question about Bruce's GGP preamp

[ray bronk]

Hi Guys,

Someone read to me the chapter out of Bruce's book, Audio Reality, the chapter on the Grounded Grid Preamp. My question is he mentioned in passing about using a FET for a CCS, but decides to have the B Minus supply anyway. I am just curious if anyone has tried the CCS anyhow. He also mentions the second tube is being used as a CCS on the plate side. Just curious if anyone has used a Solid State device for the CCS instead of a tube? Just curious. It would seem that there would be a lesser parts count if he at least did the first CCS. He would not need the B Minus supply at all.

Thanks.

Ray Bronk

[barretter]

Why don't you ask these questions on Rozenblit's own website - that's what it's there for.

[ray bronk]

It's real simple. I still do not know what I did, but I have been banished from his board. So I can not ask that question there.

Besides this forum is a whole lot bigger than his little message board.

Ray Bronk

[SY]

I haven't built his particular circuit (nor seen it, except second hand), but as someone who has traveled the CCS route several ways, I wouldn't hesitate to use a solid state current source- IF it's designed correctly, it will run rings around a tube version in terms of source impedance and bandwidth. And unlike a pentode, SS can be used as a source (e.g., a plate load) as well as a sink.

[ray bronk]

Hi Sy,

If you look at this circuit, he uses a tube for one of the CCS at the plate. This way, he doesn't have to use resistors, and it sounds better. The other one I think, if memory serves me correctly, is at the Cathode, where he just mentions the use of a FET. He even says that this would then eleaveate the need for the B mimus supply. I would think that something like an LM317 and whatever value resistors would be a lot cheaper than an isolation transformer, and its associated parts. I am more interested in the Cathode version of the CCS versus replacing the second tube.

So being a novice at this, would I have to use three different CCS circuits on each of the three tubes?

Ray Bronk

[Gordy]

The company Analog Metric make a kit that they call Grounded Grid. I do not know if it is a rip-off of the Transcendent design or something completely different.

The circuit was here at this link: http://www.analogmetric.com/store/ga...?id=90&img=366

I'm no vacuum tube expert, however it looks like the output stage is a SRPP configuration, and that the lower triode also forms a Long Tail Pair with the input triode. They use a resistor (and not a CCS) as a tail for the Long Tail Pair.

If I was to build it I would be inclined to do it exactly as designed, and then change it one part at a time later on. In that way it is likely to work from the off, and then you can learn how the modifications influence the design as modifications progress.

[SY]

Looking at the circuit Gordy linked to (you'll have to tell me if it's the same as the GG), it's a cathode-coupled SRPP. R13 and R14 could and should be replaced by a decent quality CCS. If it were me, I'd bite the bullet, put in a -10-15V supply, and use a bipolar cascode CCS in that spot. Very cheap, easy, compact, and high performance. If you have a large negative rail and either a spare separate heater supply or choose tubes with the appropriate max heater-to-cathode voltage rating, that current sink can also be a pentode, which will work nearly as well.