new GAN amplifier

This in my signal path, no chance, not ever!
https://assets.peavey.com/images/large/118741_33943.jpg

Cheers George

George, I have a challenge for you. Take your most uncolored full range speakers, ones that are hard to drive, choose your amplifier ( s ),.....now, take a reasonbly priced mixer, such as a Peavey PV 6BT mixer ( my buddy has one ).......connect it into this system......now, using a great mic, such as the world renowned Neumann U87, and, with a Stevie Ray Vaughn Fender Strat ( of which I love the sound )......I will be the singer, my buddy will play the guitar, and let us see ( hear ) what " this " system can do. Maybe, add a drum machine.....You can choose your own musicians........,

I also believe, hard to drive speakers, are ridiculous

Your opinion Mr D.
This is where we differ big time, I would not call Klipch Lascala speakers or Hafler amps state of the art audio devices,having owned the Lascala’s and repaired a couple of Haflers.

I’ve found the most "uncolored full range" speakers, usually to be among the very hardest to drive, due to all the work that goes into them to make them full range, uncolored, and using the drivers in their most linear range with complex xover do do it. This all adds up to an inefficient speaker, with very low impedance dips and nasty - phase angles.  

Cheers George

I had this debate with George on another thread, that concerned the purchase of an older Rowland amplifier. I have owned all kinds of amplifiers. Those that use mosfets, and those that use bjt devices. I am currently running a pair of mono blocks, designed by Hafler, that were made for the movie / cinema industry, that are, to my ears, amazing. They are biased in class A, run extremely hot, use Hitachi mosfets, and drive my Lascalas, wonderfully, and easily......If it sounds good to you, so be it.....also, when it comes to recordings, doesn't  the microphones, cabling, recorders, mixing consoles, eq boards, compression boards, etc., all add to the final sound we are listening to ? I also believe, hard to drive speakers, are ridiculous.....have owned some, and, never again....

Post removed Nov 19, 2019

That was too strong for him could have caused him mental damage, it wasn’t going to help.

Yes, lets get back to the OPs topic which you side-tracked ...

 🤦‍♂️ whatever

And it’s a different amplifier when done, and not indicative of a comparison of two sets of output devices .... sunshine. Yes, lets get back to the OPs topic which you side-tracked ....

georgehifi6,190 posts11-15-2019 2:13pmMany (me included) just don’t like Mosfet sound.
Listen to some older Threshold Pass amps that used bi-polars, you’ll change your mind.

Cheers George

Give it a rest sunshine it’s doable, and not as complicated as you make out, your full of it, I would estimate a days or less work for a good tech, with the components and schematic of the donor mosfet amp at hand.

Now lets get back onto the OP’s topic.

On the TO3, I mean that quite seriously. I can’t remember the last time I saw anyone use a TO3 in a production design. Your idea of plentiful and cheap is likely different from mine. I don’t buy components off EBay unless I am finding something obsolete. You can find the odd TO-3 in stock at stocking distributors, but they are a rarity these days and legacy devices.


If you change the output stage, bias circuit, and the drive circuitry before the output stage, which means 2 stages of what is likely a 4-6 stage amplifier (and likely feedback to account for different bandwidths), then it is not the same amplifier any more. You can’t change 33-50% of an amplifier and say you are just comparing the output devices.  Yes end of story. Your claim that this allows you to simply compare output devices is not true.

It's a different amplifier.

Sorry, same amp with different output/driver stage and bias change.That allows one to directly compare same amount of Mosfet devices to the same amount of BJT devices

Can you even buy TO3 transistors any more

Of course you can don't be an *****, and they're still cheap and plentiful,  just look around.https://www.ebay.com/itm/1pairs-OR-2PCS-Transistor-MOTOROLA-TO-3-MJ15003-MJ15004-100-Genuine-Origina...

End of story, no more on this as it's not about the title "new GaN Amplifiers" 

Output stage, the stage before the output stage, hopefully the feedback network, the bias circuitry for the output stage ..... It's a different amplifier.

Can you even buy TO3 transistors any more? (TO3, as opposed to TO3P which is a different beast). I think with the exception of MIL they have all been long obsoleted.

Its highly unlikely that anyone ever did a mod like this unless the amp was gutting for its chassis and power supply.

Include to the the complete chassis, transformer/s, power supply, the heatsinks and input stage to that, which is around 80% of the amp.

What’s left is the driver/output stage and bias mods. So yes I see it as doable, as he said he’s doing, but I think it would be limited to T03 case substitutions, otherwise would get messy.
And yes two different amps one Mosfet the other BJT using the same 80% above components.

@atdavid is correct. By the time anyone had modified a MOSFET amp to run with BJTs it would be an entirely different amplifier. There simply would be no way to compare 'before' and 'after'. Its highly unlikely that anyone ever did a mod like this unless the amp was gutting for its chassis and power supply.

