Hi Guys,
I have been aske by one of my customers about designing a transistor 12 band graphic eq. My first idea was to use gyrators but the customer stated that he wanted to use active LC filter with discrete transistors. I do not have any experience with that but this is the result that LT Spice is showing. What do you think about that or do you have any experience with that? Thank you very much.
I have been aske by one of my customers about designing a transistor 12 band graphic eq. My first idea was to use gyrators but the customer stated that he wanted to use active LC filter with discrete transistors. I do not have any experience with that but this is the result that LT Spice is showing. What do you think about that or do you have any experience with that? Thank you very much.
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I think this design space has been well covered by many commercial manufacturers, Soundcraftsman, MXR and others. I'd look at those schematics and whatever published performance info you can find. They did what they did for a reason and deciding on a circuit without understanding the effect on noise, dynamic range and such is the hard way to do it.
That circuit has 4 poles - each L and each C contribute one pole. A standard resonator would be 2-pole, ie an RLC circuit - you don't want a high Q and you want minimal phase variation so 2-poles should be prefferable to 4-poles (and more tractable).
Isn't this Schiit Loki Max what your customer is asking for?
https://www.schiit.com/products/loki-max
"Pure LC Equalization
On our more affordable tone controls like Loki Mini and Lokius, we use gyrators to simulate an inductor on the lower frequency bands. This is because big inductors—and we’re talking 0.5H and 1.5H in Loki Max—are physically large and expensive. To get the performance we needed, we had to specify 80% nickel cores, making things even more exotic. But the result is that every band of Loki Max—from 20Hz to 16kHz—uses nothing but LC filtering."
https://www.schiit.com/products/loki-max
"Pure LC Equalization
On our more affordable tone controls like Loki Mini and Lokius, we use gyrators to simulate an inductor on the lower frequency bands. This is because big inductors—and we’re talking 0.5H and 1.5H in Loki Max—are physically large and expensive. To get the performance we needed, we had to specify 80% nickel cores, making things even more exotic. But the result is that every band of Loki Max—from 20Hz to 16kHz—uses nothing but LC filtering."
@Tom Vyborny
This is much easier to do with op amps and will get you better performance too. Maybe this link will give you some ideas.
https://sound-au.com/project75.htm
This is much easier to do with op amps and will get you better performance too. Maybe this link will give you some ideas.
https://sound-au.com/project75.htm