Well, here the bench device N channel 2SK60 is on its maiden voyage playing music from one speaker routed through the Pass Korg preamp and using a Fire tablet as source (mere .375 V output). Even without warming, up, sounds extremely precise and has a pleasing character in mono. Not extremely loud at present, but a reasonable volume output. I will try a more robust source later. Of course, reservations about ultimate sound until final product is built and working.
I have decided that although a single heat sink would work, discretion is the better part of valor. I will use two heat sinks and make the amp a direct amp without the Bulwark boards (no room), relying on external preamplification and/or the internal 4650 preamp. NP in his monograph said that input impedance is high and it can be used this way without a dedicated front end. Hopefully, the heat sink surfeit will keep things between 120 F and 130 F. Internal Sony preamp for the time being. This 4650 internal preamp is no slouch, even though simple, and I played it through my 'big rig' and it sounded excellent, and also sounds excellent through headphones, though it is markedly inappropriate for headphones.
I will test the second stuffed amp card with the rig on the speaker then start contemplating the chassis stuffing.
I am amazed I got this far and got a channel to work.
I have decided that although a single heat sink would work, discretion is the better part of valor. I will use two heat sinks and make the amp a direct amp without the Bulwark boards (no room), relying on external preamplification and/or the internal 4650 preamp. NP in his monograph said that input impedance is high and it can be used this way without a dedicated front end. Hopefully, the heat sink surfeit will keep things between 120 F and 130 F. Internal Sony preamp for the time being. This 4650 internal preamp is no slouch, even though simple, and I played it through my 'big rig' and it sounded excellent, and also sounds excellent through headphones, though it is markedly inappropriate for headphones.
I will test the second stuffed amp card with the rig on the speaker then start contemplating the chassis stuffing.
I am amazed I got this far and got a channel to work.
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I completed as far as I could with my N channel VFET (SONY 2SK60) amplifier. Output boards completed, along with Theseus P/S filter and Nimittz input PCB's. Tuscon daughter boards are installed, I have two others from my M2x to choose from. I have the power supply brick and back panel parts with DPDT switch, waiting for the enclosure. I wanted to finish these items as spring chores have now arrived, outside I go for a while.
I'm happy with my production this year, my first DIY speaker build in 50 years is in progress, 8" Utah drivers in bass reflex enclosures circa 1972 were the first and only.
I'm happy with my production this year, my first DIY speaker build in 50 years is in progress, 8" Utah drivers in bass reflex enclosures circa 1972 were the first and only.
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Second card tested and working in mono bench setup. Spooky effect noted, even with raspy hookups and ad hoc alligator clips. Female vocal heaven? So that is two working cards that can make music.
I listened to mono setup while making lunch yesterday. My parrot liked it and seemed disappointed when I turned it off.
Now, place transistors in center of two heat sinks, and test second VFET/Mosfet pair with a card to make sure they are working, then contemplate chassis stuffing.
I listened to mono setup while making lunch yesterday. My parrot liked it and seemed disappointed when I turned it off.
Now, place transistors in center of two heat sinks, and test second VFET/Mosfet pair with a card to make sure they are working, then contemplate chassis stuffing.
Also ponder whether you want to explore (a) front ends with Edcor transformers; and also (b) front ends without Edcor transformers. A little searching on this website for "Marauder" (one of 3 front ends without transformer) will unearth some listener evaluations and reviews, saying the no-transformer front end is sonically preferable. The opinions of other builders may or may not be interesting/relevant to you, of course.
I have the Bulwark cards and implementing them is partly ergonomics of the chassis, partly just getting the basic amp built and working in the chassis first. This is kind of a tribute job to the first commercial VFET amp with a mod. I think there might be room for the Bulwark cards but I don't know yet.
Second set of SK60/MOSFET mounted on heat sink bias easily around 16v, so that makes two sets of SK60/MOSFET that seem patent. Second set makes music in mono using the built in Sony TA 4650 preamp, which has good gain overall, maybe as high as 20 db or so. I will have to listen to it later because my wife is clunking around kitchen blaring news channel.
Ran the audio signal through the Sony TA 4650 preamp (powered by small 20V SMPS attached to internal 4650 input wiring) and one channel to bench VFET to single audio speaker. That had a marked hum production. When I went from 4650 preamp output to Korg preamp, and then to single bench VFET amp input, no hum. Headphones on 4650 preamp output sound great, no hum. So, I don't know where the hum comes from, the Korg gain stage seems to mop it out. Hopefully, when all under one chassis instead of external power supply with alligator clips, it won't be there any more. 4650 preamp seems to have a gain of about 20 db or so at full output.
Heat sink with VFET/MOSFET attached in middle of heat sink in cool room after an hour gives variable T across the heat sink with a high of about 115 right over the VFET area out to 106-110 F VFET outer limit on heat sink and 94 Mosfet outer limit on heat sink. Heat sink adjacent to VFET seems to stay around 106-110 F or so, so a single pair VFET/MOSFET on a single heat sink seems to be OK. I can keep my finger on heat sink fins for 10 to 20 seconds adjacent to VFET, and almost indefinitely adjacent to MOSFET. I'll try again when the air is warmer.
Anyway, two sets of VFET/MOSFET on heat sinks making music with two valid output cards, so I guess the next steps are the chassis stuffing.
I think the sound from the single speaker (Radio Shack Realistic mini AV, maybe about 88 to 90 db efficient, but with limited output below 100Hz, but a very good quality soft dome tweeter) sounds quite good, with a very smooth and timbre-ally detailed upper midrange, even with the ad hoc setup and I can't tell that the 4650 preamp at full output damages the sound quality (as long as the hum isn't there).
Heat sink with VFET/MOSFET attached in middle of heat sink in cool room after an hour gives variable T across the heat sink with a high of about 115 right over the VFET area out to 106-110 F VFET outer limit on heat sink and 94 Mosfet outer limit on heat sink. Heat sink adjacent to VFET seems to stay around 106-110 F or so, so a single pair VFET/MOSFET on a single heat sink seems to be OK. I can keep my finger on heat sink fins for 10 to 20 seconds adjacent to VFET, and almost indefinitely adjacent to MOSFET. I'll try again when the air is warmer.
Anyway, two sets of VFET/MOSFET on heat sinks making music with two valid output cards, so I guess the next steps are the chassis stuffing.
I think the sound from the single speaker (Radio Shack Realistic mini AV, maybe about 88 to 90 db efficient, but with limited output below 100Hz, but a very good quality soft dome tweeter) sounds quite good, with a very smooth and timbre-ally detailed upper midrange, even with the ad hoc setup and I can't tell that the 4650 preamp at full output damages the sound quality (as long as the hum isn't there).
I hope it is a small board. Smaller the better for Sony TA 4650 chassis ergonomics.
ha!
another one made for Mass-Popularization of Proper Audio Approach
it made my heart warm seeing that Pa is achieving lately - probably more than dozen of still existing periodicals, together
though, I believe it's time for another proper Papamp, where both elbow grease and some real hardware are involved
(if you leave that niche unattended for too long, you know what you can expect - avalanche of Babelfishes
)