The inguz amplifier is another variation on LM3886 topologies:
Gain ~18dB; output impedance ~8 ohms. Inductor keeps ZOut high as Avol drops. Deliberately unbalanced Howland bridge, meaning no need for resistor tolerances beyond 1%.
The first build is a four-channel version (bridgeable, but mainly to drive bi-amped Linn floorstanders); pictures to follow over the next couple of days when it's cleaned up a bit.
I see a little instability (RF pickup) with open-circuit input. A few pF across input should cure that, but this build will be permanently plugged in to my Squeezebox, so that's not a concern.
So far this has only been running into cheap, bad speakers. But it makes cheap, bad speakers sound good.
Gain ~18dB; output impedance ~8 ohms. Inductor keeps ZOut high as Avol drops. Deliberately unbalanced Howland bridge, meaning no need for resistor tolerances beyond 1%.
The first build is a four-channel version (bridgeable, but mainly to drive bi-amped Linn floorstanders); pictures to follow over the next couple of days when it's cleaned up a bit.
I see a little instability (RF pickup) with open-circuit input. A few pF across input should cure that, but this build will be permanently plugged in to my Squeezebox, so that's not a concern.
So far this has only been running into cheap, bad speakers. But it makes cheap, bad speakers sound good.
Some pictures
Power supply is +/- 24V, C-R-C filtered. I wanted to build C-L-C but didn't really have room for large chokes (as you'll see from the internals photos, there's barely room for 4x15000u capacitors).
PSU schematic
The enclosure is approx 8x11x3 inches, copper, acrylic, brass, mahogany. Here's a "rough assembly" version -- the final should look quite fine. Weighs a ton.
Enclosure (rough)
Internals: cramped. One word of advice to anyone else thinking of building four channels point-to-point: "reconsider". That transformer is pretty darn huge too.
Internals (1), Internals (2)
Enjoy 🙂
Power supply is +/- 24V, C-R-C filtered. I wanted to build C-L-C but didn't really have room for large chokes (as you'll see from the internals photos, there's barely room for 4x15000u capacitors).
PSU schematic
The enclosure is approx 8x11x3 inches, copper, acrylic, brass, mahogany. Here's a "rough assembly" version -- the final should look quite fine. Weighs a ton.
Enclosure (rough)
Internals: cramped. One word of advice to anyone else thinking of building four channels point-to-point: "reconsider". That transformer is pretty darn huge too.
Internals (1), Internals (2)
Enjoy 🙂
This looks very neat. I'll work my way through the .PDF tonight.
The Point to Point approach is nicely done as well. Congrats.
/Hugo 🙂
The Point to Point approach is nicely done as well. Congrats.
/Hugo 🙂
First sounds
Some first impressions about how this thing sounds. I only spent a couple hours yesterday evening, trying it with a wide mix of material. The speakers aren't bi-amped yet, so this was running two of four channels.
Bridging should "just work", but it's unstable. I already moved the 33pF compensation caps to 47pF. Some tweaking definitely needed there (eg reducing the series 4k7) -- I'd like to have bridged-mode work properly.
Anyway. Sounds. First impression: just a giant open soundstage -- more detail, more space, than I've ever heard at home before. Nothing localized to the loudspeakers; just sound all around the room, firmly positioned from snares to bass to horns and guitar. Bud Powell (Vol3) came alive. Mingus (Ah Um) was incredibly "real" - cleanly separated. Wes Montgomery (Smokin' at the Half Note) you could really feel the club setting; atmosphere, clear-as-a-bell guitar, and absoultely "right here" drumkit. TM Juke (Wilderness) I could listen to all night, now.
Some little harshness on vocals. India Arie was beautiful, but felt like she was singing in the recording room and me listening outside an open door.
The damping factor is really low, so I expected bass to be boomy and flabby. It definitely doesn't have the typical solidstate "tautness", but instead a very live-music sound. Even the heaviest music I tried (Keith Hudson - Depth Charge; Fugazi - Ex-Spectator, with two drummers) had no sense of boominess, just lots of presence, and much more "reality" than I'm used to.
Already, across the board, even with known-not-good recordings, it opened up details and atmospheres I've never heard before. So far then, I'm pretty happy. 🙂
Some first impressions about how this thing sounds. I only spent a couple hours yesterday evening, trying it with a wide mix of material. The speakers aren't bi-amped yet, so this was running two of four channels.