Excellent cust svc

Great pricepoint

IMHO, Gfi is making a lot of sense here

Still awaiting my Voyager (GaN), but still loving my EVS 1200 (class D)

This is what you said "sunshine" and to my point, you are essentially making a different amp.  The one who doesn't have any decent tech knowledge is you. I have designed many amplifiers, discreet and on integrated circuits, hence why what you post sounds so ridiculous to me. You can't simply change an output stage on a power stage between MOSFET and BJT. It don't work that way sunshine.   Now if you had any tech knowledge you would know:

• Typical output stages have 0 voltage gain so quoting in this case that they have higher voltage gain is silly.
• In an amplifier, output current is mainly a function of thermal limitations. I can cheaply buy a 100A MOSFET, more than enough for almost any power level so to say a BJT can handle higher current is just wrong. That has not been true for decades.
• Output impedance is a function of device and circuit, not just the device so making a claim a BJT has lower output impedance is specious. You can try to make the claim there is less difference in base/emitter voltage compared to gate/drain voltage over loading, but higher biasing of the output stage with modern FETs can negate that advantage. As well a BJT requires a very high current to drive it and that current gain is variable w.r.t. output current leading to distortion inducing mechanisms elsewhere in the amplifier that a FET amp may not experience ..... And also why you cannot simply swap the output stage! ...and have it work properly.

Actual "tech", not a cut and paste tech ....

There’s a post a member put up a couple of weeks ago (go find it), who does mods for his customers, where he takes a Mosfet amp removes the complimentary N/P channel Mosfet output stage and replaces it with complimentary NPN/PNP Bi-Polar (BJT), and he and his customers say it all in their description of the sound change.

You can’t just swap out the output FETs for the BJTs

Please don’t say I said this sunshine, because I didn’t.
I said there’s a member who converts Mosfet amps into a BJT amps, and of course there’s more to it than just changing the output devices only a fool would think or suggest otherwise.

You can do it, if you had any half decent tech knowledge you would understand, end of story.

You can't just swap out the output FETs for the BJTs. There are a lot of other things that need to be addressed. It is not the same amplifier any more.


Again, do you know how to design amplifiers? I get the impression no or your replies would be more technical. Hence what you are posting is mainly heresay.

Of course there are different drive conditions and they are all addressable in changing over mosfets to bjt, you just choose not to believe it. 🤦‍♂️ 

And I'll post once again the pro's for going bi-polar

"BJTs tend to have better, more linear gain characteristics…and can give you a lot higher voltage gain than MOSFETs.…They're also able to handle higher output currents…and have a lower output impedance.…That gives BJTs a huge advantage over MOSFETs…for building amplifier circuits…that need to provide a significant amount of output power…and or drive loads that have low input impedance.…MOSFETs are going to have a harder time…driving a low impedance load…because they have a higher output impedance.…"

 

No that is not an opinion that is a experience. The drive requirements for a set of bipolar transistors and a set of mosfets is much much different. Add in different biasing requirements, different thermal compensation, different bandwidths for a given drive circuit, etc. If you change the two you don’t have the same amplifier anymore. Do you design amplifiers or are you just repeating others?

what you wrote below, I cannot just accept on the face as factual.

That's your opinion, it is, and if your are a tech you'll know that it's very possible to do this to the driver/output stage.
Cheers George

This, what you wrote below, I cannot just accept on the face as factual. The drive requirements, biasing, temperature compensation, bandwidth vs. drive, etc. are so significantly different between a BJT pair and MOSFET pair, that unless you essentially modified the whole amplifier, you could not do this and at which point you essentially have two different amplifiers and at that point, any comparison has lost all meaning.

georgehifi6,173 posts11-16-2019 2:38pm

How can you know "what to listen for"

There’s a post a member put up a couple of weeks ago (go find it), who does mods for his customers, where he takes a Mosfet amp removes the complimentary N/P channel Mosfet output stage and replaces it with complimentary NPN/PNP Bi-Polar (BJT), and he and his customers say it all in their description of the sound change.

How can you know "what to listen for"

There’s a post a member put up a couple of weeks ago (go find it), who does mods for his customers, where he takes a Mosfet amp removes the complimentary N/P channel Mosfet output stage and replaces it with complimentary NPN/PNP Bi-Polar (BJT), and he and his customers say it all in their description of the sound change.

That’s why I said if you live with the two for a while you will hear the difference.

If you read what was said at the seminar, you can apply that to what you might hear, again especially on the harder to drive speakers.

I hear Mosfets into my hard to drive speakers as "polite" but a bit of a "yawn" that lack that punch, drive, boogie factor, and an openness that BJT’s have that can also be detrimental with bad recordings.
Some call it "Mosfet Mist" other call it "Tube’ish" I think maybe it’s because they aren’t as linear as BJT’s just like tubes with with 2HD as outlined in the seminar.

