Arjen,
When you say Input Riaa shorted, do you mean directly at the preamp's input or shorted at the head shell.
You should in fact shorten at the head shell, this can make a big difference in picking up EMI signals.
This will much better discriminate with the situation where without the short the Cart is driving the wires.
In your schematic the phono preamp's gnd is connected to 5, which should be the case when using the TT's powers supply.
But when using batteries, you can disconnect from 5 and make the whole phono preamp floating.
This galvanic separation could or could not give you an advantage.
But as Marcel suggested, it's also very informative to see what the spectrum does when moving the arm to another position.
Hans
When you say Input Riaa shorted, do you mean directly at the preamp's input or shorted at the head shell.
You should in fact shorten at the head shell, this can make a big difference in picking up EMI signals.
This will much better discriminate with the situation where without the short the Cart is driving the wires.
In your schematic the phono preamp's gnd is connected to 5, which should be the case when using the TT's powers supply.
But when using batteries, you can disconnect from 5 and make the whole phono preamp floating.
This galvanic separation could or could not give you an advantage.
But as Marcel suggested, it's also very informative to see what the spectrum does when moving the arm to another position.
Hans
Should it? The biggest spur with shorted cartridge is -119 dBV at the phono preamplifier output at 1 kHz. That's just over 1 µV at a nominal signal level of 150 mV.
When you measure over small enough resolution bandwidths, you always end up seeing spurious signals if there are any being generated anywhere. It helps to have poor measuring equipment that can't measure over very small bandwidths, then you don't see the spurs and also don't need to worry about them 😉
When you measure over small enough resolution bandwidths, you always end up seeing spurious signals if there are any being generated anywhere. It helps to have poor measuring equipment that can't measure over very small bandwidths, then you don't see the spurs and also don't need to worry about them 😉
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Exactly 1kHz and multiples... or sometimes 8kHz and multiples ==> could be USB packet noise, an artifact of your soundcard+cabling, not the RIAA preamp. As usual, the test is to short the output of the RIAA pre. Since this sort of test is needed all the time I've made myself a few RCA cables with a short in the plug (and leaving the center pin unconnected), and that must go to the source side of things. The error scales with the shield resistance of the cable used.
This kind of error, similar to GND loops, is best eliminated with an USB isolator (and of course a floating soundcard supply, if applicable).
I also have some plugs that are shorted inside, so I can test this.
I couldn't agree more. In 'ye olde days' I was already satisfied if my build didn't pick-up a high power SW radio station. Nowadays we can look > 120 dB into the signal and 'see' things that I probably won't hear. I spent most of this Sunday trying to improve my build with some of the advice you guys gave, where the result was 'more of the same'. In the end, one of my two RIAA channels stopped working. which seems to come from one of the two muting relays.
So, where I could have been listening to music, I am now somewhat frustrated with the lack of results from my efforts. Sometimes 'good enough' should be good enough. That was one of the reasons I went for single supply, single stage RIAA design with a simple NE5532. I will call this a day and focus on putting the new transformer in my turntable (did I mention the TT is originally 120V~ brought back to a 230V~ environment - and wanting to get rid of the auto tranny?), try to fix the 'broken' channel, and start enjoying music.
Thanks to everyone who has contributed, especially to @MarcelvdG for his novel design.