[L0rdGwyn]

Alright here's Golden's response:


He then sent voice notes (I had dm'd him on telegram) so bear with me as I translate his thoughts:

He clarified that what you said isn't necessarily wrong but that it is assuming that a tube or transistor is going to behave identically in all situations, which they won't.
Solid state devices typically perform more linearly--- so usually you don't see this behavior on them.
But tube devices, in his experience of testing them, generally perform better with a lower line level input voltage, so that's why he recommends at least trying it to see if it improves your subjective experience. He said this is because they are not perfect devices and they don't perform linearly in all situations.

He also said you are correct about increasing the noise by turning up the volume on the amp, but that noise and distortion are separate issues that are effected differently.
He basically said only put the volume as loud as you can without hearing noise, if you hear noise turn the amp down and dac up.

He said if you can do this without getting a problematic noise floor at the output, it's probably worth doing. If your amp is noisier and you get a ton of noise by doing this, then it's not worth doing. The aegis is a quiet tube amp so I feel like it's worth giving it a shot?

There are far too many unknown variables in those measurements for me to draw any conclusions. What I will say though is that any amp, tube or solid state, that is generating 1.4% THD at 700mVrms output into any load is poorly designed.

 

[Kdot]

There are far too many unknown variables in those measurements for me to draw any conclusions. What I will say though is that any amp, tube or solid state, that is generating 1.4% THD at 700mVrms output into any load is poorly designed.

I think this is just an example he could provide quickly, he said he has seen this behavior on most of the tube amps he has tested.

 

[L0rdGwyn]

I think this is just an example he could provide quickly, he said he has seen this behavior on most of the tube amps he has tested.

Well I would say those measurements are not representative. An amplifier that is generating an order of magnitude greater distortion when the source level goes from 70mVrms to 1Vrms, with output adjustment being done by a potentiometer, means something is wrong. This is of course assuming that the source is contributing negligible amounts of distortion between those two output levels. I can tell you that is not the case in Aegis, and I have confirmed that just now with a DAC output at -6dBFS (around 1Vrms) or -18dBFS (around 250mVrms). With the output adjusted to 700mVrms into a 32ohm load, the THD is unchanged, as I would expect.

 

[GoldenSound]

There are far too many unknown variables in those measurements for me to draw any conclusions. What I will say though is that any amp, tube or solid state, that is generating 1.4% THD at 700mVrms output into any load is poorly designed.

This limitation as explained was nothing to do with the output stage. The output stage of that amp can deliver quite a bit of power and as shown in the other measurement, when not limited by the input stage distorting more due to high input voltage, it's fine.

Additionally this behaviour has been observed in the vast majority of tube based devices I've tested from various manufacturers (Feliks, Riviera, Woo, Kallyste etc), to varying degrees and with the effect stopping at differing levels. I'm sure some devices won't have it, but in general, it does seem that full tube amps (or hybrid tube amps) do often see a benefit from a slightly lower input voltage. As full 2V line level often causes the device to produce more distortion simply from that initial tube stage, regardless of what the output stage is doing

 

[L0rdGwyn]

This limitation as explained was nothing to do with the output stage. The output stage of that amp can deliver quite a bit of power and as shown in the other measurement, when not limited by the input stage distorting more due to high input voltage, it's fine.

What is the topology of the input stage? And you are adjusting output levels to 700mVrms by turning up the volume potentiometer, correct?

 

[GoldenSound]

What is the topology of the input stage? And you are adjusting output levels to 700mVrms by turning up the volume potentiometer, correct?

That specific amp was the Kallyste Amethyste. I'd avoided mentioning the name as the discussion isn't really specific to this unit. As stated above, this effect has been observed in I think every single device with a tube input stage that I have tested regardless of manufacturer.

I'm sure that there are some which might not do this, I've just not tested any.

 

[goldwerger]

BTW, I've been running my Aegis on max volume and controlling the volume using my DAC based on a recommendation from GoldenSound (when I can, on more sensitive headphones I can get occasionally too much noise).

Here's what he said about it, it applies to OTL and OTC amps:


Another thing to experiment with!

Experimenting with voltage levels is very beneficial when you can manage it from more than one component.

When I use the Decware/zmf otl into the Decware taboo TC, I play with both gain levels and find unexpected sweet spots depending on headphone sensitivity (noise floor) and amp requirements.

