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FH9HVX - Budget Conscious 100w Class AB for Lean Times

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#1,121
Vunce’s build is sweet. In case you guys haven’t seen my FH9HVX:

https://www.diyaudio.com/community/...-a-budget-conscious-heatsink-solution.355302/

1658279742561.jpeg

griddle-amp-final-01-jpg.849179
 
#1,122
So I'm lining up ideas for my next amp project which will probably be upgrading my Adcom GFA5400. I wonder if replacing the Adcom drive board with the FH9HVX would be a good approach? It already has 3 sets of IRFP240 & IRF9240 FETs per channel - could I drive all 3 of them in parallel? The Adcom service manual says they're matched.

One thing against this idea is that my 5400 is 100% pristine so it's worth something, but not so much once I hack it up. I looked at some dead 5400s but they might have bad FETs so I'm trying to figure out what approach is best here.... inputs welcome.

Thanks.
 
#1,123
The circuit was not tested with 3 in parallel, you could just connect one to start and leave the other two unconnected if you are looking to keep the Adcom chassis semi-stock so you can revert back. I would pull all of the IRP’s off and make a new set of FQA’s with the proper snubber helper boards and mount on the same bolt is the central IRFP. That way, it’s reversible.
 
#1,124
xrk971 said:
The circuit was not tested with 3 in parallel, you could just connect one to start and leave the other two unconnected if you are looking to keep the Adcom chassis semi-stock so you can revert back. I would pull all of the IRP’s off and make a new set of FQA’s with the proper snubber helper boards and mount on the same bolt is the central IRFP. That way, it’s reversible.
Click to expand...
So the question is - is the FH9HVX driver superior to the Adcom? the distortion numbers are a bit better.
 
#1,125
I don’t have any Adcom amps so can’t say. The specs of the Adcom are decent. What I would say is that the layout and component choice of the FH9HVX would probably be better than a mass produced amp. Depending on what you use for the PSU, your mileage may vary. I do know that I really like the sound of the FH9HVX and how quiet it is. Definitely better than 100dB SNR with a good PSU.
 
#1,128
So I've decided to put my big expensive Class A amp on hold for now and build one of these, since it can be done much more cheaply and I haven't yet bought most of the expensive parts for the Aleph J/M2. Plus I'm about to pull the trigger on a pair of Dali Oberon 5s, which are 6ohms/ 88dB.

I'm going through the FH9HVX BOM and trying to decide what to use for a PS...I'd like to use the All Cees, but I'm not seeing any 400 or 500VA dual-secondary Antek transformers of around 34-36V. Am I missing them?

I already have dual SLBs populated for my class A amp...are these way overkill for this amp? Actually, now that I'm typing this, I'm not sure all the components are high enough in voltage for a 100w FH9HVX anyway.

If I were to go with this SMPS instead https://micro-audio.com/store/product/smps630-g/ what output voltage would be best? +/-44VDC or +/-55VDC?
 
#1,131
I've decided to go with the Micro Audio. They have options for AUX Voltage (Regulated) of +/-12, 15, or 18VDC. And Driver voltage of +12, 15, or 18VDC. I think these are geared towards Class D amps. I don't think it matters what I pick for the Aux and Driver voltages for this amp, does it? Would any of these voltages be more likely to be useful in the future if I were to repurpose this PS?

Also, does remote MOSFET mounting work ok with the FH9HVX without the little remote snubber boards? It looks like most people aren't using them but I thought that was likely to cause oscillation.

One more question:
Is a KSP92BU the correct substitute for V121 (MPSA92-AP, which is obsolete and no longer available)?
 
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#1,133
pinkfloyd4ever said:
I've decided to go with the Micro Audio. They have options for AUX Voltage (Regulated) of +/-12, 15, or 18VDC. And Driver voltage of +12, 15, or 18VDC. I think these are geared towards Class D amps. I don't think it matters what I pick for the Aux and Driver voltages for this amp, does it? Would any of these voltages be more likely to be useful in the future if I were to repurpose this PS?

Also, does remote MOSFET mounting work ok with the FH9HVX without the little remote snubber boards? It looks like most people aren't using them but I thought that was likely to cause oscillation.

One more question:
Is a KSP92BU the correct substitute for V121 (MPSA92-AP, which is obsolete and no longer available)?
Click to expand...
I like to order it with 12v always on to power accessories and +/-15v aux switched on to power preamps etc. The driver voltage is for certain Class D amps so doesn’t matter.

That KSP92BU should work fine. Both are -300v 625mA PNP with EBC pin out and Hfe circa 40. Looks like a perfect match.
 
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#1,138
I finally got my garage mostly cleaned this weekend, all that's left is the workbench, maybe this coming weekend. Then I can finally tap some holes and finish up my FH9HVX. Going dual mono with 2x Antek AS-2238's that I've had waiting for quite some time now, an XRK SFP soft start, 2 All-Cee's boards, and a pair of X's SSR speaker protection with the instant off boards. One of the two amp FH9HVX board's is built up sans V123, V131, and V132, I've also built and tested an All-Cee's board. I tentatively plan to offboard them with flying leads and some of X's MOSFET snubber boards (the blue square ones). Would I be moving resistors R131 and R132 to the snubber boards?

I'm really looking forward to listening!
 
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