Main issue or not, a CMRR of 30dB is below standard for such a pretentious amplifier. If you do it, do it right, but not this way.
Also the distortion of the input buffer is to high for such an amp.
I get 38ppm (with 2SK170-BL). While the rest of the amp is symmetrical/complementary, to me it's a great mystery why that buffer has not been made the same way. Ten times lower distortion at the expense of only two additional jfets and two resistors.
Also the distortion of the input buffer is to high for such an amp.
I get 38ppm (with 2SK170-BL). While the rest of the amp is symmetrical/complementary, to me it's a great mystery why that buffer has not been made the same way. Ten times lower distortion at the expense of only two additional jfets and two resistors.
john curl said:One should not criticize, unless they can do better.
Agreed. Fortunately, I can do better and I'm certainly not the only one.
quote
Anyone can use an opamp.
PMA, in my experience, using op-amps can be easier than discretes generally, but I'd say to get the best out of an op-amp, you need top know how to use them. There are too many cases where I see sloppy layout, not enough decoupling, using non-unity gain stable OPA's in 0dB gain applications (then they try to fix it by 'slugging' the feedback loop) etc. Discretes have their place, but I don't believe 'anyone' can use an op-amp and necessarily get good results.
One other point to be considered is that OPA's have come along way - thankfully we are not dealing with 741 type devices anymore (however, does anybody remember the 'Texan' amplifier based on - I think - a 741 opamp and CFP output stage - I'd love to look at that circuit again for nostalgic reasons - from the 1970s').
Anyone can use an opamp.
PMA, in my experience, using op-amps can be easier than discretes generally, but I'd say to get the best out of an op-amp, you need top know how to use them. There are too many cases where I see sloppy layout, not enough decoupling, using non-unity gain stable OPA's in 0dB gain applications (then they try to fix it by 'slugging' the feedback loop) etc. Discretes have their place, but I don't believe 'anyone' can use an op-amp and necessarily get good results.
One other point to be considered is that OPA's have come along way - thankfully we are not dealing with 741 type devices anymore (however, does anybody remember the 'Texan' amplifier based on - I think - a 741 opamp and CFP output stage - I'd love to look at that circuit again for nostalgic reasons - from the 1970s').
john curl said:How can we fix this CMRR with just one added resistor?
A series resistor of 3k43 before the non-inverting input (that is, if R82=100k). Still not perfect as now the division ratio also depends on Zo of the stuff connected to the input. To make it independent you will also need an additional input buffer.
Bonsai said:There's a challenge Edmond. Show us your stuff.
Sorry, but I don't feel challenged and I don't feel the need to drop a schematic, as I have already told how to fix it.
BTW, has JC ever shown a schematic? No! One more reason to not drop a schematic.
Cheers,
E.
john curl said:Very good Edmond, you get a gold star. You are only off by a factor of 2 or so, due to the amplitude loss across the fet follower, itself. Fire up the simulators gentlemen, and get me an exact value. Cap value changes are OK, as well
I didn't specify the input buffers at all. So what are you talking about? Of course, 3k43 is a theoretical value for buffers with Zo=0.
has JC ever shown a schematic?
Originally posted by john curl I am posting the JC-1 input stage through SY.
This REV F is missing +IN/-IN input resistors (R + R//C), that carefully balance for impedance mismatch. Anyway, CMRR depends on output impedance mismatch as well. CMR is not an issue here, this is not a mike preamp.
John, I have finally removed all opamps from my home audio chain.
John, I have finally removed all opamps from my home audio chain.
PMA said:John, I have finally removed all opamps from my home audio chain.
Man, this is GREAT news! You should be very proud of this achievment. Three legs good, eight legs bad!
- Status
- Not open for further replies.
- Home
- Amplifiers
- Solid State
- John Curl's Blowtorch preamplifier