Babbelfish J PCBs

[BillWW]

Choky,

You are correct on dc offset seems to take longer with the smaller devices.

When I used the irf9610 those stabilize really fast in a second it seemed. When I switched to the zvp3310a, they took a lot longer too like the j176. It seems to be maybe the dissipation of the devices shifts the dc offset of the smaller devices more than the larger irf9610.

Here are my next tweaks to try in order of importance to me:

#1. I will try the heatsinks on the LTP tonight and see if that helps
some with them tied together.

#2. I will have to order a smaller 2.2uF capacitor to try, but maybe with no capacitor sounds appealing too.

#3. I guess I could just place a timed relay to ground the output so that I would not have to worry about my speakers? This last one, I would have to research for a while how to do. It would be nice to have a meter that would check the dc offset before allowing it to connect to the speakers too.

[Zen Mod]

Originally posted by BillWW
Choky,

You are correct on dc offset seems to take longer with the smaller devices.

When I used the irf9610 those stabilize really fast in a second it seemed. When I switched to the zvp3310a, they took a lot longer too like the j176. It seems to be maybe the dissipation of the devices shifts the dc offset of the smaller devices more than the larger irf9610.

Here are my next tweaks to try in order of importance to me:

#1. I will try the heatsinks on the LTP tonight and see if that helps
some with them tied together.

#2. I will have to order a smaller 2.2uF capacitor to try, but maybe with no capacitor sounds appealing too.

#3. I guess I could just place a timed relay to ground the output so that I would not have to worry about my speakers? This last one, I would have to research for a while how to do. It would be nice to have a meter that would check the dc offset before allowing it to connect to the speakers too.

1: make thermal bridge between two jfets,not heatsink; with heatsink it will take longer time to reach thermal equilibrium

2: OK

3: relay to ground?
ground?
I'm sure that you didn't meant to short output to ground but to implement spk relay with delay ,hehe,but for every case I must answer this...

[BillWW]

Originally posted by choky



1: make thermal bridge between two jfets,not heatsink; with heatsink it will take longer time to reach thermal equilibrium

2: OK

3: relay to ground?
ground?
I'm sure that you didn't meant to short output to ground but to implement spk relay with delay ,hehe,but for every case I must answer this...

#1. The bridge is fine now.

#2. I tried all different configurations using different capacitors including no capacitor. I got it to be stable with no capacitor, but felt better about leaving one scaled down, so I ended up using a 2.2uF film capacitor for the dc feedback resister and a 1pF bypass cap on the 220Kohm feedback resister. This sounds the most musical to me and so now I feel my finishing touches are done with my Aleph 3 conversion to Babelfish J.

#3. After adjusting the DC offset, I found the amp stabilizes below 100 mV fast now. I ended up letting the amp warm up and adjusted the DC offset to a negative value of DC offset, because this lowers the initial DC offset to within 100 mV within a couple of seconds. So, I am not worried about my speakers now, while waiting for the amp to stabilize on the DC offset.

With the above mods on this thread, it does sound slightly more detailed and refined compared to my zvp3310a. They are similar, but the jfet still sounds slightly better. I guess it has taken time to get used to it to really know how it sounds and maybe it is breaking in and sounding sweeter too.

You would not believe how many capacitors I tried in this amp tweaking it, so save yourselves trouble and use the 1 pF and 2.2 film capacitor with the previous Aleph 3 conversion that Choky posted earlier in this thread and it should sound very nice!!!

Regards, Bill

[Zen Mod]

Originally posted by BillWW



#1. The bridge is fine now.

#2. I tried all different configurations using different capacitors including no capacitor. I got it to be stable with no capacitor, but felt better about leaving one scaled down, so I ended up using a 2.2uF film capacitor for the dc feedback resister and a 1pF bypass cap on the 220Kohm feedback resister. This sounds the most musical to me and so now I feel my finishing touches are done with my Aleph 3 conversion to Babelfish J.

