I have been asked by management to comment on a couple of subjects
relating to the updates on the original ACA.
Power supply:
It's not that the original 19V supply had any real problems, but it ran
warmer than I liked, had some RF noise (they all have some), and
being surplus had availability issues.
We have tested several 24V desktop switchers for use in these
amplifiers, and selected one, the Meanwell GST120A24-P1M.
A good price has been negotiated from distribution , it is reliable with
warranty, runs cool, and was quieter than the others tested. It will be
available in the store.
Performance of the newer ACA:
The name has gotten confused, originally being ACA 1.1 on the artwork,
then ACA 1.5. Doesn't matter, it's now the 1.5 for sure.
I have run some distortion and power curves on these various versions
to give some idea of the differences in performance. You will see these
below, and to put it simply, the ACA 1.5 has lower distortion, and with the
24V transformer, more power. Probably the cheapest and most effective
tweak you would ever want.
You can use also this supply on the original ACA, but you will want to
adjust the DC value on the output up to 12V. You can also adjust the
feedback resistor and bias resistors down to the values of the ACA 1.5.
The ACA 1.5 being stereo, there is the possibility of driving it with
balanced lines so as to have more power. You can install the XLR
input on the back, and if you have a balanced source, you're all done,
you just connect your speaker across the black output terminals,
with the left ch being "+" phase, and the right ch being "-" phase
(the channels each being inverting, the red terminals are ground,
and not used).
Any questions, you can post them here.
🙂
relating to the updates on the original ACA.
Power supply:
It's not that the original 19V supply had any real problems, but it ran
warmer than I liked, had some RF noise (they all have some), and
being surplus had availability issues.
We have tested several 24V desktop switchers for use in these
amplifiers, and selected one, the Meanwell GST120A24-P1M.
A good price has been negotiated from distribution , it is reliable with
warranty, runs cool, and was quieter than the others tested. It will be
available in the store.
Performance of the newer ACA:
The name has gotten confused, originally being ACA 1.1 on the artwork,
then ACA 1.5. Doesn't matter, it's now the 1.5 for sure.
I have run some distortion and power curves on these various versions
to give some idea of the differences in performance. You will see these
below, and to put it simply, the ACA 1.5 has lower distortion, and with the
24V transformer, more power. Probably the cheapest and most effective
tweak you would ever want.
You can use also this supply on the original ACA, but you will want to
adjust the DC value on the output up to 12V. You can also adjust the
feedback resistor and bias resistors down to the values of the ACA 1.5.
The ACA 1.5 being stereo, there is the possibility of driving it with
balanced lines so as to have more power. You can install the XLR
input on the back, and if you have a balanced source, you're all done,
you just connect your speaker across the black output terminals,
with the left ch being "+" phase, and the right ch being "-" phase
(the channels each being inverting, the red terminals are ground,
and not used).
Any questions, you can post them here.
🙂
Attachments
and yes , question regarding 1.1 vs. 1.5 version , is certainly most intriguing and important one in last decade .....
Is 12V the correct value for bias adjust for 24 V PSU? .....so half the rail voltage?
For the 19 V PSU it was 10 V .....but the 100% correct value is maybe 9.5 V ?
For the 19 V PSU it was 10 V .....but the 100% correct value is maybe 9.5 V ?
It's not actually very critical. I would stay with the quoted numbers, as
they gave the maximum output wattage.
they gave the maximum output wattage.
It looks like there will be one small difference. I was asked to provide
mounting holes on the 20mm pattern as well so that the board will
also mount nicely on the bigger sinks in the store. There's room for them.
mounting holes on the 20mm pattern as well so that the board will
also mount nicely on the bigger sinks in the store. There's room for them.
😀and yes , question regarding 1.1 vs. 1.5 version , is certainly most intriguing and important one in last decade .....
It seems there is not much gain in power to drive the ACA in balanced mode. 7W vs. 10W at 1% distortion in 8 ohm?
Threre is a relative big improvement in performance going from 19V to 24V. Is 24V the optimal voltage or could we still se a improvement going to e.g. 28V?
