Low Voltage Tube Solidstate Guitar preamp design ...

Minion · 22nd April 2009, 01:36 AM

Hi, I am trying to come up with a pretty simple Tube guitar preamp design ... I"m not good with tubes (not even good with solid state) but I came up with a design borrowing parts from other designs with some other ideas thrown in ....

I was wondering if you guys would take a quick look and tell me if if would work ....

The first stage is a basic Non-inverting opamp which is intended to give a signal boost to help overdrive the Tube stage ....

The next stage is a 12ax7 Dual triode , it runs off of a 65v Plate voltage and 12 for the heaters ... it has a Pot between triodes to controll the signal going to the second triode ....

The next stage is just a simple Non-Inverting buffer with a bit of gain , it is to give a low inpedance signal to the next Inverting stage ...

The next stage is a Inverting Active 3 band tone controll , the purpose is well, to controll the tone ....

I know it is probably a pretty crappy design but will is work ??

Thanx a Lot guys/gals ....

Chris

Wavebourn · 22nd April 2009, 01:54 AM

Try to experiment: move the 1'st opamp on place of the 2'nd one, with additional diodes in deedback (2 in series in one direction, and the 3'rd one in another direction in parallel with them). Such a way you may get more "tubey" overdrive.

As the result, you will have a tube preamp and a diode overdrive that gives nice logarythmic asymmetrical curves.

Minion · 22nd April 2009, 02:59 AM

Hi Wavebourn ... Luv yer work... Thanx for the Tips...

Most of the Guitar amps I have built have been solid state and I usually use Diodes as clippers (symetrical and asymetrical) so I was thinging about adding some clipping doides (Red LED"s are My Favorite) ...

But overall does the design look like it will work ?? at least put out sound ??

I was going to put it in front of a Bridged 150W TDA7293 Power amp , I built an amp recently which this design is based which sounds awesome , accept It was a PAIA Kit and a 15 band EQ and a single TDA7293 (they sound good in guitar amps as they actually sound good when clipped and bit) ...

Thanx a Lot...

Wavebourn · 22nd April 2009, 03:19 AM

You are welcome.
Try both ways and listen. I did not check tubes' working points, though... But I believe that your buffer will start saturating before tubes even approach their voltage limit.

firechief · 22nd April 2009, 03:17 PM

Minion
I would think that the AC signal on the plate of the second tube section would be 20+ volts P t P and that is too much for the op-amp to handle. Perhaps you don't need the second op-amp at all. By the way, can you point me to the values on the tone controls you have used? I cant quite view the drawing well enough.

Minion · 23rd April 2009, 12:31 AM

I don"t know what the output signal voltage from the second tube stage will be but the design I borrowed the Tube stage from has an opamp buffer after the tube stage so I think it should work ...

As for the tone controll section here is a bigger picture ...

Cheers

PS: here is the schematic I coppied the tube stage from with some minor modifications....

http://www.paia.com/prodimages/siabsch.pdf

leadbelly · 23rd April 2009, 12:59 AM

Quote:

Originally posted by Minion
I don"t know what the output signal voltage from the second tube stage will be but the design I borrowed the Tube stage from has an opamp buffer after the tube stage so I think it should work

You should be OK. The cathode resistors on the tube are unbypassed so the gain won't be so high.

Minion · 23rd April 2009, 02:13 AM

Hi, Thanx , Would I get more gain if I put a capacitor in paralell with the cathode resistor ?? What Value for how much gain ?? Just out of curiosity ...

Cheers

leadbelly · 23rd April 2009, 02:54 AM

Quote:

Originally posted by Minion
Hi, Thanx , Would I get more gain if I put a capacitor in paralell with the cathode resistor ?? What Value for how much gain ?? Just out of curiosity

Well, if you put one there you'll probably overload one of the opamp stages as firechief suggested. You can put a 20-25uF there if you want to try. If you do your gain will be close to 100 for that triode.

gingertube · 23rd April 2009, 04:38 AM

While it is not completely low voltage the Hughes and Kettner Tubeman schematic might be worth looking at for some ideas.
It was discussed on this thread (with links to schematics).
H&K Tubeman Circuit Questions (added schematics!)
Cheers,
Ian

