If I was in Europe, I’d be looking at Toroidy for a transformer. They have a pretty wide catalog of standard transformers and will make you a custom one for a reasonable price if they don’t offer one that works in their catalog. I haven’t personally ordered from them (yet) but I did get some custom toroids quoted awhile ago. I’ve read only good things about them here.
https://sklep.toroidy.pl/
https://sklep.toroidy.pl/
I am starting to build one of these and was wondering how much could I hot rod it? When I read that the class D chip could handle around 35v, and indeed MPS designed it to run at full power to output 90watts, I was wondering what I would need to change on this amp and power supply if I wanted to maybe run the unit at 30v or maybe even push my luck and try for 32v? Would I gain anything by pushing it? Maybe 75watts instead of 50?
A question if I may…
I’m doing a build of this power amp, using Pete’s recommended power supply.
I’m going to use the DIY Iron Preamp for the front end.
As I look at the schematic for the power amp boards, I’m trying to understand JP1 and 2. I’m assuming normal operation is to leave these unjumpered.
JP2 is labeled Amp enable, Short to Disable.
JP1 is labeled as Faults. Pin 1 goes to OTW (assuming Over Temperature Warning). Pin 2 is Fault (assuming that is protection mode).
While JP2 has an explanation, I’m unsure what jumping JP1 would do unless it’s just a test point for diagnosis.
I’m doing a build of this power amp, using Pete’s recommended power supply.
I’m going to use the DIY Iron Preamp for the front end.
As I look at the schematic for the power amp boards, I’m trying to understand JP1 and 2. I’m assuming normal operation is to leave these unjumpered.
JP2 is labeled Amp enable, Short to Disable.
JP1 is labeled as Faults. Pin 1 goes to OTW (assuming Over Temperature Warning). Pin 2 is Fault (assuming that is protection mode).
While JP2 has an explanation, I’m unsure what jumping JP1 would do unless it’s just a test point for diagnosis.
I seem to remember doing something with JP2 when I first built the amp and setting it up but my memory is so poor that I don't remember what exactly. I did just take the top off to check it and can tell you with certainty that I'm running the amp normally without either JP1 or JP2 jumpered.
Hello everyone and Merry (post) Christmas!
I just finished my build, but having a couple of problems. Three posts ago I wondered about running this amp at a higher voltage...guess I don't have to wonder, LOL, mine is naturally running at 30v because I'm getting over 121v from the wall.
Given that, I have two problems. I have my R4 at 160k ohms, but neither channel can get low enough. I know the 30v is part of it, but my left channel is sitting at 17v at its lowest point and the right channel is 14v. Why is one so much higher than the other and what does R4 need to be to get me down to 11v? I am going to start off setting it at 11.75 as others have been pleased with that.
My other problem is output voltage....with a .75v input (at 1khz) I am only getting about 8.9v output or roughly 12x gain. Not sure where to begin troubleshooting this problem. Both sides of both tubes glow and I checked supply voltage at the intersection of R22 and R23 (both boards are steady at 30.03/30.04v).
I just finished my build, but having a couple of problems. Three posts ago I wondered about running this amp at a higher voltage...guess I don't have to wonder, LOL, mine is naturally running at 30v because I'm getting over 121v from the wall.
Given that, I have two problems. I have my R4 at 160k ohms, but neither channel can get low enough. I know the 30v is part of it, but my left channel is sitting at 17v at its lowest point and the right channel is 14v. Why is one so much higher than the other and what does R4 need to be to get me down to 11v? I am going to start off setting it at 11.75 as others have been pleased with that.
My other problem is output voltage....with a .75v input (at 1khz) I am only getting about 8.9v output or roughly 12x gain. Not sure where to begin troubleshooting this problem. Both sides of both tubes glow and I checked supply voltage at the intersection of R22 and R23 (both boards are steady at 30.03/30.04v).
I will post pictures later, but I now have a working amp! Yay! I had to use 220k+ for R4 to get the voltage low enough. This unit has beautiful tone, crystal clear sound, very wide sound-stage, lots of detail and tight bass. Just really lovely sounding. I set the gains to x36 like others have and it still has more gain than expected - threw off my subwoofer levels lol. The bias is set about 11.9v as that happens to be where it stabilized once it ran for a bit. I do have some hiss though - not sure where that is coming from. Not a lot, but the amp isn't dead quiet like some of my others.
JP1 is just there if you wanted to wire LEDs or something else to know when the class D chip has a fault. These signals are driven to ground when there is a fault like a shorted output (pin 2) or if the part is getting hot and near shutdown (pin 1). When not driven they are high impedance (open drain). Don't pull them up above 5.5V or so.
Wow, that is beautiful!
You can actually set the bias almost anywhere you want. It does change the distortion (in particular the harmonic makeup of the distortion). Usually around 1/2 the supply voltage gives the lowest distortion, but not always. And yes, to get there you may have to change the plate load resistor (R4) - I should have explained that a bit more clearly!
The best way to set this is by using an audio analyzer to get the desired harmonics using an FFT. But with a BTL class D that can be difficult, as you need something with a floating differential input, as well as a steep low pass filter.
