I am running them on my SR1's - 3.8 Ohms / 86 db, and they work fine.
1.5 amp bias and no disco...
1.5 amp bias and no disco...
Link to Nelson’s post with the Zenductor 2 article:
Post in thread 'Burning Amp 2024!'
https://www.diyaudio.com/community/threads/burning-amp-2024.414636/post-7820909
Post in thread 'Burning Amp 2024!'
https://www.diyaudio.com/community/threads/burning-amp-2024.414636/post-7820909
That's Hot! (F and C, pictured below)
The floor was reading 23.6 C so that's not quite 60 C above ambient (well... floor might be cooler than air temp) , bias was about 1.37 v, visible on the DVM there. Heatsink was hotter down by the device.
So! Anyone meditating about elegant cooling options? Someone pointed out to me that you could stack a 2nd heatsink on top of the first, and I think I have some thermally conductive glue here somewhere. I went to the Parts List in the Zenductor 2 .pdf hoping to find a part no. for the heatsink but there was none. I'm afraid I don't know the term for this form factor...
Or maybe I build a base and put a fan on it. Maybe even a little shroud. Hmmm, can I grab fan power off the SMPS without noising the audio up? Board is ~120 mm across, maybe one of those fans NBrock liked for his F5M-Redux (were they 120's? I'll have to go back and look).
Or you got a better idea?
These fans https://www.amazon.com/dp/B071Y4MGFK?ref=ppx_yo2ov_dt_b_fed_asin_title&th=1 are keeping the temp down around 110 F / 44 C, but I think I want a better integrated solution long-term.
Amp sounds groovy! Very Satisfying.
The floor was reading 23.6 C so that's not quite 60 C above ambient (well... floor might be cooler than air temp) , bias was about 1.37 v, visible on the DVM there. Heatsink was hotter down by the device.
So! Anyone meditating about elegant cooling options? Someone pointed out to me that you could stack a 2nd heatsink on top of the first, and I think I have some thermally conductive glue here somewhere. I went to the Parts List in the Zenductor 2 .pdf hoping to find a part no. for the heatsink but there was none. I'm afraid I don't know the term for this form factor...
Or maybe I build a base and put a fan on it. Maybe even a little shroud. Hmmm, can I grab fan power off the SMPS without noising the audio up? Board is ~120 mm across, maybe one of those fans NBrock liked for his F5M-Redux (were they 120's? I'll have to go back and look).
Or you got a better idea?
These fans https://www.amazon.com/dp/B071Y4MGFK?ref=ppx_yo2ov_dt_b_fed_asin_title&th=1 are keeping the temp down around 110 F / 44 C, but I think I want a better integrated solution long-term.
Amp sounds groovy! Very Satisfying.
I plan to "skyscraper" the heat sinks since I have a toddler and a curious "Tom-cat" in the house. The "skyscraper" seems like simple solution using some thermal grease between the heat sink stacked interface. It worked well on my high biased ACA Mini skyscraper amp. No need to glue them, just friction fit stack with thermal compound spread on the interface.
For the same heatsinks (you could go with shorter ones by the way) the Mouser part number is: 532-530001B02500 ($5.26/ea)
For the same heatsinks (you could go with shorter ones by the way) the Mouser part number is: 532-530001B02500 ($5.26/ea)
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Some pics from amp camp:
One of my four transistors ran about 10K hotter than the other three:
You can see it also in the picture showing all four heat sinks:
This is with both bias currents dialed in to 1.35V over the resistor.
Too much data is a dangerous thing... ;-)
One of my four transistors ran about 10K hotter than the other three:
You can see it also in the picture showing all four heat sinks:
This is with both bias currents dialed in to 1.35V over the resistor.
Too much data is a dangerous thing... ;-)
And a picture of my first amp under test, fed from YouTube music, and connected to an 8 Ohm resistor and my headphones. I was too impatient to wait for the speakers...
You can rase the value of the 2 watt Source resistor on the hotter Mosfet, probably to .56 or .68 ohms without issues.
In general, the amp works fine if you want to adjust the bias down. The 1.4 figure is considered maximum, and I drive my SR1's with 70 deg sink temperatures.
In general, the amp works fine if you want to adjust the bias down. The 1.4 figure is considered maximum, and I drive my SR1's with 70 deg sink temperatures.
Thanks! I wasn't sure whether making the two transistor paths unequal was an ok option.
What I think/hope/plan to do (but it still has to be seen whether I'll actually get around to it...) is to measure distortion as a function of bias, maybe over the whole chain including my speakers, and see whether there is a setting I actually like best. (But then the speaker might dominate, and the amp bias might make very little difference. To be seen/heard.) According to Nelson's writeup (see copy of one of his graphs below) there should be about a factor two of variation in distortion, from ~0.15% at 1.4V to ~0.25% at 1.0V inductor voltage, at 1kHz and 1W. Maybe I'll like higher distortion better, and at lower bias the transistor temperatures and uneven sharing will become a non-issue.
A separate but related question: So if I wanted to get a bit more negative 2nd harmonic distortion while listening over headphones, I should terminate the amp into 4 Ohm instead of 8 Ohm (in parallel with my 300 Ohm headphones)?
