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Old 31st July 2011, 11:21 AM   #381
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Old 31st July 2011, 12:09 PM   #382
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Old 2nd August 2011, 03:51 PM   #383
webby is offline webby  United Kingdom
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Originally Posted by woodturner-fran View Post
Tell you this - it sounds great, really great.

Fantastic work on this design salas. More need to build this phonostage!
Hi all,
I would like to build an Itch, plus a line stage / pre amp to go with it.
Maybe a 6sn7 based line stage as I am buying the parts for the itch.
Is it a good idea to add another gain stage to the itch or build a separate line stage?

1 x psu, SSHV and itch with line stage,
or
1 x psu, SSHV,itch
1 x psu, SSHV line stage

Any recommendations for the volume control, I am using a passive pre with an Alps pot.
Not too expensive or complicated please?

I have the partridge 997s in a separate box, sounding fantastic. But will probably fit them internally to shorten the signal path.

Fran, what cap combo did you settle on in the end, I may as well benefit from the experience of other builders.

A couple more questions...
PSU
For UK builders, these transformers might be good. Rod Coleman recommended these in another thread.
150 VA
150 va, 240v primary, what secondary should I specify for the Itch and line stage?

Heaters,
Should I use separate transformers for each channel, 50va 9vac.
Can you recommend suitable products?

Are you building SSHV from parts, is there a kit PCB for these?

Sorry for the long post, I have itchy fingers to build something.

Many Thanks
Ian
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Old 2nd August 2011, 10:39 PM   #384
Salas is offline Salas  Greece
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I would use separate regulators for the phono and line. Making it integrated or not its just a matter of personal choice, but no AC carrying cables where the phono's housed, transformer(s) & rectification+big filter caps in a separate box remain a must. I would not make a 15-20dB gain line stage. 10dB max. There are no PCBs for the Itch of course, special project for buss bar detectives, only 3 prototypes in existence counting Fran's and no completion news revoli's, too hot for a PCB and a good reliable future anyway. As for heaters the more you separate stuff the less interactive but the more complex and big it gets. It already needs 2 heater PSU's, one 1/2 B+ floating, the other grounded. Its NOT an easy project, takes some persistence, especially to debug possible grounding issues etc. 800-1000x gain for an MC cart from SUTs & valves, hot shunt regs, cables, you get the picture. Fran's build had a good step by step presentation, problem solving, comparisons, conclusion, read it as an example.
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Old 2nd August 2011, 11:01 PM   #385
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I'm using a 6SN7 aikido pre with mine and am very happy. That might be a good starting place... and there are PCBs available for this, in fact there are kits with all you need except transformers at the tubecad site.

EDIT: I just went back and re-read your post. If I understand you correctly you are wondering if you need a pre with gain instead of your passive..... probably not is the answer I think. But maybe watch the input impedance? Salas/others may be able to better advise you here.....

Personally, I'd build the pre as a separate unit - its easier to build this way, and allows you to move it around and use it in other systems. All of the stuff Salas has mentioned too...

You could use separate windings for the 2 heater supplies, but I used 2 separate transformers because I got some cheap from farnell in a sale (€3 each!)

Volume control: can't get simpler than a gigaworks pot from ebay, excellent performer at very low cost. Better than an alps blue.... I know they look cheap and don't feel like a goldpoint, but the ones I've used have lasted well.

Caps: I'll go look and post back later - there have been so many!! I think I now have all K72P-6 for the RIAA, FT3 for coupling (I think) and MGBO 2uF for local PS. If you hav e a read over my posts in that thread you'll see the evolution!


No kit for the itch - I don't think it really lends itself to a PCB too easily and you'd hand wire it easily enough. There is a shunt kit I think from Quanghao in the vendors area, and I think someone has one up for sale in the swap meet at the moment. I used mouser for the SSHV, heater components and itch components, russian ebay sellers for the caps and 6N1P (sockets too) and langrex (ebay again) in the UK for the rest of the valves. You'll need heatsinks etc for the heater regulators and of course the shunt.

As Salas said, it is a reasonably complicated build. Its very high gain for valve stuff, so expect to spend some time sorting out hum, and when you get past that, swapping caps etc. But the result is rewarding!!


Fran

Last edited by woodturner-fran; 2nd August 2011 at 11:04 PM.
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Old 2nd August 2011, 11:40 PM   #386
Salas is offline Salas  Greece
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Quote:
Originally Posted by woodturner-fran View Post

EDIT: I just went back and re-read your post. If I understand you correctly you are wondering if you need a pre with gain instead of your passive..... probably not is the answer I think. But maybe watch the input impedance? Salas/others may be able to better advise you here.....

