fcel said:
Nope.,.,.
I've built a mini and a a30. I want to build an a3 with an a30 front end using brians boards. I am thinking that with 2 less devices per channel I can take the bias up a notch and get that sweet sound without more heat than a stock a30....although it will be a little harder on the devices since there will be 33% less of them.
I see your question now. I'm afraid I won't be in a position to answer that questions since it deals with design. I would ask Mr. Pass himself or search this forum?
My A30 runs real hot. I suspect I may have more questions after I have done more listening.
My A30 runs real hot. I suspect I may have more questions after I have done more listening.
mpmarino said:
I hope that it is ok for me to copy a small section of text from the pass masters A30 manual, it says what needs to be said.
The following is taken from the A30 manual.
We have increased the number of output power Mosfet devices from four per channel to six. The greater number of devices lowers the distortion and improves the damping factor by about 50%, and also allows us to run the bias up a bit, giving higher heat sink temperatures but with the same on-chip temperatures.
In short spreading the load across fewer devices will yield greater heat meaning that you may need to lower the bias or voltage to keep it cool.
Good job on getting it working. I haven't had time to finish mine yet.
I still have about 6 Aleph amp pcb sets left, and about 50 power supply boards (just got them in for Mark's KSA GB). I put them on my bottom of my chipamp.com order page if anyone wants them. I would recommend getting the amp pcb sets soon, as I don't know if there will be a reorder when they are gone. I expect to have extra power supply boards for quite a while.
Here is a picture from fcel:
--
Brian
I still have about 6 Aleph amp pcb sets left, and about 50 power supply boards (just got them in for Mark's KSA GB). I put them on my bottom of my chipamp.com order page if anyone wants them. I would recommend getting the amp pcb sets soon, as I don't know if there will be a reorder when they are gone. I expect to have extra power supply boards for quite a while.
Here is a picture from fcel:
An externally hosted image should be here but it was not working when we last tested it.
--
Brian
mark stones said:
I hope that it is ok for me to copy a small section of text from the pass masters A30 manual, it says what needs to be said.
The following is taken from the A30 manual.
We have increased the number of output power Mosfet devices from four per channel to six. The greater number of devices lowers the distortion and improves the damping factor by about 50%, and also allows us to run the bias up a bit, giving higher heat sink temperatures but with the same on-chip temperatures.
In short spreading the load across fewer devices will yield greater heat meaning that you may need to lower the bias or voltage to keep it cool.
Yes.. I have read that, thanks. He suggests higher heat sink temps which is what I am trying to avoid. My amp will be the same form factor as my oversinked mini a and I don't want to run into thermal issues. Not to mention I am sure the distortion of the a3 op section won't bother me a bit 🙂. I have also read that individual device bias..not total bias will yield better sound. I think that may have been from the master himself . OK..trying again..anyone?:
I am building an 'a30' with a 'a3' output section using brians boards. In other words, The a30 will be short 2 OP fets per channel . Do I need to mod anything in the front end or can I run the front end per the a30 schematic? I am thinking I can, as long as I am willing to play with r13brian(r19pass).
Thanks in advance,
Marc
Whoops..guilty as charged. a little search revealed this:
quote:
Originally posted by dw8083:
Was the Aleph 3 (not Aleph30) ever manufactured with balanced inputs from the Pass Labs factory?
I thought there was such a version, perhaps a later version?
Originally posted by Nelson Pass:
The factory did not make a balanced Aleph 3, but you can easily
use the Aleph 30 input without penalty.
D'oh!
quote:
Originally posted by dw8083:
Was the Aleph 3 (not Aleph30) ever manufactured with balanced inputs from the Pass Labs factory?
I thought there was such a version, perhaps a later version?
Originally posted by Nelson Pass:
The factory did not make a balanced Aleph 3, but you can easily
use the Aleph 30 input without penalty.
D'oh!
Here are more pics of fcel's amp:
http://www.briangt.com/gallery/aleph-fcel
Looks great!