If you have good ears you can tweak it up and down by ear, maybe 2V at a time, then listen.
Be careful with the supply voltage. The MP7770 isn't very tolerant of overvoltage, so even a transient that hits 35V will pop it.
This amplifier, set at 11.9v bias (arbitrary as that is as low as mine goes) , in combination with the Pass Korg B1 preamp, is probably the best sounding unit I have in my collection. Compared to a Firstwatt Burning Amp 3 with matching Burning Amp 3 Preamp, the treble is much more extended, detailed, and clear. Compared to both the Burning Amp combo as well as XRK's TPA ClassD amp, this NuTube combo has superior imaging and soundstaging, being wider, taller, and especially deeper with better layering and instrumental separation. Obviously, given the type and amount of harmonics, the tone colors are much richer. The bass is tighter and less plumy than the Burning Amp, very similar to the TPA ClassD. Maybe less punchy than the TPA, which could be related to the much bigger output inductors of the TPA unit. The amp is very transparent to whatever is in front of it. This combo is definitely my new reference!
Thank you Pete for bringing this design to the community!
Thank you Pete for bringing this design to the community!
Hello everyone.
I just finished stuffing the boards and power supply. Everything passed the smoke test, so I started checking voltages, while I wait for the chassis from Landfall systems.
As many of you I cannot (with R4 at 100Kohm) reach a bias of 13 V. Mine gets, at the lowest, to 15.5V.
As Mr. Millett stated, however, that bias point of 13V is to reduce distortion, but on a nominal PS voltage of 28V. Mine is 30.5 V. This because my AC voltage at the socket is higher than the nominal 120V (mine is actually 125 V). As I dabble on old tube radios as well that is a problem because it stresses the tube rectifiers... I am tempted to leave well enough alone but while waiting, I may use my Variac and lower the Power supply input at 120V and see what happens.
By the way, has anyone measure the Voltage gain? With a sine wave at 2KHz and 60 mv input I get approx. 1 Volt with no load at the output. That is approx. a gain of 17. I can make it lower with RV2 but not higher. Is this normal? Thanks!
Marco
I just finished stuffing the boards and power supply. Everything passed the smoke test, so I started checking voltages, while I wait for the chassis from Landfall systems.
As many of you I cannot (with R4 at 100Kohm) reach a bias of 13 V. Mine gets, at the lowest, to 15.5V.
As Mr. Millett stated, however, that bias point of 13V is to reduce distortion, but on a nominal PS voltage of 28V. Mine is 30.5 V. This because my AC voltage at the socket is higher than the nominal 120V (mine is actually 125 V). As I dabble on old tube radios as well that is a problem because it stresses the tube rectifiers... I am tempted to leave well enough alone but while waiting, I may use my Variac and lower the Power supply input at 120V and see what happens.
By the way, has anyone measure the Voltage gain? With a sine wave at 2KHz and 60 mv input I get approx. 1 Volt with no load at the output. That is approx. a gain of 17. I can make it lower with RV2 but not higher. Is this normal? Thanks!
Marco
@phyciocc
You have probably read my posts above? - I am in the same situation as you, with 30v supply from 121v from the wall. Putting something over 220k for R4, like a 223k or so, is enough to give you the adjustment range you need. I bought 10 1% 220k resistors and picked the two highest to use. 219k was not enough, I needed 223, or even slightly higher would be fine.
Others in this post have suggested a gain of around 36 sounded best to him, but it is best to experiment and see what sounds best to you. Full gain is apparently around 40x. Hopefully you are measuring correctly, from the +/- binding posts and not positive post to ground? That will throw off the voltage you see regarding gain. I made that mistake at first with only 12x of gain 😜 Once the bias was set correctly, and I was measuring correctly, my gains were at proper levels and I could adjust as desired.
You have probably read my posts above? - I am in the same situation as you, with 30v supply from 121v from the wall. Putting something over 220k for R4, like a 223k or so, is enough to give you the adjustment range you need. I bought 10 1% 220k resistors and picked the two highest to use. 219k was not enough, I needed 223, or even slightly higher would be fine.
Others in this post have suggested a gain of around 36 sounded best to him, but it is best to experiment and see what sounds best to you. Full gain is apparently around 40x. Hopefully you are measuring correctly, from the +/- binding posts and not positive post to ground? That will throw off the voltage you see regarding gain. I made that mistake at first with only 12x of gain 😜 Once the bias was set correctly, and I was measuring correctly, my gains were at proper levels and I could adjust as desired.
Hello Steve, your amp is one of the nicest builds I have seen on these forums.. Could I ask where you obtained your enclosure?
Thanks,
Ken
Thanks,
Ken
Thank you Ken 🙂 It's just an aluminum case from China via eBay. It is beautifully finished - there were no manufacturing defects that I could see. I knew I needed at least 80mm of height to fit the boards vertically, so that's all I searched for. I wish it came in black, but it doesn't. I loved the case so much I tried to find the amp kit that the heatsinks are predrilled for but never found anything. I would totally buy another one just the build the amp it was designed for lol.
Yukon888:
I just emailed them to order one of these up and it seems Pete M recommendeds a 3" wider chassis now. Yours looks like the original dimensions?
Cheers,
Pete