Ray: Yes, I've not heard anything I prefer. FWIW, I've taken it to several diy get togethers, it's surprised quite a few people, and has worked very well with every amp we paired it with.
I confess, I didn't build it, though, I had ordered a kit, but cancelled it when a used one came along for less than kit price.
I've added a sub-out, that's all. It's not at all fussy as to which 12au7's or variants its fed, either!
Best, Don
I confess, I didn't build it, though, I had ordered a kit, but cancelled it when a used one came along for less than kit price.
I've added a sub-out, that's all. It's not at all fussy as to which 12au7's or variants its fed, either!
Best, Don
Hi,
Don, did you leave it stock or change the feefback resistor or coupling caps?
sorenj07, that 2.7 DB of gain is almost nothing. I am glad you like it. I'm kinda interested in this 5842 tube circuit or the 6688 tube. But for now, I'll either get a GGP or maybe a used minimax. Kinda interested in knowing more about this 12SQ7. is it a drop in replacement for the 12AU7?
Ray
diyAudio Memb
Don, did you leave it stock or change the feefback resistor or coupling caps?
sorenj07, that 2.7 DB of gain is almost nothing. I am glad you like it. I'm kinda interested in this 5842 tube circuit or the 6688 tube. But for now, I'll either get a GGP or maybe a used minimax. Kinda interested in knowing more about this 12SQ7. is it a drop in replacement for the 12AU7?
Ray
diyAudio Memb
If you want low output Z, how about 100 ohms, measured?
The Super Linear Cathode Follower will do this with a 6DJ8.ECC88 at 12mA - and sounds transparent to boot. For even less OPZ, use a 6H30 at 25mA, and get perhaps even better sound. It's the last "totem pole" section in the alinked schematic, but maybe you'd like to build the whole thing...
Regards, Allen
http://www.vacuumstate.com/schematics/fvp5a_s.gif
The Super Linear Cathode Follower will do this with a 6DJ8.ECC88 at 12mA - and sounds transparent to boot. For even less OPZ, use a 6H30 at 25mA, and get perhaps even better sound. It's the last "totem pole" section in the alinked schematic, but maybe you'd like to build the whole thing...
Regards, Allen
http://www.vacuumstate.com/schematics/fvp5a_s.gif
Hello Allen,
What do you think about cascoding or bootstrapping the current source in the output stage. Would this be worthwhile and did you ever try this? Kind of like this "Super Symmetrical Cathode Follower" towards the bottom of the following John Broskie blog: http://www.tubecad.com/2007/04/blog0104.htm
Ray,
You are blind but plan to build a kit? I'm impressed, I know some blind people, one who even runs a full recoding studio (!!!) but they sure couldn't even think of building anything in electronics. How do you plan to do this?
The FVP5A circuit is the earlier version of the current SVP-2 model, and that is available as a full kit, with all parts and good instructions. Not too hard to build as everything is on three PCBs - no hard wiring. Please email me directly for pricing etc, but it's in a different price region compared to the GG preamp...
Martin,
The FVP5A design was intended as the simplest possible to do a really good job.
For a full on state of the art attempt, I offer the RTP3D:
http://www.vacuumstate.com/schematics/rtp3c_s.gif
which uses a cascoded current source just to be sure.
I wonder how much advantage it brings, it's certainly getting into the area of diminishing returns, but if you are going for an ultimate - why not?
Regards, Allen
You are blind but plan to build a kit? I'm impressed, I know some blind people, one who even runs a full recoding studio (!!!) but they sure couldn't even think of building anything in electronics. How do you plan to do this?
The FVP5A circuit is the earlier version of the current SVP-2 model, and that is available as a full kit, with all parts and good instructions. Not too hard to build as everything is on three PCBs - no hard wiring. Please email me directly for pricing etc, but it's in a different price region compared to the GG preamp...
Martin,
The FVP5A design was intended as the simplest possible to do a really good job.
For a full on state of the art attempt, I offer the RTP3D:
http://www.vacuumstate.com/schematics/rtp3c_s.gif
which uses a cascoded current source just to be sure.
I wonder how much advantage it brings, it's certainly getting into the area of diminishing returns, but if you are going for an ultimate - why not?
Regards, Allen
Hi Allen,
Well, to start with, and to answer your question, How will I build the kit, very carefully. heheh. Actually, in truth I would probably have to ask or pay someone to build it for me. I can solder reasonablly well. but would lack someone to read me the schem.
In high school I built a 5 tube radio. I build it so well, that the Q of one of the mixer stages was to tight. So I had to add a cap to take care of that problem. But the upshot was, the radio was built so well, that theacher asked me, "You mean you are finished." Yeah, I am. It was so nice and neat. I hated to disassemble it. He was impressed. I still have that old Weller soldering gun. I certainly wouldn't use it on something like this. heheh. Anyhow, I will look at your page, and see what you have to offer. Thanks.
Ray Bronk
Well, to start with, and to answer your question, How will I build the kit, very carefully. heheh. Actually, in truth I would probably have to ask or pay someone to build it for me. I can solder reasonablly well. but would lack someone to read me the schem.
In high school I built a 5 tube radio. I build it so well, that the Q of one of the mixer stages was to tight. So I had to add a cap to take care of that problem. But the upshot was, the radio was built so well, that theacher asked me, "You mean you are finished." Yeah, I am. It was so nice and neat. I hated to disassemble it. He was impressed. I still have that old Weller soldering gun. I certainly wouldn't use it on something like this. heheh. Anyhow, I will look at your page, and see what you have to offer. Thanks.
