gotta make a christmas present there for my electronics mentor figured since he's got boxes and boxes of vinyl (around 5000) i'd finally make him a preamp, anyone got any good designs? i've got about 2 or 3 matched pairs of 12au7's i'd like to use up, i've looked on the net and am having trouble finding much..
Look in the back of the RCA tube manual. One of the sample circuits is a tube phono preamp with RIAA curve. it is based on one 7025. (12AX7) I would think the 12AU7 was a bit low gain for the application. Very simple circuit. You would need one per channel. SO two 12AX7 and a handful of small parts. You also need power supply.
You could probably make something with one 12AX7, but I don't see how you could get RIAA that way.
You could probably make something with one 12AX7, but I don't see how you could get RIAA that way.
Gday.
Ohashi looks interesting,
with 3x12AX7/ECC83 and 12. res/log , 4. cap`s
it`s "low part". Haven`t a clue about the sound,
but i assume minimal use of passive components
can speak for quality. It shouldn`t sound worse than AR SP3
i reckon. Have you looked at the phono stage of the
Audio Innovation 500.
Ohashi looks interesting,
with 3x12AX7/ECC83 and 12. res/log , 4. cap`s
it`s "low part". Haven`t a clue about the sound,
but i assume minimal use of passive components
can speak for quality. It shouldn`t sound worse than AR SP3
i reckon. Have you looked at the phono stage of the
Audio Innovation 500.
Attachments
Konnichiwa,
Well, the 12AU7 is not particulary useful in a Phonostage.
If you can scrounge up a single ECC83/12AX7 and a single ECC88/E88CC/6922 you could build the Phonostage I described here:
http://www.diyaudio.com/forums/showthread.php?postid=335624#post335624
The thread following on has a lot of discussion on this, suitable PSU, implementation etc....
Sayonara
Rockmonton said:
Well, the 12AU7 is not particulary useful in a Phonostage.
If you can scrounge up a single ECC83/12AX7 and a single ECC88/E88CC/6922 you could build the Phonostage I described here:
http://www.diyaudio.com/forums/showthread.php?postid=335624#post335624
The thread following on has a lot of discussion on this, suitable PSU, implementation etc....
Sayonara
Simple 12AX7 / ECC83 Phono Preamp
I will likely give the RCA schemtic a whirl with 12AX7.
Here is another simple design I came across:
http://www.turneraudio.com.au/htmlwebpgs02/schemsimplephono.htm
I will likely give the RCA schemtic a whirl with 12AX7.
Here is another simple design I came across:
http://www.turneraudio.com.au/htmlwebpgs02/schemsimplephono.htm
Attachments
The "RCA circuit with RIAA Eq"
I have that('66 RCA tube manual), that schematic, and I would like to consctruct that phono preamp to connect my phonograph directly to my headphone preamp.
I can build it; it is a very simple circuit.
BUT...
QUESTIONS...
The +250V; where does it come from (this question goes for all 12AX7/7025-based preamps)? Can I incorporate a solid-state voltage control? I need to build a self-contained preamp; a unit that goes on it's own shelf.
If I was put in an empty room and told that I needed to construct this thing I would use a 250 V transformer and a couple of diodes wired for full-wave rectification. I wouldn't know how to filter the voltage, so as to make it a "smooth", or "constant" 250 V, though.
OTHER QUESTIONS...
Is -V applied to anything?
Is any voltage applied to the heater of the tube?
If anyone has an answer could they please post a detailed message or simple shematic on the subject of the +V control?
Should I know the answer to all these questions by now?
Thanks,
Trevor
I have that('66 RCA tube manual), that schematic, and I would like to consctruct that phono preamp to connect my phonograph directly to my headphone preamp.
I can build it; it is a very simple circuit.
BUT...
QUESTIONS...
The +250V; where does it come from (this question goes for all 12AX7/7025-based preamps)? Can I incorporate a solid-state voltage control? I need to build a self-contained preamp; a unit that goes on it's own shelf.
If I was put in an empty room and told that I needed to construct this thing I would use a 250 V transformer and a couple of diodes wired for full-wave rectification. I wouldn't know how to filter the voltage, so as to make it a "smooth", or "constant" 250 V, though.