22nd April 2009, 01:36 AM	#1
Minion diyAudio Member Join Date: May 2006	Low Voltage Tube Solidstate Guitar preamp design ... Hi, I am trying to come up with a pretty simple Tube guitar preamp design ... I"m not good with tubes (not even good with solid state) but I came up with a design borrowing parts from other designs with some other ideas thrown in .... I was wondering if you guys would take a quick look and tell me if if would work .... The first stage is a basic Non-inverting opamp which is intended to give a signal boost to help overdrive the Tube stage .... The next stage is a 12ax7 Dual triode , it runs off of a 65v Plate voltage and 12 for the heaters ... it has a Pot between triodes to controll the signal going to the second triode .... The next stage is just a simple Non-Inverting buffer with a bit of gain , it is to give a low inpedance signal to the next Inverting stage ... The next stage is a Inverting Active 3 band tone controll , the purpose is well, to controll the tone .... I know it is probably a pretty crappy design but will is work ?? Thanx a Lot guys/gals .... Chris

22nd April 2009, 01:54 AM	#2
Wavebourn diyAudio Member Join Date: Sep 2006 Location: Pleasant Hill, CA	Try to experiment: move the 1'st opamp on place of the 2'nd one, with additional diodes in deedback (2 in series in one direction, and the 3'rd one in another direction in parallel with them). Such a way you may get more "tubey" overdrive. As the result, you will have a tube preamp and a diode overdrive that gives nice logarythmic asymmetrical curves. __________________ If I disappear suddenly, that means I finally created a time machine and pushed wrong button that brought me to Stalin's Russia. In any experiment any result is the result. Even if it is negative.

22nd April 2009, 03:19 AM	#4
Wavebourn diyAudio Member Join Date: Sep 2006 Location: Pleasant Hill, CA	You are welcome. Try both ways and listen. I did not check tubes' working points, though... But I believe that your buffer will start saturating before tubes even approach their voltage limit. __________________ If I disappear suddenly, that means I finally created a time machine and pushed wrong button that brought me to Stalin's Russia. In any experiment any result is the result. Even if it is negative.

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22nd April 2009, 02:59 AM	#3
Minion diyAudio Member Join Date: May 2006	Hi Wavebourn ... Luv yer work... Thanx for the Tips... Most of the Guitar amps I have built have been solid state and I usually use Diodes as clippers (symetrical and asymetrical) so I was thinging about adding some clipping doides (Red LED"s are My Favorite) ... But overall does the design look like it will work ?? at least put out sound ?? I was going to put it in front of a Bridged 150W TDA7293 Power amp , I built an amp recently which this design is based which sounds awesome , accept It was a PAIA Kit and a 15 band EQ and a single TDA7293 (they sound good in guitar amps as they actually sound good when clipped and bit) ... Thanx a Lot...

22nd April 2009, 03:17 PM	#5
firechief diyAudio Member Join Date: Sep 2008 Location: Near Seattle Wa	Minion I would think that the AC signal on the plate of the second tube section would be 20+ volts P t P and that is too much for the op-amp to handle. Perhaps you don't need the second op-amp at all. By the way, can you point me to the values on the tone controls you have used? I cant quite view the drawing well enough.

23rd April 2009, 12:31 AM	#6
Minion diyAudio Member Join Date: May 2006	I don"t know what the output signal voltage from the second tube stage will be but the design I borrowed the Tube stage from has an opamp buffer after the tube stage so I think it should work ... As for the tone controll section here is a bigger picture ... Cheers PS: here is the schematic I coppied the tube stage from with some minor modifications.... http://www.paia.com/prodimages/siabsch.pdf

23rd April 2009, 02:13 AM	#8
Minion diyAudio Member Join Date: May 2006	Hi, Thanx , Would I get more gain if I put a capacitor in paralell with the cathode resistor ?? What Value for how much gain ?? Just out of curiosity ... Cheers

23rd April 2009, 04:38 AM	#10
gingertube diyAudio Member Join Date: Oct 2004 Location: Adelaide South Oz	While it is not completely low voltage the Hughes and Kettner Tubeman schematic might be worth looking at for some ideas. It was discussed on this thread (with links to schematics). H&K Tubeman Circuit Questions (added schematics!) Cheers, Ian

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