power supply
I am getting, -35v and +36v(unloaded) from the output of my power supply, is this to close to the margin for the regulators(L7824CV/L7924CV).
The power supply consists of transformer 2x 27v27 at secondary's(2x24v24 was specified!), Pos and neg = 1x 10,000uf, 4x .47r, 1x 10,000uf on each rail.
I am getting, -35v and +36v(unloaded) from the output of my power supply, is this to close to the margin for the regulators(L7824CV/L7924CV).
The power supply consists of transformer 2x 27v27 at secondary's(2x24v24 was specified!), Pos and neg = 1x 10,000uf, 4x .47r, 1x 10,000uf on each rail.
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I'm thinking you'll be fine with +/- 36v without a load. The datasheets indicate max input voltage of 40v for 24v regulators, so you are already below this threshold. Once you put a load on it, the voltage is likely to sag a bit, depending on how robust of a transformer you've used. If you need to bleed off a few volts, Jack and I have already provided some guidance above.
Change R14 to 300ohm for max gain, add a resistor of choice that matches the cartridge to the input.
My Pearl 2 build guide says it was designed for MC cartridges.
"Pearl II addresses the major request received over the years - more gain for moving coil cartridges.
Phono stage design is difficult to do well. Everything matters. Any low level phenomenon occurring in the parts of a phono stage shows up greatly amplified at the loudspeaker. This phono stage has about 55 dB gain at 1 Khz, and another 20 dB at 20 Hz, and when you add 10 dB or so on a line stage preamp and another 30 dB with a power amp you end up with 115 dB of voltage gain, which is getting up toward a million to 1."
Of course there are high and low output MC cartridges.
"The overall gain of the circuit as shown is 55 dB @ 1K Hz. Decreasing R14 from 1K to 300 Ohms gives 10 dB more gain when desired for lower output cartridges. R15 which normally would be shorted to 0 ohms can be replaced by a resistor to provide more gain as an alternative to reducing the value of R14. C15 has been placed on the board to allow for additional adjustment of equalization. In both cases these values are up to you."
A question: Does changing the value of R14 have an impact on the efficacy of the additional cap that was recommended from R14 to ground?
"Pearl II addresses the major request received over the years - more gain for moving coil cartridges.
Phono stage design is difficult to do well. Everything matters. Any low level phenomenon occurring in the parts of a phono stage shows up greatly amplified at the loudspeaker. This phono stage has about 55 dB gain at 1 Khz, and another 20 dB at 20 Hz, and when you add 10 dB or so on a line stage preamp and another 30 dB with a power amp you end up with 115 dB of voltage gain, which is getting up toward a million to 1."
Of course there are high and low output MC cartridges.
"The overall gain of the circuit as shown is 55 dB @ 1K Hz. Decreasing R14 from 1K to 300 Ohms gives 10 dB more gain when desired for lower output cartridges. R15 which normally would be shorted to 0 ohms can be replaced by a resistor to provide more gain as an alternative to reducing the value of R14. C15 has been placed on the board to allow for additional adjustment of equalization. In both cases these values are up to you."
A question: Does changing the value of R14 have an impact on the efficacy of the additional cap that was recommended from R14 to ground?
For the Denon 103 I would want at least 60dB gain. That corresponds to a value of around 560 R for R14. You could try anywhere between that and 300 R for even more gain (but it will get noisier). For the Hana ML 58dB or more will do. R14 around 750 Ohm in that case. For my Benz Wood SL (also 0,4mV output) I'm using 777 R for R14.
Loading: put a resistor in the R20 spot. Judge by listening. I would try 470R-1k for the Denon and 100R-470R for the Hana as a starting point. Guideline is a minimum of 10x the internal impedance of the cartridge (40R for the Denon, 8R for the Hana).
Loading: put a resistor in the R20 spot. Judge by listening. I would try 470R-1k for the Denon and 100R-470R for the Hana as a starting point. Guideline is a minimum of 10x the internal impedance of the cartridge (40R for the Denon, 8R for the Hana).
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