Tube Amp soundstage

@dtapo
You may have already answered your own question, comparing first hand. Trust your ears. Maybe there is some magic in the distortion and 2nd and 3rd order harmonics.   

Gotta ask oneself why many of the high-end class A solid state designers and amp builders continue to try and build circuits and test various output transistor types to try and make their amps sound like valve tube amps. Getting closer, not fully 3D or as layered yet.   

Ralph’s post is perfect to demonstrate how the design and implementation are applied to get the desired outcome from an amp. Designers of both tubes and transistors make choices and tradeoffs to achieve their goals. Tubes have a relatively high output impedance and are not easily capable of driving a loudspeaker directly – where the opposite is true for transistors. This is why most tube power amplifiers have large output transformers and transistor amplifiers do not. The transformer addresses the tube output issue but certainly has sonic drawbacks. This is why a number of Ralph’s designs "fix" this problem by creating output transformerless amplifiers. It’s all about the implementation.

lots of feedback kills image depth, easy test with an SPL meter, genius ( mindful designer ) Roger Modjeski designed RM-9 with variable feedback :-) ears are required

A bit of a correction here- feedback, properly implemented, does not kill image depth. **Improperly** implemented feedback does that and other things (brightness, harshness) as well.


For feedback to really do its job, it needs to be really a lot. Like over 35dB or so. Less than that and you have those problems above. One thing about sound stage BTW- to do it right you need zero phase shift in the audio band. This is why in our tube amps we've had 2Hz to 200KHz bandwidth, since you need to go 1/10x or 10x the cutoff frequency to prevent phase shift components in the passband - in this case the audio band of 20Hz to 20KHz.

But you can get around this with a class D implementation, since you can apply a lot of feedback with class D- so much that the amp goes into oscillation. The trick is to use the oscillation as the switching frequency. Then the amp might only have good bandwidth to 20KHz, but it can have so much feedback that its able to correct for phase shift that might otherwise be present on account of the filter at the output of the amp. Class D distortion is caused by errors in the the encoding and by something called 'dead time' (topic for another thread) but both tend to cause lower ordered harmonics. Because of this, a class D amp with a lot of feedback can have as much depth and stage width as a tube amplifier.

"I wondering if someone could explain to me the reason my tube amp has a deeper soundstage than my SS amps?"

Maybe the SS amps just aren't designed that way. I have a ML 335 that has as much if not more soundstage than any KT88, EL34, etc based amps I've owned. But then again maybe the tube amps I've had were not designed that way.

I don't have the tools (a brain) to quantify why the OP's statement seems mostly true. But I let my ears accept what I hear even though I don't know the hows or whys. The measurement folks just reject everything as being in our heads and don't care about what they hear.