This is sort of a continuation of previous thread https://www.diyaudio.com/community/...er-light-phono-amp-inside-the-tonearm.268400/
that one diverged rather hence new thread.
The new version features a lower noise front end, but is a bit more cramped as a result.
There is a NE5534A RIAA stage at the left, one on each side for L+R.
The board is 8mm wide and 95mm long.
Then two 2nd-order Sallen Key stages implementing a 4th-order Butterworth high-pass "rumble" filter, detail on one stage (two channels):
The opamp here is NE5532A dual.
The response to 5mV rms 1kHz input, both channels:
No special precautions against mains hum, other than short leads to the QA403 analyzer, and the high freq hash is probably from laptop or LED lighting or both. Power was +/-9V from batteries, the QA403 is galvanically isolated which no doubt helps.
And the response, weighted with inverse RIAA:
The rumble filter slope is clear, about 14dB down at 10Hz and ~36dB down at 5Hz.
Schematic:
Its a little hard to read, but the RIAA feedback network is 3.3nF || 22k and 12nF || 270k, with 330R to ground. Caps are PPS and resistors thin-film, 0805 and 1206 size
that one diverged rather hence new thread.
The new version features a lower noise front end, but is a bit more cramped as a result.
There is a NE5534A RIAA stage at the left, one on each side for L+R.
The board is 8mm wide and 95mm long.
Then two 2nd-order Sallen Key stages implementing a 4th-order Butterworth high-pass "rumble" filter, detail on one stage (two channels):
The opamp here is NE5532A dual.
The response to 5mV rms 1kHz input, both channels:
No special precautions against mains hum, other than short leads to the QA403 analyzer, and the high freq hash is probably from laptop or LED lighting or both. Power was +/-9V from batteries, the QA403 is galvanically isolated which no doubt helps.
And the response, weighted with inverse RIAA:
The rumble filter slope is clear, about 14dB down at 10Hz and ~36dB down at 5Hz.
Schematic:
Its a little hard to read, but the RIAA feedback network is 3.3nF || 22k and 12nF || 270k, with 330R to ground. Caps are PPS and resistors thin-film, 0805 and 1206 size
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Does this go inside the tonearm or at the junction of tone arm wiring and external cable to amp?
I like the tiny size great job.
I like the tiny size great job.
The problem is I now have to figure out how to make a suitable tonearm, which is a whole new problem! One issue is the number of wires needed to feed through the tonearm bearing - 6 instead of 4 is going to increase torsion forces from the wires, and with an I2S bus instead that would become several twisted pairs which would be much stiffer.
