Sound experiences 6SN7
I have a simple EL34 SE amplifier in Ulralinear connection using one half of 6SN7 (kathode resistor not bypassed) as a preamplifier. Enough gain for a CD player. Supply is 375V for the EL34 and 350V for the 6SN7.
I just wanted to share my sound experiences with different anode resistors and bias settings:
The higher currents (>4mA) sound either clean, good but uninvolving (low anode and medium kathode resistors) or hard and irritating (higher anode resistor, lower kathode resistor)
The lower currents (<4ma) sound either very warm and dark (high anode resistor and low kathode resistor) or just pleasant with a nice spectrum of harmonics (medium anode resistor, high kathode resistor).
I found that using the 6SN7 in my amplifier in typical configuration (47k anode, 1k anode) just doesn't sound involving but rather cold.
When reducing current in order to achieve nice sounding distortion, I found it sounds better and more realistic with nice harmonics when doing this by increasing the kathode resistor rather then increasing the anode resistor. The latter will lead to very warm and tubey, dull 2nd harmonics sound.
Does this make sense ? - What is your experience with the different 6SN7 bias settings ?
Interestingly, I found that the sound tendency is independent of the tubes used. I tested lots of 6sN7 brands.
Sonically I didn't experience mystical "2nd order cancellations" through the output tube. I found the harmonics of the 6SN7 just "go through" the EL34 without cancellations. Can somebody bringt light to this cancellation myth ? - Does it appear in SE amplifiers like mine ?
GŁnther, from Austria.
I run them at 8 - 10ma with plate load resistors of not greater than 27K in resistively loaded amplifier circuits.
I've also had pleasing results with 6SN7 SRPP running on 350V - 400V with 1K cathode resistors for about 6 - 8mA total. (Fashion statement circuit that imo sounds pretty good and measures ok too.) Grid circuit resistance in the output stage typically 100K..
Difficult to discuss what you are hearing without understanding more about operating points, etc. Distortion spectra would be useful to know.
I also prefer tubes like the 6SN7 or 6J5 at currents in the order 8-10mA. IMHO the driver should add as little sound of its own as possible. If run deep in the linear region it should be possible to change the op point over a wide range without big impact on the sound.
I second Kevin on the SRPP ... I used to run mine a bit on the strong side (470R and pretty close to 500V if memory serves me right) but it sounded really great. I used 6CG7 actually.
For my experience, the load resistor is as low as possible, 2-3 times of internal resistance is maybe the good choice. The higher of load, the harder, more tension.
Here is more detail on my amplifier:
Page 5 only !!!
BUT I removed one stage of 6SN7 because I have enough gain with one stage.
You might wonder, why the designer biased with 1,5k on the kathode, which results in low current. But it's just because it sounds prettier than with 1k.
I think the output tube does not contribute much on the "plesant soundig" distortions, because when using 22k/1k on the 6SN7, the 6SN7 should be most linear and one should hear only the output tube's distortion but there is not much to hear - just flat and uninvolving sounding.
Here is a list of anode and kathode settings I tried (measured the currents too but forgot): Of course I've choosen the settings so that the current does not get too low and I've always below -2V grid voltage.
22k/1,5k --> nice sound, low amplification
22k/1k --> hard, flat sound
47k/1k --> good but still flat and uninvolving
68k/1k --> like 22k/1,5k but greater amplification !
75k/680R --> hard sound
75k/1k --> nice sound
82k/680R --> warm, tubey sound
I don't have a spectrum analyzer.
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