Very nice, and as you say - other than a little wire salad - clean and informative. Looks like you took full advantage of the many ground pads on the PS board for the 'star'. Is the green wire from the AC entry module connected back to the PS? Can't see a termination there.
I'd be interested in hearing about the adjustment process/sequence and values you used - but that may be something included in the upcoming formal build guide. As the earlier posts show I struggled a bit there, but through that process now have a better understanding of the interdependence. Most likely less intimidating than it first appeared.
SQ wise, have you had time to try any adjustments of P-3. I understand that is basically a user preference area, but I'm aware you have the lab tools to make some links between the art and the science there.
Lastly, what are the specs on the transformer, and can you give some basic info in the speakers you are driving?
I'd be interested in hearing about the adjustment process/sequence and values you used - but that may be something included in the upcoming formal build guide. As the earlier posts show I struggled a bit there, but through that process now have a better understanding of the interdependence. Most likely less intimidating than it first appeared.
SQ wise, have you had time to try any adjustments of P-3. I understand that is basically a user preference area, but I'm aware you have the lab tools to make some links between the art and the science there.
Lastly, what are the specs on the transformer, and can you give some basic info in the speakers you are driving?
Last edited:
The AC safety earth is brought to the chassis. (it's actually not connected in the photos...)
Yes, the abundance of pads on the PSU ground was used to good effect, the amp is very quiet. The green from the FE board is connected to the PSU as you suspect.
Basically I built and tested the FE as a seperate unit, set it's operating bias and offset, and them built the rest of the amp. Bias and offset on the output stage are very straightforward, it's essentially an F4, (this is a complimentary, not SE, output stage) so you merely need turn the pots to adjust them, there is no "see-saw" like an F5.
I haven't messed with it that much, but I have dialed P3 for minimum distortion. This nulls out a bunch of the 2nd harmonic, making it very, very clean and detailed, at the expense of warmth. I put it back to neutral, which is 2nd harmonic (slightly) dominant.
Plitron 18V+18V 400VA. Used as it was on hand. Speakers I have heard it on are Zaph audio ZA5.2. Zaph|Audio - ZA5 Speaker Designs with ZA14W08 woofer and Vifa DQ25SC16-04 tweeter This amp sounds much better than the F5T with these speakers.
No, they are Hifi2000/Modushop 300mm deep, the chassis is the diyAudio 4U deluxe.
0.5V measured across the 1ohm source resistors. Approx. 11W/device and 135W total bias.
This has a 18v+18V transformer making 23.5V rails. I measured 35W into 4ohm, I'm sure slightly higher figures, perhaps up to 50WPC/4ohm could be attained with smaller source resistors.
Increase the rail voltage and the power will easily go up. The one built for the build guide will have 32V rails.
Last edited:
Interesting! From the F5T article I read that decreasing (or removing) source resistor will deliver, for a given bias figure, more power into class A. This also brings to a thermally instable circuit.
What is the soft spot for this trick? Is it somewhat related to the number of output devices used? I'm asking because for the 4-6 deep complimentary are used 1 Ohm resistors, while for a more simple 2 deep complimentary, Nelson suggests 0.33 Ohm resistors.
' for the illustrated guide?