*NEW* VBNIGC schematic

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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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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)?
 
leadbelly said:
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.

planet10 said:
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.
dave
 
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.
 
ttan98 said:
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.
 
roots600rr said:


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.
 
ttan98 said:
Marantz model 7 has all 12Ax7, incl. o/p stage 12ax7 as a cathode follower.

You'll find plenty of people who slam the M7 in the tube forum.

You'll find lots of 12AX7's in commercial designs because they were cheap, and there is a direct commercial benefit in simplifying the design by using as few different varieties of tubes as possible.

Really, defending a given tube by saying such and such commercial product uses it is like saying the 4558 is the greatest opamp ever made :)
 
leadbelly said:


You'll find plenty of people who slam the M7 in the tube forum.

You'll find lots of 12AX7's in commercial designs because they were cheap, and there is a direct commercial benefit in simplifying the design by using as few different varieties of tubes as possible.

Really, defending a given tube by saying such and such commercial product uses it is like saying the 4558 is the greatest opamp ever made :)

M7 is a Classic, after more than 30 years after it was released, there are so many clones around. Those who slam it, I like to ask them has any one of them design a classic? End of story.

12AX7 is easy to design, reasonably price, many high quality tubes from different made are available, and sounds fine to be, you may prefer other tube, lets agree to disagree. Please note, I did not say 12AX7 is the greatest tube around. There is no such this as greatest tube or op amp ever made.
 
ttan98 said:
M7 is a Classic, after more than 30 years after it was released, there are so many clones around. Those who slam it, I like to ask them has any one of them design a classic? End of story.

12AX7 is easy to design, reasonably price, many high quality tubes from different made are available, and sounds fine to be, you may prefer other tube, lets agree to disagree. Please note, I did not say 12AX7 is the greatest tube around. There is no such this as greatest tube or op amp ever made.

1) If you think that commercial products are the benchmark, I don't know why you are around DIY, and I recommend you stay away from DIY because you will save a ton of money by buying commercial products.

2) I never knocked the 12AX7, I just said that recommending one for a cathode follower is ridiculous advice. The key parameter for a cathode follower is good (high) transconductance, and the 12AX7 has just about the lowest transconductance of any tube ever used in audio. The M7 uses the 12AX7 because it's the cheapest way to make a phono stage, and they just extended it into the rest of the preamp stage so they wouldn't have the expense of using one more different tube.
 
leadbelly said:


1) If you think that commercial products are the benchmark, I don't know why you are around DIY, and I recommend you stay away from DIY because you will save a ton of money by buying commercial products.

2) I never knocked the 12AX7, I just said that recommending one for a cathode follower is ridiculous advice. The key parameter for a cathode follower is good (high) transconductance, and the 12AX7 has just about the lowest transconductance of any tube ever used in audio. The M7 uses the 12AX7 because it's the cheapest way to make a phono stage, and they just extended it into the rest of the preamp stage so they wouldn't have the expense of using one more different tube.


ebay M7 clones expensive! No. If you build from scratch, point-point wiring and gather parts, and compare with the clone which supply all the parts, there wouldn't be that much difference in price, furthermore it is easier for beginner to build via PCB which the clone supply.

I understand 12ax7 not suitable for cathode follower but if I design it correctly it will still sound good, read al the reasons I give above.
 
troystg said:
So again, why are you trying to re-invent the wheel? Digi and Franz already made one using the 6922 tube and 38xx chip.

No, about that I would agree that there's tons of room for improvement in the original 6922 design. IMHO the original is a bit of a joke since it's just tacking on a super simple tube circuit onto something that doesn't need it, and justifying it by making some handwaving arguments about how it is doing some really important task. If you want something special make the tube do the voltage amplification and make the chip act as a voltage follower.
 
leadbelly said:


No, about that I would agree that there's tons of room for improvement in the original 6922 design. IMHO the original is a bit of a joke since it's just tacking on a super simple tube circuit onto something that doesn't need it, and justifying it by making some handwaving arguments about how it is doing some really important task. If you want something special make the tube do the voltage amplification and make the chip act as a voltage follower.


Well, there you go, offer some advice on the tube component and I will start looking for a better way to implement the SS component.

I'm all for making something "better", but it appeared that this thread was going backwards not forwards.
 
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leadbelly said:
No, about that I would agree that there's tons of room for improvement in the original 6922 design. IMHO the original is a bit of a joke since it's just tacking on a super simple tube circuit onto something that doesn't need it, and justifying it by making some handwaving arguments about how it is doing some really important task. If you want something special make the tube do the voltage amplification and make the chip act as a voltage follower.

Actually the tube provides a very important function in this amp. When using the inverted version of a gainclone, everthing on the input side (including preamp or CD player on the input) becomes part of the feedback loop. The cathode follower is a very effective way of closing this short-fall off as it stops the loop at the tube.

Improvements to the circuit mostly involve increasing the tube's rails and putting a CCS on the bottom of the CF.

dave
 
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