Peculiar start up sound
I respectfully disagree with your comment Steve, both my ACAs are running in bridged made and teh start up noise persists.
I respectfully disagree with your comment Steve, both my ACAs are running in bridged made and teh start up noise persists.
R16 (in the ACA16 mods schematic) drops the voltage into the drain of the input Jfet. It allows use of higher voltage on the power supply and provides some supply filtering to the input as well. I have been using a value of 499 Ohms more recently with a linear CRCRC supply of 28.5V.
The shielded transformers on the linear power supplies I built in seperate cases from the amps get hotter than the ACA heatsinks during a long session at the moment. But it’s summer here in NZ and temps are touching the 80’s. The transformers are sitting almost fully exposed to the air. I may have to build a heat pipe around the base of each toroid to take more heat to the heatsinks at the sides.
Sound is different because theres a lot more power available to a single channel than in stereo mode. I'm running mine in bridged mode now and the difference in bass/dynamics is very apparent. In stereo mode, listening to anything "complex" like rock/etc... sounds like a mess in stereo mode, but in bridged it opens up nicely.
I really view dual monoblocks as a step between ACA stereo -> bridged -> F5 -> F5t -> F6 to show what improvements/changes practically result from those changes in hardware.
The little ACAs are great amps to experiment with the different options for monoblocks. They are compact and lightweight. I tried both bridged and parallel modes with my first set, and found that the parallel mode worked better with my speakers.
Then I went on to build other First Watt clones, but not before making a pair of larger ACAs using higher voltage linear PSUs and the old Hafler DH-220 chassis. I never tried connecting those as monoblocks, because one has a different set of Mosfets – the IRFP140. Check out ACA amp with premium parts. The development went on from there.
Then I went on to build other First Watt clones, but not before making a pair of larger ACAs using higher voltage linear PSUs and the old Hafler DH-220 chassis. I never tried connecting those as monoblocks, because one has a different set of Mosfets – the IRFP140. Check out ACA amp with premium parts. The development went on from there.
The ACA had been a wonderful gateway, as it was intended. I went on to build an M2x, Aleph J and F6. They all sound great in their own way. After building the M2x with a shared PSU, the others were built with dual-mono supplies. The F6 is the most heavily modified of the trio; the Aleph J was just given a really good set of PSUs.
Now I'm working on an enhanced version of the original "Penultimate" Zen V4, the amp which I regard as parental lineage for the ACA. See where the old Hafler transformers are going to be put to good use.
Now I'm working on an enhanced version of the original "Penultimate" Zen V4, the amp which I regard as parental lineage for the ACA. See where the old Hafler transformers are going to be put to good use.
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I don't find/hear that at all? I'm sure the speakers play a large part. I only built one and have always used it in stereo. I'm positive two in mono would be better, but one has been great for me...
r16 is a gate leak resistor, it biases the input jfet so that the gate of the output mosfet has a voltage at around 4 volts and so that the drain of the output mosfet is biased to 1/2 the B+....r16 plays a big role in the ACA. while its value is not critical 100k to 1 meg will work fine..
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