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Old 24th September 2017, 08:08 AM   #251
2 picoDumbs is offline 2 picoDumbs  Australia
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Old 24th September 2017, 10:13 AM   #252
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About possible Babelfish J interest
yup
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Old 24th September 2017, 07:44 PM   #253
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About possible Babelfish J interest
I changed the source resistors to 0.33R 3W carbon composition (vs Panasonic metal thin film), and the bias is now about 1.63 to 1.68amps (the bias pot seems to have little to no effect (7 to 8 turns no effect) on actually changing the bias, only changing Source resistors did anything, is this normal?) The distortion went dow to 0.14% to 0.15% THD and the profile is predominant H2 and H3 about -15dB lower and nothing else - so this is good. Should sound very lush and vivid. Still well above what I think it should be at (circa 0.04% or less?). Should I just leave it alone now or pursue trying to see if it can go lower in THD?

About possible Babelfish J interest-babbelfish-amp-0-33r-testing-jpg

Zen Mod: what did the Spice simulations predict for the THD and the spectrum?
I am taking the data in a different location so the mains peaks and harmonics a little different.

Left Channel:
About possible Babelfish J interest-babelfish-fft-1-68amp-2-83vrms-8ohms-fft-left-ch-jpg

Right Channel:
About possible Babelfish J interest-babelfish-fft-1-63amp-2-83vrms-8ohms-fft-ch-jpg
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Old 24th September 2017, 08:21 PM   #254
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About possible Babelfish J interest
TP3+R24 combined value is what's influencing Iq , besides voltage across R29

so - lesser ohms of TP3+R24 ,Iq lower ..... more ohms there , R29 is dominating

regarding THD ........ I would say that's good enough , not taking in account methodology of measurements ........ what's most important is that you confirmed K3 15db down vs. K2

Spice is ( as we know always enthusiastic) predicting something as 0.015% , 8Vpp@8R , with 0R33 biggies and app. 1A6 Iq

more oomph and THD goes even lower , but who cares
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Old 24th September 2017, 08:44 PM   #255
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Thanks, ZM. I'll stop now and just enjoy it. Been listening for past couple of hours on my Scan Speak 10F/8424 tops plus RS225-8 FAST speaker. Very nice sound.
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Old 24th September 2017, 08:52 PM   #256
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now .... you can just contemplate what's possible with more sensitive and more efficient speakers .....
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Old 24th September 2017, 08:54 PM   #257
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Maybe run a square wave then if all good, you're all good.

The only thing I would suggest is if you have room for 2 x 200VA transformers I would put those in.
2 x 100VA is probably not really adequate for this amp. You could use those 100VA transformers on another amp or preamp.
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Old 24th September 2017, 09:05 PM   #258
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what ? those are 100VA Donuts ?

I'm using 250VA ones for dual mono ..... 200VA should be minimum

not saying that THD is going crazy because of that , at 1W , but things will go berserk up

or , if one likes Musical Fidelity approach ..... 80VA thingie feeding amp with 80W of dissipation

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Old 24th September 2017, 09:11 PM   #259
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Quote:
Originally Posted by xrk971 View Post
My smallish 100w (per channel) trafos are sagging to about 20v rails under load.
It's advisable to use 200VA per channel bare minimum.
Determine what is the biggest trafos you can fit and go with those.
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Old 24th September 2017, 09:26 PM   #260
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I got the smaller ones mostly as an experiment to see if the ground loop noise could be fixed, Did not want to plunk too much down before I knew that was the fix. I can use these for other projects now and will probably order a pair of 200VA's.

I have tried this with a 96dB/1w full range dual PA130-8 with an AMT super-tweeter and it does indeed come alive with more efficient speakers. It's really not sufficient for the 10F/RS225 FAST which really needs a 100w/ch amp to shine.
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