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Old 27th January 2011, 04:46 AM   #71
Salas is online now Salas  Greece
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Quote:
Originally Posted by kevinkr View Post
If not common mode it will buzz..
It looks OK bcs it doesn't buzz when the primary is floating and a cart pin is touched.
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Old 28th January 2011, 05:58 PM   #72
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Quote:
Originally Posted by Salas View Post
Went to Mikvous's place today to examine another Itch he made. With my Rev1 changes included.
Salas
A couple of probably dumb questions from an inexperienced enthusiast. This additional circuitry just replaces the Maida 300v, nothing else changes?

Secondly can you tell me what PP is on PSU circuitry? I am sure it is incredibly obvious but has got me stumped.
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Old 28th January 2011, 06:06 PM   #73
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PP is polypropylene. In place of the Maida, an HV Mosfet shunt reg was used in Rev1. Also the 470k-220k divider has changed to two equal resistors (whatever handy above 200K). Its needed to lift higher because in Rev1 the upper tier tubes cathodes sit even higher for potential from their heaters. What kind of cartridge are you planning to use?
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Old 28th January 2011, 06:36 PM   #74
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Thanks for that, I was misreading the circuit and had not related PP to the cap..... Cartridge is high output MC Dynavector 10x4 MkII 2.5mV output. Should be enough?
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Old 28th January 2011, 06:54 PM   #75
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Yep, its got 43dB gain without an input step up transformer. Try a 3K3 load resistor for that cart instead of the 47K recommended at a point also to compare when you will finish.
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Old 5th February 2011, 06:00 PM   #76
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I am looking for some guidance on the PSU for this as detailed in post number 3 please. There is a 100 high esr cap on the adjust pin of the 317. Is this 100uF and what level ESR is "high"?? Thanks
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Old 6th February 2011, 10:32 AM   #77
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Hello

The 'cooking' of an LM317 based reg has some peculiarities and some preferences. That one in the schematic was for a split. I.e. the two heaters regs remained in the PSU box and a final big electrolytic cap was decoupling the heaters in the phono box. It is depicted on the schematic. So the real termination were not just the polypropylenes but a combination of the poly, the 1m connecting wire and the final electrolytic. Yes those Cadj capacitors were not recommended as special low ESR capacitors but as plain spec. Say a Nippon SME or a BC Component standard quality will do fine. If you will have space to host all the regs and sinks in the phono box and can have the transformers, bridges and main filter caps in the PSU box, that will be the best, as it was done in the second build. Normally you will use a roomier box than that wooden one of the first build example. In this case you must have 0.1uF capacitors for each LM317 from input to ground so to decouple the incoming long connecting wire, and only use 100uF plain quality for Cadj and Cout. No poly caps, no final big electrolytic.
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Old 7th February 2011, 05:02 AM   #78
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Many thanks for that. I like the two box approach and am planning on building the boxes once I have done a rough build of the system first so I can see how much space I want. I quite fancy the look of wood on the box sides and ends and have some nice oak that would look great but am thinking about lining the boxes with something to provide electrostatic shielding. Whats the best way to create the umbilical chord between psu and phono. Looks like you used a cable gland at one end rather than two plugs. To get the right type of cable between the boxes is it necessary to make your own using good wires, sleeving and say a 5 pin plug? Thanks for your help. I am enjoying this thoroughly, it's keeping me sane!
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Old 7th February 2011, 05:57 AM   #79
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If you will consider electrostatic shielding its best you will keep the PSU and the phono circuit including the valves inside grounded ferromagnetic metal enclosures. You can attach wooden face plates or side panels of choice by all means. If fully wooden, you can line with copper sheets. In those two builds by Michael (mikvous) the input valves although exposed did not prove susceptible to hum and buzz even without metal caps as it happened with the higher internal impedance Steve Bench cascode circuit for instance. Provided that the main unit is not in proximity to a transformer AC field, its not especially troublesome in the Itch design. But it can always measure better harmonic noise, so the former mentioned approach is the optimal one, although you can go by nicely with exposed valves as in the examples. As for the umbilical, no special thought went into it. It should be rated for handling 300V DC and be flexible enough. The cable gland just saved even more wiring breaks and attachments for yet another multi-pin connector PSU side, being captive to one box did not bother the builder, but following the usual approach of having connectors on both ends won't be noticeably detrimental either I suppose. You could use one separate heavier gauge 4 wire chord for the rectified DC PSUs of the filaments, and one HV umbilical if you fancy. Detached routes and will look more business like even.
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Old 8th February 2011, 11:28 PM   #80
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Thanks for that. Copper sheeting sounds good. I used to have tons of copper sheet obtained from a friend for doing some welding for him. It was for making circuit boards but had a fault. I used it to build a roof on my garage, it looked great and lasted really well - at the time copper was not that expensive. Unfortunately I no longer have the garage or the sheeting. I guess I will have to buy some more...
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