Cheers George

How can you know "what to listen for" wrt transistor type when you don't even know the underlying amplifier topology and distortion mechanisms, intentional voicing, damping versus frequency, bandwidth, etc.   You simply can't.  You can't take something you heard on a limited set of products and apply that to all products.

Maybe, if those listeners don't know what to listen for.
But for those same listeners short term living with each amp, listening to many albums over a few days you eventually would pick it, especially if the speakers are hard to drive.

Cheers George

I am going to go out on a limb and say you wouldn't know without being told if the amplifier had FETs, BJTs, etc.   Topology is going to make far more difference to the sound.

Also note this difference between the two taken from a seminar on Mosfet V Bi-Polar (BJT), which to me gels with what I notice/hear.

"BJTs tend to have better, more linear gain characteristics…and can give you a lot higher voltage gain than MOSFETs.…They're also able to handle higher output currents…and have a lower output impedance.…That gives BJTs a huge advantage over MOSFETs…for building amplifier circuits…that need to provide a significant amount of output power…and or drive loads that have low input impedance.…MOSFETs are going to have a harder time…driving a low impedance load…because they have a higher output impedance.…"

Cheers George

Many (me included) just don't like Mosfet sound. 
 Listen to some older Threshold Pass amps that used bi-polars, you'll change your mind.

Cheers George

George,
Even though Pass may have less feedback than Bryston, I hate the euphonic sound of Pass.  There are many more factors determining the sound than the amount of feedback.  

The larger Bryston 4B SST2 puts out 300 at 8 ohms, 500 at 4 ohms, and the tech estimated 600-700 at 2 ohms. Definitely better, but unfortunately all this doesn’t correlate with the sound.

Yes you are correct Viber, I myself never liked the Bryston sound, and I put that down to just one of the things that I've never liked and that is that they use an excessive amount of global feedback, to get their specs.

I myself prefer much less feedback (so long as the amp still achieves good measurements) and also if the design allows the use of just local feedback (again so long as the amp has good measurements).
EG: my ME amps, Gryphon’s, Agostino, early Pass ect ect
https://ibb.co/kGJMXcr
https://ibb.co/0hTPp6f
https://ibb.co/N94rSTt

Back to the 2 ohm thing, hey George.

Yes MrD, and they are needed if one has some of the very best speakers around which dive to 2ohms or even lower, and you wish to get the very best out of them with no compromises.


Cheers George

All 8 of my current class d amps are rock solid and not going anywhere but I feel good knowing that as time goes on there are more and more great sounding and cost effective options out there.

We seem to be freely mixing new solid state technology (GaN), output impedance,and power supply current delivery .
A bit more structured logic would help.

George,
You are correct that many amps, but I will add not just class D, will not keep doubling their maximum power output from 4 to 2 ohms.  Once the max current capability is reached, say at 4 ohms, then at 2 ohms the max power is only 50% of that at 4 ohms.  50% lower than that, or 25% at 1 ohm.  This is particularly important for electrostatics whose impedance could be 1 ohm at HF.  With some music that has high power HF percussion in triangles, snare drum and cymbal crashes, that is a big problem.  

An example is my Bryston 2.5B SST2 amp, which puts out 135 watts at 8 ohms, only 180 at 4 ohms.  The Bryston tech estimated only 100 at 2 ohms, and probably only 50 at 1 ohm.  The larger Bryston 4B SST2 puts out 300 at 8 ohms, 500 at 4 ohms, and the tech estimated 600-700 at 2 ohms.  Definitely better, but unfortunately all this doesn't correlate with the sound.  Despite Bryston's official line that all the amps in the series with different outputs sound the same, my listening at home with the 2.5B SST2 shows much better transients and clarity vs the 4B SST2.  With the 2.5, inferior power specs but better sound within its power limitations.

GAN technology has great potential and many things in the future may benifit .you may have some that are not better then a very well implemented digital,or class AB amplifier ,it has much more to do withThe engineering design.
i will wait before jumping in .
the best new thing since sliced bread has been stated before !!

Back to the 2 ohm thing, hey George.

The doubling of output from 8 to 4 ohms suggests a good power supply.

Most Class-D can double from 8 to 4ohms
It's when test bench measured independently, from 4ohms to 2ohms is where they usually *** themselves, many actually go backwards instead of doubling or even increasing.

Cheers George 

The doubling of output from 8 to 4 ohms suggests a good power supply.  Good for starters.

I mentioned that am expecting one in my Life with Ric Schultz EVS 1200 thread


I will start a new thread when I do

It’s good for it to have it’s own thread, new amp using the new GaN technology.
So long as the claims are kept real, and BS is not posted.

Wasn’t it this one or another (Nuprime) that claimed to have "super fast 500,000hz!!! switching frequency" which is just 500khz like most others?
BS No. 1 if it was.

Cheers George

@twoleftears.....FYI, This has been brought to light, previously, on another thread, based on Class D...