I finished my ACA monoblocks last weekend but didn't have time to listen to them (only let them run for a while and set bias). I bought two generic 19V 4.7A laptop chargers and these seem to work fine, although they do get warm after a while (not as warm as my own laptops charger though, so nothing to worry about). Can't wait to try them out on my Little Reds when I get back from my work trip tonight.
I have a medical grade XP Power 24V 130W switcher (http://www.farnell.com/datasheets/310596.pdf) and would like to use this to power both amps, as I suspect that it will be more reliable than the two generic chargers. With PFC and 120KHz switching I'm hoping it will be a better performing and better sounding option. I have installed 30000uF output caps on the amps, and given the high sensitivity of the Tannoys I'd rather use a robust supply that can be left on continuously to avoid switch off thump. I've used massive heatsinks that barely warm up so have no concerns about amplifier heat over time. Also, living in Scotland means that any increase in room ambient temperature is welcome
To add a degree of filtering to the PSU I installed 0.1ohm series resistors and upgraded the onboard decoupling from 10uf to 1000uf Rubycon ZLH. Right now I get about 20.5V before and 19.5V after the series R.
If I use the 24V supply, do you think I'd be better to add a larger series R (2.2ohm?) to knock the supply back down to 19V or so, or stick with the lower series R and higher rail voltage? All caps are happy with 24V so no issues there. My temptation would be to go with the higher series R to clean up the supply, but have read this might compromise supply regulation. Would this be an issue given the pretty constant current drawn by the ACA,and larger onboard decoupling caps?
Thanks to Nelson, as ever, and to the rest of the team.
I have a medical grade XP Power 24V 130W switcher (http://www.farnell.com/datasheets/310596.pdf) and would like to use this to power both amps, as I suspect that it will be more reliable than the two generic chargers. With PFC and 120KHz switching I'm hoping it will be a better performing and better sounding option. I have installed 30000uF output caps on the amps, and given the high sensitivity of the Tannoys I'd rather use a robust supply that can be left on continuously to avoid switch off thump. I've used massive heatsinks that barely warm up so have no concerns about amplifier heat over time. Also, living in Scotland means that any increase in room ambient temperature is welcome
To add a degree of filtering to the PSU I installed 0.1ohm series resistors and upgraded the onboard decoupling from 10uf to 1000uf Rubycon ZLH. Right now I get about 20.5V before and 19.5V after the series R.
If I use the 24V supply, do you think I'd be better to add a larger series R (2.2ohm?) to knock the supply back down to 19V or so, or stick with the lower series R and higher rail voltage? All caps are happy with 24V so no issues there. My temptation would be to go with the higher series R to clean up the supply, but have read this might compromise supply regulation. Would this be an issue given the pretty constant current drawn by the ACA,and larger onboard decoupling caps?
Thanks to Nelson, as ever, and to the rest of the team.
I've spent a couple of hours listening to my ACA monos with standard 19V 4.7A laptop PSUs. Preamp is MFA TVC and speakers are Tannoy Little Reds. I have been using UCD180HG with beefy linear supply until now.
The ACAs have a superficially softer (less edgy) sound, yet small details float free of the mix so there is no lack of transparency. Warmth without a lack of focus. There is noticeable weight and focus to bass, making kick drums more physical than I was aware of with the UCDs (I increased the output caps to 30000uf to prevent problematic roll-off or phase shift in low bass - I won't be turning the amps off with speakers connected though!).
The UCDs are more powerful and dynamic. They seem to have a tighter grip on the loudspeakers but this comes with a slightly edgier presentation.
With some vinyl I need to run my TVC preamp at full volume, but don't feel the need to use the +6dB switch on the back of the preamp, so I have enough range.
All in all a lovely little amp that does a great job of making me smile and unwind.
Thanks to all for the help.
The ACAs have a superficially softer (less edgy) sound, yet small details float free of the mix so there is no lack of transparency. Warmth without a lack of focus. There is noticeable weight and focus to bass, making kick drums more physical than I was aware of with the UCDs (I increased the output caps to 30000uf to prevent problematic roll-off or phase shift in low bass - I won't be turning the amps off with speakers connected though!).
The UCDs are more powerful and dynamic. They seem to have a tighter grip on the loudspeakers but this comes with a slightly edgier presentation.
With some vinyl I need to run my TVC preamp at full volume, but don't feel the need to use the +6dB switch on the back of the preamp, so I have enough range.
All in all a lovely little amp that does a great job of making me smile and unwind.
Thanks to all for the help.
I did some experiments with small changes in the bias voltage in post 576 of this thread. But I have no data with a 24V rail. Changes in the bias voltage affect open loop gain and distortion. You may wish to experiment.
Last edited:
Hi guys,
I recently built the ACA and it sounds very good. I keep wondering if the sound would be improve if I would use lateral mosfet.. I have a bunch of NOS TO-3 2SK134 I have had for nearly 30 years..can someone tell me if I could use it as Q1 on the schematic. If it's possible I would probably buy a second set of PCB and have a second ACA.
Would I have to modify any values of the ACA to make it work with the 2SK134.
I also have a bunch of 2SK176 if you think the 2SK134 won't work.
Thanks for the help,
Eric
I recently built the ACA and it sounds very good. I keep wondering if the sound would be improve if I would use lateral mosfet.. I have a bunch of NOS TO-3 2SK134 I have had for nearly 30 years..can someone tell me if I could use it as Q1 on the schematic. If it's possible I would probably buy a second set of PCB and have a second ACA.
Would I have to modify any values of the ACA to make it work with the 2SK134.
I also have a bunch of 2SK176 if you think the 2SK134 won't work.
Thanks for the help,
Eric
I've had a set el84 tube amp and currently using a Sure tk2050 D amp. I also use fullrange MLTL's w/ wildburro drivers.
I'd like to build the new ACA kit. They sure look nice. I'm guessing the output would be about the same as my set amp. (5-6 watts). Is the SQ on par with the set and tk2050 amps? I listen at low volumes.
Mark
I'd like to build the new ACA kit. They sure look nice. I'm guessing the output would be about the same as my set amp. (5-6 watts). Is the SQ on par with the set and tk2050 amps? I listen at low volumes.
Mark
Thanks, The Sure SQ is somewhat close to the tube set quality. I sold the tube amp. Got tired of messing with it. I do like Class-A amps and mono blocks. The ACA might just fit my needs.
Mark
Two problems would have to be solved. First is the biasing. Q2 would probably be ok but Q1 would have a problem and the bias pot could not adjust the output to 10V. One solution might be to use a MOSFET for Q4 so that there would be a positive voltage on it's gate. The second problem would be a change in the open loop gain. I'm not 100% sure about this but I recall lateral MOSFETs have a transconductance of about 1 mho while in the HexFets it's in the range of 5 to 10 mho. So it would take a lot of tinkering to get the amp to function, then the performance might not be as expected.
The chassis have now finished production and be shipped by Air on Monday or Tuesday directly to the USA. When they arrive at the warehouse they'll go straight out to everone that has pre-ordered first.
Thanks everyone for their support over the last year on making this happen. It's been a fun and rewarding journey and I can't wait to see pictures of finished kits in place in various systems. I'll post some more hi-res pictures of the final chassis as soon as I have them.
You can pre-order the chassis until they've all been accounted for.
Thanks everyone for their support over the last year on making this happen. It's been a fun and rewarding journey and I can't wait to see pictures of finished kits in place in various systems. I'll post some more hi-res pictures of the final chassis as soon as I have them.
You can pre-order the chassis until they've all been accounted for.
