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Designing a Gomes i/v stage for tda1541a

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#41
Or this hybrid gomes... THD (simulated) with cancellation between tubes (which is difficult to achieve in real life).... 0.0009%

Screen shot 2012-03-01 at 7.45.54 PM.png
 
#42
Hi,

studiostevus said:
This is the alternative mu follower I have doctored... THD of 0.22%... no cancellation between tubes, lower B+.... biased with the TDA1541 offset

I am not convinced.... Thorsten, you have surely tried both mu follower and gomes topologies, and have advocated the gomes typology several times on this forum. Which one to pursue?
Click to expand...

You need to pursue whichever fits your requirements.

The Gomes Stage set up correctly gives comparably low distortion, low noise and low output impedance without recourse to negative feedback.

Other circuits may produce better measured performance in one aspect or another or better subjective performance. It also depends on the Tubes you decide to use and the application.

You know what I have implemented for commercial products and it includes Hybrid Mu-Followers (diyhifisupply Universal Tube Stage), Gainstage/CCS Loaded Cathode follower (AMR CD-777), Gomes Stage (AMR CD-77 and 3D Sonics Shanling Modifications) and Super-Mu-Follower (AMR PH-77) and plain resistive loaded common cathode stages (AMR AM-77/AM-777), heck I have even used solid state and (Gasp, Shock, Horror) generic Op-Amp's for some OEM Designs.

Ciao T
 
#43
So I finally got around to building this. I have decided to do the grounded cathode version, with fixed bias from the TDA1541a. It sounds pretty great, even in a proto setup (final setup will be dual mono psu and salas HV shunt), better than my discrete I/V powered by Salas LV shunts.

Still need to tweak it a little bit, I didn't have the correct resistors to choose the optimal biasing point. What are other ways of further improvements? How to go about distortion cancellation?

Behold the plot (didnt manage to calibrate ARTA properly, so it looks better than it is)...
Screen shot 2012-06-24 at 9.41.06 PM.png
 
#44
Today I tried to improve the operating point of the Gomes stage to a more linear area of the 6072a tube. Strangely, it measures worse.... Where do I go wrong in my thinking?

Old setup:
I/V = 33R, so fixed bias is 6.6mV (based on -2mA idle current from tda1541a)
Rk = Rak = 51R
Screen shot 2012-09-09 at 12.43.49 PM.png

New setup:
I/V = 33R, so fixed bias is 6.6mV
Rk = Rak = 18R
Screen shot 2012-09-09 at 1.48.59 PM.png


Based on the datasheet I expected distortion/harmonics to improve....
http://www.mif.pg.gda.pl/homepages/frank/sheets/093/6/6072.pdf
 
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