• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

SVP and FVP preamp builders

OK so with bibs and bobs i had available i put 11 ohm resistor 10nf cap polypropylene and 2 diodes oposing between the safety ground and signal ground. This had no effect. I tried it because I should have earlier but did not.

The other is the safety ground and neutral trace seem to be leaving some sort of artifact on the output signal. Hard to get a good pic of it though.

The yellow trace was taken with no amp connected and a shorted input. Phono stage selected and full gain on linestage.
 

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So after hijacking my own thread

I decided go stop chasing my tail for now and finish off the second channel of the preamp .

I thought the linestage sounded pretty good with one channel. That 2 must be better. And suprise suprise it was. Infact it was incredible. All credit to the designers of the circuits i used.

If only i could get this MC pre subsonic rumble free. As a note on that i noticed that tonight while testing the subsonic noise was less but still there. Did not get a chance to see why.

Anthony
 
5687 can be microphonic but experience has shown me that this is an instability issue rather than real microphonics. Adding grid stoppers and elevating the heaters usually tames the instability. However since this is a stacked arrangment you will need to be clever about how you use your 5687 elements to ensure that the upper voltage follower is elevated above its cathode. The best solution would be to use one bulb to do voltage follower duty for both channels.

Get the 5687 right and it will sound far fuller and more natural than any 6922, and will have less gain to waste as well (excessive gain is the bain of the FVP design).

Shoog
Hello.

This may be an awakening of this thread in an entirely different direction...be forewarned. And, many may be too asleep to respond, but I am hoping that someone is watching, listening and thinking.

I've been listening to a 5687 WOT line preamp for 12, 13, ... years (from Diego Nardi's SP14 article) and it always sounds rich and full, with lots of PRAT (Pace Rhythm And Timing).

I've also been convinced many years ago that I should build one of Allen Wright's preamps.

So, what to do but build an FVP5A/SVP1. But, what about that output stage? ACK!

Pick your valve for the line voltage amplifier stage, E88CC or 5687. The gain is too much. What does any cathode follower do to reduce gain? NADA. So, why do we want one there? ...cannot find a good reason.

Why not make the output stage with an output transformer? What happens? 1. We lose three valves, 2. We no longer have a requirement for an elevated voltage reference for the upper valve heater,

It seems like Dreamland.

Very Best,

Robert
 
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The gain in the SVP is necessary to work with the phono stage, mainly for MC input. You could just use the cathode follower.

As far as 5687 go. See if you can get some Sylvania GB. ( make sure they are proper GB, some will say GB but not have gold pins) we tried a bunch of 5687. These were the best. I also don’t use E88cc in the phono. I use 5842.
 
The gain in the SVP is necessary to work with the phono stage, mainly for MC input. ...
Hi handwound et al,

The gain of the phono stage can be varied to suit the phono cartridge, MM or MC, to produce a line level output voltage comparable to the voltage levels of other sources in-systeme. In other words, the gain of the output stage is not key to achieving adequate output for a MC cartridge.

Allen covered this in his notes on the FVP5A/SVP1 schematic: "R2 sets the phono stage gain and can range from 15R to 150R. Typically 47R for most MC's ." He also noted on this schematic: "For MM usage set R1 at 100R and change the 392R in the second cathode to 1K6." I think he meant to say ...set R2 to 100R... as evidenced by his note for the FVP5: "R2 can range from 150R down to 15R, which adjusts the phono gain from 40dB up to 60 dB - with no side effects. MM or MC, your choice." Also, R1 shows as the cartridge load in both schematics. In his notes for the FVP5 he did not, however, mention the change of the second phono valve cathode resistor to 1K6. So he left us with some questions; has anyone built for MM phono?

RC
 
Oh! That would explain the point you made. Does that mean that you are using an R2 value of 15R for max gain?
Yes I am, also played with the second stage gain.

I am thinking of trying 2 or 4 fets in parallel. But still 1 tube.

I also found on a RTP thread that there are other devices that could be used for more gain.

I have considered attenuating the linestage inputs, but I am uncomfortable sacrificing possible quality for convenience.

I have built a few for friends, and a couple insist on remote. But I am not a fan, and people with better ears than me can hear the difference.

I do have a volume control, but it’s switched.

In my mind it’s not too much of an issue. You are at the preamp and turntable at the same time. But it can be an issue for remote guys that switch to a line source are a record finishes. Waaaay too loud, but hey, put it on mute.
 
Semi complete in previous picture. The raw HT and heater supplies are in an external box. I am not using super reg. But I am using 8 shunt and Ccs regs. Each node has its own. I have built them with 2, then 4 and finally 8. Each time it got obviously better. Uses more power than most power amps.
 
5842 are single triode. But what’s in a name. I originally but it with E88cc, in fact it was built 20 odd years ago as an FVP
Where in the schematic do you use 5842? (What brand of 5842 do you use?) Since it is 43/33 higher mu than E88CC, I could envision using it in the second phono stage to achieve higher V out of the phono stage.. Which JFET do you use in the phono stage input?
Thanks, RC

P.S. For other makers who are using Super Regs...are you using one for both channels, or two, one for each? What Op Amp to replace the LF351 that shows in TPCB. 2nd Ed?
 
I use western electric 5842. I use them in both phono stages. Luckily I have access to Toshiba 2sk369 bl. As I am still able to buy them locally.

I have a bunch of Raytheon 5842, they still perform better than most E88cc. Except for Siemens CCAs from late 50s early 60s. But the western electric 5842 are the best in my experience.