Stax Cp-X Electrostatic Direct Pickup System

[tubes4life]

Hi Stefan,

It's very possible that the difference I heard was due to the tubes. The tubes that came with the amp were Amperex 6KG6s which were still available in quantity at the time but probably for aftermarket service purposes. In any event, I never looked into other tubes that might have sounded better. I agree with you totally that different brand of tubes can make or break a piece of equipment in a specific system. I roll tubes extensively, however, I never did it with my 3a. Amazing! I was probably too intimidated by the various adjustments necessary when tubes are changed.

I'll be happy to send you the schematics and the setup instructions of 3a. Please let me know where I should sent them. You can PM me the address.

It seems that you're well-versed in tube designs. Do you think it's worth the effort looking into replacing the 10db FET amplification circuit with a tubed version in the Stax POD box?

Cheers,
Andy

[decca4]

Hi Andy

I am happy if I inspired you to try different tubes. When I red your remarks about the two amplifiers sounding different I was a bit surprised. I think that you can make your H3A sound just as good as the H3AA. The only difference will be in out put power I believe.

Unfortunately you can never be absolutely sure by just choosing a good manufacturer, however you should never consider any other than the best. The ones that always have delivered in my experience are GE, Mullard, Telefunken, Sylvania and the English manufacturer that makes the Gold Lion KT 88. The name slips my mind. There are most certainly other reputable ones that I have not tried like Western Electric and such. I have heard some 6KG6 sounding just awful so it is certainly worth trying different brands. I will look into my tube manuals and see if some of the brands I trust have made any of these.

When it comes to replacing the FET amplification I believe it is a must in order to realize the full potential of the CP-X. Ones I get mine up and running a re-design will be the first priority. When I have done so (with the help of more knowledgable friends) I will certainly share the design of the circuit with you.

I have actually managed to upload some pictures to my gallery and will post some picture within the next days.

My biggest problem with putting my POD-X back in shape is how to fasten the meters to the chassis. Mine are free floating at the moment. Also I don't know how far the face plate should be mounted from the chassis as the mounting parts are missing. Do you think that you could take a measure please?

I will send you a private message with my address.

Cheers/Stefan

[tubes4life]

Hi Stefan,

The meters are glued to the underside of the top plate with the meters exposed through the retangular cutouts. (See previous picture.) The top plate is held in place by 4 screws through 4 standoffs. Their sizes are shown in the following pictures.

I'd love to get rid of the FET voltage amp. I actually put one in many years ago. It used 2-12AX7s and I had to make an outboard power supply for it since there wasn't enough space in the POD enclosure. It actually sounded pretty good. However, when I moved to my current house, RF interference became a problem and I had to revert back to the FET.

My 3a with the Amperex 6KG6s actually sounds pretty good with the Quads 63. I may roll some tubes if I find it difficult to go back to the Cary 805 and the Canary 300 which I normally use for the Quads.

Cheers,
Andy

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[decca4]

Hi Andy

Thanks for the valuable info. I think that I will try to make an arrangement so that the meters are fixed to the chassis instead. The stand offs are ca 10 mm if I read it right. There is also a single lamp, is that one fixed into any particular place or just placed between the meters without any particular arrangement?

I looked a bit for tubes for you H3A and it was not so uplifting. The brands out there are not familiar to me and the ones mentioned had shifting reviews. The Svetlana should be avoided as far as I understand. There was a Chech variety that had some favourable mentionings but priced ridiculously high and also short in supply. However I found this page that may merit some further investigation.

http://www.vacuumtubes.net/RES%20Audio% ... power.html

I looked at some pictures of the power amplifiers that you are also using. They really look very nice but my guess is that the Futtermans will beat any 300B configuration. Last week I listened to "the Lars" an impressive looking 300B design and favourably reviewed in Stereophile. At first they sounded very very good but after a while you got tired of the "hit a sofa with a salami" sound in the low register. The notes in the low register never stopped and therefore smeared the whole register. The mid and top registers were very seductive though.

Now I will make a try to post my first pictures which will be of my H3AA. If it does not work please look at my gallery

Cheers/Stefan

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[tubes4life]

Hi Stefan,

Thanks for the link. I'll look into the GE and Sylvania tubes for the 3a. Single ended amps sound quite different from the push-pull ones. With careful tuning and tweaking one can minimize the mushy low end.

I took a picture of the actual placement and orientation of the lamp under the top plate of the POD box. The lamp must be placed right in the middle of the meters otherwise the meters will not be illuminated evenly. Pay no attention to the scribling on the meters or the holes on the left. The holes were drilled to accommodate the extra two tubes I put in to replace the FETs.

