The Holy Grail Follower Output Stage

[ggetzoff]

L.H.Q.,

Your opto-coupler biased, no degeneration follower is brilliant. I own the the XA-25 and it’s the best amp I’ve ever heard, with a large period at the end. Of course it has the UGS front end, so it’s not just a follower.

Years ago I built the F4 and it remains one of my all time favorites. With the IXYS 600v HiperFET this could allow everyone on the forum the chance to have an XA-25 follower. Just brilliant.

 

[lhquam]

The F4 was my 2nd amp build after the F5. I really enjoyed the F4, particularly with the Impass tube preamp.

 

[dBel84]

agreed love the F4. It has been replaced by M2OPs which I am running with Vicor flapac SMPS - actually just grabbed a 24V one so that I can test the HGF with linear vs switchmode psu

 

[eriksson]

gary s - Australia
dBel84 - USA
yoaudio - USA
EIArte - USA
kannan_s - USA
von Ah - USA
tom1066 - USA
ACnotDC - Germany
chermann - Austria
Arthur-HK
william2001 - USA
jostwid - Switzerland
ItsAllInMyHead - USA
Integra - Canada
Sonnenschein - Germany
birdbox - USA
eriksson-Sweden

 

[asanden]

gary s - Australia
dBel84 - USA
yoaudio - USA
EIArte - USA
kannan_s - USA
von Ah - USA
tom1066 - USA
ACnotDC - Germany
chermann - Austria
Arthur-HK
william2001 - USA
jostwid - Switzerland
ItsAllInMyHead - USA
Integra - Canada
Sonnenschein - Germany
birdbox - USA
eriksson-Sweden
Asanden - The Netherlands

 

[manniraj]

gary s - Australia
dBel84 - USA
yoaudio - USA
EIArte - USA
kannan_s - USA
von Ah - USA
tom1066 - USA
ACnotDC - Germany
chermann - Austria
Arthur-HK
william2001 - USA
jostwid - Switzerland
ItsAllInMyHead - USA
Integra - Canada
Sonnenschein - Germany
birdbox - USA
eriksson-Sweden
Asanden - The Netherlands
manniraj - USA

 

[lhquam]

I am now listening to the amp with "mediocre" pairings of the FQA28N15/FQA28N15 FETs with no global feedback.
With A/B switching between the Holy Grail and my ZD25, which has 30dB or more global feedback, I cannot hear any difference. Tomorrow I will have my local "golden ears" do the A/B test.

These FQA FETS are amazing in the zero degeneration, source follower OS. I will show some comparisons with other FET combinations. Totally different growth in the harmonics vs. Watts.

 

[robert8]

gary s - Australia
dBel84 - USA
yoaudio - USA
EIArte - USA
kannan_s - USA
von Ah - USA
tom1066 - USA
ACnotDC - Germany
chermann - Austria
Arthur-HK
william2001 - USA
jostwid - Switzerland
ItsAllInMyHead - USA
Integra - Canada
Sonnenschein - Germany
birdbox - USA
eriksson-Sweden
Asanden - The Netherlands
manniraj - USA
Robert8 - USA

 

[mordikai]

gary s - Australia
dBel84 - USA
yoaudio - USA
EIArte - USA
kannan_s - USA
von Ah - USA
tom1066 - USA
ACnotDC - Germany
chermann - Austria
Arthur-HK
william2001 - USA
jostwid - Switzerland
ItsAllInMyHead - USA
Integra - Canada
Sonnenschein - Germany
birdbox - USA
eriksson-Sweden
Asanden - The Netherlands
manniraj - USA
Robert8 - USA
mordikai - USA

 

[gary s]

Your list is steadily growing (21 at the moment), what is the magic number to go ahead? I hope your supplier has enough of the FETS.
I assume you will be posting a final schematic, BOM maybe, pcb layout and an adjustment procedure for all members to follow.
Good luck with the organization of all of this.

I see there are around 1400 pieces of the FQA28N15 in stock at 3 authorized distributors in the US, but there are zero of the FQA36P15 in stock at the same authorized distributors. There are many thousands showing at heaps of Chinese supply houses on Octopart - but one would have to wonder if any are genuine.

 

[lhquam]

Yes, the list is growing and I will be looking for help with the distribution of PCBs and FETs. At this rate I will have to limit how much measuring and matching I can do, and the work involved in mailing the PCBs and FETs.

My best guess is that I can get between 20% and 30% yield (maybe more) of good pairings, assuming additional parts from my source have similar parameter statistics. I have 50 more pairs on order, which should provide 5 to 8 amplifiers. Before I order more I need to be assured of the product quality and confirmed orders.

 

[gary s]

Thanks for the update on all of this. For the members interested, do you have any idea at this stage on a price per amp for 4 fets and 2 pcb's without postage costs at this stage?

 

[lhquam]

Depending on FET pair yields, a rough guess is $20-$30 for FETs.
$20 for PCBs unless I have then fabricated elsewhere.

 

[ra7]

gary s - Australia
dBel84 - USA
yoaudio - USA
EIArte - USA
kannan_s - USA
von Ah - USA
tom1066 - USA
ACnotDC - Germany
chermann - Austria
Arthur-HK
william2001 - USA
jostwid - Switzerland
ItsAllInMyHead - USA
Integra - Canada
Sonnenschein - Germany
birdbox - USA
eriksson-Sweden
Asanden - The Netherlands
manniraj - USA
Robert8 - USA
mordikai - USA
Ra7 - USA

 

[gary s]

Thanks for the update, not sure where you currently get your pcb's made, but you should consider JLCPCB, would be much cheaper I feel and their quality is right up there. I have never had an issue with them.

 

[Vunce]

Depending on FET pair yields, a rough guess is $20-$30 for FETs.
$20 for PCBs unless I have then fabricated elsewhere.

Will you still share the Gerbers so builders not on the list will be able to play in the sandbox?

 

[arthur]

I am now listening to the amp with "mediocre" pairings of the FQA28N15/FQA28N15 FETs with no global feedback.
With A/B switching between the Holy Grail and my ZD25, which has 30dB or more global feedback, I cannot hear any difference. Tomorrow I will have my local "golden ears" do the A/B test.

These FQA FETS are amazing in the zero degeneration, source follower OS. I will show some comparisons with other FET combinations. Totally different growth in the harmonics vs. Watts.

What are the FET pair, there seems a typo

 

[gary s]

Yes a typo, should be FQA28N15 / FQA36P15 as mentioned in previous posting's.

 

[lucadvt]

gary s - Australia
dBel84 - USA
yoaudio - USA
EIArte - USA
kannan_s - USA
von Ah - USA
tom1066 - USA
ACnotDC - Germany
chermann - Austria
Arthur-HK
william2001 - USA
jostwid - Switzerland
ItsAllInMyHead - USA
Integra - Canada
Sonnenschein - Germany
birdbox - USA
eriksson-Sweden
Asanden - The Netherlands
manniraj - USA
Robert8 - USA
mordikai - USA
Ra7 - USA
lucadvt - Italy

 

[EUVL]

I have 50 more pairs on order, which should provide 5 to 8 amplifiers.

I guess they each want 2 amplifiers, so enough for 4 subscribers ?

Enjoy your matching. 🤓


Best,
Patrick