Stereomour with Rothwell phono stage = distortion

[G-horn]

I just bought a Rothwell Rialto from the original owner. I connected it into my stereo system only to find the sound to be terribly distorted and overblown.

My system uses a Denon DL-103R, Rothwell Rialto, Stereomour 2A3 amp, and Hedlund horns with Lowther DX3 16ohm drivers, plus a self-powered sub.
It sounds very good with the CD component playing, but I can’t figure out how to make it play nice with vinyl.

Could it be something wrong with the phono stage?
Or is it something to do with the sensitivity of the components in the vinyl playing chain not being compatible?
DL103R: output voltage is 0.25mV, load impedance 100 ohms
Bottlehead Stereomour amp: power 3.5 Watts, sensitivity full power at about 0.4v, gain is 12.5 at the 8 ohm tap (but I have the output at 16 ohm)

I have tried my other MC cartridge, a DL-103 with the same result.
Tried different interconnects, different line inputs on the amp, switching to the MM setting in the phono stage (sounds better but still distorted)
Tried it with an NAD amp - not as bad but still distorted
Of note, my tube amp (Alps) volume control with these very efficient speakers can only be rotated just a fraction, never past half way on the dial.

Can you please offer some assistance to help me get the records singing again?

[Doc B.]

You mention that your CD player works fine with the Stereomour and that the phono preamp does not sound good with other amps either. I looked at the Rialto specs and there is nothing there that looks like a problem with the Stereomour, though it looks a little light on gain for a .25mV nominal MC cart like the DL-103R ( I found a nominal spec of .4mV for .5V output on the MC setting). Probably worth contacting Rothwell about this since the issue seems to be in the phono preamp/cartridge combination.

[G-horn]

Thanks Doc for the quick reply. I have sent an email to the Rothwell company to see what they think.

Regarding the volume control on the amp, do I need to change it out to an attenuator with a different resistance?

Best of the season to you!

[Paul Birkeland]

The Rialto has 62dB of gain on MC, so your 0.25mV nominal cart becomes about 300mV of signal at the output RCA jacks, which is what I tend to get from the headphone jack of a cell phone or tablet.  The Rothwell has a fixed input impedance for the MC input of 100 ohms, which should be high enough for the DL-103R, but just barely.  The Rothwell has an output impedance of 75 ohms, so driving long cables and pretty much any volume control will not be an issue.