[ctechdx]

Hello folks,

I was looking for a diy tube preamp project, and found out this one which i think could be even better, but im newbie on this and need some opinions about.

I found a tube tone control baxandall. I want something that gives me some tube coloration and de bax filters is a plus coz i can shape sounds even further.

This pcb is being selled in eBay and Amazon. The sellers says its a good quality circuit, made to be built with good components.

I want to hear from u guys, what u think about this project. Can It give me some coloration + bax filters with a good audio quality?

Thanks,

[ctechdx]

Here is the product info:

"This is a bare PCB of a low noise , tube based tone control stereo amplifier by means of two low noise triode tubes 12AX7.
 
The board is designed with high quality components in mind, including Wima film capacitors, silver mica capacitors,Philips electrolytic filtering capacitors, low noise metal film resistors and Mallory decoupling capacitors. Being a bare PCB, users can put in their components of their preference.
The board only requires a +250Vdc input voltage and 6.3V filament voltage.
 
Board thickness : 1.6mm, gold plated surface
PCB Dimension : 95mm x 108mm
 
Finishing : double-sided solder resist for best durability and reliability."

[scott2000]

Not sure it would be too far from playing with your home stereo with tone controls....(like bass and treble)

Maybe it could be something....Maybe  more of a makeup amp for the tone controls ...

Not sure you'd hear anything extraordinary outside of the tone control shaping... or you get some hum from your power supply depending....

But color can be abused out of a bunch of things .......  may jump from one end of the color wheel to the other real quick trying though...

[abbey road d enfer]

I want to hear from u guys, what u think about this project. Can It give me some coloration + bax filters with a good audio quality?

This kit seems to be reasonably built and the schemo is adequate. I don't really know what you expect but, as already mentioned, don't expect something spectacular. Note that the circuit inverts polarity (a positive signal comes out negative) so you may have to compensate that inversion in the rest of the chain.

[ruffrecords]

Also the output impedance of the circuit is quite high - probably in the region of 50K - so you  will need to feed it into something like a DI box or add a buffer to the output.

Cheers

Ian

[abbey road d enfer]

Also the output impedance of the circuit is quite high - probably in the region of 50K - so you  will need to feed it into something like a DI box or add a buffer to the output.

Cheers

Ian

Not really. The output stage is under large NFB (when set at neutral). The actual output Z is about 1-5k depending on amount of B/C.
But you're right, a buffer is desirable, and it being inverting is too.

[ruffrecords]

Not really. The output stage is under large NFB (when set at neutral). The actual output Z is about 1-5k depending on amount of B/C.
But you're right, a buffer is desirable, and it being inverting is too.

I should have said drive capability. As we all know, small signal output impedance is no indicator of drive capability.

Cheers

Ian

[Michael Tibes]

What might be the level that circuit can handle? And maybe add a simple cathode follower to lower the output impedance?

Michael

[abbey road d enfer]

What might be the level that circuit can handle? And maybe add a simple cathode follower to lower the output impedance?

Michael

Although a cath-follower has a low output Z, often it does not have much more drive capability than this Baxendall circuit. For wanting a much higher drive, the cath-follower should operate with about 10 mA of quiescent current, with a dissipation of about 1W in the tube. A White follower would be more suitable. For good measure it should be preceded with an inverter.

[ruffrecords]

As Abbey suggests a buffer preceded by an inverter would be ideal which basically means two more triodes. One way to achieve this is to use an SRPP stage. This has excellent drive capability and also some gain. However, their distortion is quite high. To reduce this to acceptable levels you can use some NFB to create a unity gain inverting buffer.

Cheers

Ian

[Michael Tibes]

Although a cath-follower has a low output Z, often it does not have much more drive capability than this Baxendall circuit. For wanting a much higher drive, the cath-follower should operate with about 10 mA of quiescent current, with a dissipation of about 1W in the tube. A White follower would be more suitable. For good measure it should be preceded with an inverter.

Wow, one never stops learning! I guess there are hundreds of websites and dozens of books which recommend cathode followers as output stages because of their drive capabilities. Great to have some helpful people here who really understand things :-))

Michael

[Rocinante]

I am curious, as I too like learning this, are there any examples you guys think would be a good contender for the output stage?

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