Hello Bottleheads,
I am building this gain stage from Decware's Zkit4 to use as a buffer in front of an LM3875 gain clone. The chip amp has plenty of gain on its own, so I'm wondering about the simplest way to achieve unity gain with this circuit.
Here's a link to the schematic on the Decware site:
And here's a link to the Zkit4 page on the Decware site:
ZKIT4
Thank you for your help!
I am building this gain stage from Decware's Zkit4 to use as a buffer in front of an LM3875 gain clone. The chip amp has plenty of gain on its own, so I'm wondering about the simplest way to achieve unity gain with this circuit.
Here's a link to the schematic on the Decware site:
And here's a link to the Zkit4 page on the Decware site:
ZKIT4
Thank you for your help!
The quick answer is that if you want unity gain don't use that circuit. It will have a voltage gain somewhere around 15 and a highish output impedance. It is not a buffer.
If you want unity gain use a cathode follower.
If you want unity gain use a cathode follower.
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It looks like an LTP - build one per channel, feed the output to the inverting input, compensate to taste and serve...
If you are going to build non-inverting buffer, go to cathode follower, as DF96 wrote. If you want a inverting stage use common cathode circuit.
a common cathode with lots of gm degeneration....a cathode follower could be simpler....
Useless.
Go for a cathode follower, as recommended above.
You would get a better audio quality, lower impedance and avoid ground loop problems with a transformer loaded unity gain stage, but that would cost 10 times more...
USELESS!
It has a Zout in the ballpark of 15k together with an expected THD of almost 1% into 100k load. As I said, useless in any hifi-application.
So as everyone else says, go for a CF. But, for what reason do you need a buffer at all? If it is for impedancematching reasons you will do better with a 2SK170 SF as it will work with the voltages of your sand-amp.
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Thanks for the feedback, guys. I got a few of these boards from Steve Deckert at Decware when I visited their facility earlier this year for a few bucks. I'm afraid I've conflated two different questions here. The first was whether this circuit would be useful as a buffer. With your comments and some research, I now realize it isn't.
The second question was just how you would characterize this circuit. Thanks for your responses on that too. Decware sold these boards a while back for use as a mod in CD players. I think some people made line stages with them. So my second question was just to get your opinion on what you thought the circuit itself would be called and what it might be good for.
The second question was just how you would characterize this circuit. Thanks for your responses on that too. Decware sold these boards a while back for use as a mod in CD players. I think some people made line stages with them. So my second question was just to get your opinion on what you thought the circuit itself would be called and what it might be good for.
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It is difficult to think of a purpose for that circuit in a normal domestic music system. It has too much gain and too high output impedance to be a line stage. Certainly not a buffer. No use for I/V after a DAC. OK, I give up; what did Decware say it could be used for?
From the Decware site for the Zkit4:
"This is a circuit board that you can use to build a class A single-ended-triode stereo gain stage.
It could be used as the heart of an extraordinary sounding preamp, or as a tube output stage in a CD player. If you change the values of a couple parts this could also be a wonderful gain stage in your next amplifier project.
It is set up for a 12AU7 with heater voltages between 10 and 12.6 volts applied to pins 4 and 5. Drop the heater voltage down to 6.3 and you can use 6DJ8 and similar tubes."
They recommend running the B+ at 95VDC, and the heater at 10.5VAC, claiming that the "starved filament will reduce heat, increase life and increase even order harmonics"
As I'm still new to all this, I'm too ignorant to have an opinion. My follow up questions reflect a desire to learn from you guys. The comments here have been helpful in directing my own study. One thing to note is that people who have built this thing all have uniformly glowing praise for it. Who knows what peoples' ears are telling them...
"This is a circuit board that you can use to build a class A single-ended-triode stereo gain stage.
It could be used as the heart of an extraordinary sounding preamp, or as a tube output stage in a CD player. If you change the values of a couple parts this could also be a wonderful gain stage in your next amplifier project.
It is set up for a 12AU7 with heater voltages between 10 and 12.6 volts applied to pins 4 and 5. Drop the heater voltage down to 6.3 and you can use 6DJ8 and similar tubes."
They recommend running the B+ at 95VDC, and the heater at 10.5VAC, claiming that the "starved filament will reduce heat, increase life and increase even order harmonics"
As I'm still new to all this, I'm too ignorant to have an opinion. My follow up questions reflect a desire to learn from you guys. The comments here have been helpful in directing my own study. One thing to note is that people who have built this thing all have uniformly glowing praise for it. Who knows what peoples' ears are telling them...
Thanks Lars. Yes, I was looking for an impedance matching mechanism.
The back story on this is that I have an amp and preamp from Adcom purchased around 17 tears ago. Since then, I have moved on to much better sounding equipment so the Adcom gear has been sitting for a while. A couple of years ago, I fired it back up for use in my hobby room with a pair Magneplanar SMGa speakers that we've had for almost 30 years. The Maggies have been rebuilt by the factory a few years ago and are very good sounding.
When I hooked them up to the Adcom, I wasn't all that impressed. The whole sound was just kind of dull, with poor dynamics, not very good top end, etc. Then, on a whim, I picked up one of those Musical Fidelity X-10 buffers which puports to act as an impedance-matching mechanism. The difference in the sound with the old Adcom was startling. Really, a big improvement.
I've been building all sorts of tube amp kits lately, including a number of the Bottlehead kits, reading a lot, taking some classes, etc., to try to learn more. As a little diversion, one weekend, I built a Daniels chip amp. Sounded quite good! Then, I started driving it with one of my Bottlehead tube preamps. To me, that sounded even better! So, now that I am relocating the Daniels LM3875 from the wood cutting board to a proper chassis, I thought I would incorporate a tube stage of some sort so I could drive it directly with a solid state DAC/PRE or even something like a Squeezebox Touch and still have a bit of that warm euphonic sound that the MF buffer and my other tube pres seemed to add.
The back story on this is that I have an amp and preamp from Adcom purchased around 17 tears ago. Since then, I have moved on to much better sounding equipment so the Adcom gear has been sitting for a while. A couple of years ago, I fired it back up for use in my hobby room with a pair Magneplanar SMGa speakers that we've had for almost 30 years. The Maggies have been rebuilt by the factory a few years ago and are very good sounding.
When I hooked them up to the Adcom, I wasn't all that impressed. The whole sound was just kind of dull, with poor dynamics, not very good top end, etc. Then, on a whim, I picked up one of those Musical Fidelity X-10 buffers which puports to act as an impedance-matching mechanism. The difference in the sound with the old Adcom was startling. Really, a big improvement.
I've been building all sorts of tube amp kits lately, including a number of the Bottlehead kits, reading a lot, taking some classes, etc., to try to learn more. As a little diversion, one weekend, I built a Daniels chip amp. Sounded quite good! Then, I started driving it with one of my Bottlehead tube preamps. To me, that sounded even better! So, now that I am relocating the Daniels LM3875 from the wood cutting board to a proper chassis, I thought I would incorporate a tube stage of some sort so I could drive it directly with a solid state DAC/PRE or even something like a Squeezebox Touch and still have a bit of that warm euphonic sound that the MF buffer and my other tube pres seemed to add.
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