There's more to it than just the heat dissipation.
--Can the power supply supply sufficient current? In this case, probably so.
--What effect will increasing the bias have on the SOA of the output devices? That's a little more risky.
--And, of course, the heat. Actually, I'd say that this is the least of your problems. Use fans and you can get rid of quite a bit of heat.
Grey
--Can the power supply supply sufficient current? In this case, probably so.
--What effect will increasing the bias have on the SOA of the output devices? That's a little more risky.
--And, of course, the heat. Actually, I'd say that this is the least of your problems. Use fans and you can get rid of quite a bit of heat.
Grey
(i love mine)
350.5 in class a
Ian - good point. I don't know how much of the amps output is SE Class A and how much is regular Class A. If anyone knows please let me know.
As far as why, for me and this is just my opinion but the Aleph series is a bit polite for me and I find the XA series lacking as well.
Maybe I am just nostalgic I find the old Threshold designs of Nelson's - like the SA-12e or the SA-4e series to have a terrifficly engaging quality but they lack in the transparency of the X series. I do find the X 350.5 to be the most engaging of the X series but I would still like to try to increase both the SE class A and the regular class A output to get it closer to amp that would combine both of the qualities that I stated above. Mybe the increase doesn't need to be that much?
Thanks for your thoughts.
Ian - good point. I don't know how much of the amps output is SE Class A and how much is regular Class A. If anyone knows please let me know.
As far as why, for me and this is just my opinion but the Aleph series is a bit polite for me and I find the XA series lacking as well.
Maybe I am just nostalgic I find the old Threshold designs of Nelson's - like the SA-12e or the SA-4e series to have a terrifficly engaging quality but they lack in the transparency of the X series. I do find the X 350.5 to be the most engaging of the X series but I would still like to try to increase both the SE class A and the regular class A output to get it closer to amp that would combine both of the qualities that I stated above. Mybe the increase doesn't need to be that much?
Thanks for your thoughts.
The X circuit depends on maximum linearity in the circuit, and
really shines in limited feedback situations.
Bias is very important to these amplifiers, and we like to run it
high, mostly limited by the hardware heat dissipation.
Of course there's nothing to keep you from cranking up
either/both the SE (just lower the value of the power resistor
drawing SE current) or PP bias (just turn the pots up).
You can get away with a significant increase, but you must take
care to keep the amplifier cool, and this might mean the
addition of fans. Alternatively, you can accept the shorter life
which comes with higher temperature - the amp may fail in 10
years instead of 20.
Also, you can reduce the AC incoming voltage, which will reduce
the dissipation (and power rating) but allows for more bias
within a given dissipation.
As a practical matter, if you keep the sinks well ventilated you can
think in terms of a 25% increase in bias, and this will give you
56% more Class A. If you drop the AC line to 110V, you can take
it up 70% more or so without penalties.
really shines in limited feedback situations.
Bias is very important to these amplifiers, and we like to run it
high, mostly limited by the hardware heat dissipation.
Of course there's nothing to keep you from cranking up
either/both the SE (just lower the value of the power resistor
drawing SE current) or PP bias (just turn the pots up).
You can get away with a significant increase, but you must take
care to keep the amplifier cool, and this might mean the
addition of fans. Alternatively, you can accept the shorter life
which comes with higher temperature - the amp may fail in 10
years instead of 20.
Also, you can reduce the AC incoming voltage, which will reduce
the dissipation (and power rating) but allows for more bias
within a given dissipation.
As a practical matter, if you keep the sinks well ventilated you can
think in terms of a 25% increase in bias, and this will give you
56% more Class A. If you drop the AC line to 110V, you can take
it up 70% more or so without penalties.
Mr. Pass,
Thank you for your reply. That is so cool that you took the time to write. Thank you.
What I was looking for would be about a 50% increase in the amount of the class "A" . Which, please correct me if I am wrong, would bring it to around 80-85 watts of class "A"? That should be good enough to cover most of the frequencey range for most speakers in class "A" - at a moderate playback level. What do you think?
Again, thank you for writing Mr. Pass.
Thank you for your reply. That is so cool that you took the time to write. Thank you.
What I was looking for would be about a 50% increase in the amount of the class "A" . Which, please correct me if I am wrong, would bring it to around 80-85 watts of class "A"? That should be good enough to cover most of the frequencey range for most speakers in class "A" - at a moderate playback level. What do you think?
Again, thank you for writing Mr. Pass.
Mr. Pass,
I am sorry I multiplied incorrectly - the amount of class A would be more around 60-65 watts not 80-85 watts.
What's the lower ressitor value and where should I install it to get the 56% increase in SE class A?
Where are the bias pots? How much would I need to turn them up to also get the 56% increase?
Where should I measure the temprature of the amp, would it be at the heatsinks and what temp is acceptable? It may shorten the life but I don't want to do any damage?
Thanks, again.
I am sorry I multiplied incorrectly - the amount of class A would be more around 60-65 watts not 80-85 watts.
What's the lower ressitor value and where should I install it to get the 56% increase in SE class A?
Where are the bias pots? How much would I need to turn them up to also get the 56% increase?
