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Old 1st March 2004, 05:12 PM   #21
ThorstenL is offline ThorstenL  Germany
Previously: Kuei Yang Wang
 
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Konnichiwa,

Quote:
Originally posted by GAK
- silver/mica or polysterene?
I prefer Mica types, I will agree that this may be a matter of taste.

Quote:
Originally posted by GAK
Any suggestion for the signal resistors (215K , 48K7 , 100R) ?
I use standard precision metal film, nonmagnetic leads, sadly magnetic endcaps.

Quote:
Originally posted by GAK
What is PTFE valve sockets?Those with the can that covers the valve?
No, those where the inserts are PTFE. They tend to be however also those that take covers, often an apropriate choice for low level circuits.

Quote:
Originally posted by GAK
In the future I'm planning to use an MC cartridge.Step-up with xformers or active?
I like really good transformers better than solid state stepup and never got valve based stuff to work quietly enough. I had the original S&B TX-103 (quite expensive) designed to conform with my personal sonic prejudices.

The Phonostage as shown will work well with a TX-103 as MC Stepup and a TX-102 as volume control (without the +6db stepup recommended). Overall gain for MC will be up 68db, usually enough for all but extremely low output (< 0.2mV) MC's....

Quote:
Originally posted by GAK
Any comments-suggestions for the following PSU?
Looks on one hand a little overkill (a stereo chassis will draw around 30mA only) and at the same time not anywhere near quiet enough in terms of ripple rejection.

I would recommend a simple LM317 type adjustable regulator with a voltage limiting series transistor. This tends to work well enough, the original design was aimed to be used with that. Use a snubbered (Buddah style) solid state bridge made from soft switching diodes with 240V secondary.

The original idea was to use a pair 115V+115V : 9V+9V Transformers back to back, use the 9V+9V with a dual schottky diode for the heater supply and use the second transformers nominal primary as the HT source. Added RC or LC filtering for the raw voltage feeding the HT Stepup transformer is easily implemented.

A simple RCRC Filter after the bridge and an LM317 plus voltage boost transistor give a quiet supply. The RC decoupling per stage makes sure that the Signal current AC loops are closed through the local film capacitors and not the regulator.

I hope this helps to understand what was originally intended.

Quote:
Originally posted by GAK
Teflon?
Kuei: Do you believe that PTFE sockets are better for phonostage?
I don't believe, I know.

Quote:
Originally posted by GAK
What about other projects like amps , preamps?
The lower the levels the more you get trouble with DA (dielectric absorbtion), especially in areas where the dielectric is not "prebiased", but also where miller capacitance etc. is concerned, also PTFE Sockets tend to have a somewhat dampening effects on microphonics. Clearly all this is beneficial everywhere, but the lower the signals the greater the benefit.

Current production PTFE Sockets cost a mint, old stock military sockets are still quite common however. Once of these days I will actually buy some ceramic Octal & UX-4 sockets, salvage the contacts from them and apply them to homemade sockets in solid PTFE stock or maybe C37 infused wood (loads of air in wood - surprisingly good dielectric once suitably dry and sealed)....

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Old 1st March 2004, 05:26 PM   #22
analog_sa is offline analog_sa  Europe
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Kuei

Have you actually compared a 317 based regulator to a tube-series regulator in a phono stage?

And you really preferred the 317?!?!?

What about giving up the regulator completely and using multiple LC filters. With maybe a gas tube at the end to keep the voltage constant. Low noise and strong bass are not the most essential sound priorities for everyone.
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Old 1st March 2004, 07:16 PM   #23
ThorstenL is offline ThorstenL  Germany
Previously: Kuei Yang Wang
 
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Konnichiwa,

Quote:
Originally posted by analog_sa
Have you actually compared a 317 based regulator to a tube-series regulator in a phono stage?
Yes.

Quote:
Originally posted by analog_sa
And you really preferred the 317?!?!?
Nope, i found very little difference. The LM317 solution is simpler, cheaper and actually quieter.

Quote:
Originally posted by analog_sa
What about giving up the regulator completely and using multiple LC filters.
This is what I am doing with my current "in system" phonostage. But as uncompromising an approach as I took there may not be for everyone. The point with the ECC83/ECC88 Phonostage is to provide a good basic quality phonos that is easy and fairly inexpensive to realise (it was originally aimed at a commercial application).

Anyone who wants a truely outstanding phonostage has to work harder than that, but to many it will likely serve well. Think of it as the "Valve - El Cheapo" to give you an idea where it fits in in the whole scheme of things. It is not "the latest & greatest", far from it. But it is "pretty good".

