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SO if the choke would follow the filter caps, I would see an increase in rail voltage? It seems at one time I had around 35 volts no load with the chokes where they are, but lost the volts with the load of the amp. If I place the choke after the filter caps, I would get my volts back as well as retain the filtering of the choke?
I was conterned about the rail going over 30 volts, though I do have the 499 ohm
resistor on the drain of Q4, as well as the other changes suggested to good effect!
SO if the choke would follow the filter caps, I would see an increase in rail voltage? It seems at one time I had around 35 volts no load with the chokes where they are, but lost the volts with the load of the amp. If I place the choke after the filter caps, I would get my volts back as well as retain the filtering of the choke?
I was conterned about the rail going over 30 volts, though I do have the 499 ohm
resistor on the drain of Q4, as well as the other changes suggested to good effect!
If your amp sounds good with a choke input filter, no need to worry much about lower voltage at the amp boards. A choke input filter is very effective, and behaves as you have described — the output voltage settles to its value when under load. Since your caps are already rated for the higher no-load voltage then you’re Ok.
You could try adding 1.0 uF or 2.2 uF film caps on the output of the rectifiers. Those would filter the diode switching noise. See how the power rails respond, and listen to the amp.
You could try adding 1.0 uF or 2.2 uF film caps on the output of the rectifiers. Those would filter the diode switching noise. See how the power rails respond, and listen to the amp.
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I added a 8.2 poly film cap between rectifier and choke. Voltage about the same,
but nice and quiet. Dropped bias to 12.4 volts. The ACA has more robust bass than my Tubelab SSE tube amp which has about 6 watts a channel, but the ACA sounds very similar to the tubes, not disappointing to me at all.
Good enough to let it stay the way it is, so no more excuses to not get taxes done!
I added a 8.2 poly film cap between rectifier and choke. Voltage about the same,
but nice and quiet. Dropped bias to 12.4 volts. The ACA has more robust bass than my Tubelab SSE tube amp which has about 6 watts a channel, but the ACA sounds very similar to the tubes, not disappointing to me at all.
Good enough to let it stay the way it is, so no more excuses to not get taxes done!
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......to those who wonder if the amp camp has the potential to sound better with
higher voltages, I would say yes. I have been experimenting with power supplies, and different arrangements. I am using an 300 VA Antek 3225 torodial that has 25 volt secondaries. I tried setting it up dual mono, running each secondary through its own bridge and then through a 10mH choke, then 20,400uf of filter cap reserve for each channel. I could only muster about 22.5 volts per channel under load. It was quiet, sounded good. Tungsten suggested swapping the order of the choke by placing it second in line after a poly cap to filter out possible diode bridge noise. My voltage rails picked up maybe a half a volt with that arrangement.
I then removed 1 choke, paralleled the two 25 volt secondaries, and added 27,200uf of filter after the bridge. Then I ran this into the 10mH choke, then split that into the individual 20,400uf cap reserve that each channel has. My voltage rail now is 30.5 volts under load, and I have bias set at 15.5 volts. The power supply is no longer strickly dual mono, but I was gambling that what I might gain with the higher rails would compensate, and I believe it sounds like it has paid off.
The amp sounds more alive and in room than ever before. I am happy.
I have also applied the other suggestions that Tungsten Audio has documented, all of them worthwhile.
I am using an IRFP 044 for Q1 and IRFP 140 for Q2. Great sounding!
......to those who wonder if the amp camp has the potential to sound better with
higher voltages, I would say yes. I have been experimenting with power supplies, and different arrangements. I am using an 300 VA Antek 3225 torodial that has 25 volt secondaries. I tried setting it up dual mono, running each secondary through its own bridge and then through a 10mH choke, then 20,400uf of filter cap reserve for each channel. I could only muster about 22.5 volts per channel under load. It was quiet, sounded good. Tungsten suggested swapping the order of the choke by placing it second in line after a poly cap to filter out possible diode bridge noise. My voltage rails picked up maybe a half a volt with that arrangement.
I then removed 1 choke, paralleled the two 25 volt secondaries, and added 27,200uf of filter after the bridge. Then I ran this into the 10mH choke, then split that into the individual 20,400uf cap reserve that each channel has. My voltage rail now is 30.5 volts under load, and I have bias set at 15.5 volts. The power supply is no longer strickly dual mono, but I was gambling that what I might gain with the higher rails would compensate, and I believe it sounds like it has paid off.
The amp sounds more alive and in room than ever before. I am happy.
I have also applied the other suggestions that Tungsten Audio has documented, all of them worthwhile.
I am using an IRFP 044 for Q1 and IRFP 140 for Q2. Great sounding!
Very interesting to hear about your results. Basically what you did was swap a dual mono LC "swinging choke" filter for each channel to a CL-C arrangement, with separate final stage caps for each channel. You probably get most of the benefits of dual-mono this way.
The higher voltage seems to work well with the Mosfets. I like that you were willing to experiment with the IRFP044 for the current source while using IRFP140 as the common source amplifier. I have a few of the IRFP044 devices that I plan to use in a similar manner.
The higher voltage seems to work well with the Mosfets. I like that you were willing to experiment with the IRFP044 for the current source while using IRFP140 as the common source amplifier. I have a few of the IRFP044 devices that I plan to use in a similar manner.
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Howdy and good day to you!
