Hiraga Le Monstre

[Dan K]

Further update.

Amp has been sounding very decent, but not really getting any warmer than just above ambient.

I did a bit of reading on the original output devices (Toshiba 2SD844) vs the ON NJW0287G items that I have. The newer transistors can take twice the current of the original items, so (unless I've missed something) I can safely crank the bias up above the JLH recommended 0.6A. I've swapped out the Kiwame 470R resistors for 500R. I now have 0.67A across each of the output devices and the casework is sitting at 30.7/ 30.5 deg. on either side. Max temp that I can detect inside is 52deg at the top of one of the bias resistors.

Sounding very good now, although the voltages are lower than I would like. I can't do anything about that without swapping the transformers. JLH design allows up to 13.5V

 

[S-Man]

0.6A X 24V is only approx 14W per channel in the output stage (some of the voltage is dropped in the 1R resistor(s)).

If you look at something like a Michel Alecto with 58V rails and 200mA quiescent current, the dissipation is about 23WPC in the output stage.

Class A doesn't have to be hot, as long as you keep the power low.

 

[Dan K]

0.6A X 24V is only approx 14W per channel in the output stage (some of the voltage is dropped in the 1R resistor(s)).

If you look at something like a Michel Alecto with 58V rails and 200mA quiescent current, the dissipation is about 23WPC in the output stage.

Class A doesn't have to be hot, as long as you keep the power low.

Thanks S-Man

Begs the question Why do all the Le Monstre builds have huge heatsinks?

The SLB appears to put me in a quandry regards rail voltage: The active rectifier only drops 0.2V (if that) . The BJTs should loose up to 3V. Mine are now set at 1.5V giving 11V rails from a pair of 0-9V 120VA traffos.

The 120VA transformers don't have any descernable temperature rise above ambient, making me think that I could have gone with 100VA. Ideally I think they would need 11V secondaries with 12V being too much.

 

[martin clark]

OTT heat sinks bring not only huge capacity - but also, near-isothermal operation: keeping all the attached devices v close to a constant temp.
That matters for circuits with no temp compensation - like this one, using j/mos FETS , as the Monstre does.


PS to be clear - 'La Monstre' was named for Hiraga's huge cap+ battery PSU design for an <8w amp with negligible PSRR - and not its rather meagre output capability!

 

[Dan K]

Quick update

Amp now has 45 hrs on it and is sounding very beautiful. It really is an impressive thing, absolute clarity without any hint of glare.

I've ordered another pair of traffos to get it running at +/- 12.5V. I also want to throw another 1.5V away through the SLB BJTs as I'm interested to hear if I can gain a further benefit from lowering the noise on the rails to stupidly low levels. Maybe I can get the noise down to 0.5mV? Perhaps I've already gone far enough at 1mV? We will find out.

I've decided to swap the 100R pot out for 2x 50R Kiwame resistors as they are in the feedback loop. I'll set the DC offset via the front end resistors, which I'll replace with 1K pots.

Also decided to change the cement output bias resistors to 1R1 (via 2x Kiwame 2R2 5W items), this should give me a better way of upping the bias on the output devices whilst allowing the front end resistors to go back to a value closer to nominal.

Part of the beauty of this amp is the simplicity. Really gets you thinking about how every change effects everything else. It's an experimenter's amp

 

[bugbear]

I had my doubts about it, higher THD than I would like (about 0.5%), poor damping factor etc... but it more than lives up to its reputation. Magnifique Monsieur Hiraga

Setting aside any questions about the design or components, the notion that any amplifier with 0.5% THD can sound half-good (let alone better than half good) has remarkable implications.

I wonder how high the THD could be allowed to rise (by reversing the component tuning) before it didn't sound half-good.

BugBear

 

[Arkless Electronics]

Setting aside any questions about the design or components, the notion that any amplifier with 0.5% THD can sound half-good (let alone better than half good) has remarkable implications.

I wonder how high the THD could be allowed to rise (by reversing the component tuning) before it didn't sound half-good.

BugBear

Component quality is almost zero importance to sound quality and none to the measured THD. I would very happily build state of the art amp prototypes using 30 year old parts from TV sets etc and would expect little or no improvement from the same amp made with brand new top quality parts. DanK is completely wasting his money on fancy resistors and especially as his amp will be only limping along without the proper setting up, for which he needs test gear I don't think he has. There is no other way.

I got the one I worked on down to 0.5% THD at 6WPC yes. The 8W published power could only just be obtained but it was at maybe 8% THD!
At the volumes I was listening at I was probably using only 1W (much louder than people think!) and the distortion from a low feedback class A amp such as this falls monotonically so it was prob more like 0.1% at my listening level.

When I got the unit in the described issue was mains hum. The owner was using as part of an active system to drive compression horn drivers of maybe 105dB/W so hadn't even noticed that it only gave 1W for 1% THD and max power of 2W for about 10% THD!!

 

[Dan K]

Setting aside any questions about the design or components, the notion that any amplifier with 0.5% THD can sound half-good (let alone better than half good) has remarkable implications.