Bridging should "just work", but it's unstable. I already moved the 33pF compensation caps to 47pF. Some tweaking definitely needed there (eg reducing the series 4k7) -- I'd like to have bridged-mode work properly.
Anyway. Sounds. First impression: just a giant open soundstage -- more detail, more space, than I've ever heard at home before. Nothing localized to the loudspeakers; just sound all around the room, firmly positioned from snares to bass to horns and guitar. Bud Powell (Vol3) came alive. Mingus (Ah Um) was incredibly "real" - cleanly separated. Wes Montgomery (Smokin' at the Half Note) you could really feel the club setting; atmosphere, clear-as-a-bell guitar, and absoultely "right here" drumkit. TM Juke (Wilderness) I could listen to all night, now.
Some little harshness on vocals. India Arie was beautiful, but felt like she was singing in the recording room and me listening outside an open door.
The damping factor is really low, so I expected bass to be boomy and flabby. It definitely doesn't have the typical solidstate "tautness", but instead a very live-music sound. Even the heaviest music I tried (Keith Hudson - Depth Charge; Fugazi - Ex-Spectator, with two drummers) had no sense of boominess, just lots of presence, and much more "reality" than I'm used to.
Already, across the board, even with known-not-good recordings, it opened up details and atmospheres I've never heard before. So far then, I'm pretty happy. 🙂
Congratulations on a beauty build!
I will be building the Mauro Penasa- twisted pear audio version when the parts arrive in a month or so, 2 Channel .
I use all single driver diy speakers; the ones I have running now are fostex fe126e, fairly efficient.
Your description of the sound of this amp has my attention. I have not yet built point to point so that may be a challenge. The parts count is low on the amp;helps keep it simple.
Can I ask you where you sourced the big p.s. 15000uf caps and the transformer?
nice amp!
doggy [pic. of my fe126e]
I will be building the Mauro Penasa- twisted pear audio version when the parts arrive in a month or so, 2 Channel .
I use all single driver diy speakers; the ones I have running now are fostex fe126e, fairly efficient.
Your description of the sound of this amp has my attention. I have not yet built point to point so that may be a challenge. The parts count is low on the amp;helps keep it simple.
Can I ask you where you sourced the big p.s. 15000uf caps and the transformer?
nice amp!
doggy [pic. of my fe126e]
Attachments
Nice spks!
Thanks! Nice speakers. I want to try this on my friend's Gallo A'Diva fullrange spheres - I think he'll jump out his skin. "-)
The transformer was just lying around. In a previous life it powered a Quad405 (at 240v -> 40+40), but it was something else before that. The power supply caps came from Vetco Surplus in Bellevue WA (ten for $15, just couldn't resist...)!. But the powersupply for this amp really isn't anything "special" -- it doesn't need all that snubberized C-R-C thing to work -- I just built the best I could with available parts, in the hope that if everything turns out good I'll be able to resist opening the box up for tweaking. If you're building Mauro's Ref3, or a BrianGT, this one would work off the exact same main power rails.
Point-to-point is doable if you build each segment separately (I soldered all the decoupling caps segment into a little lump first; then the compensation R-C leg and the series feedback resistors; then wired up to the chips after mounting the chips on their heatsink/support). The first channel was a mess, and 2/3/4 went much more smoothly. Also I didn't think too hard about which direction the power leads would come in from, and now they're in the way a bit. So really I can't recommend it as a construction method... it would be much easier to put together using Veroboard or such, if (like me) you never etched a PCB before.
Hope you like the Mauro Ref. I fully expect it to be stunning. (Mr Penasa's been doing this stuff waaaay longer than me, so I would trust his design to sound at least as good as mine 🙂
-ing
Thanks! Nice speakers. I want to try this on my friend's Gallo A'Diva fullrange spheres - I think he'll jump out his skin. "-)
The transformer was just lying around. In a previous life it powered a Quad405 (at 240v -> 40+40), but it was something else before that. The power supply caps came from Vetco Surplus in Bellevue WA (ten for $15, just couldn't resist...)!. But the powersupply for this amp really isn't anything "special" -- it doesn't need all that snubberized C-R-C thing to work -- I just built the best I could with available parts, in the hope that if everything turns out good I'll be able to resist opening the box up for tweaking. If you're building Mauro's Ref3, or a BrianGT, this one would work off the exact same main power rails.
