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    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Tube Phono Preamps

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Great to see this thread pop up, as my next project (I'm currently in the throes of building SY's RLD) will be a proper phono stage. I'll admit to following the "build X to Y dollars" scheme somewhat, as the budget just ain't there for an MC setup - yet.

With that in mind I'm leaning towards Eli's modified RCA circuit, as it seems to have hit the sweet spot between cost, gain, performance and relative simplicity. I've looked at two designs that use battery bias, but I'm not very certain - read knowledgeable - of the designs themselves, nor am I convinced the claimed "performance enhancements" :)D) of battery bias outweigh the added maintenance hassles. I have enough batteries to change/charge as it is! I could be totally wrong on those points, though.
 
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In my designs the batteries generally outlast the tubes used. I replace at 2 - 4 year intervals. (Some brands of A22/A23 batteries do not seem to last quite as long) Quiet source of bias voltage (floating if necessary) and in the case of mu followers allows for some interesting design flexibility in setting operating points and achieving a high effective load impedance on the driving stage.
 
Another take on improving the RCA design:



Sorry, Kevin, it's another outsider :)

EDIT: Oh, but lookee what else I found in my files.



Nice round values for the parts on that one and 12AX7's are real easy to find. Just bop a guitarist on the head and pick his pockets.
 
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Ok, I'll bite Wavebourn. Splain that to the noobs, please.

Did a reverse image lookup and found that one of the time constants is dependent on the cart's inductance (and would only work on MM). I take it that the other two are handled by the resistor divider and bypass caps in the anode load of the pentode?

Have you built it or heard it? I have to admit it's a cool minimalist concept.
 
Hi

try this:
http://www.multitask.it/fono junior/figura6-fonojunior.bmp

it running fine with a good precision on riaa
Also the over load ig good.
In addition, due to the configuration of the amplification stage followed by CF you can change the gain adding or not the cathode capacitor (+ 6dB with both inserted) without any changes on equalization.
The loss of the riaa network, with this configuration is 0,2-0,3 db
The gain tube is 12AX7 with 250 vdc ( up to 300 Vdc) the CF can be a ECC82.
You can use also 12BZ7 instead 12AX7, halving the resistor on anode, it sounds fine

the components:
R2= 47 Kohm ½ w, R1,R7= 1 Kohm ½ w, R3,R6= 150 Kohm 1 w R4,R9= 100 ohm ½ w
R5,R8= 12 Kohm 2w R10,R14= 2K2 ohm 1 w R11= 7K49 ohm ½ w (vedi testo)
R12= 1.090 ohm ½ w R13 = 220 Kohm ½ w R10,R14= 2K2 ohm 1 w
R15= 220 Kohm ½ w
C1= 0,1 uF 400Vdc polypropilene C2= 0,33 uF 250 Vdc polypropilene
C3= 4,7 uF 400 Vdc polypr. C4= 0,29 uF 250 Vdc polypr.
C5,C6= 47 uF / 350 Vdc C7,C8= 100 uF 16 Vdc



bye

Walter
 
This is what I built. I used the 6n23p instead of a 6dj8 and to my ears the sound is amazing. Of course it is for MM carts...

I used lr8 regs for the HV and dc on the filaments. Power supply is in a separate case, so there is no hum what so ever.
 

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An externally hosted image should be here but it was not working when we last tested it.

What differences make three variants? What's the western equivalent?

Different manufacturers' guaranty:

The 5th element is optional. It consists of a dash ("-") followed by a single character or a combination of characters, and denotes special characteristics (if any) of the tube:

V (Russian: В) - increased reliability and mechanical ruggedness (such as low susceptibility to noise and microphonics).
R (Russian: Р) - even better than V
Ye (Russian: Е) - extended service life.
D (Russian: Д) - exceptionally long service life.
I (Russian: И) - optimised for "pulsed" (i.e. switching) mode of operation.
K - made for vibrations (like missiles, ...)
 
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I have built four of these so far and all performed well, just another idea for you.

http:homepage.ntlworld.com/lez/LesBox/Let us build one.pdf

My ISP is taking away my web space in a few days time so it won't be available for very long.
 
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Wow, thanks to all of you for these great suggestions. Following some earlier comments: I agree that the forum is not necessarily the best genre for documenting information like this. A wiki page would be more suitable. Maybe I'll look into adding one.

I've still got a lot of thinking and comparing to do, but a couple of ideas are gaining traction in my mind.

(1) A GlassWare Aikido PH-1 with either the Janus tube-based power supply/shunt regulator or 2 x PH-5 B+ supply with custom heater supplies for a true dual-mono build.

(2) The Tubes4HiFi PH16, which is eminently affordable and gets rave reviews.

Has anyone heard either or both of these projects? How do they compare on soundstage, dynamics, detail, and musicality?

Still thinking about the P2P projects too.
 
I have just built Akido PH-1 with PS-1 power supply. Preamp uses 12ax7 12at7 pairs.

All I can say is that I am floored by the sound quality.

I used some rather expensive resistors: naked z-foils for load resistors, metal foils for RIAA network, kiwame for Rk, Mills MRA for RC, etc. Coupling caps are CDE.

The PS-1 heater side LD1065 generates quite a bit of heat so proper ventilation is a must (I still have to drill holes in the chassis).

It took me couple months to complete this project, mostly waiting for parts, but I think it is well worth the effort. The documentation that comes with PH-1 board leaves out a lot and knowledge and experience certainly helps in building it and especially in troubleshooting.

An externally hosted image should be here but it was not working when we last tested it.


An externally hosted image should be here but it was not working when we last tested it.


An externally hosted image should be here but it was not working when we last tested it.
 
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