ACA amp with premium parts

Craigl59: So cutting the trace wasn't that bad, I'm going to do my other amp and make it dual 36v so I can take a few pics if that is helpful. Just have to dig in there with an x-acto knife, the trace is really thick so it is not too hard and that was my first time ever doing it.
Great idea to make a BoM available, I had to do some digging to figure that out when I started.

I would say that if you are building power supplies I would definitely go with the higher voltage!

I think the final frontier would be to make some outboard 36v linear power supplies with some decent reserves..

Oh, and I need to adjust the resistor on the LED's at the new voltage... they are bright!

Tungsten:I think my next project is going to the F6, I think you mentioned that you built yours with FQH44N10's did you get them matched, any other tips or mods to think about from the beginning of the build?
 
I think the final frontier would be to make some outboard 36v linear power supplies with some decent reserves..
Like so..
A larger chassis for the amp will be a good idea.
 

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As noted above, the IRFP150s have a higher gate capacitance (and gate charge) than is typically used in the ACA. Nonetheless, they can make very good current sources in the Q2 position on the ACA board. Several intrepid amp builders have tried the FQH44N10 in the Q1 position, quite recently in fact, and have loved the results. That would be my best recommendation.
 

Craigl59

Member
2006-05-17 4:01 pm
Have been building Gareth's PSUs (AudioSy.net) for preamp purpose and didn't realize until I checked that they do not have sufficient amperage current for the ACA. The ACA, apparently, draws 1.5 amps and, with the recommended 2* PSU reserve, that means at least 3 amps. The most the Single Rail Artemis PSU can generate is right at 1.4 amps.
So am going to have to shelve this project or design a PSU myself -- not likely with my current knowledge.
TungstenAudio: Do I remember you recommending a supplier of PSU boards somewhere above? If I could find one designed for 5 amps, 36 volts, that would kickstart the process.
Will finish this week a custom version of the WB2018 Linestage and Korg B1 preamps combined together in a single chassis so you can shift between SS and Valve preamps with a single toggle switch selection. The two PSUs are Gareth's and will be mounted outboard in their own enclosure -- if HiFi2000 ever sends the chassis, that is. Slow times in Italy over this holiday.
Zammjazz27: And thanks for the trace cutting help. Will, perhaps, try this as well.
 

Craigl59

Member
2006-05-17 4:01 pm
Here is the Premium ACA BoM I prepared to order the parts 'en toto' for the blank PCBs available at DIY. There is one omission -- couldn't identify the proper 2SK170JFET part at Mouser and would appreciate any assistance. Thought this might be of help to those coming to this site as I did without any knowledge of the premium versions available. Please provide your suggestions for improvement. Note that these are also the higher quality resistors and such to accurate tolerances.
Oh, and TungstenAudio: The Resistor combination of R4 and R4b could be combined with a correct total value of R4=0.51 ohms. Should this be preferred or is there another reason for placing the two resistors in parallel (current?)?
 

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My higher voltage ACA builds have used very traditional linear power supplies; 300VA transformers, 24V secondaries, CRCRC filters. I did try a chassis mount Meanwell 27V SMPS in place of the linear rig, and it fell a little short in bass extension and definition.
The latest VFET amps use a larger 36V brick style SMPS, which look promising for the ACA if used with an appropriate filter. These are available on the store. It is a good, easy way to have a great sounding VFET amp without having to build your own PSU. And if you are willing to build your own dual channel linear PSU, it can make the VFET amp sound even better.
There are some newer chassis mount SMPS from Micro Audio that also look promising, but I haven’t tried one yet. Only a couple DIY builders have reported on their use.

For the time being, I remain convinced that a carefully built linear PSU will sound superior to the commercial SMPS units. More effort, worth it.
 
Craigl59, looks like a great BoM, thanks for putting in the work, on Tumgsten's later schematic it shows 121ohm resistors at R5, and R6.

Are you building one from scratch, I'd be tempted to do the same as I have used and abused those circuit boards trying everything, the only parts remaining from the kit are the jfets!

I think it'd be great to add a BoM for Rhthatchers filter boards as it doesn't look like those will be offered as kits again. I also add a Nichicon FW 1000uf 50v cap across the V+ input of both boards as well, I use that same cap in the rhthatcher board when I went to 36v.

You don't have R16 which Tungsten has at 200 ohms, that bumps up to 1000 for the 36v option. I am sure a different value would be needed for R13, I haven't adjusted that yet as the LED's are bright on the 36v supply. Also the part numbers for the switches would be cool both the single and dual options.

I am also wondering if their is any benefit possible by going with a more "boutique" cap at C1 like an Audio Note or Mundorf? I swapped out output coupling caps on a Sony Sacd player with Black Gates and it was an obvious improvement. Would also like to find some better rca's and binding posts.

And... I am all in on building a dual mono 36v linear power supply like the one Tungsten has pictured above! Where do we start?
 
As noted above, the IRFP150s have a higher gate capacitance (and gate charge) than is typically used in the ACA. Nonetheless, they can make very good current sources in the Q2 position on the ACA board. Several intrepid amp builders have tried the FQH44N10 in the Q1 position, quite recently in fact, and have loved the results. That would be my best recommendation.
With the FQH44N10 in Q1 I tried the IRFP 140 and FQH44N10 in Q2 and preferred the FQH as it sounded fuller with better bass.
 

