valve preamp for quad 303

[hug96]

HI,

I was thinking yesterday about simplifying my quad 33, and then realised that the output level was only 0.5V for full amplifier output.

I then thought it could be a good idea only to have a minimalist preamp, with unity gain, only to adapt the impedance ( quad 303 input impedance is quoted as 22K and 33 output impedance is 1K).

so I was thinking, would a simple circuit with a potentiometer and a simple classic cathode follower be a good idea of realisation? would it work well ?

I'd be happy to have some advices.

Hugues.

[SY]

It will work very well as long as the cathode follower is designed competently. I published a circuit like this here and on my website- you don't have to do the full-blown circuit, but there are some basic design hints in the article which will (I hope) help you avoid the most common mistakes.

[Eli Duttman]

Hugues,

You want to use a high gm type, for a low O/P impedance. The current production JJ ECC99 is very well suited to this job.

I_B should be substantial, as charging and discharging the interconnect cable capacitance is not problematic.

A bipolar PSU allows you to avoid a cap. in the I/P circuitry.

The 10M45S "chip" will allow you to CCS load the CF, with very little muss or fuss. CCS loaded CFs yield superior performance.

[hug96]

thanks for the answers.

so, I'd like to start on a simple cathode follower with single psu.

I've seen some vintge circuits with ecc82 cathode follower but don't know if this could be useful as tube amps have usually higher Z imput thant solid state...

so I'm looking for a simple circuit if anybody can help me ( the 2 capacitors, 5 resistors kind) but well calculated, as I've read many times that poorly conceived cathode followers gave very poor results...



thanks for your help !

Hugues.

[pete.a]

Hello there, My first system was a 33/303/Fm3 Circa 1997

Have you surfed through the net and discovered the Quad improvent site ?
I used to own a set of 303 amps , that i ran as Bi amped , one amp per speaker, just using a tweaked 33 pre ( i added a seperate on off button and fitted a 50k noble vol pot ) Big difference..didn't need to change much more after that.
I then changed the main power supply caps in the 303 . I had a valve FM3 tuner. I think that was the best sounding radio for a long time..until all the stations here went compressed ..sorry to ramble... Have you tried any other amp combination yet , as the old 303 can sound a bit soft . There's no doubt about it's build quality..bomb proof...

I have since that first system had the upgrade bug ... sold the quad stuff , tried a couple of amps and have now
built my own system using kits...and im now very satisfied..all transistor..as house isn't suited to valve ..small children !

[hug96]

Originally posted by pete.a
Hello there, My first system was a 33/303/Fm3 Circa 1997

Have you surfed through the net and discovered the Quad improvent site ?
I used to own a set of 303 amps , that i ran as Bi amped , one amp per speaker, just using a tweaked 33 pre ( i added a seperate on off button and fitted a 50k noble vol pot ) Big difference..didn't need to change much more after that.
I then changed the main power supply caps in the 303 . I had a valve FM3 tuner. I think that was the best sounding radio for a long time..until all the stations here went compressed ..sorry to ramble... Have you tried any other amp combination yet , as the old 303 can sound a bit soft . There's no doubt about it's build quality..bomb proof...

I have since that first system had the upgrade bug ... sold the quad stuff , tried a couple of amps and have now
built my own system using kits...and im now very satisfied..all transistor..as house isn't suited to valve ..small children !

actually, I'm very satisfied with my system. I just thought that the signal goes through a lot of useless components through the quad 33 ( too much gain, eq control etc...)

so I was thinking of a minimalist preamp, more to be seen as an experiment.
and I'm on holiday now, so I thought this would be nice to do it now.

so I found this circuit in a morgan jones book with an e88cc, and I happen to have a spare 6922 jan philips.






what do you think of that schematic? should it be working alright?

any comments welcomed !

Hugues.

[SY]

MJ's circuits are well-engineered and an excellent model to follow.

[hug96]

hi,

here is the circuit i'm gonna try.

I'm reusing a transformer I already have...

I'm not sure about the value of the volume pot, 47K or 100K?

Thanks for your help, Hugues.