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FH9HVX - Budget Conscious 100w Class AB for Lean Times

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#442
Very close to getting to listen, in fact, I could probably hook it up and bypass the little preamp which I tested last night - running too hot , so need to drop the bias a little.

Selector switch hooked up , little VU meters up and running



..dB
 
#444
it has been a tight squeeze 😉 . I will sadly not be able to use the black beauty potentiometer I had planned for this - not even sure the smaller nobel one will fit, but I have a handful of small alpha pots that will - so always other options..dB
 
#445
That’s amp is packed to the gills! Nice work.

Regarding the ACP+ bias. Yes it runs a bit hot - more for driving 32ohm headphones. Just double the source resistors to cut current in half to 70mA will reduce dissipation 4x. It will still drive 250ohm headphones just on fine and be a very powerful preamp.
 
#446
Vunce said:
@wtnh,

I use Takman “Rex” (2%) carbon film resistors when called for. Very reasonably priced.
Click to expand...

I ordered these Takman “Rexs” (1 watt) for the CF feedback resistors from Partsconnexion. On my Fluke 179 the resistors I received measure within 0.5% of the rated value, and within 0.05% of each other in each pair!

Thanks for the pointer, Vunce.
 
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#447
Resistor issue: 1 watt in R108 and R141

Hmmm! The Takman “Rex” 1 watt resistors don’t really fit on the PCB in R108 and R141. I don’t have any, but 1/2 watters will probably fit well, so get them instead, pending the following:

I ordered 1 watt because I believe X said 1/2 watt causes some issues at sustained high output. Which one really needs to be 1 watt? The Takman Rex 1 watt could be squeezed in if you “loop-back” the leads.
 
#449
Francois G said:
Hmmm! The Takman “Rex” 1 watt resistors don’t really fit on the PCB in R108 and R141. I don’t have any, but 1/2 watters will probably fit well, so get them instead, pending the following:

I ordered 1 watt because I believe X said 1/2 watt causes some issues at sustained high output. Which one really needs to be 1 watt? The Takman Rex 1 watt could be squeezed in if you “loop-back” the leads.
Click to expand...

You can also use two parallel 1/2 w and straddle the second across tall legs of the first like a fence.
 
#452
No listening yet. Most of DIY time was spent hanging "barn door" styled doors in the house. Started laying out the front plate for the amp so that will be one less thing to hold it all up once I get the little peamp section worked out

.. dB
 
#453
Well not unexpectedly, it sounds great!! Thanks X.

a few challenges along the way but all worth it.



I have a low level hum coming from the preamp but when that is removed, it is silent - so a little more messing but am going to listen without the pre till I sort the preamp out .

thanks again for putting this great project together.

..dB
 
#455
Yes, it is a tight squeeze.

Odd thing is that the left is dead quiet and they share the same power supply and ground. The 24v supply is actually a DC-DC converter that takes the rail supply and puts out 24v. It is a low noise unit that is sitting below the output relay.

This preamp board is the one that I was doing all the work on, I will go over it carefully to see if the is anything odd.

In the meantime, I moved it up to the study and it is doing very well with my near field monitors.

.. dB
 
#457
I am going to have to do a small shoot out with my M2X. I didn't expect to keep as much microdetail and nuance as I am hearing with the FH9HVX ( needs a better or easier to write name ) Has really good bass control too. Colour me impressed. I built this amp more for fun ( and coolness in the summer ) than expecting great things and it has certainly impressed.

looking forward to others getting their amps built and hearing others opinions.

..dB
 
#458
Hi Dbel84,
That’s what Vunce and I have been saying about this amp for a while. If it was the only amp I had - I wouldn’t be too broken up about it. 🙂. Given the low parts count, accessibility of parts and ease of build, great sound, nuanced detail, bass control, 100w on reserve, cool running, etc. it checks a lot of the boxes.

I too am looking forward to other reviews.

Thanks for building it for grins. 🙂
 
#459
Honestly, it was those inductors that sealed the deal 🙂 . I have had a set of e-bay clones of this amp concept in my drawer for some time with the idea that I would put together a relatively simple AB amp that doesn't run anywhere near as hot as my other amps. I have a few older ADCOMs that would work too but I particularly wanted an integrated amp for my office. When I saw your thread, I knew this was the one to build.

You have designed a very elegant board which makes for an easy build ( as long as you get the led's the correct way around ) Mounting it the way I have was a little more tricky because of the little BD transistor but easy enough to find a solution.

Now that I have it off the variac, it is running full rails of 60V , I kept the bias as suggested although this is when "hot" initial start up is double the current draw when cold / initial start. I use the same chassis for my M2X and it runs at close to 60deg C , this amp is probably 30 odd - will have to measure it. No POPs on start of shut down ( massive pop with the ACP preamp installed - it pushes about 1.5V into the output when it shuts down ( luckily the relay cuts in pretty quickly but not quickly enough to prevent all noise )

thanks again for making this available to DIY

..dB
 
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