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Interest for Final GB for F5X Power Amp

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EUVL

EUVL

Member
Joined 2003
xen-audio.com
#1
Over the years we have been asked many times for F5X PCB sets and matched devices.
We have declined every time because a set of boards without the case is no use.

One of the senior members here has expressed a willingness to supply the case for a limited batch to DIYers.
So we wish to know if there is still any interest before we make the necessary preparations.

It will be a last-time GB limited to 10 sets.
They will include matched FETs incl. regulator FETs, PCB set and fully machined case.
You should be looking at a total building cost (fully finished) for a stereo amp of around 3000€.

Please indicate any interest here.
There will be no guarantees if we go ahead, but we shall try our best to make it happen, some time in 2019.


Patrick
 
#4
Not right now. Still too early.

But you know curve trace matched octets of Toshiba JFETs at coonstant temperature have their price.
So are unibtanium 2SK1530 / 2SJ201 NNNNPPPP match.
Search around and you will have an idea.
PCBs are nothing in comparison.

The case will have to be made in the EU.
So expect something like 600€ miniimum, plus transport.
There is no case like ours anywhere, not even commercial ones.

The next major expenditure are transformers.
2x 600VA Toroidy will be around 200€.
And then it depends on what boutique parts you use for the rest,

I do not think it will be less than 2000€ in total.
But it is meant to be a reference amp and not a budget amp.
The same goes for the F5X Preamp, to be released about the same time frame.

We are only checking interest npow because we need to make some plans for the case.


Cheers,
Patrick
 
#19
I have been asked whether one can join the GB without the case.

As you can see in the main thread, the entire PCB layout is designed round the case.
So many of these PCBs are close to useless to you if you use some other case.

Maybe in the future I'll change my mind and just let you have the amp PCB only.
But for this particular GB I wish to have 10 more of our reference amp built properly.
And that means including the case.


But many thanks for your interest nonetheless,
Patrick
 
#20
One more important point to mention up front, as I discover today.

I just checked our inventory and unfortunately we only have 5 sets NNNNPPPP perfect matched octets for the 2SK1530 / 2SJ201 to offer.
They have Vgs matched to << 10mV, and transconductance matched to < 2% for all 8 FETs.
Matching is done using our own designed curve tracer, under continuous mode and at 65°C (10kg) heater block temperature.
So this is identical conditions to a working amp in the F5X.

The first subscribers will (eventually) have priority to those NNNNPPPP devices (first come first serve).
And of course perfection has its price.

For the remaining subscribers, you may :
1) chose to buy those MOSFETs from someone else (and trust his matching); or
2) obtain NNNN-PPPP sets from us at reduced price.

Our NNNN-PPPP sets typically have a Vgs difference between N and P of < 150mV.
Within the NNNN or the PPPP, the match is just as perfect as mentioned above.
Using NNNN-PPPP has, IMHO, little or no disadvantage in a F5X, as opposed to a single-ended F5.
The left and right halves will compensate each other to cancel >90% of the residual even harmonics of each phase.
And you will also get a recipe from us how to tweek the circuit to cancel the N-P unbalance.

This is different from the famous P3 pot from Nelson for the F5, in that we restore the imbalance in the open loop.
And not by fiddling with the feedback circuit (as in the P3 pot).

Details you can see here :
https://www.diyaudio.com/forums/pass-labs/183362-f5x-euvl-approach-12.html#post2812698 Post #597
https://www.diyaudio.com/forums/pass-labs/183362-f5x-euvl-approach-16.html#post3259403 Post #789

Note that the measurement shown in post #789 are all ONE single-ended phase output of the F5X.
When you applied the load across the balanced outputs, all even harmonics will be reduced by 20~30dB, from our experience.
That is of course assuming you have tightly matched devices for left and right halves of the amp.


No issues with the JFETs. We have more than plenty. 😉


Patrick
 
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