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Old 25th March 2004, 12:12 PM   #1
svokke is offline svokke  Belgium
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Default check my simple circuit

I want a solid state phase splitter in a tube amp. I can't use a tube, because my transformer can't supply more heater current.
This is my first solid state phase invertor, so please check if it will explode, do nothing useful or work.
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Old 25th March 2004, 12:17 PM   #2
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I suggest that you simulate this in the freeware LTSpice. What type specs do you want? Have you calculated gain, bandwidth etc?

Yes, it looks not exactly right but it depends of what you were thinking of.
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Old 25th March 2004, 12:42 PM   #3
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it will work (may not optimally tho.).

I would replace R3 with a current source.
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Old 25th March 2004, 03:55 PM   #4
azira is offline azira  United States
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First question, only because I don't feel like looking up the datasheet, will those transistors support a Vce of 220?

Ok, you've got 120k of resistance per leg. From a 220 volt source, that's 1.83mA of bias current. That's reasonable. But the collectors of your Qs is at 37Volts. This means your +/- swing will be limited on the - side. You should try and bias the collectors at 1/2 VCC.

Secondly, since you've got 100k of collector resistance, your gain is going to be pretty high (gm*Rc ~ 7800) so your input signal level will be very sensitive.

Do you just need a phase splitter? You might want some emitter resistance. If you make Rc and Re about equal, you'll have something that does a gain of 1. Maybe split up your 100k into 2 50ks. You'll have to adjust your bias a bit.
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Old 25th March 2004, 04:04 PM   #5
zobsky is offline zobsky  India
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Default Re: check my simple circuit

Quote:
Originally posted by svokke
I want a solid state phase splitter in a tube amp. I can't use a tube, because my transformer can't supply more heater current.
This is my first solid state phase invertor, so please check if it will explode, do nothing useful or work.

i was thinking of a similar thing in my post http://www.diyaudio.com/forums/showt...069#post353069 , ..although this would be close to the input (maybe preceeded by a tube buffer)

the downside is that you would require a +/- 15V supply for the DRV134 line driver / phase splitter opamp

if tube heater current is your only limitation, why not just buy a small filament transformer to address that issue?


the one (really dumb and naive) question i have about this opamp (not being a SolidState DIY'r) is "what governs the output voltage of the line driver, the input or the supply voltage?"


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Old 25th March 2004, 06:19 PM   #6
svokke is offline svokke  Belgium
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I tried simulatin the circuit using LTSpice, but I didn't succeed in that. I just couldn't get 2n6517 to work in the program. So I simulated it with the demo version of circuitmaker.

Quote:
I would replace R3 with a current source.
I used a current source made of a lm317 regulator. It simulates a lot better than a plain transistor in the tail position. I can't use it in the real world though because it needs more current going through it to work well. What kind of current source would you recommend?

Quote:
Secondly, since you've got 100k of collector resistance, your gain is going to be pretty high (gm*Rc ~ 7800) so your input signal level will be very sensitive
In my simulations, gain is 31 (with a current source as tail) I think this is ok, the tube counterpart in fender/marshall/vox amps has an even larger gain.

Quote:
First question, only because I don't feel like looking up the datasheet, will those transistors support a Vce of 220?
Vce max is 350V for this transistor
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