Craigl59

Member
2006-05-17 4:01 pm
ZJ27: Thanks for the helpful review; will make those additions/adjustments and repost later this week. Am using all-copper fittings for RCA and speaker terminals sourced from China. Have tried the very expensive all-copper ones on Amazon and they are OK but no better. Can add those EBay sources but they change rather quickly and you have to budget at least 3 weeks time for shipping. Shipping is becoming a pain all over the world.
For "starting now" the only issue I have is finding a PSU PCB that will accommodate 36 volts at 5 amps. Will raise this with Gareth tomorrow but don't think there is one commercially available on the Internet (asked TA above and there was no response).
Please suggest a specific boutique cap make and value for C1 and I will order. Agree this is a likely possibility.
 
The basic, and certainly one of the best performing ways to construct a linear PSU is simple point-to-point. No PCB required. Fine examples of this exist in several threads. There are PCBs avaiable if one feels so inclined. They generally do not impose voltage or current limitations on their own. That is a matter of the capacitors which have been selected for the job. The Universal PSU boards on the diyAudio store may be pressed into service for single rail supplies, being mindful of the voltage polarities.
I have used several third-party PCBs for various builds. These have tended to be limited runs offered in the Group Buys forum. That's why I don't often discuss them. No point going into detail about something which isn't available. One variety of PCB which is still available is XRK's Smooth Like Buttah (SLB), which is offered in both single and dual rail. It is a capacitance multiplier, and does require some understanding of how this type of circuit operates for best implementation. I used two of the single-rail boards to build my 36V PSU for the VFET amp, as pictured above.
The choice of what kind and size of PSU to implement is influenced by the chassis in which the amp will be constructed. Or the size one may find available for building an external supply. In the case of the ACA, the basic kit chassis is too small to accommodate anything other than and external supply, whether linear or SMPS. Moving to a larger chassis does offer more options. Have a look at the picture below for an example of a parts fit study in the Mini Dissipante 3U x 250mm chassis. That transformer is the Antek 300VA, 24V.
 

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Yes, the single-rail SLB is what I used in the external PSU for my VFET amp. It needs a transformer with 30V secondary voltage in order to produce an output voltage of 36V. Two 15V windings in series work well.
I also used the dual-rail SLB in my F6. I have built my own capacitance multiplier supplies without the aid of a PCB, so I was already familiar with the circuit. The SLB uses a complementary feedback pair (aka Szklai) for the high gain pass element. It is nice to have these PCBs available to make the job easier. The LT4320 rectifiers seem to work well at reducing the voltage loss due to rectification.
 
Craigl59, I was looking at Audio Note Kasei and Mundorf capicitors, Tungsten's spec calls for 4700 uf 35v, the closet I can see that looks good is this Mundorf which is 4700uf 40v: https://www.partsconnexion.com/MUNDORF-71837.html

Ii was initially drawn to the Audio Note Kasei as that seems to be the company working on the Black Gate replacements
There is an Audio Note Standard Foil 4700uf 25v or 63v @ $10 - $23: https://www.partsconnexion.com/ANSECAP-83859.html
The Audio Note Kasei 4700 uf comes in 25v (I'm not sure what our min rating should be here) this one has been out of stock forever, there is a 63v version but it is a whopping $125 each!

After reading up as much as I could find I was leaning towards trying the Mundorf.

Also please send along your links for copper rca's and binding posts. I'm ready to pull apart the other ACA (hopefully for the last time and set it up for dual 36 smps, and will hopefully build a dual 36v sometime this year like the one Tungsten pictured.

 
Yes, the single-rail SLB is what I used in the external PSU for my VFET amp. It needs a transformer with 30V secondary voltage in order to produce an output voltage of 36V. Two 15V windings in series work well.
I also used the dual-rail SLB in my F6. I have built my own capacitance multiplier supplies without the aid of a PCB, so I was already familiar with the circuit. The SLB uses a complementary feedback pair (aka Szklai) for the high gain pass element. It is nice to have these PCBs available to make the job easier. The LT4320 rectifiers seem to work well at reducing the voltage loss due to rectification.
Thanks again, I will do some reading etc... I would lobe to copy the one you made!
 

Craigl59

Member
2006-05-17 4:01 pm
Thanks as well, TA and ZJ27. Ordered four of these and will struggle through the part definition as they arrive. Talked with Gareth yesterday and his Artemis single-rail PSUs top out at 1 amp and he does not anticipate going into the amp level of PSU production in the future.
Transformer availability is a problem these days. Do I read TA's post correctly in that a 100VA transformer with 15+15 vdc in series will produce 30 volts and, with the rectifier, top out at 36? There are lots of relationships here.
Here are the China links:
RCA connectors -- have ordered multiple times from these sellers and they are fine -- best to stock up at these prices for future projects and avoid substantial delays in shipping:
https://www.ebay.com/itm/124369688526Speaker panel terminations:
https://www.ebay.com/itm/164966514272Am getting excited about this Premium ACA possibility and will order the chassis from HiFi2000 that are 1) large enough for dual single-rail PSUs with 2) heatsinks large enough for the 36-volt mosfet heat. Shipping is currently delayed completely from HiFi2000 and FedEx is not yet moving their packages.