The Mini-A

Jump to Latest
#401
john2wei said:
If I want to double the Q1 current , I plan to change as following
R4 =110R / R3=181R .......
Click to expand...


yes ; it will work like that , but your ears/brain combo must decide is original better than altered ;
in that case you'll decrease open loop gain , feedback ratio etc .....


john2wei said:
..... should I modify R13 to 50r?
Click to expand...


leave it as is - it's part of sort of dynamic overcurrent output protection
 
#406
jacco vermeulen said:
Eeh, what if he wants more than 2 amps ?
Click to expand...
Zen Mod said:
he didn't ask for that 😀
Click to expand...


I just want double the Q1 current and reduce half of the Q6 current.
The final output current was the same as 1 AMP,
if my calculate was correct.😱

What I really want to do was keep the same power on 10W
and reduce the heat on Q6 and Q7, is it possible?

Any advice are welcome.
John
 
#409
I've been running my mini for some time now but lately i have a problem. Both channels used to be completely hum free, but after i had wat i think was a static discharge to the amp, one of the channels has developed a buzz. The humm is present in both balanced and unbalanced mode but more audible in unbalanced.

Has anybody an idea where to look for the problem? Could it be z1-z4 that protect the input?
 
#415
Guys,
I got some matched IRF9610. Put them in this circuit http://www.rstaudio.de/AlephP/MosFetSelect.pdf and the ones that were supposed to match now sorta match but not really. However I did find matches. Is this circuit the circuit I should be using to figure out which two to use for each channel? Spose its a little self doubt and a little wanting to believe that the guy I got them from matched them right.
Uriah
 
#416
The circuit is fine, yes. The Mosfets should be matched at the current they're biased at when in the actual circuit, so at 12V and with the 390R you should be fine. The 390R resistors should be tightly matched. Presort them with the single Mosfet setup and check potential pairs with the differential setup.
One problem though is the Mosfets' temperature coefficient, so when you measure in differential mode make sure they are in thermal contact (->equal temp). Ideally match them at the temperature they'll have in the actual amp later, so have an estimate for the heatsink temperature if you mount them on the same sink as the output devices.
I have again and again found Aleph-X 100w Amplifier Construction Notes to contain a wealth of information.
 
#418
My pleasure. The Aleph-X construction notes are very well written and answered most questions I've had regarding the build and setup of my MiniA, I'm very grateful for them. The guy who wrote the article is also an active member of our forum, Eric. Thanks, Eric.

Once you get there...setting up the Aleph current source is really easy if you know how, the best description is in the Zen_v2 article: http://www.passdiy.com/pdf/zen-ver2.pdf, featuring the setup procedure on page 3. Basically you just feed the amp with a 60Hz sine (from your computer/laptop or CD), measure two voltages (AC over the power resistors) and adjust one resistor (R12 in Grey's original circuit) accordingly. This works with a dummy load or a speaker, the latter being more annoying.

Have fun, and post some pics!
 
#420
Hi there 😉

If i mind to choose IRFP 250 as output devices, do i have to change anything in grey´s circuit postet in #1?

And, when already beeing here, are there other possibillitys for the output devices for "increased quality"?
Last question here: which voltage should the 220µF caps have? are 25V enough when running the amp at ~16,7V?

Thanks so far from germany 😉
 
Last edited:
You must log in or register to reply here.
Top Bottom