Re: Aleph 3 conversion
Since I might convert a non-existing A3 to Babelfish, I looked back to the toob man's original Babelfish, and found a 4u7F (page 1 of this thread) in the place of the 220uF. Probable reason with the 4.7uF, I figure out, might be that toob man's pocket is carrying more sand than coins . . .
Am I answering the question of which part of the elephant . . . ?
BillWW said:
Since I might convert a non-existing A3 to Babelfish, I looked back to the toob man's original Babelfish, and found a 4u7F (page 1 of this thread) in the place of the 220uF. Probable reason with the 4.7uF, I figure out, might be that toob man's pocket is carrying more sand than coins . . .
Am I answering the question of which part of the elephant . . . ?
Re: Re: Aleph 3 conversion
jh6you,
Going through so many schematics got me confused. In the original Aleph 3 schematic it was 220 uF. In choky's babelfish, it is 4.7 uF.
On the first page of this thread, he says leave it out if you want. I tried leaving that 4.7 uF out and the speaker output climbed higher and higher to the rail voltage or close to it seemed.
I do not know how to stop that, so I just left my 220uF in place, since the amp has always had that there anyways.
I wonder if I could adjust the current source DC offset to lower the dc offset with this 4.7uF capacitor removed, but just might need a higher value than my current 260 ohm setting?
I'll wait and see if Choky has any ideas, because I am tired of tinkering after desoldering and resoldering so many parts to convert my Aleph 3 to babelfish rough approximation.
You know how tweaking goes. If this capacitor is removed, it might sound better? But for now, I do not know how to make it work with the 4.7uF capacitor removed.
Regards, Bill
jh6you said:
Since I might convert a non-existing A3 to Babelfish, I looked back to the toob man's original Babelfish, and found a 4u7F (page 1 of this thread) in the place of the 220uF. Probable reason with the 4.7uF, I figure out, might be that toob man's pocket is carrying more sand than coins . . .
Am I answering the question of which part of the elephant . . . ?
jh6you,
Going through so many schematics got me confused. In the original Aleph 3 schematic it was 220 uF. In choky's babelfish, it is 4.7 uF.
On the first page of this thread, he says leave it out if you want. I tried leaving that 4.7 uF out and the speaker output climbed higher and higher to the rail voltage or close to it seemed.
I do not know how to stop that, so I just left my 220uF in place, since the amp has always had that there anyways.
I wonder if I could adjust the current source DC offset to lower the dc offset with this 4.7uF capacitor removed, but just might need a higher value than my current 260 ohm setting?
I'll wait and see if Choky has any ideas, because I am tired of tinkering after desoldering and resoldering so many parts to convert my Aleph 3 to babelfish rough approximation.
You know how tweaking goes. If this capacitor is removed, it might sound better? But for now, I do not know how to make it work with the 4.7uF capacitor removed.
Regards, Bill
That time Choky must have been very tired . . .
I think the cap is necessary to be a short for AC and to be an open for DC. With the cap, we could catch amount of DC offset. Since I have 220uF, I would go with 220uF, too.
Shall we give Choky a wake-up call?
I think the cap is necessary to be a short for AC and to be an open for DC. With the cap, we could catch amount of DC offset. Since I have 220uF, I would go with 220uF, too.
Shall we give Choky a wake-up call?
jh6you said:That time Choky must have been very tired . . .
I think the cap is necessary to be a short for AC and to be an open for DC. With the cap, we could catch amount of DC offset. Since I have 220uF, I would go with 220uF, too.
Shall we give Choky a wake-up call?
hehe
who need wake-up call here.....?
because both-input and output resistor nets are scaled up 10 times (220K and 22K-they are these values to achieve Aleph J specs of ~240K input impedance and to have ~same amplification factor) ,then (to preserve same absolutely non-critical RC constant) DC gekoppel😉 220UF cap must/can be scaled down for same amount;
so-it's not missing,just divided in value ;
I choose 4U7 even if 2U2 is logical,just because I even don't need it but I also have nice ones in both sizes;ya know-bigger is better
....or not?my BJ is tried without that cap,and I wrote my experience ,regarding initial and working DC offset.
