I know a curcuit that looks like this.
Hi Joachim,
A circuit like this has been build before by a good friend of mine (Ronald) but in single supply from plus 24 volt to gnd.
This is an other kind of beast, working from plus to minus. I got to give it a try too. Thanks for your input
You'll hear from me
atb,
Audiofanatic
Hi Joachim,
A circuit like this has been build before by a good friend of mine (Ronald) but in single supply from plus 24 volt to gnd.
This is an other kind of beast, working from plus to minus. I got to give it a try too. Thanks for your input
You'll hear from me
atb,
Audiofanatic
To be honest Jose`, that constant current source is not that good with one pair of Fets at the input. The resistors R3, R8 are only 0,65V / 0.008A = 81,25 Ohm. That is a bit too low for optimum noise suppression. With two red Leds instead of the second transistor it would be 2 x 1,4V - 0,65V = 2,15V / 0,008A = 268,75 Ohm. That is better and does not add noise from the current source. That Led current source has a somewhat lower output impedance though because you loose the feedback action of the two transistors.
Adding a Led, a transdiode or a diode into the emitters of T6, T8, you can raise the value of R3, R8 too. There are other ways. I think Elviee had a thread about constant current sources. He compared so many circuits that even i lost oversight. As far as i remember, a
simple Fet with resistor was hard to beat in output resistance. If this is the best solution for this circuit concerning noise injection i can not tell. I never tried it.
simple Fet with resistor was hard to beat in output resistance. If this is the best solution for this circuit concerning noise injection i can not tell. I never tried it.
I see it.
Joachim,
It's clear, I want to do things that are not quite favorable to this circuit.
That CCS is one of them and the other thought I had was to split R11 in two R's and connect a servo to that point.
I need to wait a bit until I finish the other circuit and then I'll go experimenting with this one.
Need to go to bed now, I have to get up at 7
Audio electronics is addictive and even worst if you are designing them, yummy yummy !
Cheers,
Audiofanatic
Joachim,
It's clear, I want to do things that are not quite favorable to this circuit.
That CCS is one of them and the other thought I had was to split R11 in two R's and connect a servo to that point.
I need to wait a bit until I finish the other circuit and then I'll go experimenting with this one.
Need to go to bed now, I have to get up at 7
Audio electronics is addictive
and even worst if you are designing them, yummy yummy !Cheers,
Audiofanatic
I have worked a bit on the latest circuit. It has now a very low noise current source with a bias servo. After a lot of Fet buffers here is a high impedance BJT diamond buffer. I think a conventional diamond would not have a high enough input impedance to be usable with the rather high impedance RIIA. I am still contemplating how to set up the driven folded cascode. One way would be a TL341 plus a constant current source.
WOW
Hi Joachim,
It's getting better and better.
I like the servo in this circuit and also the output stage.
It reminds me of the LISA II Headphone amp configuration. Only the LISA has two CCS in each chain (plus and minus).
I'll try to dig up the LISA circuit, If I can find it quick !
Cheers,
José
Hi Joachim,
It's getting better and better.
I like the servo in this circuit and also the output stage.
It reminds me of the LISA II Headphone amp configuration. Only the LISA has two CCS in each chain (plus and minus).
I'll try to dig up the LISA circuit, If I can find it quick !
Cheers,
José
LISA III
Hi Joachim,
I found the schematic of the LISA III not the two but I don't know if I may post it on the forum.
I'll send it straight to you in a few minutes. And if the moderators say it's prohibited than I will not post it on the forum.
I got it from a customer that had a problem with it and wanted modifications from top to bottom. I sounds (after mod's) amazingly good and clear.
Cheers,
José
Hi Joachim,
I found the schematic of the LISA III not the two but I don't know if I may post it on the forum.
I'll send it straight to you in a few minutes. And if the moderators say it's prohibited than I will not post it on the forum.
I got it from a customer that had a problem with it and wanted modifications from top to bottom. I sounds (after mod's) amazingly good and clear.
Cheers,
José