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Old 12th June 2012, 10:14 PM   #31
tinitus is offline tinitus  Europe
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I dont understand why you choose to have passive output, by the tone control/eq/vol , and not at last use one of the tubes for that ?
and further you use a 1M ohm pot
is that good practice ?
6 tube stages, and then passive out, I dont get it
???

anyway, I think it would be better to use mosfets
as I understand it you should be able use almost similar schematic
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Old 13th June 2012, 03:47 AM   #32
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Originally Posted by tinitus View Post
anyway, I think it would be better to use mosfets
as I understand it you should be able use almost similar schematic
Are you suggesting he use mosfets through the whole amp or just the output buffer? If you mean for the whole amp, you're crazy. The 2nd harmonic distortion that tubes produce when pushed to grid current limit has no equivalent in the solid state world. It's all hard clipping and lots of odd harmonics.
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Old 13th June 2012, 07:50 AM   #33
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Originally Posted by doozerdave View Post
The 2nd harmonic distortion that tubes produce when pushed to grid current limit has no equivalent in the solid state world. It's all hard clipping and lots of odd harmonics.
well, yeah, I reckon it have been so, for many years
but I think its more of a myth today
those days might be over
you may not have noticed, but the ace might have changed hands over night
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Old 13th June 2012, 07:55 AM   #34
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Originally Posted by doozerdave View Post
If you mean for the whole amp, you're crazy.
hmm, no(yes)
I would suggest a 'hybrid', to give even more options

and further, in that respect, I put my money on a 2-channel system(not stereo), through out, speaker and all
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Old 13th June 2012, 12:37 PM   #35
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well, yeah, I reckon it have been so, for many years
but I think its more of a myth today
those days might be over
you may not have noticed, but the ace might have changed hands over night
Really? Has the response curve of transistors suddenly changed? I know there are lots of solid state amps out there with modeling to approximate the sound of classic tube amps, but it's still not the same. I know there are lots of great FET based amps, but there's a reason tubes are still produced today.
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Old 13th June 2012, 12:56 PM   #36
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I agree, I was grew up on SS. It's amazing I stuck with guitar after playing all that crap. I had lot's and lot's of "tube" effects over the years.

In my opinion, it is not practical to emulate tubes, it cost way too much and falls way to short. If your trying that hard, it's cheaper to just go tubed.
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Old 13th June 2012, 01:36 PM   #37
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Quote:
I dont understand why you choose to have passive output, by the tone control/eq/vol , and not at last use one of the tubes for that ? and further you use a 1M ohm pot is that good practice ?
Good practice? I don't know, but this is how many of the great classic amps are wired. The schematic doesn't reveal that the wiper of the 1 meg pot is usually connected to the grid of the PI.

Quote:
anyway, I think it would be better to use mosfets
I am not going anywhere near the tube VS solid state argument in the guitar amp domain. I have been building both for 45+ years, and I currently use both. Tubes and mosfets do behave quite differently when purposfully operated in their nonlinear regions. I have found that using a mosfet as a follower in an otherwise tube guitar amp design doesn't hurt the tone, and in some cases helps since the usual 12AX7 is a crappy follower. I often use a mosfet to drive the tone stack and maybe as the PI.

You can even use a mosfet buffer on a 12AX7 gain stage to increase the gain, but it DOES change the tone and overload characteristics. It makes for a more defined edge that might be good for a metal amp. It's up to the builder to find the sound he want, and it may take a good bit of tinkering to get there.
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Old 13th June 2012, 02:02 PM   #38
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Geez... I forget to check a thread for one evening and you guys go all OT on me.

Right, the tonestack will just feeding a typical cathodyne or long tailed pair phase inverter, not a power tube. As shown above is how it is done in pretty much all guitar amps I've seen. If I go with a cathodyne PI, I will have a free half of a 12AX7 to try a follower or gain stage after the tone stack.

I also have no interest in debating the SS vs Tubes argument. Both devices have their uses, and faults. When I do the layout for the turret board, I'm going to be leaving room for a FET based input buffer, and one to replace the cathode follower before the tone stack to free up V3B. This design will not be finalized for quite a long time, and will be my "test bed" for high gain preamps. The schematic above is merely my starting point.
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Old 13th June 2012, 02:13 PM   #39
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Quote:
Originally Posted by tubelab.com View Post
Good practice? I don't know, but this is how many of the great classic amps are wired. The schematic doesn't reveal that the wiper of the 1 meg pot is usually connected to the grid of the PI.



I am not going anywhere near the tube VS solid state argument in the guitar amp domain. I have been building both for 45+ years, and I currently use both. Tubes and mosfets do behave quite differently when purposfully operated in their nonlinear regions. I have found that using a mosfet as a follower in an otherwise tube guitar amp design doesn't hurt the tone, and in some cases helps since the usual 12AX7 is a crappy follower. I often use a mosfet to drive the tone stack and maybe as the PI.

You can even use a mosfet buffer on a 12AX7 gain stage to increase the gain, but it DOES change the tone and overload characteristics. It makes for a more defined edge that might be good for a metal amp. It's up to the builder to find the sound he want, and it may take a good bit of tinkering to get there.
George, ever used a CCS for increasing the gain of a 12AX7 gain stage? Would it be worthwhile to try for the first stage in a preamp like this?
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Old 13th June 2012, 03:08 PM   #40
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If I go with a cathodyne PI, I will have a free half of a 12AX7 to try a follower or gain stage after the tone stack.
I would say go cathodyne, and use the other half to boost the signal before the PI since the cathodyne has slightly lower than unity gain. You'll also want the anode voltage as high as possible on the cathodyne PI to keep your headroom up. If you don't already read "The Valve Wizard" site, there are a few good points to be careful of with the cathodyne PI shown on this page.

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Originally Posted by Stormrider View Post
I also have no interest in debating the SS vs Tubes argument. Both devices have their uses, and faults.
Sorry guys, I shouldn't have gone there. I wasn't going to, but I was full of energy early this morning. haha
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