Simple phono preamplifier

[frd1996]

The input level depends on the cartridge types. There are cartridges that output 5mV (e.g. audio technica at-120e). There are even few cartridges out there that output 6-7mV (I think Rega). As was stated previously RIAA will boost low frequencies by another 20dB. That in result will give amplification factor x1000 (60dB) for low frequencies.

Additionally, if you are going for a low voltage power rails, pay attention to pick the opamp that can output rail to rail. Some of them cannot do that and would clip before reaching rail voltage level.

[Abminor]

The diagram from the website seems to suggest that r2 isn't part of the Allen right MOD and changing its value doesn't affect this adjustment

Yds, but check further down on the page. If you change the gain with R2 you need a small adjustment to R3.

r3.png (37.1 KiB) Viewed 1971 times

[nige2000]

The input level depends on the cartridge types. There are cartridges that output 5mV (e.g. audio technica at-120e). There are even few cartridges out there that output 6-7mV (I think Rega).

the output for tt in question is 3.6mv

As was stated previously RIAA will boost low frequencies by another 20dB. That in result will give amplification factor x1000 (60dB) for low frequencies.

i missed that ,
if it came to it could i lower the gain a bit, hmmn........ not much useful effect

Additionally, if you are going for a low voltage power rails, pay attention to pick the opamp that can output rail to rail. Some of them cannot do that and would clip before reaching rail voltage level.

ok ill look into it

[Abminor]

looks very simple, was thinking of building one for a friend,

but would like to incorporate volume control, so probably followed by a potentiometer
is that viable?

I was thinking a bit about this. The only problem I can see is that if you put another resistor across the output, you effectively make a high-pass filter so you will roll-off the low frequencies. I modified my Spice simulation to include this and when your pot has a resistance of 10K, the volume at 20Hz is just -0.5dB off the RIAA curve. However, as you decrease the volume by changing the pot resistance to 1K, the volume will be -12dB off, while at 100ohm, it would be -30dB. So for low listening levels you will lose all the bass. If you want a volume control, I think it's safer if you just include a second opamp and implement the volume control around that.

[Fran]

I have a phonoclone here if anyone wants it. Just would need to add transformers and bridges and hookup wire.

[Abminor]

Well after the thrill of 'designing' my own board and enjoying the solder fumes, I find that the exact design is available, on a fully populated board, for about 10 euro! You can even swap resistors and capacitors in and out to match the impedance of your cartridge. I put the links below in case someone else needs a good quality and inexpensive phono amp. (You still need to make the power supply and put it in a fancy box with RCA jacks, which is the expensive part!)
https://www.amazon.co.uk/Electronics-Sa ... ds=md-a310
http://www.electronics-salon.com/index. ... t_id=54698