GK1 to 100N+ Output oltage Offset

Rhythm Willie · « **on:** 19 Jul 2005, 05:44 am »

I am currently running in the "plus" upgrade to the 100N monos. It is actually getting gradually better - I was a bit sceptical about any improvement in the early hours of testing.

Thanks to Ginger, who has let me babysit his GK1 (whilst he is away in Townsville working on "naval secret military business"), I have been able to compare the signal straight from my Sony XA7 ES variable outputs to the GK1.

I noticed something a bit unusual on measuring DC output offset.

Through the GK1 the voltage it seems to bounce around + & - zero rather rapidly by small amounts. Through the Sony it is virtually stable.

Is this a trait of The GK1 or valve preamps in general?

AKSA · « **Reply #1 on:** 19 Jul 2005, 10:46 am »

Dennis,

Probably a bit of leakage in the output cap on the GK1. It's got a few volts across it, and it's largish, around 1uF.

Cheers,

Hugh

Rhythm Willie · « **Reply #2 on:** 20 Jul 2005, 01:17 am »

Hugh,

Thanks for the explanation, I was'nt worried about it & it does'nt affect sound,speakers etc ,but I have a prying mind that likes to know why.

Would you recommend the output cap be repaced?

PS I believe I have a leaky power supply cap in another old pre amp I have(& want to compare to the GK1). Is there anyway of finding out which one (of 8) is playing up or do you just replace one at a time.

AKSA · « **Reply #3 on:** 20 Jul 2005, 02:03 am »

Dennis,

I wouldn't replace the cap at all. Auricaps are very good quality, and it's very unlikely to be faulty, to be honest.

It may also be that your mains power is hiking up and down; SA has a compromised grid at present, particularly during winter months when demand from electrical heat pumps is high. Remember, output offset on the AKSA does move up and down with mains; it's always safe because of the tolerance in the system, but it does move up and down and I never even pay any attention to it these days.

Hope this allays your fears!! How does it sound? Do you like it?

Cheers,

Hugh

ginger · « **Reply #4 on:** 20 Jul 2005, 06:00 am »

Dennnis and Hugh,
Just back from a full system check on Laser Airborne Depth Sounder System on Fokker F27 aircraft and decided to check for new posts while I kill time to knock off hour (we work 8 till 4 unless something goes to custard). Laser, Sat Nav, Attitude and Heading Reference Ring Gyros, Platform Servos and all Computers working just perfectly - I think the system likes me. Thought about all you poor buggers freezing down south - the temperature here plumeted to 25 degrees today and rained cats and dogs. Predictable - its the first day of the 3 day Cairns Show (I get a public holiday on Friday for this).

Dennis,
As a quick check to see if its the tube stage output couling cap you can temporarily switch the Bypass switch on the back of the GK-1 to the up position which (on my GK-1) bypasses the tube driver and runs the GK-1 output straight off the volume control after the SS buffer. Remember to switch it back afterward so you are getting a true "view" of the GK-1 sound.

Just off to the airport security office to pick up my airside driving permit - Rule 1 seems to be give way to 747s.

Cheers from sunny far Far North Queensland (FNQ in local vernacular), well it was sunny yesterday.

Ginger

Rhythm Willie · « **Reply #5 on:** 20 Jul 2005, 10:19 am »

Ian,

You lucky bugger, it has been 1 degrees C here the last couple of mornings
(according to the VW Mk 5 Golf's temp gauge). I can't wait till spring (we are heading up to the Gold Coast in October to thaw out & visit the theme parks just before the Indy500).

Flicking the switch immediately stabilised the offset - you were right. Flicking it back & it's all over the place (+- up to 15mv).

Have a nice time in warm & sunny? North Queensland(did I see some rain forecast}.

Dennis

AKSA · « **Reply #6 on:** 22 Jul 2005, 12:25 am »

Hi Dennis,

This is flicker noise, sometimes called 1/f noise, generated by the tube, and relayed at very small leakage currents across the GK1 output cap and the power amp input cap. It does absolutely no damage, and has no sonic effect. It's a bit like the speed of your car at cruise; it's moving up and down all the time, but the accuracy of the speedometer can't pick it up. When the output of the amp is measured in tens of volts, and the flicker noise is around +/-15mV, the wandering around is insignificant.

If it bothers you, you can reduce the input cap on the AKSA to 1uF. However, you can't buy the type I use at this rating without going to a far higher voltage rating, which is not actually a good thing for high resolution. Conclusion? Snookered.......

Cheers,

Hugh

AKSA · « **Reply #7 on:** 25 Jul 2005, 06:25 am »

Dennis,

How's that GK1 of Ginger's sounding now?

Cheers,

Hugh