audio-talk

It indicates that -1.3V is about 19-20mA of current

Yes (if you are looking at the same curves as the Telefunken ones), but at 150v on the anode.

Hi,

Finally found the problem. The 0.1uf caps coupling the RIAA to the second stage were leaking DC onto the grids and hence the valves was conducting really hard. I found a couple of other caps in the spares box and voltages are now about bang on.

Gain is now much much greater and the bass is seems fine.

I have some hum but the current PSU really is nothing very exciting an EZ80/UF4007 hybrid rectifier 8uf polypropylene 20H choke 200uf electrolytic. This feeds the a cascade DN2540 CCS and then the two voltage stabiliser tubes with 56nf Russian teflon. I will have to work on this.

Thanks for all the help in trying to find the fault.

Cheers
Ian
.

Ooh ! Well found. Not had that problem myself, what sort of caps were they ?
Good you've got it sorted then.

Not paper in oil by any chance were they?

The bit I dont understand was if the cap was leaky, how the voltage on the grid was -1.3v? The valve doesn’t care where it comes from as long as its -1.3v

Yes - well I'm guessing that maybe Ian checked the ( -1.3v) bias on the 2nd stage with the unit switched off, in which case the cap leakage wasn't in play.

Hi,
Yes I made the mistake of measuring the grid with the power off, just the battery bias. It was only when I simply couldn't get the thing to behave that I measured it with the power on. The caps were Jupiter beeswax. I had heard some adverse reports but never had the problem myself. I won't be using them again.

Cheers
Ian

Common problem with old valve equipment. Caps have gone leaky. And weren't marvellous to start with. When I was a kid we had an, even then, old valve radio, dad was forever replacing the o/p valve. In hindsight (and with better knowledge!) it's pretty safe bet the reason was leaky coupling cap making too much anode current ergo too much anode heat. Some years ago I overhauled a valve radio for a neighbour, it had the same problem. Simple fix with a modern audio grade polyprop.

I thought that I should give some feedback on the performance of this phono-stage, particularly give the help and support I received to solve the issue with the second stage of the circuit.

The circuit I have is slightly different to Marks in that I had to play with the value of the jFET source resistors to get the current up to approx 12mA through V1 (reduced value to 4R from memory). Everything else uses the same values as Mark. I am yet to play with different voltages through G1. The RIAA stage is built with carbon composite resistors all matched to give the same value as per the schematic. The RIAA caps are all Russian silver mica's. I am currently using Russian 6J9P in the first stage and D3A in the second (I do have some E180F's and will try these at some point).

I should probably mention that my previous phono is a C3G based designed by Andrew. There were a few changes to its design suggested by Andrew, in that I removed the grid leak bias from the second stage and used a cathode resistor instead. The phono has a Cinemag SUT on the front to allow it to be used with my Kontrapunkt B cartridge.

So having got the circuit to measure properly on the bench I then put it into my system and the first thing I noticed and was surprised by was how quiet it was. A gentle hiss with my ear against the speaker. No hum. This surprised me as the PSU is an EZ80/diode hybrid feeding a 6uF polyprop, 20H choke 220uF Electrolytic (has to go at some point), then a DN2540 CCS and voltage regulator tubes with 56nF Russian teflon across the output to reduce voltage regulator tube noise.

The next thing I noticed was absolutely no lack of gain the circuit works perfectly well with 400uV output of my cartridge. With regard to the actual sound, its really hard to put it into words, I am never any good with hifi descriptions. However, I will say that the response seems flat across the board, it seems to excel in almost across the board, bass is deep tight and articulate (more so than the C3G phono). The treble is also extended and very clean. It seems very dynamic with all instruments seeming to have real attack, drums particularly stand out. It also images really well. Once I had the phono working I have found it addictive, its hard to turn the system (just on more album then I'll switch off!!). It's certainly a keeper.

A few months ago I was down South at my brother house who has a very high-end Naim system with the same turntable I use and he demonstrated Pink Floyd's Dark side of the moon. I came home a little depressed due to the amazing depth his system could give to it. Now using Mark's phono seems to have leveled the playing field.
I will at some point try it with a different shunt regulator such as the Salas SSHV2, but to be honest I am pretty happy with it the way it is and the stabilizer tubes look cool.
Cheers
Ian

Very interesting Ian. I suspect the C3g phono is based on the one Andrew designed for me some years ago. Sounds like the jfet version is somewhat of an improvement - do you put that down to the jfet instead of SUT? Or is there more going on in the circuit?

(I'm going to whisper this quietly as it's all SS, but I've weakened and subscribed to the latest group buy for Salas' simplistic folded phono. It'll be interesting to see how it performs - reports are favourable.)

I'm very pleased it's worked out so well for you, Ian !
The phono as used with step-ups is very transparent in the mids and HF due to the specific choice of parts, the high-quality valves and the shunt-regulated supply. The specific thing the jFet mod on the front does, is to extend the bass response down to the single-Hz range compared to a step-up. This decreases the phase rotation below 50Hz hence increases bass tone and tightens up timing and dynamics quite a lot.

I certainly think that given I spent less than £20 on load of jFETS (needed several for the matching) that the schematic offers a very cheap way of getting very high performance out of a MC cartridge. I think some people have said they don't like the sound with the jFET, this might just be a taste thing, or they have much better SUT's than I have! I certainly understood the Cinemag's to be fairly well regarded for the price point. Whatever the answer I think I will be staying with the jFET.

Mark did you ever consider a CCS on the anode of the second stage, instead of the resistor?
Cheers
Ian

IDM wrote: I think some people have said they don't like the sound with the jFET, this might just be a taste thing
Ian

I think it was me . I couldn't get it to sound totally natural to my ears on female vocals, though I am very picky. I think Nick's version ( his first commercial phono ) of this circuit sounded better there - haven''t put in the work to find out why though ...

IDM wrote: .... or they have much better SUT's than I have! I certainly understood the Cinemag's to be fairly well regarded for the price point. Whatever the answer I think I will be staying with the jFET.
Mark did you ever consider a CCS on the anode of the second stage, instead of the resistor?
Ian

Well I've been using the Tribute Cobalt toroidal core step-ups for years and they are super clean and transparent. Ali has a pair now, and says they beat a long list of other SUT's he's got, in the mids & treble.
For (perhaps ) the same reason, I could never get a CCS on an anode to work for me - they weren't quite convincing. I last tried this on the current D3a/D3a circuit, using Gary Pimm's self-bias CCS and it was very good but not quite good enough ....

Yup, have Hashimoto HM3, Mayware T24,Luxman 8020, Audionote kit SUT. Tribute beats all in mid and top, Luxman has slightly better bass.

My cart is a little unusual, being 38 ohm internal impedance.

I don't know if this is the best place to post this, but this brought a smile to my face when I remembered tuning the jFET operating conditions by ear on this project :
https://positive-feedback.com/audio-dis ... generator/

IslandPink wrote: ↑Sat May 04, 2019 1:34 pm I don't know if this is the best place to post this, but this brought a smile to my face when I remembered tuning the jFET operating conditions by ear on this project :
https://positive-feedback.com/audio-dis ... generator/

Do you think you were tuning for "1% negative phase 2nd harmonic"? I read that and just thought, wow. Some people think a lot more about this stuff than I do, and then do something about it. There's a good argument in there not to tune your stuff for soundstage.