The ACA has pretty low gain (14dB I believe) so it's certainly possible you need to
crank it up more compared to your other amp. That said, it should only take
about 1.3V RMS input to drive the ACA to 5W.
What source are you using? Do you know its output level?
Is there some way for you to measure the output level at the preamp?
crank it up more compared to your other amp. That said, it should only take
about 1.3V RMS input to drive the ACA to 5W.
What source are you using? Do you know its output level?
Is there some way for you to measure the output level at the preamp?
I've successfully built my stock kit ACA pair and I'm surprised at how good they sound right off the bat. So that is with the 19v switchers. I have a pair of 24v switchers with adequate current supply. I will do the re-biasing this weekend and give them a try. I am curious though, will the change to 24v supplies increase the watts? the gain? dynamics?
Thanks.......
Thanks.......
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Hey Variac,
Glad to post my impressions, but don't have a way (or know how to) determine change in gain or power.
In the end though, it's about how it sounds of course!
zekeblue,
If you increase the voltage rail from +19V to 24V, you should theoretically get 8 watts/ch instead of 5. Overall gain should remain at 14dB because no changes were made to the feedback resistors R11,R12 or to the operating point of Q1 which is the main amplification element here. I would not advise messing with the feedback resistors as that will affect the output impedance which knowing the damping factor of 3 (read: amp camp article), is already a rather high 2.67 ohms. Increasing feedback will reduce overall gain, but lower output impedance at the same time (which is good). However, lowering gain on an amplifier that already has low gain (14 dB) will require more gain from your preamp to reach a 'reasonable' volume. Changing the feedback will change the sonic landscape, sometimes for the worse. It's a fine balance that Papa has determined.
Will the dynamics change? Maybe. That depends on how hard you are pushing this amplifier (i.e. how loud you listen), what your speaker efficiency is, how large your room is, how far away you listen, etc...but a change of 5 watts to 8 watts is not much in my world.
But do share your experiences.
Best,
Anand.
If you increase the voltage rail from +19V to 24V, you should theoretically get 8 watts/ch instead of 5. Overall gain should remain at 14dB because no changes were made to the feedback resistors R11,R12 or to the operating point of Q1 which is the main amplification element here. I would not advise messing with the feedback resistors as that will affect the output impedance which knowing the damping factor of 3 (read: amp camp article), is already a rather high 2.67 ohms. Increasing feedback will reduce overall gain, but lower output impedance at the same time (which is good). However, lowering gain on an amplifier that already has low gain (14 dB) will require more gain from your preamp to reach a 'reasonable' volume. Changing the feedback will change the sonic landscape, sometimes for the worse. It's a fine balance that Papa has determined.
Will the dynamics change? Maybe. That depends on how hard you are pushing this amplifier (i.e. how loud you listen), what your speaker efficiency is, how large your room is, how far away you listen, etc...but a change of 5 watts to 8 watts is not much in my world.
But do share your experiences.
Best,
Anand.
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I now have the ACA's running with 24v/6amp switching supplies. Tough to compare with so much time between listening, having to re adjust for 12.5v after waiting an hour. I will listen this way for a week and switch back to 19v to see if I can tell more definitively.
Initial impressions are positive. It does seem that gain is slightly higher based on my typical volume control settings. It also seems like there is more "punch" or liveliness in the music. On the potential downside, I think I may be hearing (note the tentative language) something that I might describe as over-saturation.
I'm not solidly confident in any of these impressions. Placebo and expectations are very powerful. Hence, my desire to go back to 19v after a bit to compare again.
Two questions for anyone that cares to offer opinion....
1- Might there be any sonic benefit (or electrical risk) in changing the voltage in the pot adjustment up or down a bit? If that sense of over-saturation is real, perhaps this could reduce the effect.
2-Heat! I'm using the stock chassis so far. With 24v, the sinks definitely are hotter. I can put my hand on it for about 5-7 seconds before it gets too uncomfortable. With the 19v, it was definitely hot, but I could keep my hand on the heat sink. Is this too hot? I have a little usb fan blowing across them for now, but would like to do away with that if it is ok. How hot is too hot?
If I decide to keep these little guys and run them at 24v, I can also make that move to a larger single chassis.
I am pleased with the sound overall. I've been running a Dennis Had Inspire single ended pentode at about 10wpc, so I'm talking competitive here. I'm feeding the ACA's with his Inspire LP-2 preamp. Speakers are based on Omega Super Alnico Monitors (single driver, 95db) that are quite sensitive to upstream changes. It is actually a quad amped four-way active speaker system with Yamaha beryllium tweeters high passed at 15kHz, 2nd order, Rythmik based 8" mid-woofers and a pair of Rythmik F12 subs. The Omegas and the mid-base modules have a Marchand active xover in front of them (picture - before the ACA's and before rebuilding the little tweeter cabinets after realizing that pointing up was the best arrangement).
Given this system design, the ACA's have everything below about 70Hz eliminated and sent to the woofers, so I don't have a good sense of bass performance with the ACA's. I will give them a chance to run full range out of curiosity.
