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Valve Itch phono
Valve Itch phono
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Old 7th June 2012, 02:28 AM   #691
Salas is offline Salas  Greece
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Valve Itch phono
In post #615 I see the CRC is 2 pcbs and 2 wiring pairs away from reg's raw dc input. Twist those wires and put say 0.1 to 1uF cap across the DC in connector. Better take out C7.
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Old 13th June 2012, 12:42 PM   #692
revoli is offline revoli
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Deep deep joy. Salad is a god. After what must be nearly two years I have finally got round to switch on of my phono itch. Ill health has alas kept me away from this project except for very small and occasional forays into my workshop. I also found playing with high voltages whilst high as a kite on prescription drugs not a good idea. However finally we have lift off. A couple of component issues now resolved and she sounds great. I am currently trialling some hard hitting rock to see how it holds up to the more demanding end of my record collection.

As you can see I still need to box this thing but before I do I need to tweak.

First off earthing. I have a simple earth running through the whole thing and no shielding anywhere so some buzz but surprisingly not bad. Tips on earth improvements greatly accepted otherwise I shall read through the thread again.

Secondly I am using a 3k3 resistor at phono input following Salas recommendation for my Dynavector 10X4 (specs 2.5mv output, 47kohm load impedance). Can anyone tell me how this is calculated in case I ever change cartridges. Is it worth playing with this or other components in an effort to fine tune? It feels slightly harsh occasionally although even after an hour of playing I think it may be mellowing (or is that just psychological?)

Thirdly I worked to the very early designs as changing mid project would have been a level of complication beyond me at the time. Is there anything in the later mods that anyone would recommend as making a substantive difference.

Anyway many thanks to all for a great project that has helped keep my sanity over last two years.

Regards
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Old 13th June 2012, 03:33 PM   #693
Salas is offline Salas  Greece
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Hi Revoli

Nice that you got around the build after time and hardship. Be well.
Regarding some buzz it looks like its a shielding priority on glance. No metal container for the pre, and transformers are near about. Shorten all wiring to tightest possible, narrowing the aerial loops.
Not sure if the signal input wiring is shielded from looking at the pic.
If not, that could help a bit for now. Also by looking back you can refer to Fran's GND wiring scheme.
If buzz receeds it can sound mellower even because it adds harmonics of its own, but having a Dyna 10X4 myself also in my stash I know it can show some bite occasionally.
Regarding the idea behind choosing its load resistor value, its about securing a times 10 higher resistor than the published internal resistance of the cart and trying a few higher values in steps up to 47K. 3K3 is the base and you can listen to some values above that. If the tonality won't be fully acceptable after that, try VTA tweaks, if still not content, some careful step by step addition of value to the 15nF RIAA HF capacitors can tilt the curve mellower. Say by using sub nF silver mica bypass caps to gradually go up to 16nF total.
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Old 15th June 2012, 04:10 PM   #694
revoli is offline revoli
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Salas thanks for the tips. Will work through these. Boxes under construction then rebuild inside its new home. On previous form that should take about a year...... I also have a bunch of different valves to test in it as they are reasonably cheap and it seemed a good idea at the time. Great project, great sound. Another step on the ladder to reach sound nirvana.
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Old 16th June 2012, 04:47 PM   #695
revoli is offline revoli
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Default Earthing

I have read with intrest the posts from Fran and Salas on earthing this. Think I know what I am doing but before commiting wire to wire could someone just confirm my queries. I have taken Frans drawing and scribbled on it as I am fundamentally lazy. On my notes page attached:
1. Am I right in how I wire the capacitors at the input jacks with 0.01uF caps?
2. I cannot read Frans writing circled in pink. What does it say?
3. At top right in red am I right, 0.01uF caps, 15R 5W resistor and a couple of inverted UF4007 diodes and no other direct connection to chassis for bus bar?

Is it worth putting shielded cable anywhere else? I also have an amount of expensive silver wiring I could use in here Its quite thick but is it worth bunging in on signal path - shielding it first?

My final build will be two box so a sort of hybrid star/bus bar earth. I am assuming I can take the earth straight back from the phono box to the PSU box. Anything clever I should do between the two to stop stray signals creeping into the Phono bus bar? I assume I can replicate what is proposed for the bus bar connection in the diagram (circled in green) and connect phono earth at point E. Bit nervous on that as want to be sure earth is safe so please confirm someone!

Is it worth upgrading the C2 (47nF), C3(15nF), and C4 (47nF - 0.1uF in mine currently) (in Salas Valve Itch Rev 1.1) to paper in oil russian caps if I can get them? All after eliminating buzz of course! Thanks all.
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File Type: jpg Phon Itch Earth Wiring v0.jpg (191.0 KB, 322 views)
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Old 16th June 2012, 05:50 PM   #696
Salas is offline Salas  Greece
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Not to answer on Fran's account on details until he will be reading your questions at a point, at least I think he notes encircled in pink from left to right ''elevated heaters to 1/2 B+'' and ''grounded heaters to PSU GND point''.
The 10nF input RCA ring local to chassis caps are meaningful in a metal environment, i.e. not in yours yet. They are to ground RF before it enters the circuits traveling through shared ''clean'' signal ground paths to 0V.

