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Old 19th April 2013, 10:48 PM   #11
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Hey Jaz, yeah that's the same schematic we're talking about - trying to figure out where/how to have boost/cut for the treble section. Got any ideas on that one? And I'm assuming the pot just before the 2nd tube grid is boost/cut for bass. Perhaps the treble pot should go to the center lug of the treble Q pot? Just guessing at this point...

i have always had a super hard time doing a sim with tubes in it! i must practice...
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Old 21st April 2013, 03:11 AM   #12
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Duh, I did not read the earlier posts, and missed the link. I ran a quick sim on the circuit, and saw there is a huge dip in the mid band that none of the controls seems to able to get rid off, need to play with it some more when I get more time... While it's an interesting design challenge, but if I were to actually build one, I would just use opamps instead of tubes...
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Old 21st April 2013, 04:27 AM   #13
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hey Jaz, thanks for giving it a run. What sim software are you using and would you be willing to post the file? I'd love to actually see a Tube sim running for once! I figured I'd try a tube EQ instead of SS just for the fact that you're getting the tubey gain for whatever frequency you're boosting, just another flavor available, i guess.
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Old 21st April 2013, 10:38 AM   #14
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Quote:
Originally Posted by Gonecat View Post
hey Jaz, thanks for giving it a run. What sim software are you using and would you be willing to post the file? I'd love to actually see a Tube sim running for once! I figured I'd try a tube EQ instead of SS just for the fact that you're getting the tubey gain for whatever frequency you're boosting, just another flavor available, i guess.
I sim'd it with TINA-TI, but any of the simulators should work if you have the tube models. Anyway, I should have access to my home PC in a few days once I return from my road trip... If you have LTSpice, you can join the Yahoo user group and download a few tube amp sims, so you can see how the circuits and models work. Are you planning to use the eq in the studio?

Jaz
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Old 21st April 2013, 05:58 PM   #15
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Hi Jaz, I do have have LTSpice and am on the Yahoo Group. I downloaded some tube models and example asc files to get a feel for it. Would definitely love to see the sim you did for this one, though today I might just try my hand at it from scratch in a renewed effort to learn this beast!

What do you do on LTSpice to be able to see that notch?

Yes, in the studio as an outboard device, so I'm assuming I'll need a cathode follower on the output? I think this was meant to head straight into a power amp.

Have fun on the road!
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Old 22nd April 2013, 12:42 AM   #16
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I only ran the AC transfer function analysis with TINA, the same could be done in LTSpice, you can even break up the two sections to see each one in action. Yes, a cathode follower and/or inter-stage transformer is probably a good idea to buffer the output to the next stage.
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Old 22nd April 2013, 01:20 AM   #17
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I built the schematic out as a sim in LTSpice today...but i have no idea what to put as the output! :0 I have a sine at 400hz as the input signal. Looking forward to seeing how you did this...
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Old 22nd April 2013, 07:44 AM   #18
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Originally Posted by jazbo8 View Post
Take a look at this. Try sim it first, it may require some modifications, but should get you started.

Jaz
Something looks a bit wrong to me with this circuit. If you turn the treble Q fully to the right it shorts the grid of the second tube to ground so there will be no output.

Cheers

Ian
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Old 22nd April 2013, 09:21 AM   #19
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Originally Posted by ruffrecords View Post
Something looks a bit wrong to me with this circuit. If you turn the treble Q fully to the right it shorts the grid of the second tube to ground so there will be no output.

Cheers

Ian
Hi Ian,

Yup, the circuit does not work that well, wonder if we are only seeing a part of the overall circuit, need to dig into it some more when I get home. Steve Conner did a complicated hybrid design (just for fun!) that can be seen here.

Jaz
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Old 22nd April 2013, 10:10 AM   #20
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Gonecat,

I don't use LTSpice but here is the screen shot of the circuit I built in TINA, the output (VM1) is taken at the second tube's plate as indicated on the original schematic. In any case, I found this on MEF, which may explain why there aren't many gyrator-based tube EQ floating around. So may be that's the way to go - build a IC/JFET gyrator EQ section buffered by tube input and output, instead of trying to build a tube gyrator EQ section given the challenges it faces... Anyway, we still need to figure out why the posted schematic does not work as claimed... May be we can all learn something from it.

Jaz
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