Review and Measurements of u-turn Pluto and ART DJPRE II Phono Preamps

[ModDIY]

Hello

I received a djpre and connected with an Ortofon om10 cartridge. The problem is that the "clip" LED lights up every 9-10 hours. I leave the gain volume at 0 or 1 hrs, the LED stays on constantly when a vinyl is playing, however I don't hear any distortion.

Anyway I ordered a new phono preamp, and will compare it to the djpre, then I'm returning the djpre. In addition to the problem with the clip LED, the blue LED is too strong (no desire to change the resistance), then no on/off button...so it will start again.

 

[BMRR]

It is normal for the clipping LED to light up green when music is playing. It will light up red if there is clipping. Green = normal, red = clipping.

 

[ModDIY]

It is normal for the clipping LED to light up green when music is playing. It will light up red if there is clipping. Green = normal, red = clipping.

So it's normal, I hadn't read the instruction pamphlet.

Otherwise the sound is very excellent, I'm impressed. But the blue LED and no on/off button, and also I took advantage of Cyber Monday to get a new phono preamp at 33% off.

 

[cgallery]

I have a question about the Pluto and other single op amp phono stages.

It clips at 31mv, is that limited by the power supply?

How much headroom would the Pluto achieve if the circuit were to run on, for example, +/- 12v (for example)?

 

[SIY]

It clips at 31mv, is that limited by the power supply?

Remember that phono circuits clip at different voltages at different frequencies. So, for example, at 20Hz, the gain is ten times bigger than at 1kHz, so that will reduce the clipping level. And that's OK because cartridges are velocity devices so they'll have a lot lower output at LF. The other way around when we look at (say ) 20kHz...

That said, overload can be power supply limited or opamp limited. Much of that depends on topology.

 

[cgallery]

Are any generalizations possible? It seems like a single op amp with RIAA in the feedback loop. If we assume, for example, that the Pluto runs on +/- 5v, that going up to a +/- 12v may yield a 240% improvement in headroom at 1k (so 74mv instead of 31mv)?

 

[egellings]

Are any generalizations possible? It seems like a single op amp with RIAA in the feedback loop. If we assume, for example, that the Pluto runs on +/- 5v, that going up to a +/- 12v may yield a 240% improvement in headroom at 1k (so 74mv instead of 31mv)?

It's important to check if the op amp used in the preamp can handle the higher rail voltages.

 

[cgallery]

It's important to check if the op amp used in the preamp can handle the higher rail voltages.

Right, assuming it can, is the relationship between clipping at 1k, and supply voltage, approx. 1:1?

 

[SIY]

Right, assuming it can, is the relationship between clipping at 1k, and supply voltage, approx. 1:1?

Roughly, for that topology.