12at7 question

[catalin gramada]

Hi, does it any truth 12at7 sound better drived by low impedance source,please? I read somewhere due to its grid conduction and somehow bigger grid resistance it ask for low grid leak resistor for stability operation as 1m ussual (stated in datasheet). Are these the reasons for 12at7 demands for low impedance source, or maybe the other reasons are? For instance if I ensure perfect stable operation why should be the reason to drive it from low impedance source ?

[Helmholtz]

Hi, does it any truth 12at7 sound better drived by low impedance source,please?

What is the source and context of that statement?

A tube has characteristics but no sound of its own (except if you drop it ). The sound influence (meaning frequency response and non-linear behaviour) depends on the whole circuit including the tube. Without specifying the circuit no evaluation is possible. And "better sound" is a rather subjective assessment and depends on the function of the circuit.

The 12AT7 was primarily designed for lower impedance HF applications, while the 12AX7 being a more linear, higher gain type was optimized for audio purposes.

[J M Fahey]

Agree.
Sounds like another of those implausible fake Science theories appearing all the time in audiophool sites.

[Merlinb]

Hi, does it any truth 12at7 sound better drived by low impedance source,please? I read somewhere due to its grid conduction and somehow bigger grid resistance it ask for low grid leak resistor for stability operation as 1m ussual (stated in datasheet). Are these the reasons for 12at7 demands for low impedance source, or maybe the other reasons are? For instance if I ensure perfect stable operation why should be the reason to drive it from low impedance source ?

Yes it is true that the 12AT7 draws more grid current than the 12AX7 and therefore will clip harder when driven from a similar source impedance, and hence may suffer worse from blocking distortion. Reducing the source impedance and grid leak will help with this, but nothing guarantees a good distortion sound until you try it.

[catalin gramada]

Yes it is true that the 12AT7 draws more grid current than the 12AX7 and therefore will clip harder when driven from a similar source impedance, and hence may suffer worse from blocking distortion. Reducing the source impedance and grid leak will help with this, but nothing guarantees a good distortion sound until you try it.

Thanks Merlinb. I had not the oportunity to drive it into blast yet as I live into a flat, but definitely drived 12at7 pi from c.f. changed the sound substantially. My project becomes way more touch sensitive with a lot of sustain, not quite compression one, and easy prone to get in feedback reaction on entire range. It changed completely dynamics in something else. It was very easy to bias directly from previous c.f. so the source impedance was very low indeed, but the signal applied was few mV order so nothing to put 12at7 into grid phenomena. From comparison drived from regular 12ax7 plate sound very anemic.