Tag: 6C4C PP

Push-Pull fascination (Part 4)

Continuing with this series of blog posts around the 6C4C push-pull design. As suggested my 45 in my previous blog entry, here is the 4P1L-4P1L version:

6C4C PP version 7The first 4P1L driver stage remains unchanged, as does the output stage. The addition of the 4P1L differential pair with CCS tail and LL1660/pp IT is the main change of this design. The LL1660 is configured in ALT M or 2.25+2.25:2+2.  I guess that a different IT could be used instead to get a lower output impedance on the diff pair and improve the performance in A2. The amp has more gain that I need in this configuration as it delivers its maximum power (circa 8W) when input is 1.2V peak.

So how does it performs?

6C4C PP version 7 THD Very low distortion indeed. About 0.06% up to 8W. Mainly odd harmonics dominating the sound of this amp.

Interesting findings…

 

 

Push-Pull fascination (Part 3)

In the quest of refining the 6C4C push-pull design I started not long ago, it was suggested by 45 to try a different driver. The famous E180F russian equivalent with gold grid: 6J9P-E.    So I went back at my design and replaced the 4P1L driver with the 6J9P-E. Instead of filament bias, the bias was provided by a pair of red LEDs. The low dynamic impedance of these avoid the use of a  bypass capacitor. Setting the operating point with the existing supply is a bit tricky but I found that Va=210V / Ia=14mA provides good swing and minimum distortion. Biasing the valve at around -3.7V keeps the valve away from grid current which will increase the distortion unnecessarily. So here is the circuit:

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Push-Pull fascination (Part 2)

Thanks to the great feedback from 45, we found out that I made a mistake in modelling the LL1682 OT in my previous post. In a nutshell, I was getting half of the power, doh!

I should have started from scratch, looking at the push-pull curves and estimating at least the A1 power from a pair of 6C4C in push-pull. So following the B.J. Thomson method plotted the curves in push-pull:

6C4C PP curves Zaa=8K8

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Push-Pull fascination

I love the sweetness of my 45 SE amplifier, but you know what? A great push-pull (PP) amp has a fantastic presence, bass and dynamic response. Whenever I listen to a good PP amp, I get to the conclusion that I need to have different amps ready to be played depending to the music I want to listen to! My last two years have been devoted to what Morgan Jones calls in his book “single-ended madness”.  And yes, my 4-65a SE in class A2 is slowly coming to life and when ready so then I will be properly mad.

6C4C amps I listened so far made a great impression both in SE and in PP. Owning all components required, I embarked on refining a full DHT push-pull design and again, cap-less (excluding the power supplies of course).

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