What I think/hope/plan to do (but it still has to be seen whether I'll actually get around to it...) is to measure distortion as a function of bias, maybe over the whole chain including my speakers, and see whether there is a setting I actually like best. (But then the speaker might dominate, and the amp bias might make very little difference. To be seen/heard.) According to Nelson's writeup (see copy of one of his graphs below) there should be about a factor two of variation in distortion, from ~0.15% at 1.4V to ~0.25% at 1.0V inductor voltage, at 1kHz and 1W. Maybe I'll like higher distortion better, and at lower bias the transistor temperatures and uneven sharing will become a non-issue.
A separate but related question: So if I wanted to get a bit more negative 2nd harmonic distortion while listening over headphones, I should terminate the amp into 4 Ohm instead of 8 Ohm (in parallel with my 300 Ohm headphones)?
Oh, look, my Zenductor II grew little blue feet. How adorable 😍
You can download the latest 3D print files here.
You can download the latest 3D print files here.
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OMG the Zenductor 2 now has Gumby’s feet. Looks cool.
P.s. if I know Gumby I’m old…😂
P.s. if I know Gumby I’m old…😂
I really really appreciate the design and the building experience, but to be honest, I'm not crazy about the three footed support. It's great in the mountains or in the desert, but supporting a rectangle it's kinda wobbly if you push on one of the corners, for example when you adjust the bias.
But I consider the standoffs temporary, until the amp finds its home in a more dignified and worthy permanent enclosure.
But I consider the standoffs temporary, until the amp finds its home in a more dignified and worthy permanent enclosure.
I assume it will eventually show up here: https://diyaudiostore.com/collections/power-amplifiers-output-stages ?
My thanks to all the folks at BAF24! It was my first time building an amp, and I needed some expert attention from Jim to get it operational.
@Gruesome
I am definitely hoping some experienced builders will encase these board amps and provide the details here for us novices! It seems amenable to multiple layouts. From leaving the power supplies outside, the board power switches always on, only inputs & outputs on the case, and an easily removable top for bias play. To all-out with internal power supply, bias pot & voltage display front-mounted.
@Gruesome
I am definitely hoping some experienced builders will encase these board amps and provide the details here for us novices! It seems amenable to multiple layouts. From leaving the power supplies outside, the board power switches always on, only inputs & outputs on the case, and an easily removable top for bias play. To all-out with internal power supply, bias pot & voltage display front-mounted.
I have 5 sets of Zenductor II 3D printed feet all made up and ready to give away for install for anyone interested. First five folks who want these can PM me and will get these for whatever shipping costs to your address ($4-7 depending on distance from Seattle in CONUS). They are all blue and include all the M3 hardware. You simply remove the SAE hex standoffs & bolts and swap in the 3D printed parts. If you'd like to add in some PCB's that I have in the swap meet, shipping should be the same, or just a couple bucks more depending on total weight.
The soft TPU (thermal polyurethane) material used in the 3D printed part won't scratch whatever the amps are sitting on and has a little more friction than the metal standoffs so the amps don't slide around. Additionally, the "front leg" is wide on the bottom to reduce tipping that can occur with a tripod setup.
Thanks to all who made the Zenductor II Amp Camp possible at BAF'24 (Nelson Pass, Jim T., Nelson B., Mark Johnson, and anyone else who I may have missed). What a fun build and I can't wait to get these hooked up to some efficient speakers to play glorious music.
(If anyone wants me to print in a custom color, I'm happy to do that for a buck or two extra on top of shipping. I have blue, black, yellow, white, clear, neon green, orange, and rainbow TPU on hand)
The soft TPU (thermal polyurethane) material used in the 3D printed part won't scratch whatever the amps are sitting on and has a little more friction than the metal standoffs so the amps don't slide around. Additionally, the "front leg" is wide on the bottom to reduce tipping that can occur with a tripod setup.
Thanks to all who made the Zenductor II Amp Camp possible at BAF'24 (Nelson Pass, Jim T., Nelson B., Mark Johnson, and anyone else who I may have missed). What a fun build and I can't wait to get these hooked up to some efficient speakers to play glorious music.
(If anyone wants me to print in a custom color, I'm happy to do that for a buck or two extra on top of shipping. I have blue, black, yellow, white, clear, neon green, orange, and rainbow TPU on hand)
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Is anyone planning up a Zenductor II Max? I dunno a whole lot about it but I kinda wonder how far you could push it if you uprated the main inductor and the cooling. And probably some other details I'm not thinking of (caps n gain xformer?). I'm good with mine (for the time being 
) but would be interested to see...
) but would be interested to see...
I thought/think the first thing to upgrade is the voltage gain transformer; I think Nelson Pass showed a souped version of the Zenductor 2 with 1000 Jfets and a cinemag transformer (https://cinemag.biz//index.php) in his talk at Burning Amp 2024; I just don't know which one.
The advantage of using 1000 output transistors is that you get away without a heatsink. Otherwise I think you would want to upgrade the heatsink second.
The advantage of using 1000 output transistors is that you get away without a heatsink. Otherwise I think you would want to upgrade the heatsink second.