Valve phono stage for loan - want to try it?

[Barry]

Is your phonostage based on the Ming Da circuit?



It doesn't look like it uses passive equalisation.

Looking forward to reading the borrower's feedback.

[Frankyc2003]

Yes that appears to be the correct diagram.

[Firebottle]

Is your phonostage based on the Ming Da circuit?
It doesn't look like it uses passive equalisation.

Looking forward to reading the borrower's feedback.

No nothing like Barry, and yes you're right the Ming Da is active equalisation using the feedback path.
I didn't want to just regurgitate a published circuit, so I took the same approach that I did with my OTL design. I studied previous designs and gave a lot of thought to developing a simple circuit, particularly with concern for proper matching of the equalisation section.
I'm also very much looking forward to others feedback

When I draw out the circuit tidily I will post it up if you're interested.

Alan

[Barry]

No nothing like Barry, and yes you're right the Ming Da is active equalisation using the feedback path.
I didn't want to just regurgitate a published circuit, so I took the same approach that I did with my OTL design. I studied previous designs and gave a lot of thought to developing a simple circuit, particularly with concern for proper matching of the equalisation section.
I'm also very much looking forward to others feedback

When I draw out the circuit tidily I will post it up if you're interested.

Alan

Thanks Alan,

I would be very interested to have a look at your circuit. Would it be possible to adapt it to a fully balanced design?

Thanks again

[Firebottle]

Hi Barry,

I don't think adaption to fully balanced design would be possible without virtually doubling up the circuit

Here it is:


A couple of points on the design;
I have used LED biasing on the pentode stage to keep the bias really stable. I don't know what difference it might make to the sound, if any.

I have reduced the value of the series equalisation resistor to accommodate the output impedance of the pentode, for more accurate equalisation.

The grid blocking capacitor is after the equalisation network so that a lower value can be used. If it was before the network the value would have to be huge so to not affect the low frequency response. The only drawback with this approach is the equalisation capacitors need to be rated for full HT voltage.

I have doubled up the output capacitor rather than use one of larger value. This helps to lower the ESR, to improve the high requency performance.

Alan

[Firebottle]

Would it be possible to adapt it to a fully balanced design?

I have been thinking about this (it keeps the mind active), and have drawn out a balanced circuit.
I have only checked it as far as the biasing goes, so if you do try it please let us know how you get on.



I have accommodated the output impedance of the first '83 and the miller capacitance of the second '83 in the component values. It would be interesting to know how it performs;

Cheers Alan

[Barry]

Thanks Alan.

It looks interesting. What is the overal gain at 1KHz? I assume it is suitable only for MM cartridges.

Thanks agin

[Firebottle]

The gain at 1KHz is x 250.
You could certainly try the circuit with MC carts, it may be a little noisy though, I haven't any experience with MC.

Just put a 100 ohm resistor across the inputs to try it

Cheers, Alan

[Firebottle]

Tarzan has posted his review of my pre-amp at this post
http://theartofsound.net/forum/showthread.php?t=24413

Frankyc2003 if you could PM Tarzan with your address he will post it on to you.

Alan

[Tarzan]

Tarzan has posted his review of my pre-amp at this post
http://theartofsound.net/forum/showthread.php?t=24413

Frankyc2003 if you could PM Tarzan with your address he will post it on to you.

Alan

l did indeed- and l liked it!