If anyone else wants pics in my gallery for amps finished with the GB boards, e-mail me pictures. e-mail link on my website.
--
Brian
http://www.briangt.com/gallery/aleph-fcel
Looks great!
If anyone else wants pics in my gallery for amps finished with the GB boards, e-mail me pictures. e-mail link on my website.
--
Brian
Member
Joined 2002
Here is what my chassis state is so far.. Yes those are regulateors for my amps.. these are going to be 2 stereo block mini a's running at 15watts with 20v rail's. with regulated psu's.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
mpmarino said:
That brings up a good question. There's no doubt that it's
easier to get good measured performance with more devices
in parallel with a larger shared bias. First off, the bias is
higher, and second, the distortion associated with the Vgs
character will be lower.
At some point the capacitance of the parallel output stage
gets to be more than you want, and that argues for fewer
devices.
None of these effects are proportional, though. For a given bias
twice as many devices does not give twice as much
transconductance, nor does it give twice as much effective
capacitance, and practically speaking, you also don't get twice
the dissipation if they share the same heat sinking.
So the decision on how many devices to use comes down to
trying different quantities and seeing what you measure and
hear. More devices tends to give more bottom end emphasis,
and fewer tends to extend the top end, but this is not a hard
rule.
😎
Thanks for your advice and time Mr. Pass. The amp will serve duty driving a pair of 12" at 97dB/w from ~50Hz to ~1500Hz. I honestly think my mini would be up to it, but a 4 device a3 will be ALL good I'm sure! Just looking for liquid mids and some good 'snap' on this one. (IRFP140's are gonna be used.)
Thanks again...
Thanks again...
mpmarino said:
I have in memory that A3 has 125W dissipiation/channel and A30 "only" 100W ...
So I think you will not gain lower heatsink temp with that ...
But if you are in it because of higher bias per device - then that's something else ...
mini-A
I'm going to change subject here and ask a couple of questions on the mini-A amp. This is based on the signal and power supply boards by BrianGT.
All test performed with 75W light bulb connected in series on the primary side of transformer.
Sitiation:
1) Each channel is functional if the other channel is not connected to the shared power supply board (with CRC). Output DC is about 30mV and there is no hum. Light bulb is very dim.
2) With both channels connected to the shared power supply board, DC offset is about 150mV and there is a loud hum. Light bulb is still kind of dim.
3) For both of the above situation, all other measurements are about the same, except for the DC output which is high.
Questions:
Before I remove the light bulb, I wanted to get some feedback from this forum. Would the DC output comes down and the hum go away after the light bulb is being removed? I think I have tried all possible way of wiring the power supply ground wire but it doesn't make any difference. May be this is not a grounding issue?
Note:
The rail voltage is plus and minus 16V and I'm using IRFP240.
I'm going to change subject here and ask a couple of questions on the mini-A amp. This is based on the signal and power supply boards by BrianGT.
All test performed with 75W light bulb connected in series on the primary side of transformer.
Sitiation:
1) Each channel is functional if the other channel is not connected to the shared power supply board (with CRC). Output DC is about 30mV and there is no hum. Light bulb is very dim.
2) With both channels connected to the shared power supply board, DC offset is about 150mV and there is a loud hum. Light bulb is still kind of dim.
3) For both of the above situation, all other measurements are about the same, except for the DC output which is high.
Questions:
Before I remove the light bulb, I wanted to get some feedback from this forum. Would the DC output comes down and the hum go away after the light bulb is being removed? I think I have tried all possible way of wiring the power supply ground wire but it doesn't make any difference. May be this is not a grounding issue?
Note:
The rail voltage is plus and minus 16V and I'm using IRFP240.
No response?
I guess everybody did the start-up one channel at a time and then power up both channels when each individual channel are confirmed working properly. Anyway, here's my update ....
I took the plunge and power up both channels WITHOUT the light bulb. Both channel DC output drop down to earth level and the loud hum is gone. My mini-A is in fact working properly. Have played music through it for a couple hours already.
