Interestingly, just yesterday, I was servicing a Mesa Engineering M-Pulse 600 amp with a shorted BUZ901. Needs a matched a quad. Mesa is down to few remaining MOSFETS and saving them for in-house service. Customer will have to send it in.
Well they come from a blown mesa boogie carbine that I got for free 😂 The pcb was a wreck, decided to sell it as a preamp. It’s possible that there’s a blown one in my set, I’ve not take the time to test them yet
Thank you Nelson.I didn't expect an answer from the boss himself. Reason I ask is my rendition has a tested df of about 15 at 1khz yet spice predicts about 80. I was hoping that the real mccoy was tested at a lower f and the df wasn't flat. Back to the drawing board. ☹️
I suggest building an actual breadboard, making PF adjustable (as with a pot), and measuring DF under actual load conditions while varying PF. As has been mentioned, everything in the circuit can affect everything else, so you need to redo measurements (particularly distortion) when making changes.
Well I have to say, if this F7 simulation is anywhere near the real deal its a beautiful amplifier. I was in over my head with measurements, so I was not able to complete them exhaustively, but if my ears are any sort of scope, things arent too bad at all.
In fact, I did some AB listening with a Benchmark AHB2, to see what the differences were. Those two are a fun comparison, but then I thought to plug in my Aleph J build, and I have to admit the difference was so stark it has me wondering if there is something wrong in my Aleph. The F7 (as well as the benchmark for that matter) handle the highs so much better - yes the aleph has girth in the midrange, but with vocals it felt like it hit a brick wall when compared to the other two.
Im a bit floored to be honest - and jokes aside I will be doing a full check in on the Aleph because the difference seems, well, unfair.
In fact, I did some AB listening with a Benchmark AHB2, to see what the differences were. Those two are a fun comparison, but then I thought to plug in my Aleph J build, and I have to admit the difference was so stark it has me wondering if there is something wrong in my Aleph. The F7 (as well as the benchmark for that matter) handle the highs so much better - yes the aleph has girth in the midrange, but with vocals it felt like it hit a brick wall when compared to the other two.
Im a bit floored to be honest - and jokes aside I will be doing a full check in on the Aleph because the difference seems, well, unfair.
Hello everyone, I would like to know what the procedure is for calibrating the F7 amplifier once construction is complete. Where should voltages be measured and what values should they have? I am referring to the balance trimmer and the two 500k trimmers in front of the MOSFETs. Thank you very much.
You could do a few things to Aleph J... like remove C1 and use a copper link in its place, remove the overload/short circuit protection transistor and the associated 2 resistors R13 and R14, switch to a discrete value R7 resistor (instead of leaving the trim pot in its place,) provide some sort of power supply rails decoupling for high frequencies.... maybe 1-4.7uF (max) electrolytic and 0.1uF polypropylene film in parallel to the large capacitor bank.
The above will improve the Aleph J sound a lot, you'd be surprised by how much...
For your specific complaint, the removal of the R7 trim pot and use of a discrete value resistor (of the correct value to keep the offset in check) in its place, would benefit the high frequencies/top-end extension by quite a large margin.... consider the trim-pot capacitance as an addition to 2 x MOSFET parallel capacitance... not to mention the 2 points of scrubbing & rubbing contact resistance penalty you get with the trimpot... have a look at the internal construction of a trimpot... and think along the lines of what choice people make when they have to pick the I/V resistors (in DACs). In Aleph J, R7 is doing exactly that... an I/V conversion.
I actually did build my AJ with most of your mods, Boky! I will check my values and bias, because I just read a post of yours in reference to preference for 400mV over 450mV, with some of the symptoms perhaps easily paired with that.
Appreciate the ideas of course!
Appreciate the ideas of course!
Hi,
I am in a middle of an AJ build, which are the overload transistors that can be removed ?
I am in a middle of an AJ build, which are the overload transistors that can be removed ?
The current limit transistor in the AJ is Q3 per schematics here:
https://www.diyaudio.com/archive/gallery/data/500/AJ_Sch.png
https://www.diyaudio.com/archive/gallery/data/500/AJ_Sch.png
Hello, do you think it's possible to use two separate 105 VA toroidal transformers for the PSU F7 amp, each with a 20V secondary output, along with their own bridge rectifiers? Thank you.
This is a commercial First Watt amplifier, and there's no official circuit, schematic, or calibration available now.
So you have to ask a particular individual, who has built a specific circuit of their own.
