Holton AV800 Schematic

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#142
Frazzled said:


I will offer it to Anthony Holton to host on his site and will make it available to anyone who is currently or contemplating building the AV800.

Frazzled.
Click to expand...


🙂

Last year I did a pcb layout of the AV800 design plus extra
'stuff'. The extra stuff was external to the AV800 design,
I didn't modify the AV800 schematic other than maybe
add some extra transistor footprints to allow up to 14 output
stage transistors per rail. I don't know if the buffer stage
can handle this, Holton only verified up to 10 transistors per
rail.

I didn't build it yet because I wanted to build a prototype
AV800 first. To make a long story short, work stopped on this
project because I focused primarily on my speaker project
which is still work in progress.

I took the Holton document and placed in my Microsoft Word
document along with all the extra 'stuff' I added to the pcb
layout.

7.9 meg download.
http://home.pacbell.net/lordpk/amplifier/Amplifier.doc

Maybe you can give me some ideas that I can add to my
document.

I also created the schematic from scratch and used different
reference designators to accomodate my pcb layout.

Those extra circuits were tested 'standalone' with another
'bench test' amplifier but I have not tested everything
as one complete unit.

All this extra stuff is not really needed, but I thought I would
add it because of personal preference.
 
#143
Checking...

OK...

I removed Q3, Q4, C12, R37, D1 and D2 from the pcb.

Q3, Q4, C12 and R37 came out so I could isolate the error amp stage from the VA stage and to also facilitate testing Q3 and Q4.

Q3 and Q4 tested good with gain of 150 on one and about 180 on the other, perhaps I should pick up some more 2SA1306 transistors and match a pair although it is never stated that it is required.

D1 and D2 were removed so I could isolate the power supply to the front end of the amp only, this way the output devices are not powered up as I applied the rail voltages to R4 at the junction of D1 and R57 at the junction of D2.

I powered up the error amp stage and fed it a 1khz @100mv sine.

Finally I got a nice clean sine at the emitter of Q23 although it is somewhat attenuated, shouldn't I at least be seeing unity gain here?

An externally hosted image should be here but it was not working when we last tested it.


BOTTOM WAVEFORM IS INPUT

See part of the problem is because I had no part in the design of the AV800 I have to take certain design decisions for granted. What I have been doing is to try to reverse engineer this amp and look up all the equations as I am still new to this whole amplifier design/build thing. I have also decided to sit down and download all the datasheets for the transistors/mosfets in the circuit, so that when I test them I have a reference close by to make sure my test figures are close to datasheets.

Yes it is true, I probably couldn't find a better crash course in amplifier design than this as I have a vested interest in this amp now and I am therefore motivated to see the project come to fruition.

The one BIG question I have always had about amplifier design is how designers pick transistors, is there some sort of magical reference guide that they have or after a while do designers come to have favorite transistors for certain stages of amplifier design that they like to use. Also I have noticed a kind of regional flavor to amplifier design in that certain part numbers show up more often in say Australia than they do in North America.

Also this amplifier makes use of one IRF9610. Do you know I tried for two years to purchase these from local suppliers (READ NON INTERNET OR CATALOGUE SUPPLIERS) but do you think any of them stocked this transistor, yet they seem to be growing on trees in some places. I used an IRF9620 instead because this is what I could get my hands on.

On a side note if any of you guys have 10 to 20 IRF9610's kicking around I would love to buy them, I can pay you with PayPal right now.

Oh and the only datasheet I can find on 2SA1306 and 2SC3298 is a cross reference from NTE, and God only knows how accurate that will be, anyone have these???

Anyway enough of this rant, I don't expect to get this amp running any time soon as I have decided to learn more about the design first and see if I can make any improvements. One thing that would have saved me a TON of time is if Anthony had put some measured voltages on the schematic AND if he had offered a PCB/silkscreen overlay view in his construction guide, I have made one and it helps significantly.

Thanks for all the help that you guys have been giving, I really appreciate it.

I will continue to update as I find out more.

Frazzled!:dead:
 
#145
Re: Re: Checking...

thylantyr said:
You don't have the ability to order parts from a catalog or internet?
Those IRF9610 can be had from the manufacturer, www.irf.com
the only problem is the 50 unit minimum, but you get them
for 50 cents each vs. almost $5 ea. for a NTE replacement.
Click to expand...



Well lets see... I need two...
US$.50 = CAN$.70 X 50 = CAN$35.00
Shipping, usually these manufacturers and catalogue places ship by UPS only, US$15-20 = CAN$20-28
Lets not forget the lovely UPS brokerage fee and GST = CAN$15-20

So... fifty IRF9620 for CAN$83.00
Hmmmmmmm..... I need two... $5.00ea is looking pretty good right about now. :bigeyes: :cannotbe:

EDIT
I am not trying to sound like a jerk here but I have been down that path before and got hosed, I try to buy locally so when I get crap parts I have someone to go back to and get service, the big guys don't care especially for small potato mail orders like mine.
 
#151
Still No Joy.

Well it has been a year since I initially started this project and although I have been very busy with other things I have from time to time sat down for an afternoon and looked at the AV800 only to become very frustrated.

I am going to take a week in the spring and give this amp one last serious look to see if I can make it work, I think I may start with a new set of semiconductors and I will test them all prior to installing them in the PCB, I have gone over and over this amp and that is only thing I have left to do.

I'll check back here again when I have givin it my one last chance and let you all know how I made out.

:apathic:
 
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