#3. After adjusting the DC offset, I found the amp stabilizes below 100 mV fast now. I ended up letting the amp warm up and adjusted the DC offset to a negative value of DC offset, because this lowers the initial DC offset to within 100 mV within a couple of seconds. So, I am not worried about my speakers now, while waiting for the amp to stabilize on the DC offset.

With the above mods on this thread, it does sound slightly more detailed and refined compared to my zvp3310a. They are similar, but the jfet still sounds slightly better. I guess it has taken time to get used to it to really know how it sounds and maybe it is breaking in and sounding sweeter too.

You would not believe how many capacitors I tried in this amp tweaking it, so save yourselves trouble and use the 1 pF and 2.2 film capacitor with the previous Aleph 3 conversion that Choky posted earlier in this thread and it should sound very nice!!!

Regards, Bill

#3-just a tip-realy depending of type of your speakers (Lowther NO!)
even teeny weeny 30W speak will tolerate up to 200-250mV initial DC offset.......
even better:
just make delayed relay connection on output with time of ,say,30 secs-and .......enjoy!

[BillWW]

I have been comparing the old 220uF non-polar versus the 2.2uF film capacitor and found the film sounds more refined. The 220uF seemed to have a nice upper frequency, but sounded more distorted in comparison to the film.

The j176 jfet is for sure nicer than the previous zvp3310a version, but what seemed to matter the most was playing around with the removal of the capacitors.

The zvp3310a version I built was very nice even in comparison to my babelfish version, so for higher 30+ volt power rails, the zvp3310a version is still very close to the quality if this babelfish version.

I ended up removing the 1pF silver mica feedback bypass capacitor and also the 1nF capacitor for circuit stability that is used on other Alephs and now the amplifier sounds a lot more extended in the higher frequencies. I also had to adjust the 4.75K ohm current source resister to ground to a new value of 4.68K ohm.

I also noticed my DC offset to adjust needed more like 350 ohms instead of the 221 ohm resister. The other side still had 221 ohms left in place. Do these need to be the same value or can I leave the one alone? I thought maybe 290 ohm on each side would be more balanced on both sides of the current source fet? Ideas or suggestions?

My next phase, how do I get rid of the Zener regulation and go resisters as a current source regulator?

[Zen Mod]

Originally posted by BillWW


I also noticed my DC offset to adjust needed more like 350 ohms instead of the 221 ohm resister. The other side still had 221 ohms left in place. Do these need to be the same value or can I leave the one alone? I thought maybe 290 ohm on each side would be more balanced on both sides of the current source fet? Ideas or suggestions?

My next phase, how do I get rid of the Zener regulation and go resisters as a current source regulator?

sometimes I can' follow what you wrote without knowing exact schmtc....which version ,where...

besides-why you think that NP's CCS with zenner is worse than two bjt
CCS?

worse or not-it's surely good enough

[BillWW]

Originally posted by choky



sometimes I can' follow what you wrote without knowing exact schmtc....which version ,where...

besides-why you think that NP's CCS with zenner is worse than two bjt
CCS?

worse or not-it's surely good enough

In your Aleph 3 to babelfish conversion, your suggestions to try. There was a 221 ohm with a an additonal pot to adjust dc offset. On the other gate side of the current source there was also a 221 ohm resister. I am asking after adjusting the DC offset the source 221 ohm plus pot in series turned out to be about 350 ohm. It seems to me then 290 ohm fixed resister on the source and gate would be more equal in sharing the load?

I tried attaching your schematic with some marking to show where I am referring to also.


I thought zener regulators are more noisy then a bjt? In Nelson article on op amps he stated 4uv for bjt, while others were a lot noisier than that?