I'm still curious though ...
1) Why such a high DC output and loud hum when a light bulb is connected in series on the primary side? Voltage measurement at pertainment points (as per Pass schematic) are right on the spot except for the DC output, which is approx. 4 to 5 times higher when a light bulb is connected.
2) And where is this loud hum coming from when a light bulb is connected in series?
I guess everybody did the start-up one channel at a time and then power up both channels when each individual channel are confirmed working properly. Anyway, here's my update ....
I took the plunge and power up both channels WITHOUT the light bulb. Both channel DC output drop down to earth level and the loud hum is gone. My mini-A is in fact working properly. Have played music through it for a couple hours already.
I'm still curious though ...
1) Why such a high DC output and loud hum when a light bulb is connected in series on the primary side? Voltage measurement at pertainment points (as per Pass schematic) are right on the spot except for the DC output, which is approx. 4 to 5 times higher when a light bulb is connected.
2) And where is this loud hum coming from when a light bulb is connected in series?
Member
Joined 2002
Are you saying you get no or you do get hum when light bulb is connected in series ?
My mini a's hummed at first then i changed cables and volume pot.. I'm running every thing in passive mode with my tube buffer from the dac and i had some humage lastnight but stupid me put the volume pot right ontop of my cd player to witch has a SMPS inside 😀 well i figured that out asap..
My mini a's hummed at first then i changed cables and volume pot.. I'm running every thing in passive mode with my tube buffer from the dac and i had some humage lastnight but stupid me put the volume pot right ontop of my cd player to witch has a SMPS inside 😀 well i figured that out asap..
I get:
1) Loud hum
2) High DC output on both channel (1.5V)
ONLY when BOTH channels are connected to the shared power supply and WITH the light bulb connected in series on the primary side.
As described in my previous post, I have found out that the amp is actually working properly. I was curious as to why it's doing what it does- again, as described in my previous two posts.
1) Loud hum
2) High DC output on both channel (1.5V)
ONLY when BOTH channels are connected to the shared power supply and WITH the light bulb connected in series on the primary side.
As described in my previous post, I have found out that the amp is actually working properly. I was curious as to why it's doing what it does- again, as described in my previous two posts.
Measurement question
I bought 4 sets of the Mini/A30 boards from BrianGT. I stuffed one set as Mini's and three sets as Aleph 30's. I finished an A5 about a year ago where I learned (courtesy BDP) how to make the voltage measurements prior to installing the output boards/devices.
On all eight boards I see the ~9V drop across Z5, ~4.1Vgs on Q3, ~3.9Vgs on Q1,Q2. On seven boards I see ~4V drop across the 392R resistor (R18), the last board (an A30) I measure a drop of ~2.7V. Seven of the boards would seem to be good to go. Is this too low (ie, do I need to chase down the offending part(s))?
This resistor "sits" between the -V supply and the drain of Q2 and would seem to define the voltage drop across that resistor (I measured 2.7 volts between these points as well). What would cause the drain to be 1.3-2.3V too negative?
Thanks,
SteveA
I bought 4 sets of the Mini/A30 boards from BrianGT. I stuffed one set as Mini's and three sets as Aleph 30's. I finished an A5 about a year ago where I learned (courtesy BDP) how to make the voltage measurements prior to installing the output boards/devices.
On all eight boards I see the ~9V drop across Z5, ~4.1Vgs on Q3, ~3.9Vgs on Q1,Q2. On seven boards I see ~4V drop across the 392R resistor (R18), the last board (an A30) I measure a drop of ~2.7V. Seven of the boards would seem to be good to go. Is this too low (ie, do I need to chase down the offending part(s))?
This resistor "sits" between the -V supply and the drain of Q2 and would seem to define the voltage drop across that resistor (I measured 2.7 volts between these points as well). What would cause the drain to be 1.3-2.3V too negative?
Thanks,
SteveA
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