I returned to ACA listening this morning after letting the amp run in for a few more hours overnight. The effort to build a new pair of boards has been very rewarding. The ACA with newer output Mosfets are now even closer to the sound of my F6, save for those few extra dB that the F6 is capable of with large speakers.
In particular, the sound and impact of percussion instruments is better defined, even down into the lower octaves. The improvement to the musical foundation that this brings is very satisfying. Overall definition and harmonic presence of acoustic instruments is also improved. This is relative to the older boards which used IRFP140 Mosfets at both Q1 and Q2.
I wanted to find an alternative to the FQH44N10, and the IXTQ75N10P is definitely it. There is one modification that will be necessary to support the higher Vgs of the IXTQ parts, and that is increasing R9 from 1k to 1.2k. The 5600 uF Nichicon Gold Tune cap at C1 has also proved to be a good choice. The ACA has evolved into a wonderful single-ended Class A amp with higher voltage and bias current.
In particular, the sound and impact of percussion instruments is better defined, even down into the lower octaves. The improvement to the musical foundation that this brings is very satisfying. Overall definition and harmonic presence of acoustic instruments is also improved. This is relative to the older boards which used IRFP140 Mosfets at both Q1 and Q2.
I wanted to find an alternative to the FQH44N10, and the IXTQ75N10P is definitely it. There is one modification that will be necessary to support the higher Vgs of the IXTQ parts, and that is increasing R9 from 1k to 1.2k. The 5600 uF Nichicon Gold Tune cap at C1 has also proved to be a good choice. The ACA has evolved into a wonderful single-ended Class A amp with higher voltage and bias current.
Hi Eric
What do you not like about the FQH44N10 for both Q1 and Q2?
I have the 44 at Q2, and have a Cree C3M0160120D at Q1. I don't know if the Cree are still available, had them from past purchases for experiments, but sounds pretty balanced. I previously had some other Cree's installed, but a bonehead power disaster took their fine selves to perdition, and these were the
only ones I still had! Still, not a bad combo for my speakers, re-imagined Rectilinear Lowboys, their cabinet's anyway. Inside they have my doctored 12 inch
mystery speakers that came out of a GE Vacu-magic console, the only unit that I ever saw those 12 incher's in. I also have a 5 X 15 horn above with a B&C DE120 driver.
What do you not like about the FQH44N10 for both Q1 and Q2?
I have the 44 at Q2, and have a Cree C3M0160120D at Q1. I don't know if the Cree are still available, had them from past purchases for experiments, but sounds pretty balanced. I previously had some other Cree's installed, but a bonehead power disaster took their fine selves to perdition, and these were the
only ones I still had! Still, not a bad combo for my speakers, re-imagined Rectilinear Lowboys, their cabinet's anyway. Inside they have my doctored 12 inch
mystery speakers that came out of a GE Vacu-magic console, the only unit that I ever saw those 12 incher's in. I also have a 5 X 15 horn above with a B&C DE120 driver.
Hi
I simply wanted to change so I can keep the obsolete FQH44N10. It plays very well as is.
Sounds like you’re having a blast with these mystery speakers, that’s the spirit 👍
Your CREE are still available but at $15 a piece I’ll pass 😀
Cheers
Eric
Any recommendations where to go to upsize the 24V brickwall power supply ? Would be nice to have a beefier PS with higher rail voltage. I find the ACA it lacks some power compared to my J2 and Aleph J.
I have tons of room to put a larger power supply inside the chassis
Thank you
I have tons of room to put a larger power supply inside the chassis
Thank you
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The MeanWell SMPS bricks seem to work quite well in diyAudio projects. Here are a bunch of them over on DigiKey's website. Beware: some of them ship with rather unusual connectors, so read the datasheet and know in advance exactly what you're ordering.
Maybe the MeanWell GST360A36-G6P , at the moment it's out of stock at DigiKey but it's in stock at Mouser. Mouser also has another two Mean Wells which are even more grunty. You may also wish to consult with the circuit designer, to inquire whether he/she approves of the proposed upgrade.
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First, the ACA is not going to become a 25W amplifier in the same league as the Aleph J by changing its power supply.
It can sound very close by careful construction of a linear supply and by making a couple other modifications, but it will still be at most a 10W amplifier. This has been described in preceding pages of this thread. (New Mosfets, changes to some of the 3W resistors, etc.)
Are you willing to build a linear supply? There is plenty of room in that chassis to do so.
It can sound very close by careful construction of a linear supply and by making a couple other modifications, but it will still be at most a 10W amplifier. This has been described in preceding pages of this thread. (New Mosfets, changes to some of the 3W resistors, etc.)