Point-to-point is doable if you build each segment separately (I soldered all the decoupling caps segment into a little lump first; then the compensation R-C leg and the series feedback resistors; then wired up to the chips after mounting the chips on their heatsink/support). The first channel was a mess, and 2/3/4 went much more smoothly. Also I didn't think too hard about which direction the power leads would come in from, and now they're in the way a bit. So really I can't recommend it as a construction method... it would be much easier to put together using Veroboard or such, if (like me) you never etched a PCB before.
Hope you like the Mauro Ref. I fully expect it to be stunning. (Mr Penasa's been doing this stuff waaaay longer than me, so I would trust his design to sound at least as good as mine 🙂
-ing
I live near Vancouver B.C. so I will give Vetco a call and see what they have.
Building stuff is is as enjoyable if not more so than listening to the finished product! And better yet is bringing your own design to life.
I hope to build a 2 channel version when I can get most of the parts together; most likely from digikey.
cheers
doggy🙂
Building stuff is is as enjoyable if not more so than listening to the finished product! And better yet is bringing your own design to life.
I hope to build a 2 channel version when I can get most of the parts together; most likely from digikey.
cheers
doggy🙂
Go for it!
Thanks doggy - it's a bit scary having someone else actually plan to rely on my designs 🙂
I'd recommend trying a 4-ohm ZOut -- see the attached spreadsheet for some calculations.
Thanks doggy - it's a bit scary having someone else actually plan to rely on my designs 🙂
I'd recommend trying a 4-ohm ZOut -- see the attached spreadsheet for some calculations.
Updated: schematic (in the top post) now has two output taps, one for "high ZOut" (4 ohm output impedance) and one for "low ZOut" (low output impedance). That's an interestingly tweakable side-effect of the Howland nfb/pfb configuration...
Running the 4-ohm outputs bridged into my speakers sounds quite good. Running each channel with 4-ohm output separately, bi-amping the speakers, changes the tonal balance a lot; some of the mid is sucked out, and it's not ideal at low volumes. (My speakers are quite close to the walls, unavoidably; at a good listening-point all's well, but sitting near the walls is quite boomy).
So now I'm trying the bass/mids with low ZOut (voltage-drive) and top-end with high ZOut... "Carver-mode", anyone? 🙂
Running the 4-ohm outputs bridged into my speakers sounds quite good. Running each channel with 4-ohm output separately, bi-amping the speakers, changes the tonal balance a lot; some of the mid is sucked out, and it's not ideal at low volumes. (My speakers are quite close to the walls, unavoidably; at a good listening-point all's well, but sitting near the walls is quite boomy).
So now I'm trying the bass/mids with low ZOut (voltage-drive) and top-end with high ZOut... "Carver-mode", anyone? 🙂
Serious listening
So, yesterday my brave friend D let me run this through his loudspeakers for a good listening session. (We'd intended to A/B some RedWine-modded Squeezeboxes, but Vinnie couldn't make it, so I took the chance to crank up my own work).
First, some Gallo A'Divas. These are 5" single-driver spheres, with optional stand-mounts, or just little rubber rings to rest on. (http://www.roundsound.com/adiva.html) They're a handy size, and playing stock Squeezebox (with a Bolder Cable linear power supply) through a Yamaha receiver sounded reasonably good. Then wired up the inguz amp on the high-Z outputs, and -- it stomped all over the Yamaha. Room-filling volume, rock-solid sound stage all through the room (and a great sweet spot too), surprisingly deep lows, and quite transparent highs. Then we moved the amp onto a good isolation platform, and it started sounding *really* nice.
After a couple beers, we moved on to the hard stuff. D's main room has a pair of Gallo Reference 3s; the usual source is a Wadia CD/DAC, a pair of Electrocompaniet 220 monoblocks, and a Gallo sub-amp. Which all sounds pretty darned good. So first I plugged in the inguz amp (fed from the Squeezebox) in high-Z mode, and... wow. Those loudspeakers really are superb. With the low damping amp, the sound was a bit too full: very good lows, quite a prominent low-mid, and slightly shimmery highs. Diana Krall sounded very good; Monk at the Carnegie sounded like a proper piano, but noticeably too mid-forward. Soundstage, again, absolutely rock-solid and lots of depth. I quite like this sound, although it would get tiring for high-volume listening. Then we switched to the low-Z output, and the whole "room-filling soundstage" shifted back between the loudspeakers, back to a much more usual "precise" sound -- but extremely detailed, involving, and well-rounded. I think the highs are maybe a bit cleaner; they certainly seemed to extend a bit further with low-Z, but maybe that's just in comparison with the mid-emphasis of the high-Z drive. (And the Ref3s have this incredible wraparound tweeter which goes off into the ultrasonic blue yonder).
