I'm looking for some advice regarding the above, is there a sensibly priced signal generator to output below 1mV
Thank you
Thank you
Yes, in a lab the signal levels are on the order of volts, and you feed that into an attenuator.
But for home use, just two metal film 1% resistors will be fine, like a series 10k, and shunt 100R, for 40dB loss,
or series 10k, and shunt 10R, for 60dB loss.
If you build an inverse RIAA, that will provide the needed attenuation as part of its operation.
But for home use, just two metal film 1% resistors will be fine, like a series 10k, and shunt 100R, for 40dB loss,
or series 10k, and shunt 10R, for 60dB loss.
If you build an inverse RIAA, that will provide the needed attenuation as part of its operation.
Build a reverse riaa and feed your phone into it. Adding a 1/ 10 tap on the output will produce MC cart signal levels .
Sorry I meant below 1V , I have built inverse RIAA as below
but feeding from Behringer UCA 202 USB with 0dBu sweep for some reason doesn’t really work, even spot frequency measurements are full of some artifacts,
I’m looking at sensibly priced function generators and there is a lot of cheap stuff on EBay but not sure if any good. Something up to £100 would be great
but feeding from Behringer UCA 202 USB with 0dBu sweep for some reason doesn’t really work, even spot frequency measurements are full of some artifacts,
I’m looking at sensibly priced function generators and there is a lot of cheap stuff on EBay but not sure if any good. Something up to £100 would be great
Here you will find more information and have the opportunity to purchase pcb.
https://www.hifisonix.com/projects/inverse-riaa-network/
https://www.hifisonix.com/projects/inverse-riaa-network/
0 dBu is 0.77 V Rms, you need to attenuate the signal by ~68dB (to 300uV) elsewise you are overloading the MC amp.
that’s what I’ve been doing but even sine wave generated from UCA and measured directly from output is all over the place, I’ve got better results from headphone output on my laptop.
Any experience with any Chinese generators, EBay and Amazon are full of these.
Any experience with any Chinese generators, EBay and Amazon are full of these.
Testing with headphone output from laptop works but there is some 1kHz fed through , anyone using modern function test gen at sensible price ?
As above, you need a decent inverse RIAA network as it takes care of the signal level problem. Both MM and MC levels will be obtainable at reasonable settings of the generator. For reference, my Siglent generator goes down to 1 mV, but you need way better attenuation for a MC cartridge, plus the inverse RIAA lets you see the response. I usually just do a quick square wave test to be sure things are visually OK.
You can't sweep, but you can measure at a number of discrete frequencies. One measurement per octave is normally good enough to assess RIAA correction accuracy, but you can do more if you like. Of course it's more work than with a reverse RIAA circuit, but as I only do measurements like this once a decade, I don't mind.
The last time I did a measurement like that, on a moving-magnet preamplifier, I used a computer sound card and a 10 kohm-100 ohm voltage divider made of 0.01 % accurate resistors to generate the test signal (the resistors were actually old 5 % tolerance Philips metal film resistors that turned out to be 0.01 % accurate when I measured them with a four-wire multimeter at work). I used a 1:1 probe and a Hameg HM1505 analogue oscilloscope with cursors to measure the voltages at the voltage divider input and amplifier output, using the same oscilloscope channel for both. After measuring, I used a spreadsheet to correct for the RIAA correction and the voltage division between the voltage divider output impedance and the phono preamplifier input impedance.
It works quite well (or at least very reproducibly) for midrange frequencies, where the attenuation of the attenuator is about equal to the gain of the amplifier, so you can use the same oscilloscope vertical range for the input and output signals. For the extreme frequencies, you need different ranges, so the results become dependent on the accuracy of the gain steps of the oscilloscope. You could avoid that by using a few different voltage dividers, all made of very accurate resistors.
Thanks for all the input, I have ordered that Owon function generator now .
I repeated measurements with headphone output from my laptop but there is a lot of 1kHz noise and it skewed measurements a bit , bottom and top looks ok . It seems USB ports have lots of low frequency noise even when runnning laptop on the battery there is plenty of 50Hz component when I try to run simple sine wave at 20kHz , hopefully I’ll get some better results with a better signal generator
I repeated measurements with headphone output from my laptop but there is a lot of 1kHz noise and it skewed measurements a bit , bottom and top looks ok . It seems USB ports have lots of low frequency noise even when runnning laptop on the battery there is plenty of 50Hz component when I try to run simple sine wave at 20kHz , hopefully I’ll get some better results with a better signal generator