Thanks!
Zekeblue,
Regarding heat...pin 2 of MOSFET Q1 should not be more than 65 degrees C. Measure it to be sure.
Thanks for the sonic impressionsAnd cool system!
Best,
Anand.
Thanks!
Digital probe type thermometer on its way!
ACA Baby Steps
My head is swimming with little tiny farads, SITs, SICs, jfets, fetrons, etc from reading nearly 3000 posts on this board. The ACA kit showed up last week, and I got a chance to get going on it tonight.
I tried to buy one of these back in 2014, only to find they were sold out. I signed up to be notified when they came back in stock. Fast forward 2+ years, after completely forgetting about it, and I get an email a few weeks ago saying they are available. I didn't have to think very long before ordering.
This is one of those things that will definitely challenge me, and has been on the build-it bucket list for a while. Hoping to learn enough to eventually tackle a pre-amp build and then speakers to create an entire system. A few pics are attached. Not the best soldering, but I think it will work.
My head is swimming with little tiny farads, SITs, SICs, jfets, fetrons, etc from reading nearly 3000 posts on this board. The ACA kit showed up last week, and I got a chance to get going on it tonight.
I tried to buy one of these back in 2014, only to find they were sold out. I signed up to be notified when they came back in stock. Fast forward 2+ years, after completely forgetting about it, and I get an email a few weeks ago saying they are available. I didn't have to think very long before ordering.
This is one of those things that will definitely challenge me, and has been on the build-it bucket list for a while. Hoping to learn enough to eventually tackle a pre-amp build and then speakers to create an entire system. A few pics are attached. Not the best soldering, but I think it will work.
Attachments
I'm just ahead of you having finished my build a week ago or so. My initial impression was very positive. But with just a week with them, I am really surprised at how good these babies sound! Going up to 24v is a definite improvement. No tentativeness about that now. At first I was thinking that if the ACA's sounded good, I would jump to a FW J2. But they sound good enough that I just ordered a pair of regulated linear 24v supplies. And thinking about getting a large chassis (to replace four) for a dual mono amp. It would be an amp no longer an experiment, but a darn good amp that is a keeper!
Just some words to build your anticipation. If my experience is any indication, your anticipation will be rewarded!
Zekeblue,
Regarding heat...pin 2 of MOSFET Q1 should not be more than 65 degrees C. Measure it to be sure.
Thanks for the sonic impressions
Best,
Anand.
Well, interesting. After running about a week with a fan, it now seems to be running slightly less hot. I can hold my hand on the sinks for a good 10 seconds after they are warmed up an hour or so. Thermometer reads ~50C both on the outside of heatsinks and pin 2 of Q1. Bias is still at 12.5v (24v PS). If those temps are accurate, I guess I am fine. I read, somewhere I can longer find, to have the heat sinks not measure more than 25C above room temp. That would be 55C for me. Seems I'm ok. But I have a very quiet "Cooler Guys" fan that I can lay on top to be safe. I may get larger chassis that will fit both the amps and the guts of the linear PS that are coming, either a pair keeping them monos or a single larger for dual mono. In either case, I will make sure of larger sinks to do away with the fan.
ACA Baby Steps 2
The first one is done - I plugged it in, closed my eyes and flipped the switch. Success!! No pops, bangs or smoke! It's heating up for a bias adjustment as I type this.
Next step is to plug it in to a speaker and see if it will generate any dBs.....
The first one is done - I plugged it in, closed my eyes and flipped the switch. Success!! No pops, bangs or smoke! It's heating up for a bias adjustment as I type this.
Next step is to plug it in to a speaker and see if it will generate any dBs.....
Attachments
The first attempt was to connect an iPod to the amp then to the B&W CM1s (84 dB sensitivity). My expectations are low, but hey it's worth a try. iPod volume limit on max, volume on max. Nothing.....wait, I can barely hear Buddy Guy and "Hammer And A Nail" if I press my ear up against the tweeter. Back to the drawing board.
Insert Schiit Magni 2 Uber headphone amp between iPod and ACA, and presto! Room-rattling sound that will easily drive me from my 12' x 12' office. Sweet sound, too, even if it is mono.
Now on to the second monoblock, then pre-amp, and some high sensitivity speakers. The build list is growing!
Hi Dennis
Unfortunately, I did select the UPS option which was listed at $44 US. The only other option available to me was USPS International, which was $111 US. In the end, UPS charged an additional $97.15 CAD for brokerage and taxes, which is about $75 US. So I ended up paying $119 US for shipping for an 11 pound package from PA to AB. Basically highway robbery, as far as I'm concerned.
I have had problems with UPS charging ridiculous brokerage fees in the past, but it has been in the distant past. Recently, I have had no issues with them. Until this package arrived.
All I can say is I really do appreciate this kit and the amps, but I'm pretty disappointed in the international shipping choices offered by the diyAudio store. I'm not a shipping expert, and I appreciate the efforts by the diyAudio store staff, but I find it hard to believe there are not better choices out there. I have had other items of a similar size and weight shipped to me that cost significantly less.