Yes.
Most of my diy amplifiers are follower output stages with no input gain stage. I use a high gain preamp, one of which is a DIY FE 2022 preamp. So one gain stage with a choice of follower output stages.
The M2X has swappable input stages. This new VFET amp could probably be rigged to quickly swap front ends.
Most of my diy amplifiers are follower output stages with no input gain stage. I use a high gain preamp, one of which is a DIY FE 2022 preamp. So one gain stage with a choice of follower output stages.
The M2X has swappable input stages. This new VFET amp could probably be rigged to quickly swap front ends.
Excellent. Your description makes a lot of sense and is a reminder that I need to learn to make those calculations myself! Thanks much for the assist!
Your description of "don't crank it to 11" reminds me of a discussion I had years ago with Jeff Joseph. His concern, as a speaker designer, included the thoughts of "just don't overdo it" but focused on speakers being driven by an amp with too much distortion. He said he would rather a speaker be driven to it's limit by a clean amplifier than being driven even part way by something that reaches it's peak distortion at a lower level.
Thanks again!
As far as "easy swap" front ends, my new amp revision has an "L" bracket on the back to facilitate mounting. It's kind of like what PL does on some of their amps. Right now the standoffs are setup on the Stasis FE mounting hole width, but it would be easy to adapt other spacing requirements as needed. DC power is on XT60 and MT60 connectors. This all started back when my SS R.3's gain of 11.5db wasn't enough, and I wanted an "integrated" solution to provide more. My main heatsink is drilled and tapped to accept almost any of the amplifier circuits here, and I can add in these different front end options as desired.... or not..
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I'll be curious to hear your thoughts on the sound once you build this amp. My friend's Zu's were fast and plenty strong in the bass, which suited the music she preferred. It would have been neat to hear these driven by some of Nelson's class A stuff including these VFET amps, but we didn't get the chance before she moved away. She had a pair of Quicksilver Mid Monos, push-pull AB and her system was insane.
ranshdow - I was lucky enough to buy a McIntosh MC462 (their flagship stereo amp) and MC275 (their famous tube amp) + the C53 preamp at my old job at employee cost. Either of those would be end game amps for most people. They are both excellent, but on the Zu's, the Aleph J smokes them. The closest I can get is the MC275 with 6550s (vs. KT88s), but I always find myself going back to the Aleph J. So you can imagine how excited I am for this new kit. There is something about the tone, presentation, and how the Zu and Aleph J just 'gel'. It was like they were made for each other. Oh, I recall seeing Pass gear at Zu, so that might not be an accident! For reference, I have the DW6 with the 'Superfly' upgrade.
As an aside, I am currently on the hunt for some new speakers (to add to the gear library, not to replace anything), and I keep going in circles. There are some things that really interest me, and would pair well with either of the McIntosh amps - traditional cone-and-dome speakers with 8x db. sensitivity and demanding loads (4 ohm rated, but dipping lower at certain frequencies). However, this would all but exclude the Aleph J or any other fun stuff like we are talking about here. My search then goes to something like one of the Klipsch Heritage products (I would get the new LaScalas, but I am not sure they would be happy in my 13x18' listening room). As good as the Zu's are, I can't help but think they are not quite doing my other gear justice. My other main speakers are a older pair of Sonus Faber towers - they ROCK with the MC275, but things fall flat on the Aleph J, simply because of the power. Funny enough, the best pairing for the MC462 are the KEF LS50 Meta, as they need TONS of power and they can handle it (I often see the meters getting up in the 50 watt range). I feel the MC462 likes demanding speakers, but is a bit ham-fisted with high-sensitivity stuff.
Regardless, super excited for this kit and hooking it up to the Zu's and seeing what happens.
If you ever find yourself in Salt Lake, happy to let you take them for a test drive!
Here is what I am working with:
As an aside, I am currently on the hunt for some new speakers (to add to the gear library, not to replace anything), and I keep going in circles. There are some things that really interest me, and would pair well with either of the McIntosh amps - traditional cone-and-dome speakers with 8x db. sensitivity and demanding loads (4 ohm rated, but dipping lower at certain frequencies). However, this would all but exclude the Aleph J or any other fun stuff like we are talking about here. My search then goes to something like one of the Klipsch Heritage products (I would get the new LaScalas, but I am not sure they would be happy in my 13x18' listening room). As good as the Zu's are, I can't help but think they are not quite doing my other gear justice. My other main speakers are a older pair of Sonus Faber towers - they ROCK with the MC275, but things fall flat on the Aleph J, simply because of the power. Funny enough, the best pairing for the MC462 are the KEF LS50 Meta, as they need TONS of power and they can handle it (I often see the meters getting up in the 50 watt range). I feel the MC462 likes demanding speakers, but is a bit ham-fisted with high-sensitivity stuff.
Regardless, super excited for this kit and hooking it up to the Zu's and seeing what happens.
If you ever find yourself in Salt Lake, happy to let you take them for a test drive!
