Hyper tuning --
Now if you want to hyper tune the amp, and if you can measure the harmonic distortion way down low ---- You can add another trim in place of R10... a value of 500 ohm should work well. Or, you can jumper in a 2K pot across the existing R10 and adjust for distortion null and replace pot with a bridging R value of the trim pot value. I found some more reduction in thd this way when under load (<100 Ohms).
Here is my proceedure to try if you have the thd equipment: Apply load R to the amp.... using the dc offset pot, trim to minimum thd. You will then have a dc offset. Then, using the pot at R10, readjust for zero dc offset. Maybe a little back and forth and you will have the lowest possible thd... even beyond matching. In my case changing R10 value by only 40 ohms improved the performance under heavy loads. So, use a multi-turn trimming pot. How much improvement depends on how well you matched all your transistors. The matching of the jFET provided by jackinnj is even tighter than i did... so i cant say how much better you can get under load, but its what i do.
Thx- Richard
Now if you want to hyper tune the amp, and if you can measure the harmonic distortion way down low ---- You can add another trim in place of R10... a value of 500 ohm should work well. Or, you can jumper in a 2K pot across the existing R10 and adjust for distortion null and replace pot with a bridging R value of the trim pot value. I found some more reduction in thd this way when under load (<100 Ohms).
Here is my proceedure to try if you have the thd equipment: Apply load R to the amp.... using the dc offset pot, trim to minimum thd. You will then have a dc offset. Then, using the pot at R10, readjust for zero dc offset. Maybe a little back and forth and you will have the lowest possible thd... even beyond matching. In my case changing R10 value by only 40 ohms improved the performance under heavy loads. So, use a multi-turn trimming pot. How much improvement depends on how well you matched all your transistors. The matching of the jFET provided by jackinnj is even tighter than i did... so i cant say how much better you can get under load, but its what i do.
Thx- Richard
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BTW Richard, I want to thank you for the suggestion of the Peak tester in the article. When I re-read it last week I was just looking for a new tester.
I got the 75 model mostly because of the wider range and basic jfet testing. For small signal transistors is very quick and works for LEDs too
I got the 75 model mostly because of the wider range and basic jfet testing. For small signal transistors is very quick and works for LEDs too
BTW Richard, I want to thank you for the suggestion of the Peak tester in the article. When I re-read it last week I was just looking for a new tester.
I got the 75 model mostly because of the wider range and basic jfet testing. For small signal transistors is very quick and works for LEDs too
There are quit a few other interesting test equip out of Taiwan and China at attractive prices; Curve tracers are avail. Also, this one --> Another portable semiconductor tester that also tests 78xx and 79xx 3-term regulators and power transistors (2A and 1Kv !) etc. Model DY294 made by DUOYI Elect.
-RNM
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The new PEAK Atlas 75 Pro Telstar mentions just came out this Dec 2012. About $185 in USA. With a PC does curve tracing, too... Nice. -Thx RNmarsh
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I paid about 130€ from a reseller (direct price was higher).
The tracing capability is nothing impressive, a bit helpful for low power devices. One day i'll get a "real" Tek curve tracer to match power transistors and fets. For now I buy them already matched whenever i can
I was thinking of making the biasing more complex! I would think something like 100R in series with a 200 ohm trimpot would give decent ranging. Will try it tomorrow.
I just went to your store to look for the boards, guess I need to wait for the next batch now.
Randy
Hi, Iam trying to make a decision to buy the board. What kind of a power supply is needed? Also what are the dimensions of the board. For some reason the tech diy site doesnt calculate the shipping to UK - shows 0 as the shipping cost.
also, do we need to do any biasing adjustments - if so what exactly needs to be done?
also, do we need to do any biasing adjustments - if so what exactly needs to be done?
I couldn't find them in your store, am I just dense?
Nevermind, I see it now, not sure why I didn't see it before.