Papa sez that his J have no caps in signal route
that means -no C on input,no C in feedback and no C in CCS modulating ,but this also means no C in power supply
hey-but you know NP and his sense of humor-all that can be true
if you are silly 'nuff to believe,it's your problem,not his
so I make what I can
fact that I didn't use cap in feedback cap and my amp is stable jut tells how fine is NP's choice of JFet, and confirmation that I do my homework well-taking pieces and NP's breadcroumbs all around forum,with valuable help from Gray and few nice members 🙂
BillWW-did you couple thermally these two JFets in LTP?they are matched,naturally?
don't be scared- if not yet-couple them and try without load (off course) to set DC offset varying current through CCS
if that don't work for you (not jh6,just you 😉 ) leave 2U2 in place of that cap and enjoy ; you can loose just teeny weeny here
I don't like caps in signal route-not because I hate them , but bcse I prefer Iron instead...hehe,but-you can't put Iron easily everywhere and still be practical even in slightest amount...
so-half way in cap to Iron transition is to leave cap out and not put iron at all 😉BillWW :
diminishing returns or not...
when input capacity is low enough,that means that is low enough ;
I can't see much possible sound difference between these two values ; more important is linearity of used part, and capacitance is just one of factors in game called "preserving signal energy"...
like Gray pointed when I ask -how on earth is possible that NP drive 12 gates in one Aleph with weeny LTP?!@#$%**### ? - think on larger scalle,don't look at just one fact
sometimes shortest way is not better than longer one
sometimes is not even easier
and often is certainly less enjoyable
choky said:
Haha . . .
I know you (I mean yo) scaled it down.
The bigger seems to be not harmful . . . could be a better AC short . . .
Who forgets np has six senses . . .
4u7 or 2u2 capacitors
choky and jh6you,
I have some films, but they are almost bigger than my circuit board. I would not have any place to mount them on my stock board. That was why I left the 220uF in. I did replace all of the regular 220uF polar electrolytic with non-polar electrolytic capacitors and those sound much better than the polar electrolytic- way more spatious. Quite amazing and still fits in the stock place of these polar electrolytic.
I did try bypassing them too as in the babelfish, but it seemed to sound less spatious, so I removed them and just left my np 220uF in place. I guess overtweaking in this case seemed to ruin my 3d depth and spatiousness. It did not sound as musical.
I thought about running some longer wires so that I could try a film on this feedback capacitor, but do not think that would be safe with it dangling over the circuit board.
So, Choky have you tried the 220uf versus your 4u7?
The only one I could fit would be electrolytic 4u7.
Btw, I have not coupled the jfets together yet. I do have some metal heatsinks that look like I could tie the two jfets together. I would need to solder the two metal heatsinks together to reach each transister and that would keep their temperature gradient equalized. I do not want to touch the amp for a while, because I spent many hours working on it standing up the whole time. I still have not put the lid on the case yet, because as usual I may need to play with those heatsink coupling of the jfets. I was able to adjust it without the heatsink coupling to about 4 to 5 mV DC offset. I guess with the heatsinks it would make it drift less on warm up? It does take it a while to stablize. Maybe in a minute or so, the DC settles below 100 mv and gradually declines to 4 to 6 mV offset when the amp is warmed up at 55 Celsius.
I will try the jfet coupling to see if my DC offset starts out lower. For now I usually just unplug the banana plugs and check the DC offset before hooking the speakers up.
choky and jh6you,
I have some films, but they are almost bigger than my circuit board. I would not have any place to mount them on my stock board. That was why I left the 220uF in. I did replace all of the regular 220uF polar electrolytic with non-polar electrolytic capacitors and those sound much better than the polar electrolytic- way more spatious. Quite amazing and still fits in the stock place of these polar electrolytic.
I did try bypassing them too as in the babelfish, but it seemed to sound less spatious, so I removed them and just left my np 220uF in place. I guess overtweaking in this case seemed to ruin my 3d depth and spatiousness. It did not sound as musical.