The 30 volt rails on the ACA do run a bit hotter than 22-24 volt rails, but I can hold my hand on the heatsink for 5 seconds easy, even longer. I am using the kit heatsinks, but have mounted the amp and power inside a B&K ST 202 case. The 202 heatsinks are a bit larger than the ST 140 ones, but the case is the same. I bolted the ACA sinks to the ones in the 202 case, and they get warm, but you could hold them all day. I do also have a 499 ohm resistor on the drain of Q4 the input FET. I also have increased C4 to 1000uf, an Elna Silmic II.
It is a big difference to my ears of the sound of those mosfets used in the amp with the higher rails, a thought that was floated by Tungsten Audio.
It is a great little amp that got better!
Den
Howdy and good day to you!
The 30 volt rails on the ACA do run a bit hotter than 22-24 volt rails, but I can hold my hand on the heatsink for 5 seconds easy, even longer. I am using the kit heatsinks, but have mounted the amp and power inside a B&K ST 202 case. The 202 heatsinks are a bit larger than the ST 140 ones, but the case is the same. I bolted the ACA sinks to the ones in the 202 case, and they get warm, but you could hold them all day. I do also have a 499 ohm resistor on the drain of Q4 the input FET. I also have increased C4 to 1000uf, an Elna Silmic II.
It is a big difference to my ears of the sound of those mosfets used in the amp with the higher rails, a thought that was floated by Tungsten Audio.
It is a great little amp that got better!
Den
Hello there. I'm thinking of getting a pair of V1.6 ACA boards to build up a simple single box stereo ACA. I've found TungstenAudio's excellent mark up of all of his mods. I'll probably go with the standard 24VDC SMPS for now (maybe consider a linear PS later). A couple of questions:
1. Do all the resistor changes also apply to a plain stereo setup or are they intended for mono block setups?
2. Of the capacitor changes (to Nichicons) is one of them (say C4?) more significant than the others or do they all make a significant difference together?
Thanks,
Andrew
1. Do all the resistor changes also apply to a plain stereo setup or are they intended for mono block setups?
2. Of the capacitor changes (to Nichicons) is one of them (say C4?) more significant than the others or do they all make a significant difference together?
Thanks,
Andrew
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Hi Andrew,
The Tungsten Audio mods pertain to the regular stereo setups. They do make a noticeable improvement to an already great amp. Enjoy your adventure
One more update
How is it going Andrew? I made one more update to the amp. Added 66,000uf
to make the first filter bank. I previously had 27,000uf, but bought a couple 33,000uf Nichicon 63 volt caps which replaced the previous 27,000uf.
That has boosted my voltage rails to around 32 volts, which downstream becomes right at 30 volts under load. The amp sounds clearer, and is quieter than
it was before, which was pretty darn quiet. This assemblage sits inside an old
B&K ST-202 case. I made one other change which was I changed the 10pf silver mica cap that was paralleling the R12, a Tungsten Audio suggestion, to a 27pf
silver mica. I really like the way the amp sounds, though the extra volts do warm
it up, but I can still rest my hands on the primary heat sinks for more than 5 seconds. The exterior sinks from the B&K continue to dissipate in the rear.
I set the bias at 15.4 volts.
How is it going Andrew? I made one more update to the amp. Added 66,000uf
to make the first filter bank. I previously had 27,000uf, but bought a couple 33,000uf Nichicon 63 volt caps which replaced the previous 27,000uf.
That has boosted my voltage rails to around 32 volts, which downstream becomes right at 30 volts under load. The amp sounds clearer, and is quieter than
it was before, which was pretty darn quiet. This assemblage sits inside an old
B&K ST-202 case. I made one other change which was I changed the 10pf silver mica cap that was paralleling the R12, a Tungsten Audio suggestion, to a 27pf
silver mica. I really like the way the amp sounds, though the extra volts do warm
it up, but I can still rest my hands on the primary heat sinks for more than 5 seconds. The exterior sinks from the B&K continue to dissipate in the rear.
I set the bias at 15.4 volts.
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Compared to original ACA strd. 19V. I confirmed 24V. has an increase sound sparkle and transients. At a cost also increase heatsink temp. 49°C to 55°C.
Must be stated in that situation bias setting is proportionaly higher, and half plus 0,4V. is not enough. Sound is muffled at 12,4V. bias. Is much better 12,6V. zone it breaths much more. Further up to 12,8 or higher, decreases again lightening too much the sound in that case.
Must be stated in that situation bias setting is proportionaly higher, and half plus 0,4V. is not enough. Sound is muffled at 12,4V. bias. Is much better 12,6V. zone it breaths much more. Further up to 12,8 or higher, decreases again lightening too much the sound in that case.
Altrough in my case, I have high sensitivity fullrange speaker, (around 95dbw I guess, paper cone 8" and phonelic spider). My preferred power supply setting is 23V. Bias close to 12,1V.
Other modification to my ACA amplifier are delete the feedback circuitry, giving more bass and treble extension where fullrange are most in need. That converts the amp to pure current source as is Pass F2 amplifier by instance. Can't be used for crossovers in multiway speakers, not sure if interests sharing just here or start new thread "beware only Fullrange users"
.
Other modification to my ACA amplifier are delete the feedback circuitry, giving more bass and treble extension where fullrange are most in need. That converts the amp to pure current source as is Pass F2 amplifier by instance. Can't be used for crossovers in multiway speakers, not sure if interests sharing just here or start new thread "beware only Fullrange users"
.