Low-distortion Audio-range Oscillator - Page 28 - diyAudio
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Old 26th August 2012, 01:14 AM   #271
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Originally Posted by richiem View Post
OOOPs sorry, missed a post.... Nice work -- did you add in the harmonic attenuation of the passive notch? That would raise the 2nd by 9.5dB and the 3rd by about 5.5dB, with lesser amounts for the rest.
Absolutely, I thought that was stated fairly clearly. It's possible my math is wrong, but did take the notch into account.
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Old 26th August 2012, 10:43 AM   #272
coluke is offline coluke  Italy
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Originally Posted by zigzagflux View Post
Absolutely, I thought that was stated fairly clearly. It's possible my math is wrong, but did take the notch into account.
So it seems, and the performances of such a simple circuit are quite impressive indeed, although there is a lot of HF noise - most of it is certainly accounted for by your spaghetti setup , nevertheless quite a few of HF harmonics (up to 20 kHz or more) seem related to the fundamental: is it true?

Generally speaking, I'm not a fan of the Wien Bridge, but at a first glance this novel level controlling scheme would apply fairly well to a Bridged-T 2-opamps topology - I think I'll give it a try.

L.
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Old 28th August 2012, 12:29 PM   #273
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Originally Posted by 1audio View Post
I calculated for 25 mA. That is what the circuit draws, including the shunts. The 317 will work down to close to 2V, maybe less. You have 1.25V for the adj that is the real limiter on minimum voltage. I know the LM 317 is stable used this way. There is 5V drop across the two 100 Ohm resistors so you can shunt or replace them with something like 10 Ohm resistors and have plenty of compliance with 4 9V batteries.

25 mA is too large for a current diode and the heat output would be a problem. Don't put two in series or one will be useless since the current is defined by the smallest current limiter. any others will collapse to a minimum voltage. You could use them in parallel. That gets pricey pretty quickly.
I'd like Victor's opinion on this modification, since it's his design. Victor? Maybe I send him a PM.

I got my oscillator yesterday. It looks good. Thanks Victor!
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Old 28th August 2012, 02:04 PM   #274
DDB is offline DDB  United States
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Update on the Victor oscillator- Running overnight the distortion seems to have dropped. The second harmonic is now almost -140 dB. the higher are still lower in level at around -150 dB. I'll try to check the calibration at these low levels to make sure there is no nonlinearity affecting the readings. The Shibasoku AG16 is a little better but not much better. Essentially these are "perfect" oscillators for virtually any application.
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Have you measured performance of the 11 or 12khz oscillators yet?
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Old 29th August 2012, 04:42 AM   #275
1audio is offline 1audio  United States
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I have not measured the 11KHz or 12KHz oscillators yet. Hope to get it built very soon and get some detailed info.
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Old 3rd September 2012, 04:03 AM   #276
RNMarsh is offline RNMarsh  United States
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Originally Posted by zigzagflux View Post
For kicks, I measured the output of my DCX2496 (1.65V rms) , which is modded by using a Jensen JT-11-DMPC directly connected to the D/A pins. Significantly higher distortion than Victor’s (though still not too bad):
2 = -99 dB
3 = -107
4 = -123
5 = -109
6 = 0
7 = -121
THD = 0.0013%
Not too bad numbers... I have one of the DCX2496 - planning to use it this winter when I am stuck indoors. Right now, I need to measure better than most instruments can do but dont want to spend a small fortune on a new AP. Think I'll go the route Demian has gone.... need to see at least a clean -130. What test system did you use to measure the harmonics?

Last edited by RNMarsh; 3rd September 2012 at 04:05 AM.
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Old 3rd September 2012, 04:57 AM   #277
1audio is offline 1audio  United States
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Richard I could measure whatever you need. My floor is in the -140 dB range. Obviously measuring takes but a few minutes. Or you could borrow the Shibasoku's while I'm on vacation. . .
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Old 3rd September 2012, 07:32 AM   #278
RNMarsh is offline RNMarsh  United States
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OK. Thanks.... when do you go on vacation... I have this month free but leave for Asia in oct for a month. email me. Thx -RNM
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Old 3rd September 2012, 06:56 PM   #279
richiem is offline richiem  United States
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@RNMarsh -- I don't want to flog this overmuch, but if your measurement needs involve harmonic amplitudes, and you can live with an upper fundamental of 15 to 20kHz, then using a simple active Twin-T filter (to reduce the fundamental while leaving the harmonics unattenuated) between the source and the sound card will allow measurements down toward -140dBu.

I use the T-T with an EMU 0204 external USB sound module and it is very good with respect to noise, but due to using delta-sigma conversion, has a rising noise floor above 30kHz, which compromises the results in that area of the spectrum. Several contributors here have used this method with various sound cards, and it works very well for most of the audio range, especially if the distortion components of interest are low-order.
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Old 3rd September 2012, 08:39 PM   #280
RNMarsh is offline RNMarsh  United States
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Quote:
Originally Posted by richiem View Post
@RNMarsh -- I don't want to flog this overmuch, but if your measurement needs involve harmonic amplitudes, and you can live with an upper fundamental of 15 to 20kHz, then using a simple active Twin-T filter (to reduce the fundamental while leaving the harmonics unattenuated) between the source and the sound card will allow measurements down toward -140dBu.

I use the T-T with an EMU 0204 external USB sound module and it is very good with respect to noise, but due to using delta-sigma conversion, has a rising noise floor above 30kHz, which compromises the results in that area of the spectrum. Several contributors here have used this method with various sound cards, and it works very well for most of the audio range, especially if the distortion components of interest are low-order.
Thank you. I have a AP system One with DSP and it isnt good enough any more. I do need an alternative to the newest AP. I want to have an all portable system... no sound cards in a cpu box.

Is the EMU-0204 thier best or is there another model or brand that would be even better -- what is the best? And where can i find the schematic of the T-T you are using? I want to make this as P-n-Play as possible.

Thank you for the info. -Richard
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