Yeah, but with 88db / w / m 8" Transmission lines they still manage to shake the floorboards. For an ACA, designed as it was for efficient speakers even one pair is quite enough.
I put the ACA 1.8 in stereo mode, removed my Pass Labs XA25 amp from my system and hooked up the ACA to drive a pair of Daedalus Athena loudspeakers, A 3 way with a 95 dB sensitivity and only a 1 dB drop across the Freq range.. It played ok, but was lacking, weight and dynamics... I attributed this to the 3 way crossover losses .
So I went back to my normal config in my main system and moved the ACA to my office system.. which consists of NHT super ones from 20+ years ago... a 2 way rated at 86 dB
Sensitive.. Using a modi multibit and a Magni 3 as a preamp for the ACA.. To my surprise.. This sounds amazingly good !! I have plenty of volume and bass ! I measured 82 dB avg at the listening position 7 feet back from the speakers.. and I still had some volume to go with no signs of clipping.. So there it stays, using the modi multibit as input from my PC and my MBP into the Magni which sounds pretty damn good..
Very impressed with the little amp that could... thought I would need 2 mono ACA amps to make it sing...
So I went back to my normal config in my main system and moved the ACA to my office system.. which consists of NHT super ones from 20+ years ago... a 2 way rated at 86 dB
Sensitive.. Using a modi multibit and a Magni 3 as a preamp for the ACA.. To my surprise.. This sounds amazingly good !! I have plenty of volume and bass ! I measured 82 dB avg at the listening position 7 feet back from the speakers.. and I still had some volume to go with no signs of clipping.. So there it stays, using the modi multibit as input from my PC and my MBP into the Magni which sounds pretty damn good..
Very impressed with the little amp that could... thought I would need 2 mono ACA amps to make it sing...
Hi! I did some experimentation with Focusright Scarlett 2i2 and REW software and measured my ACA and M2X.
My setup was as follows:
- I used internal generator of RAW, set at -10dBFS, 1000Hz
- that gives about 360mV on the output of 2i2 with max monitoring volume, and it's not enough to get 2.83V on the output of ACA or M2X
- so I routed the signal via Shiit Magni 3+ pre-amp on 5.5x gain, setting the volume at the level that gave 2.83V measured on the output of the amplifier (it required 820mV output from pre-amp for ACA and 535mV for M2X)
- I am still waiting for the 8ohms 100W load resistors to arrive, so I measured with the actual speakers (Overnight Sensations) connected
- 2.83V signal from the output of the amp went (in parallel to the speakers) to the line input of the 2i2
- 2i2 line input can take up to 22dBu (9.75V), so I did not use any voltage divider network
- the gain of the 2i2 line input was set to minimum
I got nice and consistent results on my ACA (I include the direct loopback from pre-amp to check that pre-amp did not introduce any significant noise or distortion). THD measured at 0.22% (much better than oficialy stated 0.7% distortion of ACA - if you can trust that test rig setup that I used).
What was interesting to see is the harmonics signature of the amp. And you can see my ACA has all the bouqet of harmonics. Compare it to M2X harmonics that is mainly 2nd and 3rd (please disregard the mains hum in M2X measurements - neither the toroid nor the auto-formers are shielded in my M2X yet - waiting for the shielding materials to arrive).
Does anyone have and could share their measurements of ACA? It would be very interesting to compare that.
-Alvis
My setup was as follows:
- I used internal generator of RAW, set at -10dBFS, 1000Hz
- that gives about 360mV on the output of 2i2 with max monitoring volume, and it's not enough to get 2.83V on the output of ACA or M2X
- so I routed the signal via Shiit Magni 3+ pre-amp on 5.5x gain, setting the volume at the level that gave 2.83V measured on the output of the amplifier (it required 820mV output from pre-amp for ACA and 535mV for M2X)
- I am still waiting for the 8ohms 100W load resistors to arrive, so I measured with the actual speakers (Overnight Sensations) connected
- 2.83V signal from the output of the amp went (in parallel to the speakers) to the line input of the 2i2
- 2i2 line input can take up to 22dBu (9.75V), so I did not use any voltage divider network
- the gain of the 2i2 line input was set to minimum
I got nice and consistent results on my ACA (I include the direct loopback from pre-amp to check that pre-amp did not introduce any significant noise or distortion). THD measured at 0.22% (much better than oficialy stated 0.7% distortion of ACA - if you can trust that test rig setup that I used).
