good soundcards are ultimately limited by adc distortion and interference artifacts, the noise floor can be pushed very low with long records/averaging
to some degree interference from line power, sw supplies, ect can be "dodged" by choosing test frequency
but even the better monolithic adc chips have harmonic distortion in the 105 +/- dB range, so a large amplitude fundamental limits your harmonic measurement capability, also the soundcard input signal conditioning circuitry could contribute distortion at these very low levels with large inputs
presumably the adc/soundcard input distortion components are dependent on input amplitude to some power, so even a 20 dB null should be adequate to reduce the adc/soundcard harmonic distortion to negligible levels (or null + gain such that input < -20 dB at the adc )
of course the notch/highpass filter itself has to be very good, polystyrene caps are a really good idea, over size wattage and low tcr resistors may be helpful for the attenuator at power amp output voltages
to some degree interference from line power, sw supplies, ect can be "dodged" by choosing test frequency
but even the better monolithic adc chips have harmonic distortion in the 105 +/- dB range, so a large amplitude fundamental limits your harmonic measurement capability, also the soundcard input signal conditioning circuitry could contribute distortion at these very low levels with large inputs
presumably the adc/soundcard input distortion components are dependent on input amplitude to some power, so even a 20 dB null should be adequate to reduce the adc/soundcard harmonic distortion to negligible levels (or null + gain such that input < -20 dB at the adc )
of course the notch/highpass filter itself has to be very good, polystyrene caps are a really good idea, over size wattage and low tcr resistors may be helpful for the attenuator at power amp output voltages
Jackinnj and Jcx , so I did miss out on the issue of card input performance. Sorry Jackinnj , I did not figure out you meant this.
It's obvious that the large fundamental will produce its own suprious signals at the input of the sound card.
So a 'clean' fundamental signal alone is not enough !
Hmm.................back to more work.
It's obvious that the large fundamental will produce its own suprious signals at the input of the sound card.
So a 'clean' fundamental signal alone is not enough !
Hmm.................back to more work.
Firecrac -- if you are refering to my posts , it's about a 'filter' connected to the output of a regular pc sound card . The signals are generated using software on the PC. There is no separate hardware implementation of the oscillator.
The output can be reduced from the software but as it is generated using a DAC , you wouldn't want to do that . Just use a 10K pot at the output of the filter circuit.
The output can be reduced from the software but as it is generated using a DAC , you wouldn't want to do that . Just use a 10K pot at the output of the filter circuit.
The oscillator should have the greatest amplitude possible consistent with the output capabilities of the opamp or devices you use. Then use a 600 ohm attenuator to derive the voltage you need. The oscillator i described uses current-feedback opamps and it doesnt' run out of gain -- it is basically an current feedback amplifier gone amuck! I can get about 7 volts out of mine -- i have a high quality HP audio attenuator to knock down the output. For comparison the Boonton 1120 will put out 14V, the HP339 3V, the Heathkit IG-18 about 10V
Want a great oscillator idea ? -- the Krohn-Hite oscillators can be updated -- the capacitors and resistor networks are first rate, they have excellent regulated power supplies and often go for $10 to $50.
Want a great oscillator idea ? -- the Krohn-Hite oscillators can be updated -- the capacitors and resistor networks are first rate, they have excellent regulated power supplies and often go for $10 to $50.
the easiest KH generator to find is the 4300 -- there is a lot more elbow room inside the older generators, however.
An externally hosted image should be here but it was not working when we last tested it.
I wouldn't necessarily replace any of the caps or resistors -- on some of these units they use high quality GE or TRW polycarbonates. All of the switching is irreplaceable.
Take a look at Jim Williams "Bridge Circuit -- Marrying Gain and Balance" application note 43 on Linear Tech's website -- you theoreticallly can get a Wien Bridge Oscillator down to the levels of Hofer's SG-505.
(The Tektronix SG505 is a a state-variable filter so 2 sets of switched capacitors are necessary).
Take a look at Jim Williams "Bridge Circuit -- Marrying Gain and Balance" application note 43 on Linear Tech's website -- you theoreticallly can get a Wien Bridge Oscillator down to the levels of Hofer's SG-505.
(The Tektronix SG505 is a a state-variable filter so 2 sets of switched capacitors are necessary).
Fascinating collection of KH oscillators. I'm pretty familiar with them. I'm not sure how you would get the distortion lower in them. The AGC detector generates some of the harmonics and the amps themselves also generate some. You might try to lower the output and see if it helps, but thats not easy.
They have very good stability and the frequency and level setting is usually very accurate and doesn't need monitoring. The frequency switching is very fast and the low frequency limit is very low. If the as delivered performance is adequate, which it is for almost any project there is no need to alter them.
They have very good stability and the frequency and level setting is usually very accurate and doesn't need monitoring. The frequency switching is very fast and the low frequency limit is very low. If the as delivered performance is adequate, which it is for almost any project there is no need to alter them.
I just bought a Boonton 1100 from ebay ($150) ...powers up, seems ok to the seller, but other than that, "as is". Receive it in about 2 weeks.
I know where to purchase an original manual, but does anyone have a link to a PDF copy?
Any thing particular you can tell me about this model ?
20Hz -50KHz
-----------------------------
Also available to me for cheap....
GR 1306a
HP 241a
=RR=
I know where to purchase an original manual, but does anyone have a link to a PDF copy?
Any thing particular you can tell me about this model ?
20Hz -50KHz
-----------------------------
Also available to me for cheap....
GR 1306a
HP 241a
=RR=
Thanks Demian.
I'll open it up and post a pic when I get it this 1100.
(btw, I added a few lines to my above post.)
Actually I did buy ($15) the HP 241a ( pushbutton selected frequency), but supposed to have average dist., around 1%, but with stable freq.
Unfortunately it does not produce a signal, but the power indicator light works great !!
I'm waiting for a schem.
Strange, AC 120v power in - does not use a transformer, just some resistors and caps....I'll have to think about that one.
http://www.tucker.com/images/images_spec/00002607.pdf
=FB=
I'll open it up and post a pic when I get it this 1100.
(btw, I added a few lines to my above post.)
Actually I did buy ($15) the HP 241a ( pushbutton selected frequency), but supposed to have average dist., around 1%, but with stable freq.
Unfortunately it does not produce a signal, but the power indicator light works great !!
I'm waiting for a schem.
Strange, AC 120v power in - does not use a transformer, just some resistors and caps....I'll have to think about that one.
http://www.tucker.com/images/images_spec/00002607.pdf
=FB=
I had a 241 years ago. it didn't work and I didn't have the time to fix it.
It better have a transformer. At the time it was made there weren't good alternatives. It only draws 1W (Energy Star?). It may well have germanium transistors. It might be a candidate for a replacement PCB using the latest opamps.
It better have a transformer. At the time it was made there weren't good alternatives. It only draws 1W (Energy Star?). It may well have germanium transistors. It might be a candidate for a replacement PCB using the latest opamps.
FYI
App note, filter for second harmonic:
http://www.intersil.com/data/an/an9815.pdf
I don't know if it's useful or do-able for the audio range...my math is........
=RR=
App note, filter for second harmonic:
http://www.intersil.com/data/an/an9815.pdf
I don't know if it's useful or do-able for the audio range...my math is........
=RR=