Ray Bronk
I use my Weller from High School days all the time -- I used it on many, many ham radio projects -- used to run a 100 foot extension cord so I could take it up a 50 foot antenna tower and it's the best thing at de-soldering MOSFETs.ray bronk said:
I don't see how you can get a GG preamp to have an input impedance over a few hundred ohms. that's why we use them in ham radio -- the input impedance is close to the output impedance of the exciter and they aren't prone to oscillation, so you don't have to worry as much about neutralizing your final (of course, you also don't need a regulated screen supply.)
Hi Jackinnj,
KF6TI here, ... Soldering on PCB with a Weller gun. Not gonna go there and turn up a good kit.
Anyway, I would suggest you go up to Bruce's forum and ask him that question. The input impedance is 100K or 50K depending how you load it/the pot you use. The output is like 200 or 300 ohms.
Ray
KF6TI here, ... Soldering on PCB with a Weller gun. Not gonna go there and turn up a good kit.
Anyway, I would suggest you go up to Bruce's forum and ask him that question. The input impedance is 100K or 50K depending how you load it/the pot you use. The output is like 200 or 300 ohms.
Ray
Hi all, Well, I would suggest that you both go up to the Transcendentsound forum/message board, and post the question to Bruce about the Grounded Grid application. I am not necessarily defending or not, but it isn't really fair to say this is or is not a grounded grid without Bruce being here to defend his preamp.
Meanwhile, again, I am putting out the call if anyone has a GGP sitting in your closet, can I borrow it for a week or so. Would like to hear one and see what it sounds like before I buy one or not! Thanks again to everyone who suggested this or that schematic.
Ray Bronk
Meanwhile, again, I am putting out the call if anyone has a GGP sitting in your closet, can I borrow it for a week or so. Would like to hear one and see what it sounds like before I buy one or not! Thanks again to everyone who suggested this or that schematic.
Ray Bronk
All,
For an image of the GGP, try this:
Think of a singly-driven diff-amp (long-tailed pair) of classical configuration. We know that the driven side operates as a common-cathode amplifier, driven by its grid, and its output is amplified and inverted. The nondriven (by the original signal) side is driven by its cathode, its grid grounded (common); it's a grounded grid amplifier, whose output is amplified and is in phase with its input.
Okay, picture this LTP with no load on the driven side (plate connected directly to B+), and an active load on the nondriven side. It looks like a LTP with an SRPP nondriven side.
That's the GGP. I'd attach a drawing, but evidently Bruce disapproves.
I built one into my breadboard, and damned if I could get the thing quiet enough. What Bruce does is use a voltage divider off the output to the lower tube's grid (and then to ground) to apply feedback enough to quiet it down. I jockeyed the resistor values around, and the best I could get was about half a millivolt of hum. The active load will bring the Zout down (I do like the SRPP), and so will the feedback a little, but if anybody has gotten one below a tenth of a millivolt H+N on the output, I'd like to know how. He does use a regulated DC heater supply, so maybe so.
It' just looked like a much more elaborate way to get what I'm already getting to me, minus the phase inversion, which I don't think of as a big problem.
YMMV, one geek's opinion, et dissing cetera.
Aloha,
Poinz
For an image of the GGP, try this:
Think of a singly-driven diff-amp (long-tailed pair) of classical configuration. We know that the driven side operates as a common-cathode amplifier, driven by its grid, and its output is amplified and inverted. The nondriven (by the original signal) side is driven by its cathode, its grid grounded (common); it's a grounded grid amplifier, whose output is amplified and is in phase with its input.
Okay, picture this LTP with no load on the driven side (plate connected directly to B+), and an active load on the nondriven side. It looks like a LTP with an SRPP nondriven side.
That's the GGP. I'd attach a drawing, but evidently Bruce disapproves.
I built one into my breadboard, and damned if I could get the thing quiet enough. What Bruce does is use a voltage divider off the output to the lower tube's grid (and then to ground) to apply feedback enough to quiet it down. I jockeyed the resistor values around, and the best I could get was about half a millivolt of hum. The active load will bring the Zout down (I do like the SRPP), and so will the feedback a little, but if anybody has gotten one below a tenth of a millivolt H+N on the output, I'd like to know how. He does use a regulated DC heater supply, so maybe so.
It' just looked like a much more elaborate way to get what I'm already getting to me, minus the phase inversion, which I don't think of as a big problem.
YMMV, one geek's opinion, et dissing cetera.
Aloha,
Poinz
Hey Ray,
I asked Bruce if he had a loaner policy like Kevin, who is the US source for the Ah! Njoe Tjoeb CD Player. He said no and sorry.
Sorry guy, I was hoping for the best.
He did say however, that it can be modified for up to 6 inputs (from 3) and other DIY places offer Remote Pots and Stepped Attenuators.
Regards//Keith
I asked Bruce if he had a loaner policy like Kevin, who is the US source for the Ah! Njoe Tjoeb CD Player. He said no and sorry.
Sorry guy, I was hoping for the best.
He did say however, that it can be modified for up to 6 inputs (from 3) and other DIY places offer Remote Pots and Stepped Attenuators.
Regards//Keith
Hi Keith,
Yeah, I was aware of all the various things that could or can be done with the GGP. At this point, I just want to borrow one. This preamp, you either love it or hate it. There is not any in between. So if I am unable to get one, in a reasonable time period, I'll probably just say heck with it, and focus on a different preamp. I am happy that this thread has brought out people out of the woodwork with different schems, with different ideas. Now, if only one of them had a GGP to loan out.
Ray Bronk
Yeah, I was aware of all the various things that could or can be done with the GGP. At this point, I just want to borrow one. This preamp, you either love it or hate it. There is not any in between. So if I am unable to get one, in a reasonable time period, I'll probably just say heck with it, and focus on a different preamp. I am happy that this thread has brought out people out of the woodwork with different schems, with different ideas. Now, if only one of them had a GGP to loan out.
Ray Bronk
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