| jfrago |
Has anyone tried to increase the amount of class A that the amp works in to 90 watts?
How hard would it be and would it cause damage to the amp due to the increase heat it would generate?
Thanks. |
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| GRollins |
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 |
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| moe29 |
Why would you want to mod a $9,500 amp? Why not just buy a XA 160?
Or better yet, why not build an Aleph 2? :devilr: (i love mine)
That would give you 100 watts of lovely Class A.
Sorry if i sound like a jerk, but messing with such a beautiful amp is
a bit puzzling to me. |
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| jacco vermeulen |
Better to burn up than to fade away.
Expect at least 10C higher heatsink temperature and worn down knee caps in 10 years, without counter measures. |
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| Ian Macmillan |
| With the X350.5, or indeed any of the 0.5 versions, you will also need to consider how much of the class A is delivered in SE. At the very least this will complicate the situation. Why exactly do you want to change the factory default? |
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| jfrago |
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. |
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| Ian Macmillan |
| I think the answer to how much power is available in SE Class A can be found in another thread on this forum (or at least I know I read it somewhere). From memory it is around 12W. |
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| Nelson Pass |
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.
:cool: |
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| jfrago |
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. |
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| jfrago |
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. |
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| Nelson Pass |
I'm away from the office until Monday, so check back then or
the following day.
:cool: |
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| jfrago |
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. |
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| Nelson Pass |
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.
:cool: |
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| jfrago |
Nelson,
Thanks for the info and you are right for the amount of increase in class A, it's not really worth the effort.
I do appreciate you taking the time to write, that's cool. |
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| Nelson Pass |
| quote: | Originally posted by jfrago
for the amount of increase in class A, it's not really worth the effort. |
I do think so. Time to build a 10 watt amp biased at 10 amps
instead....
:redhot: |
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| elviukai |
| quote: | Originally posted by Nelson Pass
I do think so. Time to build a 10 watt amp biased at 10 amps
instead....
:redhot: |
could I go for 20W 14A?
:devilr: |
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| GRollins |
This is DIY...you can do anything you want as long as it doesn't violate the laws of physics.
You can violate the laws of man as long as you don't get caught.
Grey |
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| elviukai |
good point at first thought(that is all fun with this)
not sure about the second one meaning.. |
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| jfrago |
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 |
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| Nelson Pass |
| quote: | Originally posted by jfrago
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?
|
No, it simply will move the meter up so that you'll feel like you have
more bias.
The limitation here is in hardware. If you are fixated on Class A, then
you need to buy a Class A amplifier. I have some very nice ones. |
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| jfrago |
that's funny.
I am am still listening to the class a amps to see which one is for me.
thanks again. |
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| Nelson Pass |
This whole thing of "when an amp leaves Class A" is a red herring.
We get so many questions about it that I'm preparing a new ad for
the magazine devoted to the subject.
The Answer: forget it!
:cool: |
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| jfrago |
I agree. It's not about what's in the spec's. It's about what makes my feet move and that's what I listen for.
Cheers! |
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| mert |
I am not an engineer but I can say pure copper heat sinks would work it this case. Maybe titanium or any fancy material which is less affected by heat would also work. However, there is demand for one box, a class A stereo amplifier rated minimum 100 watts in 8 ohms.
mert |
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| GRollins |
If you have a bunch of copper heatsinks just sitting around gathering dust, I'd love to have them. Copper conducts heat better than aluminum, but as a metal it's more expensive and doesn't extrude in fancy shapes the way aluminum does. It's also more chemically reactive; aluminum just creates a skin of aluminum oxide (aka sapphire, ruby, corundum) and hunkers down for the long haul.
Grey |
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| Magura |
| quote: | Originally posted by GRollins
If you have a bunch of copper heatsinks just sitting around gathering dust, I'd love to have them. Copper conducts heat better than aluminum, but as a metal it's more expensive and doesn't extrude in fancy shapes the way aluminum does. It's also more chemically reactive; aluminum just creates a skin of aluminum oxide (aka sapphire, ruby, corundum) and hunkers down for the long haul.
Grey |
Nah, copper works the same, and even without having to do anything to get the oxide layer ;)
Aluminum looks better when anodized than copper with an oxide layer though.
Anyhow, just reach out for a few thousand dollars, and you'll see for yourself :clown:
Magura :) |
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| Sawzall |
| I remember seeing someone's effort at heatsinking with a rather large sheet of copper. I would almost bet there was commercial interest in an art work pounded out of a sheet of copper that was also an audio amp. Wife Acceptance Factor being what it is.... And the decorative art market, not to mention the absurd numbers of audio equipment sold on the basis of "looks" alone. |
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