I have just built once channel of the paradise and it is running on the bench table and I am getting very anxious to hook it up and listen to it.
However I am having difficolties making the servo section properly working.
I haven't matched the BJTs just to run it on the bench but planning on matchin before building both channels and give it a serious listening.
Preamp is outputing a DC offset at the ouput of about 4-5V and wondersa lot which I am assuming it is normal when servo is not on (please confirm this statement).
For servo I am using Ad797 and I have noticed that when servo is connected voltage output is not 0 but something like 70-80mV.
However when fully tested, it looks like signal wabbles and then gets stable in about 1 second when I suddenly switch gain at the signal generator.
I would appreaciate very much if the people who have built it already could comment on these points and share their know-how with me.
Thanks.
However I am having difficolties making the servo section properly working.
I haven't matched the BJTs just to run it on the bench but planning on matchin before building both channels and give it a serious listening.
Preamp is outputing a DC offset at the ouput of about 4-5V and wondersa lot which I am assuming it is normal when servo is not on (please confirm this statement).
For servo I am using Ad797 and I have noticed that when servo is connected voltage output is not 0 but something like 70-80mV.
However when fully tested, it looks like signal wabbles and then gets stable in about 1 second when I suddenly switch gain at the signal generator.
I would appreaciate very much if the people who have built it already could comment on these points and share their know-how with me.
Thanks.
I had no truble with my build of beta but I did match the transistors and did use the spec chip
AD797 may be the problem.
Is it motorboating? in wich case look at pre regulators to much Capacitance may be a problem there so maybe small coke or small resistor folowed by 2000uF just before PSU imput solve that.
There were no problem with oscillation on Paradise R2, still same ceramics caps where put in as by pass but some said they did not use them with no problems.
AD797 may be the problem.
Is it motorboating? in wich case look at pre regulators to much Capacitance may be a problem there so maybe small coke or small resistor folowed by 2000uF just before PSU imput solve that.
There were no problem with oscillation on Paradise R2, still same ceramics caps where put in as by pass but some said they did not use them with no problems.
What loading value are you using for he cartridge ?
Are you experimenting with the cartridge connected ?
No cartridge connected, I don't take any chance till I am confident with the built.
Input load is 100ohm, but eventually when things start working I will load it witht he cartridge equivalent impedance 4ohm and adjust input offset.
I remember having some weird bahaviour with 797 as a servo on other designs I have done while the TL081 worked just fine.
I have never understood the reason, so maybe the problem is on the servo, don't know, I will order the IC spec'ed here.
Question: if you take the servo off, what is the offset you see at the output and how much does it wonder?
I don't have too much capacitance as I am powering it up with lab PSU and then I will power it up with batteries.
The Paradise R3 seems to be very interesting and I'm planning in building one. I found enough information to build my own PCB. In the mean time after reading all these posts 
I compiled a detailed Parts List for North America using the usual suppliers Mouser, Digikey and Newark. It doesn't include the pre-regulator circuitry thought. I'll make it later on...This list may be useful to others. Feel free to point any error I may had done. I still to go through all the schematics to make sure no part is missing.
I compiled a detailed Parts List for North America using the usual suppliers Mouser, Digikey and Newark. It doesn't include the pre-regulator circuitry thought. I'll make it later on...This list may be useful to others. Feel free to point any error I may had done. I still to go through all the schematics to make sure no part is missing.
I managed to have a decent offset...at least good enough to give it a listen to.
Comment on the sound:
It is very crispy and fluid and very nice overall. Pretty quite back ground, fast preamp.
The only thing I think I need to check out is that it is at times a little glossy, I am talking about a tad glossy on the highs.
Wonderful midrange, very controlled bass, nice depth.
It is running directly out of 12V premiul SLA battery and bypass caps on the board.
Tomorrow I will put my shunt PSU design on it which I am pretty sure it will make solve what I am hearing
Now a technical question:
Beside tomorrow I am odering the OPA used here, right now I am using a discrete op amp module, but that is not the problem.
I wanted to ask how the offset is once the servo is connected and what is the offset without servo (how much is wondering).
The thing is that if offset is pretty bad, it means that servo is controlling a lot.
The offset on my board with the servo on seems to be pretty bad to me and I would like to know based on the expierence accumulated here with this pre-amp, what it could be caused by.
Comment on the sound:
It is very crispy and fluid and very nice overall. Pretty quite back ground, fast preamp.
The only thing I think I need to check out is that it is at times a little glossy, I am talking about a tad glossy on the highs.
Wonderful midrange, very controlled bass, nice depth.
It is running directly out of 12V premiul SLA battery and bypass caps on the board.
Tomorrow I will put my shunt PSU design on it which I am pretty sure it will make solve what I am hearing
Now a technical question:
Beside tomorrow I am odering the OPA used here, right now I am using a discrete op amp module, but that is not the problem.
I wanted to ask how the offset is once the servo is connected and what is the offset without servo (how much is wondering).
The thing is that if offset is pretty bad, it means that servo is controlling a lot.
The offset on my board with the servo on seems to be pretty bad to me and I would like to know based on the expierence accumulated here with this pre-amp, what it could be caused by.
there are a few sources for offset... temp-co, variance in mirror gain and resistor tolerances.
The Jfet buffer also causes a permanent offset. To my knowledge the offset is pretty stable, and when the stage is running and temp. stable the servo is pretty much just injecting DC into the household.
The Jfet buffer also causes a permanent offset. To my knowledge the offset is pretty stable, and when the stage is running and temp. stable the servo is pretty much just injecting DC into the household.
I am not concerned with the permanent offset caused by the buffer.
My concern is with the DC drifting, that seems to be pretty drammatic in my case.
It starts up at 8V or so then goes down then up again (without servo).
Also with servo in, for some reason, output is not 0 but it stayies at 50mV-60mV and drifts too much for my personal opinion.
Just want to make clear that I am not using the layout for R2 nor R3 but it was the board designed for my gainstage and re-adapted with few cuts and jumpers.
I am not using matched transistors nor using the 337/327 for the mirrors but only for the input devices.
For mirrors I am using BCP53/56 with about 40HFE gain I think.
I am wondering if on the Paradise's layout there was applied some "special trick" to deal with the thermal drifting that I can re-use here.
Also, what is the effect of building it with not matched device?
Resistors are 1% tol so don't think the culprit could be that one.
I remember one post somewhere along this long thread, where something was done for the DC drifting, but I can't remember if it was the heatsink on the Power supply or what else.
Any input here will be very helpful to complete the built with the Paradise.
Accordinlgy to what you say, if I understand corretly, if you have a preamplifier AC coupled at the input like I do, you could run it without servo as well, am I right?
If that is the case, the built I have done so far, for some unknown reason, is not even close to the actual desired result.
Thanks for the attention.