Thanks for the link, yes they do have them in stock.
Anyone know if there is any significance to the F133 on the end?
I see Arrow also has IRFP140NPBF in stock, are these the same as the IRFP140's mentioned in this thread? Part number deciphering is not one of my stronger skills, and searching for the information via Google is often fruitless.
the F133 is just the most current version of the FQH44N10 that's what I use, they are awesome and get even better if you can run them at a higher voltage! I think they sound much fuller than the 140's, the 140's are the way to go if you want something with more emphasis on the highs.
Thanks for the feedback on how they sound.
I realized they were the current version, I just wonder if anything significant has changed from the previous generation of the same part., or what specifically the F133 meant.
I did find datasheets for the older Fairchild FQH44N10 (dated around 2004) and the newer F133 version (dated around 2013), but other than the part number, to my untrained eye they looked identical.
I did order some of the F133's in from Arrow, then I found a US based seller on eBay which had (he claims) the original Fairchild FQH44N10's, in a New Old Stock condition, so I ordered 10 from him too as they were less than $2 each. I know I said I would like to avoid eBay, but hopefully it works out. 😒
So I will have plenty to play around with, I figured this way I can also prototype a few simple amp circuits on breadboards to understand the ACA design a little better.
I recently built a pair of the Mark Johnson Racam circular ACA, seemed a cheap and simple build to get me into the low power class A gang. My Aleph 30 unfortunately sits silent due to energy bills and the summer at the moment but it will breath again.!
I use a pair of traco power 100watt 24v PSU that I saw on eBay for £15 each. They seemed a better bet than no name Chinese SMPS. They appear to be well suited and the AC ripple I measure seems impossibly low. Built with 140NPBF for both devices but the rest is as per Nelson's design.
Anyway it sounds very very nice indeed. The gain a bit low for my 86db speakers. Haven't tried with my 83db speakers yet!
I've almost built the FH9VHX amp and noticed that XRK recommended the
FQA40N25/FQA36P15 pair. I don't see the 39P mentioned here and wondered if it may be worth a try.? He uses it to replace an IRF240 afterall . However I know nothing about specifying a transistor!
I've acquired a pair of Rudi's boards with the onboard Capmx so I intend to build a pair using the guidance and mods on this thread. I'm not sure if it's the sub optimal layout version. It has the speaker output right next to the AC/rectifier. I plan to maybe feed DC or hack a cap nearby to smooth the potential ripple. Id like to see if I can get a trafo/CRC PSU as quiet as the SMPS. There really is zero noise at full tilt with my ear pressed against the tweeter. Impressive.
I use a pair of traco power 100watt 24v PSU that I saw on eBay for £15 each. They seemed a better bet than no name Chinese SMPS. They appear to be well suited and the AC ripple I measure seems impossibly low. Built with 140NPBF for both devices but the rest is as per Nelson's design.
Anyway it sounds very very nice indeed. The gain a bit low for my 86db speakers. Haven't tried with my 83db speakers yet!
I've almost built the FH9VHX amp and noticed that XRK recommended the
FQA40N25/FQA36P15 pair. I don't see the 39P mentioned here and wondered if it may be worth a try.? He uses it to replace an IRF240 afterall . However I know nothing about specifying a transistor!
I've acquired a pair of Rudi's boards with the onboard Capmx so I intend to build a pair using the guidance and mods on this thread. I'm not sure if it's the sub optimal layout version. It has the speaker output right next to the AC/rectifier. I plan to maybe feed DC or hack a cap nearby to smooth the potential ripple. Id like to see if I can get a trafo/CRC PSU as quiet as the SMPS. There really is zero noise at full tilt with my ear pressed against the tweeter. Impressive.
Hi Jimk04,
I am not sure what you mean by “39P”? For ACA, only N-channel MOSFETs are used and so the FQA40N25 is a nice alternative to ubiquitous IRFP240 if for nothing more than fact that thousands are in stock at Mouser whereas the IRFP240 are out of stock. But there are some performance benefits with the Fairchild/Onsemi part: higher current, higher dissipation, and higher voltage capability. So it will generally be a more robust part. I also like the sound a bit better. On a 100w Class AB amp with a single pair - it makes more sense to use a 40A capable part for more bass slam.
I am not sure what you mean by “39P”? For ACA, only N-channel MOSFETs are used and so the FQA40N25 is a nice alternative to ubiquitous IRFP240 if for nothing more than fact that thousands are in stock at Mouser whereas the IRFP240 are out of stock. But there are some performance benefits with the Fairchild/Onsemi part: higher current, higher dissipation, and higher voltage capability. So it will generally be a more robust part. I also like the sound a bit better. On a 100w Class AB amp with a single pair - it makes more sense to use a 40A capable part for more bass slam.
Hi X. Thanks for your reply
Sorry, 39P is a typo of an abbreviation of FQA36P15! . But I was wrong anyway as you point out that is obviously a P channel!
So I guess I was surprised no-one has tried the FQA40N25 in ACA.
Sorry, 39P is a typo of an abbreviation of FQA36P15! . But I was wrong anyway as you point out that is obviously a P channel!
So I guess I was surprised no-one has tried the FQA40N25 in ACA.
RACAM ( Round ACA Monobloc ) is an ACA with non premium parts, plus a fourth order LCLC power supply filter to remove SMPS noise above ~ 10 kHz from the incoming DC. To make a RACAM quieter still, you want something with lots of attenuation at low frequencies, and very low output impedance at low frequencies. Unfortunately, capacitance multipliers have poor output impedance at low frequencies (< 50 Hz) because, in 99% of cases, they lack a high gain error amplifier.