Stock squeezebox2 and chipamp comparable with Wadia and Electro monoblocs? Yup. Not far off at all. Maybe not quite there at the top end, but good enough to keep me happy.
And, it seems this circuit in high-output-impedance mode is a very good match if you have small speakers; the low damping will fill out the bass and presence, getting a lot of mileage from small packages.
So, yesterday my brave friend D let me run this through his loudspeakers for a good listening session. (We'd intended to A/B some RedWine-modded Squeezeboxes, but Vinnie couldn't make it, so I took the chance to crank up my own work).
First, some Gallo A'Divas. These are 5" single-driver spheres, with optional stand-mounts, or just little rubber rings to rest on. (http://www.roundsound.com/adiva.html) They're a handy size, and playing stock Squeezebox (with a Bolder Cable linear power supply) through a Yamaha receiver sounded reasonably good. Then wired up the inguz amp on the high-Z outputs, and -- it stomped all over the Yamaha. Room-filling volume, rock-solid sound stage all through the room (and a great sweet spot too), surprisingly deep lows, and quite transparent highs. Then we moved the amp onto a good isolation platform, and it started sounding *really* nice.
After a couple beers, we moved on to the hard stuff. D's main room has a pair of Gallo Reference 3s; the usual source is a Wadia CD/DAC, a pair of Electrocompaniet 220 monoblocks, and a Gallo sub-amp. Which all sounds pretty darned good. So first I plugged in the inguz amp (fed from the Squeezebox) in high-Z mode, and... wow. Those loudspeakers really are superb. With the low damping amp, the sound was a bit too full: very good lows, quite a prominent low-mid, and slightly shimmery highs. Diana Krall sounded very good; Monk at the Carnegie sounded like a proper piano, but noticeably too mid-forward. Soundstage, again, absolutely rock-solid and lots of depth. I quite like this sound, although it would get tiring for high-volume listening. Then we switched to the low-Z output, and the whole "room-filling soundstage" shifted back between the loudspeakers, back to a much more usual "precise" sound -- but extremely detailed, involving, and well-rounded. I think the highs are maybe a bit cleaner; they certainly seemed to extend a bit further with low-Z, but maybe that's just in comparison with the mid-emphasis of the high-Z drive. (And the Ref3s have this incredible wraparound tweeter which goes off into the ultrasonic blue yonder).
Stock squeezebox2 and chipamp comparable with Wadia and Electro monoblocs? Yup. Not far off at all. Maybe not quite there at the top end, but good enough to keep me happy.
And, it seems this circuit in high-output-impedance mode is a very good match if you have small speakers; the low damping will fill out the bass and presence, getting a lot of mileage from small packages.
Hi inguz,
Thanks for keeping us up-to-date of your progress. You have put a lot of effort into this amp but it seems to be slipping under everyone's radar.
Have you built the normal, simple circuit GCs and how does your amp compare?
I'd be interested in a bit of technical information on the apparent feedback paths to both inverted and non-inverted inputs and the use of the output inductor to separate the feedback paths. I can't promise to understand but I'll try.
EDIT: Sorry, I just noticed your PDF in a previous post that has all the details in it, so no need to do it again. 😱 . Well done!
Regards
Greg
Thanks for keeping us up-to-date of your progress. You have put a lot of effort into this amp but it seems to be slipping under everyone's radar.
Have you built the normal, simple circuit GCs and how does your amp compare?
I'd be interested in a bit of technical information on the apparent feedback paths to both inverted and non-inverted inputs and the use of the output inductor to separate the feedback paths. I can't promise to understand but I'll try.
EDIT: Sorry, I just noticed your PDF in a previous post that has all the details in it, so no need to do it again. 😱 . Well done!
Regards
Greg
Hi Greg. This project was a "one-off", so I don't have a regular GC to compare with. But with the low-Z output tap, this is basically the same as a regular inverting GC (probably lower gain than most people would want). I did put as much effort as I could justify into the power supply beefiness, and the case, though 🙂
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