Here is what I am working with:
These come highly recommended..... I guy I know well just ordered a pair of these to go with his new FW F7
Tekton perfect SET.... he swears by their sound...
https://tektondesign.com/product/full-range-speakers/full-towers/the-perfect-set/#color
The price is quite good.... I might spring for a pair by Christmas... even if I have to pay MSRP.
At their efficiency they would seem to do great with the VFET amps.
Tekton perfect SET.... he swears by their sound...
https://tektondesign.com/product/full-range-speakers/full-towers/the-perfect-set/#color
The price is quite good.... I might spring for a pair by Christmas... even if I have to pay MSRP.
At their efficiency they would seem to do great with the VFET amps.
I hear ya! I have Tekton Lore Reference and know that there are likely better pairings for my current setup - but just keep reading and reading to find "the one." My previous Joseph Audio RM25si were quite amazing but got sold off as we were planning to move...2020 shut that down pretty quickly. Gah! So I went back to rebuilding and started DIYing more and then just sortof ran into the Tektons. The Tektons are not bad, but after owning the Josephs for so long I rather miss their clean refined sound. I think I need to get out to some audio shows in the next year or so to hear some gear so that I can narrow down the list for an upgrade.
Hopefully I'll know soon... but then... you got the front ends..
I think the answer is going to be more complicated than P or N.... there are at least eight basic combinations... and Mark Johnson brought up even more FE cards.
The original "lottery VFET" amps of April 2021, are described in a .pdf by Nelson Pass, in post #1 of (this Forum thread).
Nelson explains that because the VFET transistor has quite a low drain impedance, the VFET amplifier's follower output stage actually has voltage loss, i.e., gain < 1, see attached snippet. The output stage's gain is a rather surprising 0.63 volts per volt (-4.0 dB).
The 2021 lottery front end card using Toshiba+Edcor had a gain of 5.0 volts per volt (+14.0 dB), so the end-to-end gain of the entire lottery VFET amplifier was (0.63 * 5.0 = 3.15 volts per volt), and 3.15x equals +10.0 dB. Alternatively, performing the gain calculation using decibels: +14dB front end, plus -4.0dB output stage, equals +10.0 dB for the entire amp end-to-end. Exactly equal to the end-to-end gain Nelson wrote in the .pdf.
The 25th Anniversary edition keeps the same VFET follower output stage, whose maximum power output before clipping is 10 watts into 8 ohms, snippet below. That's 8.94 volts RMS into 8 ohms.
However, the new 25th Anniversary edition installs a no-Edcor, no-Toshiba front end called "FE2022" whose gain is 10x, set by the resistor ratio R4/R2. In other words, double the gain of the 2021 lottery front end card. By the way, 10x gain equals +20 dB. So the end-to-end gain of the entire 25th Anniversary edition is (0.63 * 10.0x = 6.30 volts per volt). In dB, it's (-4.0 dB + 20.0 dB) = +16 dB.
When the 25th Anniversary edition just barely begins to enter clipping, its output is 8.94000001 volts RMS. Dividing by the end-to-end gain (6.30x) we see that an input of 1.419 volts RMS will start to clip the amplifier. That's 2.0 volts peak (above the mid-line), i.e., 4.0 volts peak-to-trough.
So if you want to get 100% of the available output power of the 25th Anniversary edition, make sure your source can deliver 1.42 volts RMS {when FE2022 is installed} , and/or 2.84 volts RMS {when Bulwark or Marauder or Dreadnought is installed}. Back in 2021, Nelson recommended using a source that can deliver 3V RMS, which is pleasantly conservative.
Nelson explains that because the VFET transistor has quite a low drain impedance, the VFET amplifier's follower output stage actually has voltage loss, i.e., gain < 1, see attached snippet. The output stage's gain is a rather surprising 0.63 volts per volt (-4.0 dB).
The 2021 lottery front end card using Toshiba+Edcor had a gain of 5.0 volts per volt (+14.0 dB), so the end-to-end gain of the entire lottery VFET amplifier was (0.63 * 5.0 = 3.15 volts per volt), and 3.15x equals +10.0 dB. Alternatively, performing the gain calculation using decibels: +14dB front end, plus -4.0dB output stage, equals +10.0 dB for the entire amp end-to-end. Exactly equal to the end-to-end gain Nelson wrote in the .pdf.
The 25th Anniversary edition keeps the same VFET follower output stage, whose maximum power output before clipping is 10 watts into 8 ohms, snippet below. That's 8.94 volts RMS into 8 ohms.
However, the new 25th Anniversary edition installs a no-Edcor, no-Toshiba front end called "FE2022" whose gain is 10x, set by the resistor ratio R4/R2. In other words, double the gain of the 2021 lottery front end card. By the way, 10x gain equals +20 dB. So the end-to-end gain of the entire 25th Anniversary edition is (0.63 * 10.0x = 6.30 volts per volt). In dB, it's (-4.0 dB + 20.0 dB) = +16 dB.