Usually a CapMul is just a series pass transistor (or series pass Sziklai or series pass Darlington) plus passive RC smoothing on the control terminal. So the gain is quite small. For excellently low output impedance at low frequencies you want a voltage regulator and not a capacitance multiplier. Pick one rated for 2 amperes of continuous output current if driving ACA monobloc , 4 amperes of continuous output current if driving ACA stereo pair. The LD1084 chip from ST Microelectronics, mounted on a suitable heatsink with a Keratherm pad, is a great starting point.
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Usually a CapMul is just a series pass transistor (or series pass Sziklai or series pass Darlington) plus passive RC smoothing on the control terminal. So the gain is quite small. For excellently low output impedance at low frequencies you want a voltage regulator and not a capacitance multiplier. Pick one rated for 2 amperes of continuous output current if driving ACA monobloc , 4 amperes of continuous output current if driving ACA stereo pair. The LD1084 chip from ST Microelectronics, mounted on a suitable heatsink with a Keratherm pad, is a great starting point.
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Unfortunately there is evidence that Rudi's boards with the CapMx have some issues in addition to what was mentioned by Mark Johnson. The PCB layout of these is not conducive to low noise performance.
I used an earlier set of PCBs from Rudi that included an LT1084 after a CRC filter. I found that they sounded better without the regulator. (Simple to bypass with a thick wire)
My preferred configuration for the ACA is a linear PSU with a 300VA transformer with 24V or 25V secondaries. Low Vf bridge rectifier and CRCRC filtration. First C is 24,000 uF immediately after the rectifier, followed by 1% 0.5 Ohm or 1.0 Ohm for ease of current measurement. After that a CRC of 15,000 uF - 0.11 Ohm - 15,000 uF.
I used an earlier set of PCBs from Rudi that included an LT1084 after a CRC filter. I found that they sounded better without the regulator. (Simple to bypass with a thick wire)
My preferred configuration for the ACA is a linear PSU with a 300VA transformer with 24V or 25V secondaries. Low Vf bridge rectifier and CRCRC filtration. First C is 24,000 uF immediately after the rectifier, followed by 1% 0.5 Ohm or 1.0 Ohm for ease of current measurement. After that a CRC of 15,000 uF - 0.11 Ohm - 15,000 uF.
Thanks all.
Mark my Racam is the quietest amp I have. No need to make it quieter. A bit more gain would be nice for my speakers!
Thanks TA. Maybe I shall skip the Capmx and just feed from a hefty PSU.
Mark my Racam is the quietest amp I have. No need to make it quieter. A bit more gain would be nice for my speakers!
Thanks TA. Maybe I shall skip the Capmx and just feed from a hefty PSU.
Hi, I’ve seen a number of your posts about using a linear PSU for the ACA and you mention that some builds can be found, including some with point to point instead of a PCB, but I’m having quite a difficult time finding where to start. Can you help point me in the right direction?
Thanks!
First, this build will need a larger chassis. The old Hafler DH-220 chassis is excellent.
It could also be done with a Modushop Mini 3U, 350mm chassis.
Point-to-point wiring is make up as you go along.
It could also be done with a Modushop Mini 3U, 350mm chassis.
Point-to-point wiring is make up as you go along.
Thanks! That looks fairly straightforward, but being new to this I’m not 100% sure I know what I’m looking at. Is there a schematic that you used? For the second image, I assume the PSU is standalone, so what are you using to connect it to the wall and to connect the ACA to it?
If you are very new, then you need to know that building a linear PSU with point-to-point wiring can expose you to 120V AC. Not something you want to touch. I have done lots of this type of construction, so I know how to do it safely. You need to evaluate your skill level, and possibly re-consider your risk vs reward. The ACA with the extarnal 24V SMPS brick is a much safer option.
Quick ACA question. To run my ACA in parallel operation, Can I wire internally soldering to the negative binding posts inside the amps instead of using jumpers on the outside. Seems like this would be fine but wanted to check with the group.
Quick Question. My preamp is Single Ended Only and I am running my ACA in Parallel mono configuration. which pushed 16 watts into 4 ohms and 8 watts into 8 ohms. Would I gain any benefit adapting my SE cables into XLR. I know it won't get the cancelation of a truly balance cable but from what I have seen the bridged mon config puts out a more even 16 watt output into 4 and 8 ohm loads. I can get these cardas RCA-XLR adapters through Amazon Prime. Wondering if it worth a shot since they are returnable.
https://www.amazon.com/Cardas-Audio...jdCZkb05vdExvZ0NsaWNrPXRydWU=#customerReviews
I'm not a fan of adaptors ever really but would love to hear the groups feedback
https://www.amazon.com/Cardas-Audio...jdCZkb05vdExvZ0NsaWNrPXRydWU=#customerReviews
I'm not a fan of adaptors ever really but would love to hear the groups feedback
The parallel mono configuration offers a big improvement over the standard stereo ACA. Much of this is due to having separate dedicated PSU for each channel.
I can’t think of a reason that using single-ended to XLR cables might offer an improvement. Just use good quality RCA cables and you should be good to go.
I can’t think of a reason that using single-ended to XLR cables might offer an improvement. Just use good quality RCA cables and you should be good to go.