F5 power amplifier

[EUVL]

Whether you need matching or not depends on what you want to build.

If you want to build single ended, and use the Fairchild parts, then the N & P MOSFETS are NOT complementary (as I have posted years ago) and hence no matching is POSSIBLE. You can then enter into a philosophical debate as to whether you want transistors of the left channel and the right channel to be as identical as possible, or just rely on the circuit to compensate for the difference. I always match left and right channels for myself. But then I don't (have to) make these in production quantities.

If you build the balanced version, and use Toshiba MOSFETs (which are truely complementary, as I have also published here), and you want to cancel even order distortions as best as you can, then matched devices are a MUST. But of course you might not want to cancel ALL the even harmonics, but rather a mixture of 2nd, 3rd, 4th, ..... Then you should join the Swinger Club and swap until you get what you want, as Nelson suggested.

That's my opinion only.
And there are many other opinions, just as people would discuss endlessly how well you should match small signal JFETs for use in diff pairs.

Matched Quad N & P devices are not easy to obtain. You need a large pool to match from, or your "reject rate" is high.
I think the price asked for is not totally unfair, considering the effort.
I have just sold a set for less (curve tracer matched on heatsink), but that was my own stupidity.

Lucky guy, Dirk.



Patrick

[EUVL]

> but they did not have (allegedly) matching transfer curves as do the Tosh's...

What do you mean by allegedly ?
It was measured data published here openly for all to see.

F5 power amplifier


Patrick

[tinitus]

Originally Posted by EUVL

But of course you might not want to cancel ALL the even harmonics, but rather a mixture of 2nd, 3rd, 4th, ..... Then you should join the Swinger Club and swap until you get what you want, as Nelson suggested.

Might be that its about distortion figures

But when Nelson mentioned J2 amp it was my immediate understanding that the "swapping" was about "matching" NPN to PNP
Those seems to me like the great unknowns

I can see the point with regards to balanced amps
But are they not mounted on each their own individual amp boards
Doesnt this again mean that lots of other factors influence the perfect balance

Looking at calculated probability with many unknown and uncontrolled factors its more likely that a mix of "lucky" imbalance will result in the perfect balance
That is to me what Nelson talks about

In which case only the matching of paralel devices seem to make any sense

[Blues]

Originally Posted by tinitus

...But when Nelson mentioned J2 amp it was my immediate understanding that the "swapping" was about "matching" NPN to PNP
Those seems to me like the great unknowns...

On the J2 that would only be P to P matching of the input differential jfets and then N to N at the output power jfets...

[tinitus]

I believe J2 is with a single pair outputs, and why it was mentioned in relation to F5 not needing matched devices
Nelson suggested random "swapping" as being a good/only option, fore a single pair
Also that there seems to be no way to predict or calculate it, meaning completely random fore each amp/channel
At least thats how I understood it

If you match quads of 4 N and 4 P devices and split them in double pairs into left and right channel, and then claim that bias conditions will be the same fore each channel, that sounds like simple dreaming to me
But I admit to know way too little about these matters

Sure, I live in hoping too, and have bought devices matched with 3 digits numbers, to get the paralel devices right, within 0.001-0.003 tolerance fore each matched quad
Sure its fun to "believe" to have bought something very special
Tho, its a question if thats 100% reliable, or if it will change every time its measured
The stuff that dreams are made of

[bear]

Patrick, whoa cowboy!

Yes, I see your curves - how were they generated?
How closely matched were the devices you tested, and how were they matched? (static bias, or dynamic curve tracer?)

I say allegedly because I only saw the Toshiba data sheets, had not seen your posted result. All the much better if they work like that!

Everyone else, this post by NP may shed some light on the matching/biasing/harmonics thing - from back in the thread a year or more:

NP on "the sweet spot"

Btw, tinitus, here's the pix of the batch I had...

EDIT: what do you mean "within 0.001-0.003 tolerance "??
No matter what if one starts with closer tolerances it's more likely to get "textbook" or "simulation" like results than if things are all over the map. How that will sound is another matter entirely...

[Nelson Pass]

One of the advantages of DIY is that most of you have the
time and inclination to tweak the circuit that virtually no
manufacturer can devote. Yes, they often match devices for
one parameter such as Vgs, but that's it, and often this is
merely for current sharing or offset voltage.

There's more to device characteristics, and taking the time
to select devices for performance in the actual circuit is the
best way to get the most.

This does presume that you know what you want when you
see it. If a measured spec is the criterion, then your job is
easier than if you have to do extensive listening tests.

[m.massimo]

Hello everybody,
after reading all the thread, I started collecting parts to build a couple of F5 mono.
Last week I assembled the first (300VA 18-0-18, 27mFx3xrail, +24.1Vdc, -24.1Vdc, sk170BL, sj74BL, FQA12P20, FQA19N20C, mica and thermal paste, Peter Daniel board, no current and voltage limiter sections, resistor values as Pass scheme, alu hs 250x180x83mm).
First setup went smoothly, after a couple of hours, when bias was stabilized at 1.3A and offset at 0mV, I attached a speaker of no value and music flowed.
Another 2hrsx3 of testing and all was good, heatsink at 40°C behind the mosfets, mosfets case at 50°C. Then, when I turned it on the next day (from cold) I read immediately about 1500mV on both R11 and R12. I turned it off quickly, lowered pots to zero, did the setup again and I was able to get 600mV on R11-R12 stable with offset at 0mV.
Another couple of hours of continuing operation with no problems.
Next turning on from cold, today, same story. 1500mv on R11 and R12. I lowered again the pots, but now everytime voltage on R11 and R12 reach about 62mV, both increase abruptly to around 1500mV.
No parts burned, no smoke or something odd. I checked the passive parts, they are ok.
In the meantime I was testing the first mono, I assembled the other one (it's exactly the same). It works perfectly since the beginning, It's clear there's something in the first one that doesn't work properly, but I've no idea than rebuild the circuit with new active parts. I'd like to understand what happened. Have you any suggestion?

[tinitus]

Originally Posted by bear

Btw, tinitus, here's the pix of the batch I had...

Well, mine are the less valued and cheaper Renesas
And from specs I thought they looked better fore multiple outputs
Unfortunately not knowing they were the wrong ones
Despite its not the right ones, its been confirmed they will work fine

2SK1058 / 2SJ162

It says Vgs(10V/100ma)

4x K1058 0.837 / 0.837 / 0.837 / 0.838
4x K1058 0.840 / 0.841 / 0.842 / 0.843
4x J162 0.500 / 0.501 / 0.504 / 0.505
4x J162 0.508 / 0.508 / 0.512 / 0.513

Not that I know exactly what it means
Oh, maybe that they are within 5ma, I dont know
But it was fun

I have changed my mind, and will either use the them as double pairs in F5, and have "safety" spares
Or use them all in BA-2
Not really decided
Thats how it is being a bit slow, things change before even started
And new things and ideas coming up

My suggestion would be to build F5 as standard with single pair Toshibas, or maybe two
And if you want more, look at BA-1 or BA-2

My decision was based on too little knowledge, and excitement
Lack of common sense might not be the best conditons
But its ok, I dont regret it, its been a learning process, small but still something

[vdi_nenna]

M.M

I have seen this happen to my F5 with circuit protection inserted, although not as high a voltage spike. If the voltage settles then there is no issue.

Notice that if you blow cold air over the circuit, the voltage reading raises and lowers.

.62v from .59v is not that much of a change to be worried about. Also, you will have to reset the pots after some break in time.

Maybe someone else with more experience can verify this.