Bill

[Zen Mod]

Originally posted by BillWW


In your Aleph 3 to babelfish conversion, your suggestions to try. There was a 221 ohm with a an additonal pot to adjust dc offset. On the other gate side of the current source there was also a 221 ohm resister. I am asking after adjusting the DC offset the source 221 ohm plus pot in series turned out to be about 350 ohm. It seems to me then 290 ohm fixed resister on the source and gate would be more equal in sharing the load?

I tried attaching your schematic with some marking to show where I am referring to also.


I thought zener regulators are more noisy then a bjt? In Nelson article on op amps he stated 4uv for bjt, while others were a lot noisier than that?

Bill

OK-you wrote:

I also noticed my DC offset to adjust needed more like 350 ohms instead of the 221 ohm resister. The other side still had 221 ohms left in place. Do these need to be the same value or can I leave the one alone? I thought maybe 290 ohm on each side would be more balanced on both sides of the current source fet? Ideas or suggestions?

now I see on what schm you mean.....
this:
http://www.diyaudio.com/forums/attac...amp=1143758083

Bill-you really must do your homework.......NP wrote at least zillion times that resistor in mosfet's gate is primary for preventing oscillations........you can place there (in CCS) anything from 120E to 1K or even more,and you'll not change anything....
only if you change value of that resistor in audio stage (say-output's gates ) ,then you'll influence different tonal character,especially in upper part of spectrum........
besides ,regarding pot value-I put that values just preliminary-solder another IRF there,and you'll maybe have another value for current setting resistor........

[GeorgeBoles]

Hello BillWW and Choky, and everyone else,

I have been "designing" an Aleph 3 board (but with balanced inputs a la Aleph 5) for the last 3 days or so which will fit in a case I have, the plan being to make up a "Mini-A" out of some (?)non-original IRF 240s (they are marked "SEC") which were given to me. And then I thought, why not make a Mini-Babbelfish-J?

Bill,

Could you please post or e-mail me a schematic or summarize what your final setup is -

a. what did you do for the current source to the differential pair (IRF9610 and single resistor, OR the setup with the BC560 cascode, with 43 ohm source resistors as per Choky's final diagram);
b. what capacitor values did you eventually use; and
c. resistor values - did you raise them to the 22k levels of the Babbelfish-J or did you leave them at Aleph 3 levels?

Did you alter the current protection circuit around the output transistor as on Choky's schematic or did you leave it the same as on the original Aleph 3 schematic?


Choky,

Would it be possible to use the lower original Aleph 3 resistances if I kept the capacitors at 220uF? What else would I have to change? Is such a high impedance going impair noise performance?

Is it possible to leave the current protection circuit around the output transistors the same as in the original Aleph 3 design?

Finally, could I drop a couple of BJT's into the differential pair until I can get some nice Jfets?

Regards and thanks,
George.

[Zen Mod]

Originally posted by GeorgeBoles



Choky,

Would it be possible to use the lower original Aleph 3 resistances if I kept the capacitors at 220uF? What else would I have to change? Is such a high impedance going impair noise performance?

Is it possible to leave the current protection circuit around the output transistors the same as in the original Aleph 3 design?

Finally, could I drop a couple of BJT's into the differential pair until I can get some nice Jfets?

Regards and thanks,
George.

it's completely possible to use lower value resistors; I dunno consequences for that,just because I didn't tried lower values btw-for me are logical two approachs- low impedance if you use balanced input ( in range of 600 ohms ) and highish impedance if you use unbalanced input (in range of 200+ K).......both ways have own virtues....so I really can't see any reason why insist on 22K range,especially when I think that main NPs reason for using highish impedance is smaller or even nonexistent feedback cap

maybe sound will change,comparing to higher values,but I think-not dramatically

also-I didn't calculated current protection yet,just because I'm too lazy to do that ; when my hickory cab for amp will be finished,I'll mes with trivia like that; just use same resistor as in Aleph 30 and it will be OK

regarding bjts in diff stage..........why not-try it if you know how ......in every case-use some super dupper MATO dual transistors in one case-to minimize offset variations.....