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Old 14th August 2012, 06:18 PM   #461
RNMarsh is offline RNMarsh  United States
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Location: 2457 Cascade Trail; Cool, CA. 95614
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I measured the units -- 2ea of the 1Khz and found that only the even harmonics are very low. the odd harmonics are not so great -- -88-90db for 3rd and 5th and further down the road is still high. Not better than the AP. rats!

I'll contact the source of these and see what he says.

-RNM
I recieved test data on the oscillator and it does seem to meet the advetized spec. That's great news. Now I just need to be able to measure it here... and then I can get the true harmonic level of the headphone amp.
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Old 24th August 2012, 03:40 AM   #462
sonidos is offline sonidos  United States
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Well, now that everyone has gone to sleep!

The n jfets sourced from Tayda2009 turned out to work just fine.

My ebay source had some p fets (mark on body shows CAL???) and those turned out to be pretty good. I have several matches now between .8 and .9 volts as Mr. Marsh indicated.

I've tweaked the board layout enough, so I will print up some sheets this weekend and get ready to do some etching. Photos to come.

Oh, and the transistors I bought from Jan are matching quite well... Vbe very close to one another...not much difference..about 1/100 of a volt...nice.

I'll have more info coming up...there are sources out there that have good pricing on the transistors but I'll post that when I get my order in!
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Old 24th August 2012, 11:17 PM   #463
RNMarsh is offline RNMarsh  United States
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I'm still with ya here ;-)
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Old 30th August 2012, 10:26 PM   #464
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I'm still with ya here ;-)
And here I thought you had been seduced away by the sweet, sweet talk of discrete op amps!
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Old 30th August 2012, 10:31 PM   #465
sonidos is offline sonidos  United States
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Default Stock tip!

Well, not a stock tip, exactly, but a tip, nonetheless!

Now that I have my transistors on order, if some of you don't know already, here in the States you can get some parts much cheaper at Avnet Express. They have the BJTs in stock for a very, very good price. The SMT jfets are also in stock and I ordered a very small amount (25 each) to see how they measure. The small signal BJTs can be had for just over a penny in large quantities. You can get hundreds of 'em and not break the bank!
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Old 3rd September 2012, 06:29 PM   #466
RNMarsh is offline RNMarsh  United States
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Some might be wondering about the dc offset and drift and how stable it is.....
Well, after a year of service, I measured the dc offset on the output and it is exactly where it was when built a year ago. It is still .00x or just a few mV + or -
:-)
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Old 13th September 2012, 01:15 AM   #467
RNMarsh is offline RNMarsh  United States
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Default Some back-up numbers -

I got to use Demian Martin's ShibaSoku gear as another crosscheck --
THD ref 1 volt at 1KHz was .0005% 2nd and 3rd --- other harmonics are approx -20db or more down from the 2nd and 3rd (viewed via FFT).

S/N ( 1v and input shorted but 30KHz cutoff) = -106dB. It can reach -110db if a quieter power supply was used and with a reduction in fb and gain resistor values (but same ratio-gain).

Thx Demian -Richard

Last edited by RNMarsh; 13th September 2012 at 01:19 AM.
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Old 13th September 2012, 01:47 AM   #468
sonidos is offline sonidos  United States
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Very nice feedback!

I couldn't resist buying some more pfets. As it turns out, this fellow has had them for some time from a video game company that closed in '96. When I got the package a couple of days ago, I was shocked to find they had gold leads and a little M logo. The good stuff!!

I'll have some pics soon on my actual progress....finally.
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Old 18th September 2012, 05:58 PM   #469
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small BJTs all ranging about 500 to 600 for hfe. Also got a board ready to etch now. Slow but steady progress.
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Old 30th September 2012, 04:21 AM   #470
RNMarsh is offline RNMarsh  United States
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Speaking of progress.... how are you doing?
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