Split-Load Gyrator EQ

[directdriver]

I've been fascinated by EQ circuits lately. Typically I see tube circuits like the ones below using gyrator in a feedback circuit:

And then I see ones using split-load circuit with inductors.

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

And curiously a split-loading in solid state.

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My question is that can I replace the split-load driver with an input transformer and then couple one phase or both phases to one cathode follower for single ended or two cathode follower for balance output?

 

[stocktrader200]

Q1 is for impedance matching , Q2 is a phase splitter with gain, Q3 Q4 form a gain stage of approx 25 times.
Q2 could be 6Dj8 as well as Q3, Q4 replaced by other half.
you could also drive a passive tone control with 6922 using enough gain to overcome insertion loss ~20db.

 

[directdriver]

Thank you for your response.

If a pot for each band is 10K then 10 pots in parallel would present a 1K load to the split-load circuit. Will a tube like 6DJ8 able to drive that? Does it matter?

Can I use a transformer to replace the split-load tube or Q2?

 

[PRR]

....can I replace the split-load driver with an input transformer......?

No. Split-load with different loading each side is NOT equivalent to CT transformer. Note that when you put a heavy load on the cathode side, gain to the plate goes *up*. And that you can get like 10:1 boost this way (say 50k cathode resistor and <5k in series with the tuned circuit).

 

[directdriver]

Thanks for the reply, PRR. I was hoping you would reply because I saw your post one of the EQ circuit in another forum. I learned from SY that a split-load/cathodyne/concertina phase splitter requires equal load on both phases to have perfect balance. What if I use an input transformer and a long tail pair as the next stage will that simulate the above the circuit? Btw, the above circuit uses only one phase to drive the next stage in single ended, wouldn't that throw off the balance? I noticed in the solid state circuit the two resistor in the split-load resistors are not equal. Is that on purpose to offset the load on side?

 

[stocktrader200]

i would use 25 to 50k pots but 10k would work with 6922

 

[directdriver]

i would use 25 to 50k pots but 10k would work with 6922

Does increasing the pots' values affect the values of the gyrator parts, the caps and chokes? Using 10K because they are inside an existing EQ already so prefer to not have to change that. I am contemplating modifying a solid state EQ into using tubes and transformers to have balance in and balance out.

Thanks again for the info.

 

[PRR]

...a split-load/cathodyne/concertina phase splitter requires equal load on both phases to have perfect balance. ...the above circuit uses only one phase to drive the next stage in single ended, wouldn't that throw off the balance? I noticed in the solid state circuit the two resistor in the split-load resistors are not equal. Is that on purpose to offset the load on side?

Did you do the math? 5.1K one side. 5.6K||56.6K on the other. But there is gain after the volume pot. "Unbalance" would only mean not unity gain, but gain is trimmable.

Most of this can be worked out with basic voltage-divider analysis. Not that hard, but maybe tedious.

 

[gingertube]

For reference:

http://www.ti.com/lit/an/slyt134/slyt134.pdf

Audio Graphic Equalizer Circuit

Cheers,
Ian

 

[directdriver]

Thanks for all the info!

I don't plan to use gyrator circuits to simulate inductors. I wish I could delete the word Gyrator from the title. Most EQ circuits use the feedback type but I am intrigued by the simplicity of the split-load circuit as it reminds me of a transformer.


I want to use an existing solid state EQ with the following circuit including all the passive components like inductors and slider pots which are 10K each. My goal is to replace all the transistors with tube or transformer in the signal path....

The below is what I have in mind and I wonder if this will work. Can the solid state split-load circuit be replaced with a tube or transformer (600Ω:600Ω or 10KΩ:600Ω)? Please ignore the solid state output circuit as that can be replaced with a tube cathode follower or a tube gain stage with cathode follower to make up the gain and, perhaps, adding output transformer for balance output.