[andyr]

Hi Hugh,

I understand the "normal" (ie. "Tube Out") output impedance of the GK-1 is something like 80ohms or 120ohms?  Please correct me if I am mistaken. 

Is the output impedance of the "Sub Out" pathway different (given it's coming straight off the volume pot wiper)?

Regards,

Andy

[AKSA]

Hi Andy,

Yes, Zout of the tube is around 140R, the reciprocal of the transconductance at the 8mA plate current, while the Zout of the sub-out connection is dominated by the lower arm of the volume pot;  viz, as low as 1K, as high as 25K.  This will pull back the signal amplitude at various settings, but since the tube takes its signal from this same point the effect is self-compensating.

Cheers,

Hugh

[andyr]

Hi Andy,

Yes, Zout of the tube is around 140R, the reciprocal of the transconductance at the 8mA plate current, while the Zout of the sub-out connection is dominated by the lower arm of the volume pot;  viz, as low as 1K, as high as 25K.  This will pull back the signal amplitude at various settings, but since the tube takes its signal from this same point the effect is self-compensating.

Cheers,

Hugh

Thanks, Hugh.

Regards,

Andy

[rabbitz]

This is probably relevant as Hugh was kind enough to sell me a solid state only version for my second GK-1.

What I've found is that the sound, and particularly the bass, can benefit from the use of resistors and a cap after the pot. Mine goes from the pot > 2.2uF cap > 100R with 100K to ground. The difference is sound was very noticeable and the bass digs deeper. These values might not be the optimum but worked well for me. How that relates to the full GK-1 with using the SS section for bass duties, I don't know as I'm an impedance idiot.

This is probably the only SS GK-1 around and kicks all opamps, all the commercial pre's I've heard in the butt. I can't understand why there isn't a SS pre at Aspen as not everyone is a glass head.



This is my final DIY amp project due to medical reasons and it's fitting that it's the rehousing of the SS GK-1, another fine AKSA product. AKSA products have been so important to achieve my goals and my AKSA 55N+ is not going anywhere. It's taken on all comers (lots) and won easily.

[AKSA]

Hi Peter,

Thanks for the comments!

Your clever trick with the resistor in series with the output is a stroke of genius, I might suggest.  You are swamping the erratic and multinodal resistance of the wiper coming off the pot with a fixed, much larger resistor which then dominates the series transfer, reducing distortion.  This is really smart.

Another, more conventional way to do this is to fix the wiper at ground, pass the signal from the output via a series resistor of around 2/3 the value of the pot, and wire the pot to ground as a shunt.  This does reduce maximum gain, however, but it works very well and makes a cheap pot sound like a very expensive attenuator.

Peter, I hope you are well......

Cheers,

Hugh