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F5X -- the EUVL Approach
F5X -- the EUVL Approach
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Old 29th March 2012, 04:35 PM   #711
EUVL is offline EUVL  Europe
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Join Date: Oct 2003
I understand there is no place to ask this, but please try to keep this for technical discussion only if possible.

> Case & heatsinks: pending
> CRC PCBs + MPC74 resistors: pending

They were shipped together, in bulk. And they have arrived in Austria.
Please contact smyslow for details.

> 2 amp boards + 8 cap boards + protection board: pending

At Austrian Customs waiting to be handled, AFAIK.

> Protection board parts kit + spares + small parts kit: pending

You paid 2 days ago. Please give Mark 2 weeks.

> Matched output fets: trying to source?

You as a group need to get organised. Nikon1975 will help to cource.
But someone needs to take the lead.

> IEC connector : pending

Not 100% sure, but I think also with the case parts.

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Old 29th March 2012, 05:15 PM   #712
flg is offline flg  United States
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Matched Toshiba output devices are still available from Zhoufang... As of a week ago...
"It was the perfect high end audio product: Exotic, inefficient, expensive, unavailable, and toxic." N.P.
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Old 29th March 2012, 05:25 PM   #713
AndrewT is offline AndrewT  Scotland
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But Zhoufang has confirmed that he is measuring Vgs @ ~500mA with Vds set very low.
That type of selection does not suit F5 nor F5x.
regards Andrew T.
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Old 29th March 2012, 07:05 PM   #714
pchw is offline pchw  United States
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F5X -- the EUVL Approach
Zhou also raised the price for N-P match. I think his N-P match yield of his
latest match (whatever the method is) was quite low.

Since he bought a lot, I suspect it will need a very large pool to come up with
enough N-P matches. My random 20 pairs from a US supplier don't even have any N-P remotely close to within Vgs 0.25V. Out of the 0 pairs. Since all N's and P's are of same date code with respect to the type, this makes me think, if you are bad luck and purchase a bulk of P's that are grossly different from the N's, then a good portion of the lot may not be useful for N-P match at all!!

Patrick mentioned that the N-N and P-P matches are more important as they make up the 2 sides of the balanced channel, it will be interesting to know how bad it will be if N-P are totally unmatched, but the N-N and P-P are.
- Fred -
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Old 29th March 2012, 09:24 PM   #715
EUVL is offline EUVL  Europe
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The team has not done enough examples of the F5X to tell you how important.
Suffice to say that in the original, single ended F5 with totally unmatched Fairchilds (by nature), the even harmonics are still OK.
So I would not be totally worried if N-P match is not perfect.
The left-right balance cancellation will save the day.

The test team actually built one proto with 2SK3497 / 2SJ618 which are, by nature, not complementary.
The measurements are not worse than fully NNPP matched K1530/J201.
Have not yet had a chance to listen properly (that team member fully loaded with work).

Maybe you should just buy a pair of matched Ns and a pair of matched Ps from Zhou and test those with your first build.
Changing 4 power FETs later (if at all) is not a big operation.
Certainly much cheaper, considering his current asking price.

Now you see why I always build balanced (apart from constant current draw in Class A).

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Old 29th March 2012, 09:30 PM   #716
EUVL is offline EUVL  Europe
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PS :

Andrew is of course correct.

The way that Zhou matches is not truely F5X working conditions.
So even a perfectly matched N-pair with his one-point match at 500mA does not guarantee proper curve tracer match over operating range of F5.
That was why I proposed you GB your own random MOSFETs and then match under my instructions / using my equipment.
Even a 3-point match as I proposed will do.

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Old 29th March 2012, 10:59 PM   #717
NicMac is offline NicMac  Italy
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F5X -- the EUVL Approach
I think the problems are the following:

1) In order to get fairly good matches we would probably need something like 500 + 500 original virgin devices at a cost which would most likely not be inferior to 5$/device (i.e. 5.000$ total).
2) If this cost was to be divided by subscribers (n = 25) it would be 200$ per/F5X amp.
3) As only a fraction of the devises would be used, who should benefit financially from the left-overs? I'm sure the devices will maintain their value in time, but this is difficult to quantitate now.
4) Many (most?) of us already have "poorly" matched devices so why spend another 200$ at the gain of what?
5) Who would possibly have the time and measures to match the devices well in a fairly short time period?!
All other parts of the F5X build should be with the end-users in a month or so.

I don't have a solution. I would be ready to invest financially in the endeavor, but I absolutely do not have the time to do the matching or the F5X might be my last amp while having a job......

Anybody willing to spend a few weeks on matching?


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Old 30th March 2012, 04:29 AM   #718
EUVL is offline EUVL  Europe
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I am sure most of you would want spares.
Each of you would need 8 FETs. So 240 for 30 people, plus one set spares.
We are already 500. Matching reject rate 50%, and you have your 1000 devices for 5000 Euros.
And yes, same price as a set from Zhou, but properly matched.
(And also yes, he has a large pool to match N-P, be it at 500mA.)

Again yes, if most have already matched devices then little point.
But I was watching the list on the GB thread for matched devices, and the interest was not small.


Matching is the problem I cannot solve for you.
I am prepared to spend a few hours coaching, and let you borrow my equipment.
The rest you need to organise.
Ideally someone in South of Germany should do the matching.

But your call. I was just trying to help.
I am happy either way, as I don't gain anything other than that the F5X will be built as best as we possibly can.


Last edited by EUVL; 30th March 2012 at 04:41 AM.
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Old 31st March 2012, 04:54 AM   #719
MarkLai is offline MarkLai  Hong Kong
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IEC connector should have been shipped. I've put the IECs together with the kit for the Asian subscribers.

I shall be able to ship out the bare Protection pcbs latest next weekend.
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Old 14th April 2012, 07:20 PM   #720
EUVL is offline EUVL  Europe
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I have been asked by PM about sourcing MOSFETs.

You probably all know that Toshiba is stopping all audio devices, MOSFETs and JFETs alike.
The only open source that is known to have sufficient quantities for NNPP match is, as mentioned before, ZhouFang.
It has also been discussed before that his matching is not exactly at F5X operating conditions.

So if you do not wish to purchase from Zhou, the only solution right now is to GB and match yourselves.

We ourselves are in the process of acquiring sufficient devices to support future batches of F5X projects.
But it won't be 6 months or so before we are ready, and then only in the context of supporting the project,
and not as separate devices sets for general sales.

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