I thought about running some longer wires so that I could try a film on this feedback capacitor, but do not think that would be safe with it dangling over the circuit board.
So, Choky have you tried the 220uf versus your 4u7?
The only one I could fit would be electrolytic 4u7.
Btw, I have not coupled the jfets together yet. I do have some metal heatsinks that look like I could tie the two jfets together. I would need to solder the two metal heatsinks together to reach each transister and that would keep their temperature gradient equalized. I do not want to touch the amp for a while, because I spent many hours working on it standing up the whole time. I still have not put the lid on the case yet, because as usual I may need to play with those heatsink coupling of the jfets. I was able to adjust it without the heatsink coupling to about 4 to 5 mV DC offset. I guess with the heatsinks it would make it drift less on warm up? It does take it a while to stablize. Maybe in a minute or so, the DC settles below 100 mv and gradually declines to 4 to 6 mV offset when the amp is warmed up at 55 Celsius.
I will try the jfet coupling to see if my DC offset starts out lower. For now I usually just unplug the banana plugs and check the DC offset before hooking the speakers up.
choky said:
Yes, I matched all 100 of them and picked the ones that were very well matched. I will have to couple them to see what that does. None of my previous mosfets had thermal coupling though and neither do these and the dc offset seemed stable other than the long time for it to reach equilibrium. I want it to be low dc offset in like 1/3 of a second. Is that possible?
BillWW said:
but these jfets are teeny weeny comparing to your previous mosfets.....die dimensions,dissipation etc
1/3 secs is impossible
30 maybe
re-read first post in thread-you'll see what I get
Re: 4u7 or 2u2 capacitors
Bill
I do not mean that np (nelson pass, not non-polar) is 100% perfect: He must know what is the film caps and must have them.
Thank you for your kind info about your findings. 🙂
BillWW said:
Bill
I do not mean that np (nelson pass, not non-polar) is 100% perfect: He must know what is the film caps and must have them.
Thank you for your kind info about your findings. 🙂
Re: 4u7 or 2u2 capacitors
I just overlooked this post
in any case-I didn't tried any cap in place of 2U2 (4U7) ;
it's OK without,so it's better than with 😉
if you prefer without bypass-it's your particular choice and your ears are only judge.
I gave to one friend pair of BG 220UF/6V3 so he can try it ,but that will not be so soon...
anyway-try smallest 2U2 you can find - in place of 220UF-I expect that you'll be pleased
regarding DC offset settle time -I doubt that even NP's J is better in this area ;that's still mean thermal machine
BillWW said:
I just overlooked this post
in any case-I didn't tried any cap in place of 2U2 (4U7) ;
it's OK without,so it's better than with 😉
if you prefer without bypass-it's your particular choice and your ears are only judge.
I gave to one friend pair of BG 220UF/6V3 so he can try it ,but that will not be so soon...
anyway-try smallest 2U2 you can find - in place of 220UF-I expect that you'll be pleased
regarding DC offset settle time -I doubt that even NP's J is better in this area ;that's still mean thermal machine
jfets and dc offset
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.
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.
Re: jfets and dc offset
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 said:
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...
Re: Re: jfets and dc offset
#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 😎
choky said:
#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 😎
Re: Re: Re: jfets and dc offset
#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 said:
#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!
Aleph 3 to J conversion
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?
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?
Re: Aleph 3 to J conversion
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 said:
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
Re: Re: Aleph 3 to J conversion
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
choky said:
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
Re: Re: Re: Aleph 3 to J conversion
OK-you wrote:
now I see on what schm you mean.....
this:
http://www.diyaudio.com/forums/attachment.php?s=&postid=882137&stamp=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........
BillWW said:
OK-you wrote:
now I see on what schm you mean.....
this:
http://www.diyaudio.com/forums/attachment.php?s=&postid=882137&stamp=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........
Aleph 3/Babbelfish conversion
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.
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.
Re: Aleph 3/Babbelfish conversion
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.....
GeorgeBoles said:
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.....
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