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Old 6th Aug 2008, 11:32 pm   #21
Ruthann
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Default Re: Phono preamp valve kit?

Glad to hear the results were good, Trevor!

Top Cap, thanks very much for posting the pics. Nice to see the finished result.

I've been away for the last week or so, but intend to continue with the build over the weekend when I return. Thanks to everyone who replied to the thread.
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Old 2nd Sep 2008, 8:02 pm   #22
Magic Band
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Default Re: Phono preamp valve kit?

I was allways succesful with this one:
(1 channel shown; in stead of the ECC83/12AX7, I used the E83CC/12AX7AT/6072A or E81CC, and in steat of the ECC88/6DJ8 the E88CC/6922.)

http://img355.imageshack.us/img355/7...nop2wl3.th.jpg

Gain: 40-44dB
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Old 2nd Sep 2008, 8:06 pm   #23
Magic Band
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Default Re: Ever built a theremin?

Almost forgotten, the PMD-phono-amp. power supply:

The AZ41 is a DHT (so, great sounstage)!

http://img355.imageshack.us/img355/1...nop2ng1.th.jpg
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Old 3rd Sep 2008, 8:35 pm   #24
grindrod
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Default Re: Phono preamp valve kit?

I did a lot of experimentation on a 'hifi' valve phono stage some years ago and the optimum configuration was an EF86 with a gain of X20 fixed using some undecoupled cathode resistance and with the 75us pole (use a 75k resistor and 1nF 1% polystyrene) by adding a capacitor from anode to earth (the HF role off in the RIAA) this was followed by a double triode cascade amplifier with feedback from final anode to first cathode that incorporated the 3.18ms pole/0.318ms zero giving a midband gain of X10 and an LF gain of X100 (as per RIAA). It worked extremely well using an OA2 to regulate the HT at 150V and was low noise enough to use with some moderate output moving coil cartridges (0.5mV). The signal/noise was terrific using a typical 5mV O/P moving magnet. The output impedance is low enough (due to the negative feedback) not to need a cathode follower.
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Old 3rd Sep 2008, 9:06 pm   #25
barretter
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Default Re: Phono preamp valve kit?

I doubt that your equalization is very accurate. You can't just stick a CR combination with a time constant of 75 us in the signal path : you have to take into account the output impedance of the EF86 and the input impedance and Miller capacitance of the following triode. And using negative feedback for the other two poles is even more complicated. You can find all the grisly details in Morgan Jones' books.
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Old 4th Sep 2008, 8:37 am   #26
grindrod
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Default Re: Phono preamp valve kit?

Quote:
Originally Posted by barretter View Post
I doubt that your equalization is very accurate. You can't just stick a CR combination with a time constant of 75 us in the signal path : you have to take into account the output impedance of the EF86 and the input impedance and Miller capacitance of the following triode. And using negative feedback for the other two poles is even more complicated. You can find all the grisly details in Morgan Jones' books.
RIAA was within +/-1dB from 20Hz to 20kHz as it happens!
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Old 6th Sep 2008, 11:06 am   #27
dominicbeesley
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Default Re: Phono preamp valve kit?

For chassis building I have to recommed you get a few of these Q-Cut hole cutters, they make chassis building really neat and simple. I spent ages mucking about trying to get nice round holes for my valves before I found them!

http://www.lawson-his.co.uk/scripts/...Hole%20Cutters

I've not found any other supplers though.

Good luck with the build

Dom
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Old 12th Sep 2008, 2:27 pm   #28
oldeurope
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Smile Ef86...

Hi,
look at the RIAA2001.
The EF40 is similar (electrical) to the EF86.
http://riaa-2001.blogspot.com/
Please note:
No semiconductors, no electrolytics and AC heated.
Cathode follower output.

(This is not a kit.)
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Last edited by oldeurope; 12th Sep 2008 at 2:55 pm. Reason: text added
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Old 4th Dec 2008, 9:54 pm   #29
Ruthann
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Default Re: Phono preamp valve kit?

After a getting a bit sidetracked from this project, I have now jumped back into it this evening.

I've had all of the bits and pieces sitting looking at me for quite a while, but was busy playing with radio gear, and the likes.

I'll hopefully find the time to get this pre-amp done in my spare few hours over the next few days and may have a success story very soon. (Fingers crossed!)

It has of course been revised from kit to build, as I had no luck locating a kit and this is a better way to learn anyway.

Thanks to you all for your helpful input!
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