
The powersupply pcb.
Mounted powersupply pcb. Pcb file updated 2007.02.20.
Picure of all the parts needed for building the amp.
The bottom aluminium plate.
The top aluminium plate.
The front aluminium plate.
The back aluminium plate.
CAD files for the cabinet. CAD files updated 2007.06.18

This page was last updated 2009-09-13.