PPA lacks punch

[DKJones96]

I guess that's what you call it. I was listening to a song, Bodyrox feat Luciana - Yeah Yeah, at work and I noticed that the tube amp I'm using here has more punch to it then the PPA does. The tube amp has no bass boost and while I installed it on the PPA, I rarely use it.

The tube amp uses 6 6j6 tubes per channel for transformerless operation in the power stage (when using 600 ohm headphones) and in this particular song, or any song with a deep beat and/or some sort of distortion effect, it sounds much better on the tubes.

I used 2x AD8065 and 1x AD8610 in the PPA, it is biased to class A, and I used the recommended output transistors which look to be faster than the op-amps so I can't see them being the issue.

 

[jcx]

likely the tube amp can dirve 600 Ohms to higher V than a SS amp limited by AD8610 +/-13Vmax

you could also be hearing some bass boost from the higher output impedance of the tube amp with the low frequency resonance impedance peak of the headphones

 

[rds]

If it's low mid-range bass you're talking about that fits with my experience of tube amps. There often seems to be a bit of emphasis in that range with tubes, which to my ears makes drums sound punchier.

However, I haven't experienced a tube amp that can do really deep bass like a solid state.

 

[diditmyself]

You can try to add a resistor on the amps output to reduce the damping factor and introduce some crosstalk. Just a couple of Ohms. AD8065/66 are amongst the "punchiest" opamps I've tried. AD8610/20 on the other hand is dry and a bit lean, and using some other amp in the ground channel might suit you better, something like OPA627 or OPA132/134.

 

[hopeless]

For punchy yet transparent (and natural) sound, try the LT1122. It's FET so use it without worries.

 

[DKJones96]

The bass is at ~35-40Hz and I was thinking it might be a gain in the tube amp. When I get time I'll run some tests to see if it's a matter of gain or roll off.

From what I understand the reason most tube amps can't drive low is because of the transformer. I'll admit that most tube amps I don't care for when it comes to music but this transformerless design is changing my mind on that a bit.

It is, however, the most inefficient amp I own, by far. Heaters on the power stage alone take 5.4 amps at 6.3 volts to run(34 watts).

 

[jcx]

are you level matching to 1% the V at the headphone output with the cans connected when comparing? - this is the minimum requirement for valid subjective comparisons

small level differences aren't clearly heard as loudness difference, usually the louder is picked as "better" even when the unknown is in fact the same piece of equipment compared with itself

at larger volume differences Fletcher-Munson effect causes even flat frequency response systems to appear to change in frequency balance

often otl amps have output coupling C which can compromise low frequency performance - not likely a problem with Hi-Z cans

 

[DKJones96]

The outputs are actually very different looking. On the tube amp it looks like high notes riding on a sine wave but on the PPA looks more like high notes scrambling up and down along the screen.

 

[tangent]

Do your level matching with clean sine waves and a multimeter. You can get the tones from a test CD, a PC with waveform generation software, a dedicated test tone generator, whatever. Level matching with actual music will get you nowhere.