I wonder how high the THD could be allowed to rise (by reversing the component tuning) before it didn't sound half-good.

BugBear

I might be wrong, but I don't think it's quite so straightforward. THD is an RSS value obtained from the 1st to 6th order harmonics based on a 1kHz input signal. Even order harmonics occur in nature and are perceived as echoes. Valve amps can often have a very large (dominant) 2nd order harmonic which may result in a high THD, but the other harmonics might be low. I have a pair of Transcendent Pinnacles that sound absolutely gorgeous and supposidly have a measured THD of '<0.5%'

Another issue I have with THD is that it's usually only measured at 1kHz when music isn't a single tone. I do suspect there are plenty of amps out there that measure amazingly at 1kHz, but terribly at say 3, 6, 10k etc. I'm not a fan of ASR with regard to this.

 

[russel]

Setting aside any questions about the design or components, the notion that any amplifier with 0.5% THD can sound half-good (let alone better than half good) has remarkable implications.

I wonder how high the THD could be allowed to rise (by reversing the component tuning) before it didn't sound half-good.

BugBear

One point is what kind of distortion is it?, if it only distorts at higher output levels then the harmonic distortion will be low order and not offensive to the ear, low level distortion produces higher order harmonic distortion, remember your Fourier series boys and girls!, which the ear is most definitely sensitive to.

 

[Arkless Electronics]

Hmm...

Rather more to it than that. Interesting stuff in fact! Exponential or square law devices in use? At what bias level?
Push pull or single ended? How much NFB? and more....

High order distortion, especially odd order, is the worst and even small amounts can be a problem. John Linsley Hood reckoned that in a specific experiment he could hear 0.002% of the worst distortion!

Another strange one is that small amounts of NFB can sometimes make things worse by suppressing low order distortion whilst boosting high orders. Using less than around 12 - 15dB of NFB can be a bad idea...

 

[Dan K]

Given that I'm powering this amp with +/- 11V and it's putting out a very healthy sound level I do wonder if some of my other amps are actually 'limping along'

 

[earlofsodbury]

yadda yadda I'm so great please pay attention to me &c &c &c

Here's a zany and novel thought for you: you may be correct in some points you make (and wholly wrong in others), but have you ever considered reading what you write before you post it and checking whether you sound like a rude, condescending, know-it-all melt before hitting that send button? Could be a great new look for you - "Not Looking Like A Bellend" is totally, like, *IN* for Spring 2022

 

[Arkless Electronics]

Given that I'm powering this amp with +/- 11V and it's putting out a very healthy sound level I do wonder if some of my other amps are actually 'limping along'

Try measuring the THD at various power levels. The one I got in was built using all the correct devices as specified in the Hiraga article and they were supposedly matched. I didn't do the initial build. All parts were correct. It gave 1W @1% THD and 2W max for 10% THD..... Now it is true that it's not impossible for yours to be running just great as is... if you've been exceptionally lucky.... and if the devices were exceptionally well matched.... and at the precise currents they are operated at in this circuit... but I think it's likely that without all the rigmarole I went through with the one in this thread it will be way under par. Whether if gives say 1W @1% thd and max of 2W or manages say 4W for 1% and 5W @ 5% etc only measurements will tell.

 

[Arkless Electronics]

Here's a zany and novel thought for you: you may be correct in some points you make (and wholly wrong in others), but have you ever considered reading what you write before you post it and checking whether you sound like a rude, condescending, know-it-all melt before hitting that send button? Could be a great new look for you - "Not Looking Like A Bellend" is totally, like, *IN* for Spring 2022

I couldn't give a flying ****. I AM a rude condescending know it all... and after spending a lifetime at this and becoming one of the best amp designers around I make no apologies whatsoever. I'm almost never wrong (I can think of only one occasion, yes S man!). If I've not said "IIRC", "not certain but..." etc then I'm probably right. It comes with having done this for 50 years man and boy. Hope that's offended you some more.

Oh, and you know where you can shove it

 

[Dan K]

Try measuring the THD at various power levels. The one I got in was built using all the correct devices as specified in the Hiraga article and they were supposedly matched. I didn't do the initial build. All parts were correct. It gave 1W @1% THD and 2W max for 10% THD..... Now it is true that it's not impossible for yours to be running just great as is... if you've been exceptionally lucky.... and if the devices were exceptionally well matched.... and at the precise currents they are operated at in this circuit... but I think it's likely that without all the rigmarole I went through with the one in this thread it will be way under par. Whether if gives say 1W @1% thd and max of 2W or manages say 4W for 1% and 5W @ 5% etc only measurements will tell.

I will do this and report, although at the moment I've comissioned another pair of traffos from Steve (If anyone wants a pair of 120VA 0-9 secondary Tiger torroids...)

Re wasting money on fancy parts: I don't think 8off 70p resistors is comparable to another set of torroids or the massive extravagance of the mains switch.