Quote:
Originally posted by analog_sa
With maybe a gas tube at the end to keep the voltage constant.
Constant voltage is not really an issue. I prefer a good quality cap to a gas regulator (tried). Please note that the LM317 is PRE-Regulator followed by an RC filter. For those paranoid enough - you can add another 1k/22uF section to the output stage and split the input stages 180k Resistor into 2pcs of 91k and use a pair of 10uF Cap's.

With the original circuit, the LM317 regulator output (AC - be it noise or reaction to the AC current demand of the output stage) is suppressed by around 23db @ 100Hz and 40db @ 1KHz. Doubling the RC circuits doubles that attenuation.

Also note that the RC circuit drastically reduces the current modulation on the LM317 in the first place. At 20Hz only 1/4 of the current flowing in the output stage feeds back as modulation of the LM317 output, at 100Hz it is only 0.072 times the current in the output stage.

Thus the single RC circuit after the regulator insulates the Signal circuit from any signal interactions with the regulator by around 45db @ 100Hz and much more than that above 100Hz, compared to feeding the circuit DIRECTLY from the regulator. So the solid state regulator only becomes audible at very low frequencies.

If you feel 45db down @ 100Hz is not enough, doubling the RC circuits up gets you > 90db reduction of signal related "nasties" from the "bad & evil" solid state regulator at 100Hz.... As always, it is less what you but how....

Quote:
Originally posted by analog_sa
Low noise and strong bass are not the most essential sound priorities for everyone.
They are not priorites as such for me either. Low noise of course is not a priority, it is essential, as is in general a reasonably good sound.

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Old 1st March 2004, 07:41 PM   #24
Marinos is offline Marinos  Greece
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Keui

- Could you please explain me the role of the 48K7 resistor ?
- To add the 3.18 usec I need to add 3k18 in series to 1n, right?
- Any comments about the sonics compared to Claret and Pacific copies of yours? (I have tried both.. I play the pacific for now)
- Are you refering to Morgan Jones 317 style regulator ?
- What about your Mosfet regulator ?

Analog SA

- With extended low end (soft suspension driver) speakers it is impossible for me to fight low frequency oscilations with all passive PSU.

For the last 6 months I tried nearly everything SS rectifiers, dampers, GZ34, EZ81, Hybrid, RC filtering, LC filtering, mixed .... nada. It seems to me that an all passive PSU is a highly tuned sytem that needs proper measuring facilities that the average DIYer, like me, doesn't have (at the moment...).

I tried Morgan Jones regulator and I have to say that I like it very much. No oscilations or other nasties and sufficiently transparent to play with rectifiers and capacitors and get more than strong bass and low noise..

The above powers a 6BX7 grounded cathode line stage that I use and tweak for the last 3 years .
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Old 1st March 2004, 08:28 PM   #25
analog_sa is offline analog_sa  Europe
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Quote:
- With extended low end (soft suspension driver) speakers it is impossible for me to fight low frequency oscilations with all passive PSU.
I can't for the life of me see what the soft suspension has to do with anything. You may be experiencing a complex phenomena where ground loops interact with the PS over several stages to produce oscillations. The fact that a low impedance regulator stops the oscillations seems to indicate poor grounding. Of course i may be wrong I don't experience such issues as i firmly believe in star topologies in both the grounds and B+ loops and as good as possible separation between separate stages PSs. Of course the best solution for sonics is a completely separate PS for each stage anyway.
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Old 1st March 2004, 09:17 PM   #26
fdegrove is offline fdegrove  Europe
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Hi,


Quote:
It seems to me that an all passive PSU is a highly tuned sytem that needs proper measuring facilities that the average DIYer, like me, doesn't have (at the moment...).
The only part that may require some amount of fine tuning is the relation between the filtercaps and the choke(s) in an LC filter.

You'd be surprised how often I see resonance tanks passed on as power supplies....

You can get a pretty accurate idea by using a free proggie like PSUD II.

Of course no amount of sw simulation is going to tell you where the ground loop is...

With all the LF junk passing through I'm surprised the woofers have survived this kind of torture test...

Quote:
Of course the best solution for sonics is a completely separate PS for each stage anyway.
Amen.

Cheers,
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Old 1st March 2004, 10:18 PM   #27
ThorstenL is offline ThorstenL  Germany
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Konnichiwa,

Quote:
Originally posted by Marinos
- Could you please explain me the role of the 48K7 resistor ?
RIAA EQ, what else?

The type of RIAA EQ shown offers the combined advantages of "single stage" and "2-stage" passive RIAA EQ networks.

Quote:
Originally posted by Marinos
- To add the 3.18 usec I need to add 3k18 in series to 1n, right?
Yes. However if you do that consider implementaing fully switchable EQ, including 3uS, 6uS and 10uS added HF shelf and the varied LF and HF turnover points at 100uS and 75uS as well as LF rolloff points at 3180uS, 1590uS and 1270uS. Try compensating the excess gain from the LF rolloff compensation to make switchable comparisons more meaningful. If you really want an accurate EQ you need to try a lot harder than just RIAA @ +/-0.1db, whcih is easily achieved.

