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Old 16th March 2013, 12:11 PM   #1
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Default Help and suggestions for My Phono and pre amp

Hi there
I have built this amp over 2 years ago and have largely been happy (perhaps a self indicting confession as to my ineptitude) with it but not being that knowledgeable on all things valve was sure improvements could be made by others input.
I built a lot of pre amps over a 12 month period and I really liked the 6g6g setup (A valve suggested to me by a good friend of mine who sells valves under the name RetroVox). I am probably one of three people on earth who like the srpp topology as well. I must admit I much prefered its sound to other topologies.
If anyone has any suggestions re values or other ideas i would be appreciative of any input.
The power supply is all valve with an all valve voltage reg section
Heaters ar done by pete milletts dc heater design.
Thanks again
Nick
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Old 16th March 2013, 01:10 PM   #2
SY is offline SY  United States
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It's not really SRPP. The quasi-SRPP topology like yours seems to be used in every amplifier ever made in China and the majority of Japanese amps.

Is there really no grid leak on the second stage?
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Old 16th March 2013, 02:20 PM   #3
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Default Hi Sy

Hey
If you mean the 6sl7, there is 250k there but if you mean the 6g6g does not the volume pot act act as a grid leak?
I did in my defence build 3 published mu stages, 1 x ccs (10m45 ixys) and at least another 4 different amps.. I just seem to like the quazi srpp.
Nick
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Old 16th March 2013, 04:47 PM   #4
DF96 is offline DF96  England
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You haven't drawn a volume pot, just a variable series resistor. If you have a volume pot at that point in the circuit, then the ground connection (not shown) will provide grid bias. The pot may become noisy with age as even a little grid current is enough to encourage this. You may also get more noise if the track gets dirty, as the bias will disappear along with the signal.

Given that it is driving a 100k pot from a highish impedance valve the SRPP will, unusually, actually be doing something useful. Quite rare! Most designs use a 6SN7 SRPP, or other low impedance valve, driving straight into a 1M resistor or a cathode follower so there is no point in using an SRPP so it becomes merely a fashion statement.

Maybe you are one of the three people on earth who actually understand the SRPP? Lots of people like it, but most of them don't know why so misapply it.
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Old 16th March 2013, 09:27 PM   #5
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Default its a pot not a series resistor

Hi
I noted my drawing phurphy and yes it is a pot to ground and yes it looks like a series resistor.
I wish I could say i meant the design feature re the srpp but i had seen a few designs on the net that did it this way so I put it there.
I just like the sound of srpp (quasi to be correct) which i know is odd but my better half (wife) unanimously supported this topology and she has a good ear for this.
Thanks for the input.
Nick
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