Hi All,
I am a total novice - I have built an F5 (I had a lot of help), and Aleph J (also with much help) and the F6 twice. Additionally, I built a Bottlehead 2a3 SET and a handful of tube and SS phono stages. All were totally paint-by-number affairs. Suffice it to say that I can take directions and execute very well, but I don't really know what I am doing.
I have two ACAs that I am running as bridged monoblocks (v1.6 with 24v supplies). They sound great, however, I prefer the sound of the amp in the true single-ended stereo configuration. It is just short on power into my 12 ohm speakers (they are listed at 97db, but I don't know if they truly are that efficient). Of all the solid state amps I have owned, the ACA sounds closest to a tube single ended triode (and I don't have to deal with tubes). I think I just like the way single-ended amps sound.
This got me thinking: would it be possible to build an amp using the ACA boards (basically the circuit) but with more powerful output MOSFETs?
Before you say "dude, just build an Aleph J" - I have built one... I actually prefer the sound of the ACA, for whatever reason.
I think with some help from the knowledgable folks on this forum, I may be able to build a beefy ACA by using more powerful output MOSFETs.
Objectives:
Assumptions:
So, the first step is trying to figure out which output MOSFET to use. I pulled up the MOSFET the ACA kit ships with on Mouser - the IRFP240PBF. From there I filtered by the case size (TO-247AC-3), N channel, Gate Source threshold voltage = 2V and VGS = 10 (I picked these because that is what the IRFP240PBF is). I began looking for other MOSFETs that had datasheet specs that were similar to the IRFP240PBF, but had a higher power dissipation.
I came up with the following list:
The IRFP264 has the highest forward transconductance (which, I think, is the signal gain) and the lowest Rds(on). However, it's Qg -gate charge is the highest of the bunch (I think lower is considered better in this application, but I could be wrong).
Conversely, both the IRFP460BPBF and the IRFP360LCPBF looked like the closest match to the IRFP240PBF on the spec sheets, with the obvious exception being the Power Dissipation is much higher.
Does anyone have any thoughts as to which MOSFET is a good candidate for this project?
I am a total novice - I have built an F5 (I had a lot of help), and Aleph J (also with much help) and the F6 twice. Additionally, I built a Bottlehead 2a3 SET and a handful of tube and SS phono stages. All were totally paint-by-number affairs. Suffice it to say that I can take directions and execute very well, but I don't really know what I am doing.
I have two ACAs that I am running as bridged monoblocks (v1.6 with 24v supplies). They sound great, however, I prefer the sound of the amp in the true single-ended stereo configuration. It is just short on power into my 12 ohm speakers (they are listed at 97db, but I don't know if they truly are that efficient). Of all the solid state amps I have owned, the ACA sounds closest to a tube single ended triode (and I don't have to deal with tubes). I think I just like the way single-ended amps sound.
This got me thinking: would it be possible to build an amp using the ACA boards (basically the circuit) but with more powerful output MOSFETs?
Before you say "dude, just build an Aleph J" - I have built one... I actually prefer the sound of the ACA, for whatever reason.
I think with some help from the knowledgable folks on this forum, I may be able to build a beefy ACA by using more powerful output MOSFETs.
Objectives:
- Single box, stereo configuration
- Roughly 10 watts of Single-ended output into my 12 ohm speakers
- Use the existing ACA v1.6 boards without having to cut new traces or anything
- Keep it simple
- Safety, Safety, Safety
Assumptions:
- I will need a larger chassis with greater heat sinking (probably get the deluxe 4u)
- I will build linear power supply
- I can use the same JFETs and ZTX450 transistors in the circuit, but most of the other values will need to be changed to account for the more powerful output MOSFETs
So, the first step is trying to figure out which output MOSFET to use. I pulled up the MOSFET the ACA kit ships with on Mouser - the IRFP240PBF. From there I filtered by the case size (TO-247AC-3), N channel, Gate Source threshold voltage = 2V and VGS = 10 (I picked these because that is what the IRFP240PBF is). I began looking for other MOSFETs that had datasheet specs that were similar to the IRFP240PBF, but had a higher power dissipation.
I came up with the following list:
- IRFP264PBF
- IRFP460BPBF
- IRFP360PBF
- IRFP360LCPBF
The IRFP264 has the highest forward transconductance (which, I think, is the signal gain) and the lowest Rds(on). However, it's Qg -gate charge is the highest of the bunch (I think lower is considered better in this application, but I could be wrong).
Conversely, both the IRFP460BPBF and the IRFP360LCPBF looked like the closest match to the IRFP240PBF on the spec sheets, with the obvious exception being the Power Dissipation is much higher.
Does anyone have any thoughts as to which MOSFET is a good candidate for this project?
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