Fran
Depends on his amp and speakers sensitivity is the general answer since we don't know what he uses for those yet.
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Old 4th August 2011, 10:42 AM   #387
webby is offline webby  United Kingdom
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Thank you gentlemen for the info.
I think a clear nod to the separate Itch & pre!

I had already read through the whole tread, but it was hard to keep up with the cap evolution! I am not familar with the Russian caps so get confused, not to mention the bypass caps on top.

My system comprises, Tubelab Simple SE amp powering open baffle Audio Nirvana Super 8's and two Parts express 240W sub amps powering H frame Beta 15", just using split RCA signal cable from the passive pre.
The vinyl front end is an AT33PTG cartridge, .5mv output, 997 transformers, Cambridge Audio 640p phono stage.

I feel that the weak links are the phono stage and passive pre, basically a selector switch and Alps pot. So am looking to improve these items.

I will order a couple of Quanghao SSHV kits on pay day, one for the Itch and one for a Pre.
For the heaters, i have found this 2 x 9v transformer for 10 ish:
Rapid Electronics - Electrical & Power

Would you advise regulating the heater voltage with a basic LM317 type solution or is a Salas Low voltage shunt required?

Fran, i cannot find the gigaworks pot on ebay, do you have a link please?

Thanks for all the input so far.
Ian
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Old 4th August 2011, 01:58 PM   #388
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For heaters don't use SSLV better use Rod Coleman heaters
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Old 4th August 2011, 02:28 PM   #389
Marra is offline Marra  United Kingdom
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For UK builders, these transformers might be good. Rod Coleman recommended these in another thread.
150 VA
150 va, 240v primary, what secondary should I specify for the Itch and line stage?


I think the price on the web site for these transformers must be a trade price as when I contacted them they gave me an address to contact and the price including p&p was over 50 apiece.
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Old 4th August 2011, 08:52 PM   #390
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OK here's the main details of my build:

HV Ps:
260V secondary, and I think specc'd about 80mA should be enough for demand + shunt
SSHV, wired on a perf board putting out 290V. I had this Tx as a salvage from something else. Don't know the exact spec, but it doesn't heat up although isn't very large.

Heaters:
I used 2 x 9V sec transformers using the 317 reg supply as recommended by Salas. I happened to get a deal on some from RS supplies at a few euro each, the RS number was 504-644. They are 75VA each, and are probably oversized for what is needed.

Heatsinks + hardware:

You will need a decent enough heatsink for the SSHV, and the 2 x heater supplies. Also 6N2P x 2, 6N8C x 2, octal sockets, nine pin sockets, step up Tx (partridge 977 sound very good), chassis x 2, connectors for umbilical, IEC for mains plug, switch, maybe LED indicator, RCA jacks etc. The regs are all in one box and do throw out a good bit of heat, so use a chassis that has some ability to breathe. I used a mix of different wire, but mainly silver in teflon, shielded where possible from navships on ebay

Power supply from earlier in the thread:

Click the image to open in full size.

Itch circuit from earlier in the thread:

Click the image to open in full size.



All the transformers are in one box which is connected to the main phonostage (containing everything else) by umbilical. There is high gain in the amp so beware that you will probably need to be patient and work through hum etc etc. If you can filter and read my posts from earlier, and the links to other sites, its well worth your while. Very good info on grounding to be had here.

So the capacitors:

Main output caps: I used some PP 2.2uF 600V ones I had lying around and eventually I bypassed these with some russian 0.1uF 600V FT3

Power decoupling: this is on the sch as 47uF 350V, I ended up using some 2uF 500V russian MGBO caps here

coupling cap: 0.1uF K40Y-9 is on the sch, I used 0.047uF K72P-6

RIAA: I tried silver mica but ended up with K40Y-9 for both the 0.047uF and 0.015uF. These sounded best to my ears.

I also tried some 6N2P-EV but the ordinary 6N2P I had sounded better.

I used 2 different Russian sellers for the caps and 6N2P:

Alexer1 and uralspirit. I used Langrex also on ebay for the 6H8C. The partridge step ups are very good value on ebay by seller dr-tron. The other stuff I got from mouser, radionics, farnell or salvage.


Even though I started with a fairly big chassis, those bit russian caps and the regs+heatsinks fill it up pretty quickly! Pics as it currently are below.

Ask any questions, I might not be able to answer, but if I can I will

Oh and edit: here is where you can find gigawork. They're only USD15 delivered and are very transparent. I'd suggest a 50k or 100k one if you are going to build a 6SN7 aikido.

Fran
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