Your Futtermans look nice. Haven't seen one for years. Certainly brought back memories. Incidentally, I may be wrong but I thought mine had black cases. The piece on an open chassis to the right of your 3aas looks quite interesting. Is it the preamp you made?

Cheers,
Andy

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[decca4]

Hi Andy

Once more thanks for the very helpful and informative pictures.

You are right. The odd looking thing is indeed my Pre amp or phono stage. Each side has two E 288 CC tubes. It is a high grade ECC 88 passing 1,5 times more current than the ECC 88.

It was built by a very knowledgeable friend of mine who has his own ideas about circuit design. The second stage/tube uses the B+ of the first one as ground. This means that there is a difference of ca 250 volts between the input ground and the output ground. It is therefore advisable to beware of where you put your fingers when the thing is running. The red resistors are made by Danotherm. They are non magnetic induction free precision resistors. Their tolerance is 0,1 %. They are just clean and delicate in their sound character. Unfortunately they are not available any more although there may be similar ones available. I believe that GE made some. The blue capacitors are made by ERO. The tubular ones are named KP 1838. They sound very clean and convincing. Of course they have stopped making those. Why do manufacturers stop making their best products I wonder. The Pre amp is sitting on a Kenwood KT-917 tuner. The tuner has been modified by my friend who is a Senior acoustical engineer working at Sony Ericsson. He has a deep understanding of how different components and circuitry affects the sound.

I will also post a picture of my present TT set up with the RABCO and IKEDA. The golden thing is a Forsell that although pleasing, I think come second to the RABCO in many respects.

I forgot to send you my address but will do so now.

I just bought a Decca Super Gold that will be sent to Stylus Expert for mounting of a Paratracer stylus.

Cheers/Stefan
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[tubes4life]

Hi Stefan,

That's some system you have there! The preamp looks like a killer and lethal in more ways than one! Do you use a headamp or x'former or the preamp can handle the lower than average output level of the Ikeda?

Your posts inspired me to step up my search for an Ikeda and if everything goes fine I should receive mine in the next few days. Hope it will outperform my long-time favorite - the Decca SC4E.

Cheers,
Andy

[decca4]

Hi Andy

Thanks for the schematics. They arrived today. I will study them.

In an earlier post I wrote that my POD was delivered back to me in small pieces and in a later post that it was only partly dissembled and could probably be put together again. Both statements were in fact true. The other day I found the wreck that I was referring to first. So it turns out that I have two PODs. The wreck has now served me well as a donor so I managed to put the best one together. See pictures of both below. My dream is now to build tube stage in the donor shell and use that instead if the transistor one in the original. That will probably take some time. My knowledgable friend looked at the circuitry of the amp in the POD and said that he was not impressed. So now I am starting out convincing him that he should suggest an alternative transistor design to put in it's place. The tube will have to wait.

I use a pre-pre for the IKEDA once again designed by my friend. It is an ingenious design where all of the power of the cartridge is used and not just the voltage output. This means that even a low impedance cartridge like a Ortofon can be amplified without any noise or hiss whatsoever. This was used by Peter Forsell in all his demos at audio shows and also sold to a limited number of special customers. The difference to all other pre-pres is that the current is used also. The sound of this one is uncompromising. The trafos are nice but not precise and not nearly as dynamic in comparision.

I wish it would be commercially available but it is nor unfortunately. There are pictures below of it in raw form. The amp is to the left and the power supply to the right.

If you take a look at my gallery you will find some close ups of the resistors and capacitors that I mention. You will also see the resistors on the pre-pre. I mentioned that GE had made some similar ones. That is incorrect. The company is General Resistans.

I will be most interested in hearing your evaluation to the IKEDA.

Cheers/Stefan

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[Biotron]

Sadly, I need to sell some of my hifi gear. I have a Stax POD-XE and CPX cartridge and do not know what it is worth. For those of you who are familiar with this please provide some input on what to ask. I acquired this in 1973 from a member of the Stax family through John Iverson. It is truly a remarkable sounding setup. I use a Stax UA7 arm mounted on a Technics SL110 and it's an excellent combination for the CPX. I have a second UA7 arm and will keep the SL110 with a Denon 103S. I will put a list together and post it shortly with some interesting history. Thanks in advance

Galen

[STAX-POD]

Hello
Have you sold your STAX items ? Because I can probably send them back to life .
I am a lucky man because I knew personnaly Mr Hayashi junior and was in business with him during the golden time of the hifi market in 1980 until 1989.
If I can help regarding some old products....
Patrice