I do agree that, in most cases, the more you control things closer to the source at the pre amplification stage, the better and cleaner the output.

On some insulation cases, there are amps that produced too much noise if they are left unattenuated. So it is very chain and driver specific.

But it’s a good place to start from

 

[L0rdGwyn]

That specific amp was the Kallyste Amethyste. I'd avoided mentioning the name as the discussion isn't really specific to this unit. As stated above, this effect has been observed in I think every single device with a tube input stage that I have tested regardless of manufacturer.

I'm sure that there are some which might not do this, I've just not tested any.

I'm just trying to understand why, as that is not behavior I would expect to see. But again, you are either going to 70Vrms input and turning the volume up, or going to 1Vrms input and turning the volume down to get your 700mVrms output, correct?

 

[goldwerger]

I intend to pickup some interesting wood for a couple of projects this summer so I may have a spare tube holder or two with whatever I have left if that’s the case I’ll post back here!

Dibs!!!

Additionally this behaviour has been observed in the vast majority of tube based devices I've tested from various manufacturers (Feliks, Riviera, Woo, Kallyste etc), to varying degrees and with the effect stopping at differing levels. I'm sure some devices won't have it, but in general, it does seem that full tube amps (or hybrid tube amps) do often see a benefit from a slightly lower input voltage. As full 2V line level often causes the device to produce more distortion simply from that initial tube stage, regardless of what the output stage is doing

One thing that has very big impact here in my empirical experience (no measurement or science, just ears) is the choice of input (gain) tubes.

You mention the Riviera, which I have, and it is incredible how much this hybrid amp’s behavior can be impacted by this single gain tube roll. Leaving sound quality discussion aside as too OT to thread, the impact on noise floor with sensitive headphones can vary from total blackness to inapplicable.

 

[Toonartist]

Dibs!!!

My current tube holder means the EL37 remain in my main storage case so the next one will allow for 6 pairs of tubes or a combination of pairs and single rectifiers. I have to admit, I really like having them to hand like this... digging them out of the case which isn't easily accessible is a PITA.

I'll be picking up a bigger drill bit so I can line the holes for the tubes that are connected to their adapters. Maybe a single row holder for rectifiers... I'll be buried under the things. One more just for those other much needed tubes

 

[mattiastomas]

My current tube holder means the EL37 remain in my main storage case so the next one will allow for 6 pairs of tubes or a combination of pairs and single rectifiers. I have to admit, I really like having them to hand like this... digging them out of the case which isn't easily accessible is a PITA.

I'll be picking up a bigger drill bit so I can line the holes for the tubes that are connected to their adapters. Maybe a single row holder for rectifiers... I'll be buried under the things. One more just for those other much needed tubes

I would definitely be interested as well should you have some "extra"s.

 

[Toonartist]

Ok... I'll keep this in mind when buying the wood... go larger for some spares

 

[GoldenSound]

I'm just trying to understand why, as that is not behavior I would expect to see. But again, you are either going to 70Vrms input and turning the volume up, or going to 1Vrms input and turning the volume down to get your 700mVrms output, correct?

In the case of the two 'dashboard' graphs that was with me turning the potentiometer up to compensate for lower input level and achieve the same output level (to show that the distortion changes even though the output stage is not providing more/less power).

In the case of the graph below, that was obtained with the potentiometer staying at the same position

Similar graphs (showing IMD not THD but doesn't matter too much to demonstrate the effect) for other amps (for which I also after verified that the behaviour occurred even when actual output level was the same but input voltage only changed, thereby eliminating the output stage as the cause of the change in distortion):

Woo WA23:

Riviera AIC10:

(Note: X axis on the above shows output level NOT input level, so they look the same but due to differing gain structure the actual sweet spot for input voltage is indeed different)

 

[AcousticMatt]

Aegis + Caldera (or any other headphone I tried with it) was one of my favorite CanJam pairings.

 

[goldwerger]

My current tube holder means the EL37 remain in my main storage case so the next one will allow for 6 pairs of tubes or a combination of pairs and single rectifiers. I have to admit, I really like having them to hand like this... digging them out of the case which isn't easily accessible is a PITA.

I'll be picking up a bigger drill bit so I can line the holes for the tubes that are connected to their adapters. Maybe a single row holder for rectifiers... I'll be buried under the things. One more just for those other much needed tubes

That’s how a Grumpy Goose business starts….

Count me in!