There are many ways someone can wire such a build successfully, I recommend you try shielded coax (the rather thin variety) for your signal runs and evaluate result before you attempt drastic changes. Its we identify the sources of slight buzzes first or we guess by eliminating possibilities. Better is we have a very silent FFT set up and we loop the phono as we watch harmonic noise tweaking by educated trial, but I am aware that the majority of builders in this thread aren't such equipped and familiar yet.

I had used with success one end (towards bus) shorted coax for GND returns you ask about, because they had to run around a 250VA toroid in a KT88 20W design of mine. Its noise floor attached, a fully AC heated 3 stage amp that was. See also how the short bus bar and shielded returns have been arranged for ideas. Grounded copper shield around Tx does help also. Save your silver IMHO.

To guess about Riaa caps upgrade worth to Russian PIO, you should give more info on brand and type you currently employ.
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File Type: gif SalasKT88triodeTHD.gif (16.4 KB, 314 views)
File Type: jpg SKT88inside.JPG (452.8 KB, 316 views)
File Type: jpg SKT88gen&cro.JPG (333.2 KB, 308 views)
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Old 21st June 2012, 09:58 AM   #697
webby is offline webby  United Kingdom
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Hi All,

Sorry to quote myself again, I have now bought received all the parts except the heater transformers, can you advise me on the most suitable please?

[QUOTE=webby;3050146]Hi All,
Thanks for the PM's regarding the parts.
I now have most of them on the way, RIAA caps from Felipe, components & valves from Revmen.
I have also ordered a 260VAC mains transformer from jms on-line.
100 VA

I need to order the heater transformer, which would be more suitable?
Laminate or Toroidal, are there any advantages, do I need two?

Buy Chassis Mounting Transformers Clamp mount transformer,50VA 2x0-9V o/p RS 10-5941 online from RS for next day delivery.

Toroidal Transformer 230v Single Primary 50va 0 9v 0 9v

Chassis Transformer 230v 50va 9v+9v

I purchased the JMS 260V 100VA transformer, it has no centre tap, is that a problem for this build?

Would I be better buying tag strips, tag boards or fanning strips to ease my first point to point?

Many Thanks
Ian
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Old 21st June 2012, 11:08 AM   #698
merlin el mago is offline merlin el mago
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Quote:
Originally Posted by Salas View Post
Not to answer on Fran's account on details until he will be reading your questions at a point, at least I think he notes encircled in pink from left to right ''elevated heaters to 1/2 B+'' and ''grounded heaters to PSU GND point''.
The 10nF input RCA ring local to chassis caps are meaningful in a metal environment, i.e. not in yours yet. They are to ground RF before it enters the circuits traveling through shared ''clean'' signal ground paths to 0V.

There are many ways someone can wire such a build successfully, I recommend you try shielded coax (the rather thin variety) for your signal runs and evaluate result before you attempt drastic changes. Its we identify the sources of slight buzzes first or we guess by eliminating possibilities. Better is we have a very silent FFT set up and we loop the phono as we watch harmonic noise tweaking by educated trial, but I am aware that the majority of builders in this thread aren't such equipped and familiar yet.

I had used with success one end (towards bus) shorted coax for GND returns you ask about, because they had to run around a 250VA toroid in a KT88 20W design of mine. Its noise floor attached, a fully AC heated 3 stage amp that was. See also how the short bus bar and shielded returns have been arranged for ideas. Grounded copper shield around Tx does help also. Save your silver IMHO.

To guess about Riaa caps upgrade worth to Russian PIO, you should give more info on brand and type you currently employ.
Very nice pics Salas, for sure sounds very good
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Old 25th June 2012, 10:11 PM   #699
webby is offline webby  United Kingdom
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Hi All,
I am just about to order the remaining parts, and would really appreciate a few answers.
I have a Toroidal 120VA 2x18V sitting here unused, can I use this for the heaters?
Will the 10K trimmer & 470 reduce the output enough? Or am I stressing the LM317 to much?
Would save me a lot of money if i can use it.

What would be the value 10W resistor dummy load for setting the SSHV2, ie the mA target circuit's nominal consumption?

Thanks in advance.
Ian
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Old 26th June 2012, 11:02 AM   #700
revoli is offline revoli
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PSU box nearly done. Just about to order parts for cable between psu box and phono. It strikes me that I can get away with 5 core cable as per labels 1 to 5 on attached but v1.1 shows 7 (letters A to G). What is best for this please.
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