I'm currently thinking of getting several commerically built Aleph-30's to power my linearray system. The problem is that with 4-5 of them they'd be putting out 1000 watts or more. At 1000 watts it's like having a little space-heater running full-tilt. While this is great in Iowa during the winter, what do I do in the summer?
Any ideas on how I could derate my Aleph-30's to run at say 10-15 watts/channel. Then in the winter or when I want to rock out crank them up?
I'm thinking a variac might do the trick, but what's the limitations on using one?
Any ideas on how I could derate my Aleph-30's to run at say 10-15 watts/channel. Then in the winter or when I want to rock out crank them up?
I'm thinking a variac might do the trick, but what's the limitations on using one?
I was fooling with the idea some time ago, thinking of adding a relay changing between two biasresistors in my Zen4 - but dropped it, because basically I think that it is stupid robbing class a amps what the are good at - they sound good with high bias - if you try to run them into class B land - why not go all the way, and build a box full of gainclones - they sound really, really good, and I have got some awsome bass out of them, paralleling two 3875 pr. channel, and using a comibnation of big and small electrolytics - in many aspects, I like this type of amp over my zen 4 - especially when using low impedance loads. The Gain Clones have very low bias current, and thus will not heat your room by more than a fraction of a degree 
Cheers !
Hans - from Denmark, where the weather has gone crazy, making me wish I had finished some more class A amps....
Cheers !
Hans - from Denmark, where the weather has gone crazy, making me wish I had finished some more class A amps....
But what if you dont need 30-watts?
Ok, I agree that Class-A still sounds best. But what if you only NEED about 10-watts Class A most of the time. Maybe your speakers are efficent or you dont need to play loud most of the time.. And you can get some good deals on some already built Aleph 30's?
(I've currently got several TI Equibit digital amps and they just arent cutting it sonically.)
Ok, I agree that Class-A still sounds best. But what if you only NEED about 10-watts Class A most of the time. Maybe your speakers are efficent or you dont need to play loud most of the time.. And you can get some good deals on some already built Aleph 30's?
(I've currently got several TI Equibit digital amps and they just arent cutting it sonically.)
mini-a's as good?
Are the mini-a's as good sounding within their power range as Aleph-30's?
Is their a best mini-a variation?
I'm still thinking someone (Nelson?) knows how to best limit the power of an Aleph 30. I thought I heard him saying that a variac could limit power and was also useful for initial testing of an amp.
Are the mini-a's as good sounding within their power range as Aleph-30's?
Is their a best mini-a variation?
I'm still thinking someone (Nelson?) knows how to best limit the power of an Aleph 30. I thought I heard him saying that a variac could limit power and was also useful for initial testing of an amp.
I think a Variac would work, but if you want to use so many amps, you need a really big Variac. They can be very expensive, if i'am not wrong.
I think the best solution would be, to build a "Power down" circuit in to all the amps. You have to find the resistor(s) that set the bias current for the outputstage and replace it with a higher value resistor. That will set the bias to a lower value, to go back to normal bias, you then add a switch/relay and another resistor in parrallel with the first one. (The value of both resistors have to be equal to the original bias-resistor). Now you should be able to simply "flip a switch" to change the amount of bias and heat production. (You should turn the amps off before operating the switch to avoid noise and destruction of parts).
Since I don't know the A30 amps my self, I can't tell you exactly how to do it, but I have seen the circuit described above, used in other class A amps with power down function.
Hope I could help!
I think the best solution would be, to build a "Power down" circuit in to all the amps. You have to find the resistor(s) that set the bias current for the outputstage and replace it with a higher value resistor. That will set the bias to a lower value, to go back to normal bias, you then add a switch/relay and another resistor in parrallel with the first one. (The value of both resistors have to be equal to the original bias-resistor). Now you should be able to simply "flip a switch" to change the amount of bias and heat production. (You should turn the amps off before operating the switch to avoid noise and destruction of parts).
Since I don't know the A30 amps my self, I can't tell you exactly how to do it, but I have seen the circuit described above, used in other class A amps with power down function.
Hope I could help!
The problems you have to deal with are mostly offset and thumps.
Refering to the A30 schematic, you can set the amplifier to bias
at a lower level by switching the values of R19 and R14. If you
just switch R19, you will get offset, which may not be much of a
problem if the amp is capacitively coupled in the feedback loop
and you can put up with the transient noise.
If the offset and transient are an issue, then turn the amp off
and switch the values.
Refering to the A30 schematic, you can set the amplifier to bias
at a lower level by switching the values of R19 and R14. If you
just switch R19, you will get offset, which may not be much of a
problem if the amp is capacitively coupled in the feedback loop
and you can put up with the transient noise.
If the offset and transient are an issue, then turn the amp off
and switch the values.
My homebuilt A30 is a little much for it's heat sinks. I intentionally gave it higher than spec'd rails so it gets hot. If there's the slightest bit of breeze it's OK, but where mine lives there isn't much of a breeze, so I modified the power supply to switch in sets of inductors to give it a LC power supply instead of the usual C power supply. In addition to the additional filtering it lowers the rail voltage, thereby lowering power. I don't know if a stock A30 chassis has enough space to add 4 inductors. I made the mistake of getting inductors that run too close to their rated current so I get a little mechanical hum when I have them in circuit, but I can switch them off at will.
Rob
Rob
Switching the values of R19 and R14?
Can the same power lowering effect be achieved by removing 2 output transistors (Q6/Q9)? How is this different than lowering the current source current by altering R19 and R14?
Also, can the input DC blocking cap(C11) be simply bypassed if you know for certain your source has no DC offset?
What R19 and R14 values would give roughly half the power of the normal A30? I guess that would mean 100watts roughly instead of 200 watts idle.
Thanks Nelson.
Can the same power lowering effect be achieved by removing 2 output transistors (Q6/Q9)? How is this different than lowering the current source current by altering R19 and R14?
Also, can the input DC blocking cap(C11) be simply bypassed if you know for certain your source has no DC offset?
What R19 and R14 values would give roughly half the power of the normal A30? I guess that would mean 100watts roughly instead of 200 watts idle.
Thanks Nelson.
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