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Tube Phono Preamps
Tube Phono Preamps
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Old 29th March 2016, 02:39 AM   #21
Eli Duttman is offline Eli Duttman  United States
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Why don't we see more three stage phono preamps?
I suspect simply because S/N performance with 3 gain stages is substandard.

Allen Wright used split EQ, in a 2 gain stages plus buffer setup.
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Old 29th March 2016, 02:57 AM   #22
kevinkr is offline kevinkr  United States
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Originally Posted by Sodacose View Post
<snip>

Good links though. I don't know about that Muscovite dealio with the batteries and (ACK) solid state devices though
I'm pretty suspicious of the quack that designed those, batteries in audio circuits, what was he thinking.. harrumph..
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Old 29th March 2016, 10:27 AM   #23
piano3 is offline piano3  United Kingdom
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If you want CD level output then three stages are needed unless you use a cascode (all valve or hybrid) or high mu valves which may themselves create problems due to Miller capacitance.
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Old 29th March 2016, 03:07 PM   #24
rongon is offline rongon  United States
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Originally Posted by Wavebourn View Post
The one with the 6Z4P(6AU6) pentode DC-coupled to a 6N30P looks very interesting.
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Old 29th March 2016, 03:45 PM   #25
Hearinspace is offline Hearinspace  Canada
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Just posting this for others who come to this thread because of the title.

The circuit can be built without the jFet first stage for MM. No idea how many have built this but I listened to it for a year or so with a step-up in front and just put in the jFet stage a couple of months ago. Very happy with the results.

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Old 29th March 2016, 04:48 PM   #26
Mr_Zenith is offline Mr_Zenith  United States
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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" () 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.

Last edited by Mr_Zenith; 29th March 2016 at 04:52 PM.
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Old 29th March 2016, 04:54 PM   #27
kevinkr is offline kevinkr  United States
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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.
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Old 29th March 2016, 05:01 PM   #28
Sodacose is offline Sodacose  United States
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Another take on improving the RCA design:

Click the image to open in full size.

Sorry, Kevin, it's another outsider

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

Click the image to open in full size.

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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Last edited by Sodacose; 29th March 2016 at 05:10 PM.
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Old 29th March 2016, 07:49 PM   #29
Wavebourn is offline Wavebourn  United States
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Quote:
Originally Posted by rongon View Post
The one with the 6Z4P(6AU6) pentode DC-coupled to a 6N30P looks very interesting.
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Pretty standard design, actually. One of my colleagues in Israel who is possessed by anti-capacitance virus designed one with RL only, and an air variable capacitor on input.
Another friend who is more practical designed this one, I think it is a piece of an art:
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File Type: gif bokarev.gif (15.5 KB, 1096 views)
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Last edited by Wavebourn; 29th March 2016 at 07:52 PM.
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Old 29th March 2016, 08:47 PM   #30
Sodacose is offline Sodacose  United States
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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.
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