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Old 28th April 2008, 10:31 AM   #1
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Default *NEW* VBNIGC schematic

Hello. I was working on a VBNIGC and came up with this... Feel free to comment. All feedback is welcome. Circuit is fairly simple. Uses a 12au7 tube and a LM3875
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Old 28th April 2008, 02:19 PM   #2
BWRX is offline BWRX  United States
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Neither the valve buffer or the NIGC part is new, but it's still an interesting choice of parts.
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Old 28th April 2008, 05:13 PM   #3
troystg is offline troystg  United States
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Have you seen Digi's?

Franz, digi and another person collaborated on one some time ago..


VBITNGC building & comment
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Old 28th April 2008, 06:39 PM   #4
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Just a general comment that your project doesn't make sense. The ECC88/6922 in the original design makes a great cathode follower while the 12AU7 is only OK. So why go to the effort of trying to design with a tube that's worse for the job and requires a more complex power supply (i.e. can't use the chipamp rails)?
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Old 28th April 2008, 06:52 PM   #5
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As well... one of the rationales for adding the tube buffer was to close the feedback loop for the inverted gain clone -- yours is not an inverted gaineclone...

dave
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Old 1st May 2008, 03:56 AM   #6
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Quote:
Originally posted by leadbelly
Just a general comment that your project doesn't make sense. The ECC88/6922 in the original design makes a great cathode follower while the 12AU7 is only OK. So why go to the effort of trying to design with a tube that's worse for the job and requires a more complex power supply (i.e. can't use the chipamp rails)?
This is true. The 12AU7 will not work well with the chip's rail voltage. I only wanted to add a tube because I was interested in achieving the "tube sound" while utilizing this chip.

Quote:
Originally posted by planet10
As well... one of the rationales for adding the tube buffer was to close the feedback loop for the inverted gain clone -- yours is not an inverted gaineclone...

All the schematics i have seen are for the inverted setup. I was curious of the effects with a tube buffer and the Non-inverting setup.
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Old 1st May 2008, 04:45 AM   #7
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1st, you need a grid resistor of about 220k.

2nd, 12au7 tends to be a dull tube(I use many tubes/valves before), I prefer 12ax7. you can get good result from 12au7, however there are not many out that sound good, there many(brands) 12ax7 that sounds good.

12ax7 adds smooth sparkle to your system.

cheers happy listening.
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Old 1st May 2008, 05:21 AM   #8
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Quote:
Originally posted by ttan98
1st, you need a grid resistor of about 220k.

2nd, 12au7 tends to be a dull tube(I use many tubes/valves before), I prefer 12ax7. you can get good result from 12au7, however there are not many out that sound good, there many(brands) 12ax7 that sounds good.

12ax7 adds smooth sparkle to your system.

cheers happy listening.
Thanks for the info. I will try the 220k grid resistor and the 12ax7.
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Old 1st May 2008, 05:43 AM   #9
ttan98 is offline ttan98  Australia
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Quote:
Originally posted by roots600rr


Thanks for the info. I will try the 220k grid resistor and the 12ax7.
Change the cathode resistor as well, bias for about 1mA, if I remember correctly use 1kohm. That will give about 1mA, you see changing cathode curent will also affect the sound. Adjust the current to get the sound you want. Using 12ax7 the o/p impedance is about 1K, ok for GC like LM3875.Use a good quality coupling capacitor, >.22uF if you want to use 22k load on GC. Also you need about 110-120V on the anode of 2ax7 your supply voltage on yr diagram is not enough you will not get dynamics. If you want to use low supply voltage use, 6DJ8 lots around and of good quality and cheap. 6DJ8 needs about 90V anode.

I suggest you look at the net for proven circuits, many around and couple it to the GC, that way you will get good results otherwise you will have to play around with your own circuit.


happy playing around with this project, you will have lots of fun.
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Old 1st May 2008, 08:31 PM   #10
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Quote:
Originally posted by ttan98
12ax7 adds smooth sparkle to your system
I have to say that recommending a 12AX7 for a cathode follower is an unusual choice to say the least, and if this were posted in the Tubes forum you would likely be flamed.
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