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In Reply to: Re: A comparison of two 6sn7 circuits. posted by Poindexter on September 05, 2004 at 09:28:37:
My friend John, who builds the amps, knows this. He'll be on later, and hopefully he can also explain which variant he used and why.
Follow Ups:
I'm also working on a pair of 6SN line circuits, so this is a discussion that much interests me. One of mine is also the SRPP, and I'm breadboarding a singly-driven diff-amp transformer coupled right as in now; should be up by the end of the day:
The SRPP has been up for about a month or so. It sounds really good, and that tight, clean sound works because it also has a nice high, natural color of timbre. It does, however, have a lot of gain, which also makes it hum a bit too much for me, about two millivolts. The P P circuit is in address of these problems, and also to get the big old cap out of the output.
Anybody wants component values on these, I'll draw them in.
Regards,
Poinz
John tells me that the circuit he did was the VTV (Vacuum Tube Valley)6sn7 circuit. It is found here:http://www.geocities.com/northbirdten/
For the fi primer circuit, he said if you do a search for such it should come up in about 10 places.
The reason he choose the VTV circuit was for safety reasons in a seperate preamp. He said:
"I selected the VTV circuit because the output which the user is exposed to with a preamp comes off the cathode with much lower voltage than is on the plate and is less hazardous.. of course it wouldn't matter if the preamp was wired on board..
Now which is better, the VTV variant or the fi primer I don't know. From what I can tell they sound similar but I don't have a basis for a true comparison. But I am interested in finding out.
The Foreplay is the classic common-cathode-amp/cathode-follower seen since neolithic PAS3 times. Not bad, but not Kozmic. I have looked many search engine places for the Fi Primer circuit, they are all dead links. I have been playing with my breadboard all day, and the circuit so far is:
This pre has better timbral color, practically zero hum and noise, and more practical gain (Av=2.5, or 8dB), than other alternatives.
The Fi Primer Lineamp still intrigues me; show me something. C'mon.
Peace,
Poinz
Hey-Hey Poinz!!!,
That is a neat looking simple job I must say. What are you using for valves? I personally would try a CCS on the cathodes, as the HV negative rail is too much ov a pain in the backside.
regards,
Douglas
Hi, Doug,I haven't researched CCS's yet, and since I'm trying to work to a product line, I don't want to rip someone's circuit. I'm pretty familiar with plus and minus supplies, they're actually quite simple. Here's the one in this piece:
The transformer is a 35VA Amveco toroid that has two 115v 'primaries', and two 22v 'secondaries. I use one 115v winding for the primary, the other 115v for the negative secondary, and the two 22v in series for the positive rail. At 35VA, the transformer is derated about 80% in this application; it doesn't even get warm.
Watchoo know about CCS's, my man? I am interested.
Regards,
Poinz
This should be it. Here's a link:http://tinpan.fortunecity.com/saints/668/primer/
and here's the schematic:
http://tinpan.fortunecity.com/saints/668/primer/300b-se.gif
I can't read it but I'm told the only difference between the vtv and the fi primer is that with the vtv the output comes off from the cathode rather than the plate.
Sounds to me like they have similar and important characteristics for us space travelers. I find this characteristic "essential".
Thanks, John,The Fi Primer, Foreplay, and VTV circuits look all very similar, also the PAS3 and dozens of others; A plate-loaded amp followed (usually direct coupled) to a cathode follower. I am not myself wild about the distinctive sonic signature of cathode followers, although I don't think I dislike them as much as Allen Wright seems to. Maybe they can be made better by proper implementation, haven't tried it myself.
Right now I'm adjusting circuit parameters on the PP breadboard; and even with dime-each Hammond outputs, it's giving me some of the best sound I've heard. I gots to go talk to Kevin, and get some Lundahls in there.
Thanks again,
Poinz
Yes, almost identical to the JE Labs 300B, in fact. As a side note, I will add that I've used a number of variations on the 6SN7 and while it is a nice tube, to me it always requires two stages with a 300B (I supposed you could transformer couple it and get away from that). I prefer the sound of a one-stage driver and have used the 6N1P with choke load and CCS very well. But late last week I started to play with a 417A... wow, now this is a nice sounding tube. My circuit is B+ = 230v, 10K plate resistor (12w mills), Vp = 130v, 200 ohm cathode resistor, 10ma of current. Cap coupled to a 2A3, but would work for a 300B as well. Very deep sound stage, very musical.
the VTV lonestage is just about a ForePlay built with a 6SN7 instead of a 12AU7. Bit higher voltage and idle curent. I heard one of them executed with EH 6SN7's and thought it sounded pretty good.Just for the record, the 7N7 is far cheaper and available in variants which are the same as some remarkably expensive 6SN7's. And of course all you really need is a single 6SN7 section for a linestage, when properly supported.
regards,
Douglas
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