Valve Itch phono

The input grounds are connected elsewhere in the circuit - near the input valve grounds, and the output grounds kept separate and connected to a different star point near the output valve cathodes....

But other than the grounding, you have it right. But as you go actually building and figuring out the grounding as you go, it will become clearer.

I didn't ground the case of the 977 as in that pic....

Fran
 
Help with my Itch

I've built the Valve Itch but so far with disappointing results! Music signals are coming through but they are drowned in weird, hum-like noises. I'm driving it from one of these ready-made HV regulated supplies on eBay. (The SSHV Mosfet shunt regulator will come later.) After checking my circuit and connections I took some voltage readings, some of which I don't understand and would like to check them out with subscribers to this thread.

A. Upper Valves:
1. 6SN7
Anodes: 286V / 288V
Cathodes: 186V / 187V

2. 6N2P-EV
Anodes: 216V / 217V
Cathodes: 3.9V / 4.0 V

B Lower Valves
6SN7 Anodes: 5.3V / 5.4V
6N2P Anodes: 1.68V / 1.69V

Then I checked the heaters and ground lift. The lower valve heaters to gnd are OK at 6.13V.
The upper valve heater readings are my concern. Across the heater valve pins it is 6.14V. However from valve heater pins to gnd there is only 0.6V.
I checked the ground lift network and across the two 470K resistors I measured 289V as it should be. However, across the individual resistors (R7 and R8//C12) I only get 0.6V.
All measurements taken with a DVM. I also checked C12 (1uF/250V) for short circuit and capacitance and it was OK.

Can you please throw some light on these readings. The upper section voltages seem OK to me. But the lower section anode voltages to me seem too low. I was expecting 50-100V, but I'm not technically informed about this topology. More confusing are the readings for the heaters of the upper section valves.

I enjoyed building this project and I'm sure here I'll get the help needed to get it going properly. Many thanks to Salas and a whole group of contributors that have made and continue making this thread so interesting.
 
Thinking about it over lunch I swapped the heater regs and took readings with a different DVM. Now I have 139V from the -ve end of the upper section heaters, which is more credible. I also checked the anodes of the upper first stage (6N2P) and this time it is 268V and 270V. Previously I had a similar problem with widely different readings from different meters but I'm still not sure these are the correct voltages for the Valve Itch.

I still have to connect it to my system to see whether it is OK. Before doing this I'd still like to know what voltages to expect around each section valves.
 
Thanks Salas, this is to let you know that my Itch build is working without the hum and buzz noises I reported earlier. Don't really know where the problem originated from but I suspect it had to do with my wiring of the upper valve heaters section.

It hasn't been playing for more than half an hour and at first I thought it didn't have the airiness of your NJ-Fet phono which I also built (with a lot of your help). Surface noise at the start of an LP is more pronounced and bassy. My Itch sounds rather closed-in, though it seems to be opening up as it runs in. It can also be the components I use.

My build is as per your Rev1.1 but I'm using 0.1uF Teflon for interstage coupling (C4) because it seemed the best I had available. I've ordered some 0.047uF K72P-6s hoping the sound gets a bit mellower.

For C2 (RIAA) I used SCR MKPs 5% and for C3 used 12nF//3.3nF 2.5% PS (polystyrenes), again because I thought they were the best I had. I'm waiting for Merlin's GB of these caps - Thanks again Merlin.

I still have to build your SSHV Mosfet so in the long term it should sound better. Apart from the enjoyment of building it, yes, I think it's opening up as I listen. I like its full and bodied character, just needs to be a bit mellower for my taste. I'm sure it will improve with the component changes planned above. Any guidance regarding specific and priority changes would be much appreciated.

Thanks a lot and Best Regards.
Joe A
 
Subjectively, for me at least, the RIAA and coupling cap does have a pretty large effect on the sound. Its not profound, but definitely changes the tone of the build.

Like you, I am interested in hearing the comments back from the caps from the group buy, although I don't have a burning desire to change my build!!

More than one person has offered to pony up the cash for me to build one for them!!

Fran
 
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Thanks Salas, this is to let you know that my Itch build is working without the hum and buzz noises I reported earlier. Don't really know where the problem originated from but I suspect it had to do with my wiring of the upper valve heaters section.

It hasn't been playing for more than half an hour and at first I thought it didn't have the airiness of your NJ-Fet phono which I also built (with a lot of your help). Surface noise at the start of an LP is more pronounced and bassy. My Itch sounds rather closed-in, though it seems to be opening up as it runs in. It can also be the components I use.

My build is as per your Rev1.1 but I'm using 0.1uF Teflon for interstage coupling (C4) because it seemed the best I had available. I've ordered some 0.047uF K72P-6s hoping the sound gets a bit mellower.

For C2 (RIAA) I used SCR MKPs 5% and for C3 used 12nF//3.3nF 2.5% PS (polystyrenes), again because I thought they were the best I had. I'm waiting for Merlin's GB of these caps - Thanks again Merlin.

I still have to build your SSHV Mosfet so in the long term it should sound better. Apart from the enjoyment of building it, yes, I think it's opening up as I listen. I like its full and bodied character, just needs to be a bit mellower for my taste. I'm sure it will improve with the component changes planned above. Any guidance regarding specific and priority changes would be much appreciated.

Thanks a lot and Best Regards.
Joe A

Try couple with 0.047u anything and make sure your actual Riaa HF cap value is ~15n. Maybe a straight 15n cap. C2 can turn the curve heavy if its closer to 50nF+ for a 5% cap, check. Are those polysterenes taking well the DC? There is ~200V at the point. The NJFET phono pre is a tough challenge to meet fast, but take your time with the Itch to balance it out first. Is your cartridge properly loaded on the Itch last but not least?
 
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Correct Salas, that's the type, so at 160V as you say they are being pushed to their limit.
Do you think changing the coupling cap C4 to 47n teflon will have a positive effect? The smoothing cap C7 is an SCR 4.7u PPE MKP FC as per Rev1.1.
Thanks and regards.
JA

Sort out the Riaa curve caps first. And if its still heavy in tone, the 0.047u couple may help you if its partly due to rumble.
 
Hi Salas and all, I changed the riaa caps with cheap but matched film thingies rated at 250V. The result was a noticeable, if not dramatic, improvement and I am now much happier with the overall sound. The tubiness is gone and vinyl surface noise very low. I measured the voltage from the upper cathode of the first stage which is 169V and 172V from a B+ of 285V.

I am now waiting for the riaa caps GB organised by Merlino which will replace the cheapie caps I'm using now. I will also install 0.1uF 200V FT-2 teflon coupling caps which I already have. I suppose that this voltage rating is adequate. Next step will be the building of a SSHV Mosfet shunt-regulator which I am confident will further improve the Itch.

Meanwhile, thanks Salas and all contributors to this interesting and very competent design. It is not complicated to build and I encourage others requiring a phono stage to tackle it.
 
Yes of course; Woodturner's pics in particular and his build descriptions inspired me to take on the project. Salas's prompt and continued support to various builders (Merlin + RCruz among others) was equally important in instilling a sense of confidence in case problems cropped up during the build process. Pics to be posted in due course.
 
Here are a couple of pictures. Nothing fancy aesthetically. Mainly used materials I already had. Blank space on underside of amp is for SSHV and heater regs which will replace the present eBay Chinese regulator which supplies only 285V at B+. Used tagstrip/boards for component layout. Valves are russian 6n2p-ev and 6H8S. Even with no boutique components I like the sound a lot. No hum or background noise whatsoever. A satisfying project all round (despite the hitches).
 

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