Where should I measure the temprature of the amp, would it be at the heatsinks and what temp is acceptable? It may shorten the life but I don't want to do any damage?
Thanks, again.
Nelson, you said try back Tues.
Nelson,
Just to refresh your memory I was looking to increase the amount of class A in the 350.5 amp to around 70 watts and you mentioned I could do a few things like lower a resistor value and turn up a biasis pot.
So, what's the lower ressitor value and where should I install it to get an increase in SE class and how much would that increase be?
Where are the bias pots? How much would I need to turn them up to get the increase that you said around 56%?
After all is said and done around what amount of Class A should I expect?
Just as important - where should I measure the temprature of the amp, would it be at the heatsinks and what temp is acceptable?
Thanks, again.
John
It may shorten the life but I don't want to do any damage?
Thanks, again.
Nelson,
Just to refresh your memory I was looking to increase the amount of class A in the 350.5 amp to around 70 watts and you mentioned I could do a few things like lower a resistor value and turn up a biasis pot.
So, what's the lower ressitor value and where should I install it to get an increase in SE class and how much would that increase be?
Where are the bias pots? How much would I need to turn them up to get the increase that you said around 56%?
After all is said and done around what amount of Class A should I expect?
Just as important - where should I measure the temprature of the amp, would it be at the heatsinks and what temp is acceptable?
Thanks, again.
John
It may shorten the life but I don't want to do any damage?
Thanks, again.
I think that you will find this a foolish venture, and of course
you cannot expect the warranty to remain in force.
It is quite easy to damage an amplifier adjusting the bias
without some expertise and proper measuring equipment, and
of course there are lethal voltages inside. It should only be
undertaken by experienced technicians.
That said, the X350.5 has 5 potentiometers on the main board.
I don't recommend touching the potentiometers on the modules
at all.
On the main board pots P2 through P5 set the four bias points.
The bias sensing voltage is read off the pairs of wire loops
adjacent to the pots.
Keep in mind that the bias varies with temperature, and you
must watch the values for an hour or so after each adjustment,
trimming in halfway measures toward a goal value. Also, note
that the "175 mv" on the silk screening does not accurately
refer to this version and is to be ignored.
Also, the amplifier top must be in place during warmup times.
As to what values of Class A operation, I must say:
1) You are probably not going to see the improvement you
might imagine
2) You should not undertake this at all if I have to tell you what
Class A values you will get.
So I really recommend that if you must adjust the amp, adjust
P1, which sets the meter position.
you cannot expect the warranty to remain in force.
It is quite easy to damage an amplifier adjusting the bias
without some expertise and proper measuring equipment, and
of course there are lethal voltages inside. It should only be
undertaken by experienced technicians.
That said, the X350.5 has 5 potentiometers on the main board.
I don't recommend touching the potentiometers on the modules
at all.
On the main board pots P2 through P5 set the four bias points.
The bias sensing voltage is read off the pairs of wire loops
adjacent to the pots.
Keep in mind that the bias varies with temperature, and you
must watch the values for an hour or so after each adjustment,
trimming in halfway measures toward a goal value. Also, note
that the "175 mv" on the silk screening does not accurately
refer to this version and is to be ignored.
Also, the amplifier top must be in place during warmup times.
As to what values of Class A operation, I must say:
1) You are probably not going to see the improvement you
might imagine
2) You should not undertake this at all if I have to tell you what
Class A values you will get.
So I really recommend that if you must adjust the amp, adjust
P1, which sets the meter position.
Nelson,
It's been awhile but I want to say thanks for your time and I would never attemtped any of these adjustments by myself. I don't know enough and this is all theoretical.
One thing I am confused about you recently said - "So I really recommend that if you must adjust the amp, adjust P1, which sets the meter position." - does that mean increasing the voltage by 25% on the p1 pot , will increase the amount of class "a" in the PP mode?
I know you mentioned that it wouldn't give me the results I am expecting and now after some thought, maybe just a small increase of class "a" might give me what I want.
The 350.5 has such terrific speed and I just wanted a little darker background and to add some more 3D quality to the voices and instruments. And maybe just a little more transparency.
One last thing, if you could throw in a 34 inch waist for me as well, that's to keep the wife happy. I would...we would greatly appreciate it.
Thanks for your indulgence.
jfr
It's been awhile but I want to say thanks for your time and I would never attemtped any of these adjustments by myself. I don't know enough and this is all theoretical.
One thing I am confused about you recently said - "So I really recommend that if you must adjust the amp, adjust P1, which sets the meter position." - does that mean increasing the voltage by 25% on the p1 pot , will increase the amount of class "a" in the PP mode?
I know you mentioned that it wouldn't give me the results I am expecting and now after some thought, maybe just a small increase of class "a" might give me what I want.
The 350.5 has such terrific speed and I just wanted a little darker background and to add some more 3D quality to the voices and instruments. And maybe just a little more transparency.
One last thing, if you could throw in a 34 inch waist for me as well, that's to keep the wife happy. I would...we would greatly appreciate it.
Thanks for your indulgence.
jfr
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