When the 25th Anniversary edition just barely begins to enter clipping, its output is 8.94000001 volts RMS. Dividing by the end-to-end gain (6.30x) we see that an input of 1.419 volts RMS will start to clip the amplifier. That's 2.0 volts peak (above the mid-line), i.e., 4.0 volts peak-to-trough.
So if you want to get 100% of the available output power of the 25th Anniversary edition, make sure your source can deliver 1.42 volts RMS {when FE2022 is installed} , and/or 2.84 volts RMS {when Bulwark or Marauder or Dreadnought is installed}. Back in 2021, Nelson recommended using a source that can deliver 3V RMS, which is pleasantly conservative.
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If the FE2022's maximum output swing is 35 volts* peak to trough (on a 36 volt power supply), FE2022 delivers 12.4 volts RMS to the input of the VFET output stage. Math: ( (35/2) / SQRT(2) ) = 12.374
The VFET's output stage's gain is 0.63 volts per volt, so an input of 12.4 volts RMS produces 7.80 volts RMS at the loudspeaker terminals. That means 7.6 watts with an 8 ohm load. Math: 7.8 * 7.8 / 8.0 = 7.61
In order to get the full 10 watts into 8 ohms, the front end needs to deliver SQRT( 10 watts * 8 ohms ) / (OPS gain of 0.63x) = 14.2 volts RMS = 40.2 volts peak-to-trough, more than FE2022 can manage on a 36V supply.
A front end with a boosted supply > 45 volts, and/or a front end with a 5-to-1 Edcor step up transformer , can output more than 40.2 volts peak-to-trough. Enough to produce 10 watts with an 8 ohm load.
*just a guessestimate
The VFET's output stage's gain is 0.63 volts per volt, so an input of 12.4 volts RMS produces 7.80 volts RMS at the loudspeaker terminals. That means 7.6 watts with an 8 ohm load. Math: 7.8 * 7.8 / 8.0 = 7.61
In order to get the full 10 watts into 8 ohms, the front end needs to deliver SQRT( 10 watts * 8 ohms ) / (OPS gain of 0.63x) = 14.2 volts RMS = 40.2 volts peak-to-trough, more than FE2022 can manage on a 36V supply.
A front end with a boosted supply > 45 volts, and/or a front end with a 5-to-1 Edcor step up transformer , can output more than 40.2 volts peak-to-trough. Enough to produce 10 watts with an 8 ohm load.
*just a guessestimate
Mark, I assume with that increases voltage to get the FULL power, you would have an increase in heat?
Knowing how precious these transistors are, I am certainly OK running them on the conservative side to extend life.
Knowing how precious these transistors are, I am certainly OK running them on the conservative side to extend life.
High voltage supply to the front end does not affect the VFET output stage heat dissipation.
The front end current demand is very low so the heat dissipation of the front end is very low, so it is not a factor in overall amplifier temperature.
The Class A output stage dissipates the most heat when it is idling. All of its power is dissipated as heat. When the output stage amplifies a signal, some of the power is sent to the speaker and the rest is dissipated as heat.
So to stress the VFETs less, play your music LOUD. 🤓
The front end current demand is very low so the heat dissipation of the front end is very low, so it is not a factor in overall amplifier temperature.
The Class A output stage dissipates the most heat when it is idling. All of its power is dissipated as heat. When the output stage amplifies a signal, some of the power is sent to the speaker and the rest is dissipated as heat.
So to stress the VFETs less, play your music LOUD. 🤓
Bulwark, Marauder, and Dreadnought can drive the VFET output stage to make it deliver 10 watts, the output stage's max possible output power into 8 ohms ----> as LOUD as the amplifier can possibly play
FE2022 can only drive the VFET output stage to make it deliver 7.6 watts, i.e., 76% of the output stage's max possible output power into 8 ohms ----> not quite as LOUD as the amplifier can possibly play. But maybe the difference is perceptually insignificant.
FE2022 can only drive the VFET output stage to make it deliver 7.6 watts, i.e., 76% of the output stage's max possible output power into 8 ohms ----> not quite as LOUD as the amplifier can possibly play. But maybe the difference is perceptually insignificant.
The DIY FE 2022 needs a PS voltage boost!
Add a 9V or 12V PS (an obsolete wall wart) in series with the main supply to power the FE 2022.
Add a 9V or 12V PS (an obsolete wall wart) in series with the main supply to power the FE 2022.
Looking online I see DC to DC converters. Here is one that will convert 35VDC to 45VDC. I don't know how clean the output voltage is. Could possibly add a filter and then use the boosted voltage to power the DIY FE 2022 for higher signal output voltage.
https://www.amazon.com/Haosie-Conve...pcontext&ref_=fplfs&psc=1&smid=A20WU7F6MJJC8N
https://www.amazon.com/Haosie-Conve...pcontext&ref_=fplfs&psc=1&smid=A20WU7F6MJJC8N