I'm suspicious that raising the rail voltages by +/1.5V and then removing an additional 0.5mV of noise wont deliver anything at all. There is utterly no percievable noise at 1mV AC, again.. we shall see (hear)

 

[Stuart Frazer]

There was some talk of doing a group buy of this amplifier and getting @Arkless Electronics to build them, or tune them.

Anyone interested in one?

 

[S-Man]

I might be wrong, but I don't think it's quite so straightforward. THD is an RSS value obtained from the 1st to 6th order harmonics based on a 1kHz input signal. Even order harmonics occur in nature and are perceived as echoes. Valve amps can often have a very large (dominant) 2nd order harmonic which may result in a high THD, but the other harmonics might be low. I have a pair of Transcendent Pinnacles that sound absolutely gorgeous and supposidly have a measured THD of '<0.5%'
.

I'm not at all sure how distortion correlates with sound , if (barring gross distortion) it even does. I have amps with the fabled decaying harmonics and they don't neccessarily sound any better than ones with a more usual characteristic.

My KT88 PP amp produces about 0.1% THD at 1W. One channel has the fabled decaying harmonics, the other doesn't. Maybe if I played around with valves I could get both to match? It sounds very decent.

My Hawk A18 produces about 0.4% THD. This is zero GF amp that relies on carefully matched transistors and resistors to give reasonable figures. It sounds very good in some ways (but not all).

Most of my SS "feedback" amps measure very similarly, but sound different!!

There is a lot of discussion on the net on this topic... and a lot of sheep!

Another issue I have with THD is that it's usually only measured at 1kHz when music isn't a single tone. I do suspect there are plenty of amps out there that measure amazingly at 1kHz, but terribly at say 3, 6, 10k etc. I'm not a fan of ASR with regard to this.

That would take some doing. In general distortion increases with frequency at a rate related to the feedback factor, there's not reason for a step change at some frequency.
Also, the 2nd harmonic of 10KHz is 20KHz - arguably above audibility.
I'm also not a fan of ASR - it's mostly meaningless.


Despite all the above. Mr never wrong (except once) is right. You really need to measure Le Monstre to make sure it is working as intended.

All IME/O

 

[Dan K]

There was some talk of doing a group buy of this amplifier and getting @Arkless Electronics to build them, or tune them.

Anyone interested in one?

The building of the amp boards is a 20 minute job, the SLB PSU is a tutorial in soldering accuracy /technique and an eyesight test - much harder. You might also have a long wait for parts right now.

The problem /fun is in the testing and tuning of the amp boards. I'm hopeful that I've largely mitigated against this by paying over the odds for the absolute best possible matches.

These amps whilst sounding fantastic are really a great way to learn development / test engineering and that's part of the journey

 

[Arkless Electronics]

I'm not at all sure how distortion correlates with sound , if (barring gross distortion) it even does. I have amps with the fabled decaying harmonics and they don't neccessarily sound any better than ones with a more usual characteristic.

My KT88 PP amp produces about 0.1% THD at 1W. One channel has the fabled decaying harmonics, the other doesn't. Maybe if I played around with valves I could get both to match? It sounds very decent.

My Hawk A18 produces about 0.4% THD. This is zero GF amp that relies on carefully matched transistors and resistors to give reasonable figures. It sounds very good in some ways (but not all).

Most of my SS "feedback" amps measure very similarly, but sound different!!

There is a lot of discussion on the net on this topic... and a lot of sheep!



That would take some doing. In general distortion increases with frequency at a rate related to the feedback factor, there's not reason for a step change at some frequency.
Also, the 2nd harmonic of 10KHz is 20KHz - arguably above audibility.
I'm also not a fan of ASR - it's mostly meaningless.


Despite all the above. Mr never wrong (except once) is right. You really need to measure Le Monstre to make sure it is working as intended.

All IME/O

We're reading from the same hymn book on most of that anyway Yep they're 'ornery critters them amplifiers and virtually every rule in the book seems to get at least partially broken by something. If "we" knew what the secret was then all amps would have been made to sound (rather than measure!) perfect decades ago!

 

[Arkless Electronics]

The building of the amp boards is a 20 minute job, the SLB PSU is a tutorial in soldering accuracy /technique and an eyesight test - much harder. You might also have a long wait for parts right now.

The problem /fun is in the testing and tuning of the amp boards. I'm hopeful that I've largely mitigated against this by paying over the odds for the absolute best possible matches.

These amps whilst sounding fantastic are really a great way to learn development / test engineering and that's part of the journey

It is indeed a journey and the Monstre is a good way to learn quite a few things! PSRR.. or lack of.. and what that means for the PSU...
NFB being present but not enough to snap everything into no offsets and 0.001% THD... hence, as it's push pull and made from complementary devices, the need to hyper match/and/or compensate for mismatch by deliberately mismatching certain resistors etc... which leads to the need to able to watch THD and it's waveform in real time as you adjust things; still a job best done by trad analogue gear for me anyway!

keep keeping on