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Old 7th March 2013, 12:11 AM   #1821
RNMarsh is offline RNMarsh  United States
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Originally Posted by scott wurcer View Post
Even the Brisbois (Christmas bulb) oscillator works amazingly well (~-120dB 2nd and 3rd) with the AD797. The ADA4898-1 not so well (CM effects). OPA627 oscillated.

I'll try the AD797 next. Ordered a few off eBay (?). Looks like an excellent upgrade part for oscillators. Thx-RNMarsh
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Old 8th March 2013, 08:27 PM   #1822
RNMarsh is offline RNMarsh  United States
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I'm tearing into the ShibaSoku analyzer. Signal traced the monitor output to a card and opamp output. Cant find anything on the output IC -- an NEC C813c. Being feed thru ss switches from TL0x opamps... possibly the switched/selected noise filters from the front panel... they noticably increase noise level when switched in. Need schematics... will start replacing opamps like in HP-339A as it dropped noise floor a lot and these old model opamps could do same if right ones are replaced. Been looking... need schematics.... where can i find them and the NEC opamp?

Thx-RNMarsh

Last edited by RNMarsh; 8th March 2013 at 08:29 PM.
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Old 8th March 2013, 09:21 PM   #1823
1audio is offline 1audio  United States
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If you want to tear into the Shibasoku we should use my older one. Don't risk the new one. The manual has not arrived?

The system digitizes in a discrete digitzer stage (board 4 or 5 from the left I think). The filters should all be downstream from the notched audio. The harmonic processor is pretty complex.

The box way predates widespread use of FFTs so they may not have been looking at noise the same way. The TL072 is not noisy but not real quiet. However the other circuit elements may not allow a better noise floor with a lower noise opamp. This is common in instruments designed to specs.
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Old 8th March 2013, 09:41 PM   #1824
RNMarsh is offline RNMarsh  United States
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I ordered it from a japenese language site.... bet it didnt get thru.
I'm not going to try to lower the inherant noise level of the analyzer.... way too complex. But the distortion monitor/residual output stages where the filters and output opamps are located to get lower noise floor of what they are putting out for a residual signal. Dropping the noise 6dB would be a big help in seeing the harmonics at < .0001% levels. Its real tempting to use FFT on residual output to average out the random noise but try to get best results from analyzer' as is' first. If I dont find schematics, I might then take you up on doing the older unit. Thx-RNMarsh

BTW - does your unit have the space on the mother board for the GPIB card? Slot number 1 next to power supply on right facing front.

Last edited by RNMarsh; 8th March 2013 at 09:53 PM.
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Old 8th March 2013, 10:52 PM   #1825
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Default uPC813

j-fet input low-offset operational amplifier
"The uPC813 is a high speed version of the uPC811. NEC's unique high-speed PNP transistor(ft=300mhz) in the output stage yields a high slew rate of 25v/us under voltage follower conditions without an oscillation problem."

NEC LINEAR IC DB 1988 uPC811 cross ref to LF411 in same databook
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Old 8th March 2013, 11:42 PM   #1826
davada is offline davada  Canada
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Originally Posted by RNMarsh View Post
I'm tearing into the ShibaSoku analyzer. Signal traced the monitor output to a card and opamp output. Cant find anything on the output IC -- an NEC C813c. Being feed thru ss switches from TL0x opamps... possibly the switched/selected noise filters from the front panel... they noticably increase noise level when switched in. Need schematics... will start replacing opamps like in HP-339A as it dropped noise floor a lot and these old model opamps could do same if right ones are replaced. Been looking... need schematics.... where can i find them and the NEC opamp?

Thx-RNMarsh
Hi Rick,

As far as I know NEC hasn't been making op amps in quite a few years. Are they even around anymore? That looks like a house number you put up there.
Can you figure it out from the surrounding circuit? Or is it something special?

Should have read further. Never mind.
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Last edited by davada; 8th March 2013 at 11:46 PM.
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Old 11th March 2013, 09:52 AM   #1827
RNMarsh is offline RNMarsh  United States
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Did I mention the THd of the KH-4402B with 2-opamp upgrades and a couple tuning adjustments is a really nice .0001% at 10Hz and .00013% at 1Khz and at 10Khz is .00015% THD+N. at 1volt into high Z. ?

If you just need a nice, clean oscillator that is flexible in output and frequencies.... it does very well.

[With the oscillator opamp changed out (LT1486 was used). No instabilities or weirdness with the opamp change.]

Thx-RNMarsh

Last edited by RNMarsh; 11th March 2013 at 09:57 AM.
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Old 11th March 2013, 06:10 PM   #1828
RNMarsh is offline RNMarsh  United States
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On the source generator side.... the linear technology app note AN67 (pg62). Could be adapted to switched frequencies easily. Has parts per billion thd. Some one somewhere in the whole DIYAudio site might have touched on it or built it?

Thx-RNMarsh

Last edited by RNMarsh; 11th March 2013 at 06:14 PM. Reason: ppb THD
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Old 11th March 2013, 06:12 PM   #1829
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Quote:
Originally Posted by RNMarsh View Post
On the source generator side.... the linear technology app note AN67 (pg62). Could be adapted to switched frequencies easily. Has parts per billion thd. Some one somewhere in the whole DIYAudio site might have touched on it or built it?

Thx-RNmarsh
Several have, I have heard that it is twitchy. In any case I expect you would have to trim THD at every major frequency change.
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Old 11th March 2013, 06:19 PM   #1830
klewis is offline klewis  United States
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Quote:
Originally Posted by RNMarsh View Post
On the source generator side.... the linear technology app note AN67 (pg62). Could be adapted to switched frequencies easily. Has parts per billion thd. Some one somewhere in the whole DIYAudio site might have touched on it or built it?

Thx-RNMarsh
I've built it using Frex's boards. Once you get the hang of it, and set it carefully, it starts up consistently. I'll go back and find my post of the FFT for it.

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