Hoes does the ACA perfrom driving a 4 ohm speaker?
Is the output cap large enough to drive a 4 ohm speaker at low frequencies?
Threre is a relative big improvement in performance going from 19V to 24V. Is 24V the optimal voltage or could we still se a improvement going to e.g. 28V?
Hoes does the ACA perfrom driving a 4 ohm speaker?
Is the output cap large enough to drive a 4 ohm speaker at low frequencies?
IT'S ALIVE!
I plugged in speakers, input, and power supply and not realizing that the phone was still playing Spotify, flipped the power switch.
I looked for sparks or the magic smoke; one second, two seconds, three seconds and suddenly glorious music! An unknown song from Spotify, nondescript $15 dollar Tang Band drivers in my shop speakers, and clearly better sound!
So success first time. The bias before setting was 9V on one channel, 11V on the other so fairly close.
It's all buttoned up now and playing with my Alpair 7.3 Metronome Tributes in the living room. Better supported bass and balance to the sound. You can hear deeper into the music.
A huge thanks to Nelson Pass, Variac, 6L6 and the whole DiyAudio community.
-Tom-
PS: The bad news is that the sound of the air-conditioning on the "Mining for Gold" from Cowboy Junkies Trinity Sessions is now really obtrusive!
I plugged in speakers, input, and power supply and not realizing that the phone was still playing Spotify, flipped the power switch.
I looked for sparks or the magic smoke; one second, two seconds, three seconds and suddenly glorious music! An unknown song from Spotify, nondescript $15 dollar Tang Band drivers in my shop speakers, and clearly better sound!
So success first time. The bias before setting was 9V on one channel, 11V on the other so fairly close.
It's all buttoned up now and playing with my Alpair 7.3 Metronome Tributes in the living room. Better supported bass and balance to the sound. You can hear deeper into the music.
A huge thanks to Nelson Pass, Variac, 6L6 and the whole DiyAudio community.
-Tom-
PS: The bad news is that the sound of the air-conditioning on the "Mining for Gold" from Cowboy Junkies Trinity Sessions is now really obtrusive!
Attachments
Looks like Alpair 10.3 in he last photo / enough power?
Hint - I think I already know the answer
Hint - I think I already know the answer
Oops!
Yes it is the Alpair 10.3 not the 7. Sounds really great at the moderate levels I listen at.
Yes it is the Alpair 10.3 not the 7. Sounds really great at the moderate levels I listen at.
Would you mind sharing with the class the connection for the XLR connector? Assume you just move the left and right inputs to pin 2 and 3 of the XLR? Just want to verify.
With really efficient speakers - one watt out of this amp is lots of sound! Expect the more power may come in handy for less efficient speakers or auditoriums!
Great work!
With really efficient speakers - one watt out of this amp is lots of sound! Expect the more power may come in handy for less efficient speakers or auditoriums!
Great work!
Should the 2sk170 be a gr or bl? Is the quality of C2 important? I have a tube pre with output impedance of 2k. There for have changed R11/R12 to 28k/100k, preserving the original ratio 10k/39k, any affects?
better BL , but GR will work too
feel free to increase Rin as you proposed
though , 2K R out is on verge to drive even 28K
feel free to increase Rin as you proposed
though , 2K R out is on verge to drive even 28K
Thanks for that ZM. I have some nice foil resistors for those values, right on the edge. Hope about C2 needed quality! I have some ruby MBZ 1500uf 16v for there, ok? What is it doing in the circuit? Trying to build this with recycled parts mostly, with a Frankin(stien) heat sink enclosure. Will post a photo when operating
C2 is not overly critical , decent industrial quality is what's needed
most critical part of it's role is conducting modulation for funny mu follower (upper part of amp) , so money for better cap is not wasted
so , Ruby it is ....... 🙂
most critical part of it's role is conducting modulation for funny mu follower (upper part of amp) , so money for better cap is not wasted
so , Ruby it is ....... 🙂
I read that If you need a cap, 10uf +1uf MKC is what you prefer. I was digging in the recycle bin and found 2 ERO 10uf 63v MKC caps to try in the future for C3, might be interesting.....