Are you willing to build a linear supply? There is plenty of room in that chassis to do so.
I am not aware of any kits to assemble a linear power supply. These tend to be very custom affairs.
Besides, what you are looking for in terms of power and sound quality is unlikely to be found in a kit.
You have a good start already with the ACA boards assembled with the FQH44N10 and other premium parts. If you followed the recommendations for R3 and R4, then your boards should already be set for 1.6A bias current. Hopefully you also added R16, the extra resistor above the drain of Q4. With the boards in good shape, you can build a dual-mono linear supply that will deliver 30V to the power rail in each channel.
As 6sX7 has indicated the Universal PSU board from the store is a good component to ease the assembly of the CRC filter portion of your supply. A good choice for the power transformer would be the Antek AS-3224. This has a pair of 24Vac secondary windings which may be used independently to power each channel. I prefer to use block style rectifiers such as the Vishay VS-MB26 or VS-MB36 series (50V and above will work).
https://www.antekinc.com/as-3224-300va-24v-transformer/
There are more details on how to connect the primary side of the 300VA transformer to the AC inlet. Simple is better here. Maybe look inside your Aleph J for inspiration.
Besides, what you are looking for in terms of power and sound quality is unlikely to be found in a kit.
You have a good start already with the ACA boards assembled with the FQH44N10 and other premium parts. If you followed the recommendations for R3 and R4, then your boards should already be set for 1.6A bias current. Hopefully you also added R16, the extra resistor above the drain of Q4. With the boards in good shape, you can build a dual-mono linear supply that will deliver 30V to the power rail in each channel.
As 6sX7 has indicated the Universal PSU board from the store is a good component to ease the assembly of the CRC filter portion of your supply. A good choice for the power transformer would be the Antek AS-3224. This has a pair of 24Vac secondary windings which may be used independently to power each channel. I prefer to use block style rectifiers such as the Vishay VS-MB26 or VS-MB36 series (50V and above will work).
https://www.antekinc.com/as-3224-300va-24v-transformer/
There are more details on how to connect the primary side of the 300VA transformer to the AC inlet. Simple is better here. Maybe look inside your Aleph J for inspiration.
An interesting issue is the mechanical work needed to support a linear supply and transformer in the ACA chassis, given that there is no internal baseplate as in the Deluxe DIY Audio chassis. The bottom plate is a bit flimsy, and you may need to beef it up with a sandwiched metal plate under the PS which bridges the width of the chassis, or perhaps using strips of .090 aluminum to provide stiffening of the bottom plate.
This my current board, it's been a year since I built it a bit rusted. Does it need modification to run 30V secondaries? I would need 2 universal power supply boards for B+ rail
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The ACA boards would be best if modified to include R16, since I don't see any evidence of its installation. This requires making a careful cut in one of the traces on the board. There are quite a few pictures of how that was done in this thread. This is also one of the changes that makes the ACA sound a little better, as it filters the power going to Q4. If you do not feel comfortable making that modification, that's Ok, but 30V may be too much for the JFet to handle. Reduce the rail voltage to 26V with a different power transformer.
You only need one Universal PSU board. The negative side may be reconfigured to be a second B+ rail. The D+2 inputs get connected to GND, D-2 inputs get connected to the positive (+) output of the rectifier. The big capacitors C1, C2, C5 and C6 get installed 'backwards' so their negative terminals are connected to the GND terminal for that side. Don't bother installing LED3. Take a picture and get someone here to check your work. We are a friendly community.
You only need one Universal PSU board. The negative side may be reconfigured to be a second B+ rail. The D+2 inputs get connected to GND, D-2 inputs get connected to the positive (+) output of the rectifier. The big capacitors C1, C2, C5 and C6 get installed 'backwards' so their negative terminals are connected to the GND terminal for that side. Don't bother installing LED3. Take a picture and get someone here to check your work. We are a friendly community.
Hi All, After discussion with Tungstenaudio over some parts. I have put together a parts list of materials from mouser please review and let me know your thoughts as trying to get this right before ordering everything. Apologies if a bit of a beginner question for you guys. I have also added a spec sheet from what threads i have checked out.
If it is all good this should help out some of the guys as a starting point for ordering parts to do a ACA Tungsten style amp
Thanks Rob
If it is all good this should help out some of the guys as a starting point for ordering parts to do a ACA Tungsten style amp
Thanks Rob
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Agree.. this week I swapped my First Watt J2 to the ACA and it's not a fair comparison. Lots of detail on the ACA but no grunt, sounding quite a bit recessed and flat compared to the J2. Gain difference is noticeable with the power difference