OTHER QUESTIONS...
Is -V applied to anything?
Is any voltage applied to the heater of the tube?
If anyone has an answer could they please post a detailed message or simple shematic on the subject of the +V control?
Should I know the answer to all these questions by now?
Thanks,
Trevor
Re: The "RCA circuit with RIAA Eq"
Konnichiwa,
May I STRONGLY urge you to read the Phonopreamp Thread I referred to earlier?
http://www.diyaudio.com/forums/showthread.php?postid=526022#post526022
You may find most of your answers there.
Sayonara
Konnichiwa,
Sir Trefor said:
May I STRONGLY urge you to read the Phonopreamp Thread I referred to earlier?
http://www.diyaudio.com/forums/showthread.php?postid=526022#post526022
You may find most of your answers there.
Sayonara
Yes... I am getting closer
Thank you, Keui
The thread was very long, and I have difficulty maintaining focus while reading something as aimless as a forum thread, but I did gather some things from it.
I also did what I should have done before posting; I checked my personal resources.
I found out that the heater of a 12AX7 is powered by AC/DC 12.6V(series), 6.3V(parallel). That answers one question.
I will post more later.
Thank you, Keui
The thread was very long, and I have difficulty maintaining focus while reading something as aimless as a forum thread, but I did gather some things from it.
I also did what I should have done before posting; I checked my personal resources.
I found out that the heater of a 12AX7 is powered by AC/DC 12.6V(series), 6.3V(parallel). That answers one question.
I will post more later.
I have attached a shematic I made that shows the extent of my knowledge of voltage control; rectification- that's all I know. But Keui, did you mention that a 100% regulated is not necassarily crucial to the tube's function? According to "A Taste of Tubes"(pub. by Sonic frontiers in 1998) A Voltage regulator consists of a (1)trasformer, (2)rectifier, (3)Filter, (4)regulator, and a (5)bleeder/divider. That explantion also includes a helpful schematic; but the schematic uses several tubes and appears needlessly complex for this application.
What is an RC filter? NOT what does and RC filter do... what is it physically composed of? Is it similar to a capacitor?
What is an RC filter? NOT what does and RC filter do... what is it physically composed of? Is it similar to a capacitor?
Attachments
Re: Correction
Konnichiwa,
An RC filter is composed out of R(esistor) and C(apacitor) elements. I gave an example (including circuit diagram and performance graphs) in the cited thread that allows a simple passive supply to be build for the Phonocircuit I recommend and which has a noise performance by far superior to ANY active regulation circuit and which offers much better transient load tolerance etc, at the price of a few capacitors and resistors of moderate quality.
You also want to supply the Valve heaters of the phonocircuit with DC to avoid noise from the heaters coupling into the signal circuit. A simple regulated 6V supply is sufficient.
BTW, the simplicity of the circuit I suggest, also of it's powersupply is rather deceptive, the performance is very high.
Sayonora
Konnichiwa,
Sir Trefor said:
An RC filter is composed out of R(esistor) and C(apacitor) elements. I gave an example (including circuit diagram and performance graphs) in the cited thread that allows a simple passive supply to be build for the Phonocircuit I recommend and which has a noise performance by far superior to ANY active regulation circuit and which offers much better transient load tolerance etc, at the price of a few capacitors and resistors of moderate quality.
You also want to supply the Valve heaters of the phonocircuit with DC to avoid noise from the heaters coupling into the signal circuit. A simple regulated 6V supply is sufficient.
BTW, the simplicity of the circuit I suggest, also of it's powersupply is rather deceptive, the performance is very high.
Sayonora
A very simple low parts count RIAA pre-amp I know of consist of just a single EF86 per channel....
It actuallt sounds much better than the crudy RCA ones...
The RCA ones are slow sounding and distorted....total lack of detail and air....not to mention the time constantsd were off the mark..
If interested let me know I will post it...
Chris
It actuallt sounds much better than the crudy RCA ones...
The RCA ones are slow sounding and distorted....total lack of detail and air....not to mention the time constantsd were off the mark..
If interested let me know I will post it...
Chris
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