Quote:
Originally posted by Marinos
- Any comments about the sonics compared to Claret and Pacific copies of yours? (I have tried both.. I play the pacific for now)
The Claret MUST be taken as full Preamplifier and in the right system context. You CANNOT compare it to a standalone phonestage in any meaningful way. The Claret is notably off what we consider "neutral", yet in a muciaclly meaningful way. It makes virtually everything sound "good", a neat trick if you can pull it off.

Pacific and "El Cheapo" are more neutral, "El Cheapo" perhaps to a fault. This Valve Phonostage also falls more into the "neutral" camp, but tends to share some of the Pacifics attributes, except it sounds more "tube" like, in the positive meaning (e.g. not meaning syrupy colorations that oversugar everything). I prefer this basic Phono to the EAR, which i think is better than the Pacific, given sufficient care in the implementation (especially PSU).

Quote:
Originally posted by Marinos
- Are you refering to Morgan Jones 317 style regulator ?
Not sure what that is. I know Morgan personally but never felt the need to read his book (or most others for that).

Quote:
Originally posted by Marinos
- What about your Mosfet regulator ?
It's not a regulator (1) and it seems to be somewhat testy. I have build quite a few of these and never once did I have one oscillating on me, blowing up etc... It does often seem to happen to others though, hence I prefer not to recommend it. Again, the sonic differences are small after you intersperse a sufficiently large timeconstant RC Circuit after the regulator. So a recommendation based on "get it working easily....".

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Old 1st March 2004, 11:17 PM   #28
Marinos is offline Marinos  Greece
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Quote:
You can get a pretty accurate idea by using a free proggie like PSUD II.
No evidence of the problem with PSUD II.
A repeatable wrong practice in grounding ? most possible ...

Quote:
With all the LF junk passing through I'm surprised the woofers have survived this kind of torture test..
This is where the "soft suspension" comes in.... I'm kidding.
I have no other way but "seeing" the oscilation.. Of course I power down immediately.

Quote:
Not sure what that is.
This is the schematic
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Old 1st March 2004, 11:43 PM   #29
GAK is offline GAK
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The conclusion is to use four separate PSUs?One for each stage??


Too extreme for now.Let's make it simpler and if it's everything ok I'll try it in the future.

Why not to use one power xformer,rectification,p-filter and then split in two separate regulated supplies (tube or SS).One for each channel with an RC filter after each section.This for the PSU chassis.

For the circuit chassis ,an other RC filter for each channel and then Kuei's circuit as is in the schem.

Kuei:
- How much expensive is the S&B TX-103?
- What about Sowther and Lundahl?
- You have right that it's an overkill to go with the PSU I was thinking to use.

But I'd like to try tube based voltage regulators.I don't have in mind something better.
Who can help on this?

Frank: It's also an overkill to use your PSU with EL86,right?Or not?
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Old 2nd March 2004, 12:07 AM   #30
fdegrove is offline fdegrove  Europe
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Hi,

Marinos,

Quote:
This is where the "soft suspension" comes in.... I'm kidding.
You'll stop laughing when the coil gets stuck in the former...

Anyway, it sounds ( pun not intended ) as if you have DC on the output, either the DC constant of you coupling caps is at such low frequency that it somehow passes low frequency instability or you could have a faulty DC blocking cap somewhere.

Gak,

Quote:
The conclusion is to use four separate PSUs?One for each stage??
I wouldn't consider it overkill for a phono preamp...

Quote:
Why not to use one power xformer,rectification,p-filter and then split in two separate regulated supplies (tube or SS).One for each channel with an RC filter after each section.This for the PSU chassis.
After the series reg I'd just put some reservoir caps, no further filtering should be required.

Quote:
Frank: It's also an overkill to use your PSU with EL86,right?Or not?
Well, compared to the circuit with the 6AS7G, no, I wouldn't consider it overkill.
If you need a regulated 250VDC B+ a ECL805/85 and a 85A2 would do per stage ( depending on current requirements perhaps one per channel may do ) and should be better and maybe also cheaper than just one with a 6AS7G which is only needed if the reg needs to work for (a) stage(s) drawing much more current.

If the ECL82 is considerably cheaper than the ECL85/805 than that would be fine too...
I should have a schematic for one of those in my drawer somewhere...

To my mind there's little point in adding a series or shunt reg and than share amongst stages/channels in a preamp.
The least you should do is have one per channel to avoid interchannel IMD.

Cheers,
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