What was interesting to see is the harmonics signature of the amp. And you can see my ACA has all the bouqet of harmonics. Compare it to M2X harmonics that is mainly 2nd and 3rd (please disregard the mains hum in M2X measurements - neither the toroid nor the auto-formers are shielded in my M2X yet - waiting for the shielding materials to arrive).
Does anyone have and could share their measurements of ACA? It would be very interesting to compare that.
-Alvis
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I have had a similar experience with my office system (haven't been in my office since February). I'm using a pair of 24v 2016-vintage Pass ACA monoblocks (the itty-bitty ones) to drive a pair of Linaeum LFX monitors in near-field. Given the low sensitivity of the Linaeums, this shouldn't work well, but they sound fantastic (especially when I added the Titan 10" subwoofer).
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I found most recently that the VAS matters both in terms of quality, and voltage gain. I've been using a variety of preamps on the Amp Camps I've built over the years and they sounded quite good but last weekend I completed my second Whammy used it to drive some ACA 1.6s and OMG is all I can say. I am driving some custom Vifa MTMs I built about 10 years ago that measure in the 90db range and while this combo obviously was lacking in the low-low bass range, it was actually quite nice sounding. Dynamic, full and detailed.
--Tom
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Here is the reason my 95dB sensitive Daedalus Athena speakers didn’t work out.. These are a pair of Daedalus speakers and the PASSIVE Crossover network... It looks more like a self powered speaker !! Lol..
“the crossovers are made by Guy Veralrud designs unique passive crossover networks for each Daedalus speaker from scratch, using extremely high end capacitors, and handmade inductors. Daedalus uses Duelund resistors and several different high-end caps for voicing. There are no electrolytic caps in any Daedalus design.”
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Did I wire this up properly? I am still having the thump on switch off.
From psu + through 0.1R to cap, from cap to amp.
From - psu to cap, from cap to amp.
Using 10000 uf cap and 0.1 ohm resistor.
Am looking at the latest (Ver 1.8?) kit and am wanting to run as a pair of the monoblock amps at 15w each. However, my preamp only has RCA outputs. Am wondering if a standard RCA to XLR adpater at the amp input is good enough to make this work?
Thanks.
Thanks.
My understanding is you drive the ACA in bridged mono mode using an RCA input.
For balanced mono you will need to drive it using a balanced XLR source.
For balanced mono you will need to drive it using a balanced XLR source.
ACA Supply Options
Some questions regarding powering the ACA:
Thanks.🙂
Some questions regarding powering the ACA:
- I see thet the ACA performs better with the 24V supply than the original 19V supply, which is not surprising since FET's usually like higher voltages. Can the ACA be powered at even higher voltage, if so what is the max?
- The recomended supply is a switch mode supply, will the ACA run on a linear supply or even unregulated supply?
Thanks.🙂
One can drive the ACA 1.8 in monoblock bridged or monoblock parallel mode using a single RCA connector. If one has a balanced preamp one can connect it to the ACA to create a balanced Monoblock by using 2 interconnects, one From each RCA output to each ACA RCA input, with the switch in the middle “balanced” position But pretty much all balanced preamps have XLR connectors so it’s easier to just connect the XLR on the Balanced preamp to the XLR on an ACA
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My understanding is the voltage limiting factor are the JFETS which are rated at about 25v. However some people have run them up to about 30v without tragedy. Your mileage may vary.
In its original form (ACA) you better stick with 24V, the front JFET being the limiting factor, as Variac said above.
If you want to use higher voltages you will need to modify the circuit, search for Tony Tecson's high voltage mods.
The amp does not care if it's driven by SMPS or a linear PSU. Most amps linear PSUs are usually unregulated, just a trafo, a bridge rectifier and CRC or CLC or a combo of the two.
For linear unregulated PSU you will need a lot of capacitance, a factor to consider.
sure you can, except that in my case, linear power supplies were not as quiet as the smps power bricks that i used....i even made one using 48volts...
my next challenge will be 70 vdc ACA...... 😀
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if you replace the input jfets with 2sk117 and then use 36volts smps, the "as is" ACA board will work just fine...
the 2sk170 is rated -40 volts....i have a 24v ACA that i amp going to upgrade to use 36vdc smps...
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think about dissipation - that's the main reason why I'm always taking care that JFet is not having excessive voltage
though, I'm usually wrong and I'm certainly not member of Papa's AbFAB Club
though, I'm usually wrong and I'm certainly not member of Papa's AbFAB Club
^yes, device dissipation, that is what is stopping me right now, after 48 volts, going higher will be very much harder....