I am yet to receive the boards and hopefully it lands up after waiting for more than 40 days now 🙁
So noticing some things during testing. First +/- 40vdc rails. Gain is 46dB(not sure why it's so high), Bias is 40ma per trannie. When I do a sweep from 20-20khz bias is stable up to right around 10khz. From 10kHZ-20khz the bias rises to just above 60ma/per and you can smell it warming up somewhere. Is this just because gain is too high? What resistor do I adjust for overall gain? Does it need a comp cap added? do I raise or lower gain resistor to lower gain. This of course testing using sine wave from signal generator set at .1vac
Hi, I reduce gain with R3 - my value = 1K ( 1st post original schematic R3).
I don't have any instability in both of the my AB 100's without C9 - maybe you have an oscillation somewhere? Is there any soldering mistake in resistor values ?
Have you checked the output waveform with the oscilloscope?
I don't have any instability in both of the my AB 100's without C9 - maybe you have an oscillation somewhere? Is there any soldering mistake in resistor values ?
Have you checked the output waveform with the oscilloscope?
@manniraj,
I cannot change it unfortunately that so far with you nothing arrived and it also nothing came back.
I cannot change it unfortunately that so far with you nothing arrived and it also nothing came back.
Yes I understand and I should have gone with tracked shipment at least to see where exactly its held up. With no tracking its just a guessing game now 🙁
Thanks
So to be more clear. I'm looking at scope images and they look great. I see no signs of oscillation. Is it perhaps that I'm testing with 10-20khz sinewaves at just under clipping? Also there is no load on the output, open circuit. With music signals the levels at those frequencies would be drastically lower. Have you ever tested yours like this and monitored the voltage drop across the emitter resistors?
Ok the latest. I adjusted my overall gain to 26db by raising the feedback resistor from 100 to 1000. The bias is stable up to 100khz and beyond now. Actually have it rigged up on the bench with Epos speaker and sounds pretty good! I'm happy with it so far. What supply rails are people using? This is running on +/- 40vdc
Glad to hear good news!
i use is 43V rails on first one and 37V for second amp - because I had such transformers on the shelf.
i use is 43V rails on first one and 37V for second amp - because I had such transformers on the shelf.
I'm running maggies rated at 4ohm. Would like to push the rails to 50-53ish and get a real 200 watts out of this amp. Anybody think that would be an issue? I'm mounting to a heatsink that could be used for Class A to 25-35 watts. What about input electrolytic cap. I would like to change to polymer film type. How big does it have to be to get descent low frequency.
i think there will be no problem with 50-55V rails - at least the measurement @4 ohm on the first post shows stable 200W. I use 3,3 uF input cap - its around 2Hz filter. and feedback cap 100uf + 1k =1,5Hz. i think even 2,2 uF will be fine
I notice that you have built two of these. Are you bridging them? Should be no problem with bridging one correct, if you pay attention to the load. I would love to see a board configured with 5-6 output trannies to possibly bridge for 4 ohm load.
my two amplifiers have slight differences - one has more output transistors and higher output power...other one has lower emitter resistor values and different VA stage transistors and lower output power...haven't thought about bridging them....no need for that at least for me...but i think its possible.
Do you think that you could drive one or two more pairs of outputs with the same driver circuitry. I would think that the trannies being Darlingtons it may work ok. Doesnt the darlington pretty much have it's own driver transistor on board.
Thank you Mr. Pass. After many years of listening to your designs, i'm firmly in the camp of simple circuits sound better!
i missed this post ..
What do you think about the AB 100 sound compared to the A40?
I've always liked the a40 - but I never build one..
The AB100 is not as sparkling and sterile as the F5, but has a very good low end -powerful, accurate and not blurry. Mids and highs are more detailed than the Leach amp imho...of course it's a matter of taste - but I like to have many amplifiers stacked on top of each other😀
So just thinking out loud. Anybody think about designing an extra board just for added on capacity of output trannies? Short board with just trannies and emitter resistors base resistors w/connection points to main board for higher power. maybe 2-4 more outputs. I know, I know why don't I do it myself? I do not have any experience with board software.
imho 4 pairs are ok even for 4 ohm...if you need more power - you should rise rail voltage - when you rise voltage - you will need to check the transistors max junction voltage...and this mean you will need ztx 451 small transistors an maybe TIPs will be insufficient...
So I'm basing my info on the SOA charts for the TIP142/47. It shows that my operating point of +/- 48 vdc rails and a collector current of 2 amps apiece just puts it over the SOA curve for the transistor. It works out to be ~68 watts per trannie. I don't know but is that too much for a trannie rated at 125 watts. It is on a oversized heatsink.