[Pashmeister]

The 8 Ohm taps are meant for 8 Ohm speakers, that does not mean that the output impedance is 8 Ohm.

Lol OK gotcha. In summary, headphone sockets for Susvara would need to be ~8ohm output. Thanks mate

 

[DuncanDirkDick]

The 8 Ohm taps are meant for 8 Ohm speakers, that does not mean that the output impedance is 8 Ohm.

That's correct, probably somewhat under 1 Ohm (~.8 range)

 

[Articnoise]

The 8 Ohm taps are meant for 8 Ohm speakers, that does not mean that the output impedance is 8 Ohm.

Yes that's true and low output impedance normally result in better SQ.

https://www.psaudio.com/pauls-posts/output-impedance/

 

[Articnoise]

Why? I'd just like to understand your reasoning behind that.

Why what?

 

[DuncanDirkDick]

Why what?

What do you think happens when adding a resistor in series?

 

[Articnoise]

What do you think happens when adding a resistor in series?

That's easy: the amp will always have a load on its output.

If you do not connect any load, the transformer cannot reflect a load and the tubes will only see the wire in the transformer and a big coil as a load. This is basically shorting the tubes to the high voltage and it can cause damage to the amplifier eventually. Another way to think of it is the power tubes pull on the transformer which magnetizes the output transformer; this in turn creates a voltage on the output of the transformer to drive the speaker load. If there is no load, all that energy has nowhere to go, so instead it will be fed back to the power tubes causing damage. If you are unlucky the tubes can go into a growing oscillation that eventually burns them. Most of the time the output transformer is ok, but if left on long enough it can also be damaged. And playing through an unloaded tube amp will only speed up the road to damaging the amp.

Simply put: in the tube amp output section, the transformer performs the task of transforming the speaker load to a load the tubes “want” to see. For example, on an amp with four EL34 output tubes the transformer makes an 8 ohm load look like a 1200 ohm load for the tubes.

 

[DuncanDirkDick]

Okay. That’s what I referenced yesterday. Your putting eg a 10 ohm, 20w resistor between taps to generate a load when nothing is connected. Your text read like you were putting resistors in series with the headphone.

 

[Articnoise]

Okay. That’s what I referenced yesterday. Your putting eg a 10 ohm, 20w resistor between taps to generate a load when nothing is connected. Your text read like you were putting resistors in series with the headphone.

I don't understand your posts. The resistors are placed on the output of amp and is there all the time. This mean that they are there also when you have your headphones connected.

 

[BassicScience]

I don't understand your posts. The resistors are placed on the output of amp and is there all the time. This mean that they are there also when you have your headphones connected.

It's a simple matter of terminology. You said series resistor when you clearly meant shunt.

 

[Articnoise]

It's a simple matter of terminology. You said series resistor when you clearly meant shunt.

Nope

 

[Nimzerz]

…..yes. As an electrical engineer, that’s what it’s called.

 

[Articnoise]

Tube amps with transformer coupled output would like to have a resistor in parallel with the headphone, because if you turn on the amp without anything connected then bad things can happen.

It is also possible to put a resistor in series on the positive of each channel and another resistor in parallel with the headphone load, known as an L-Pad.

https://robrobinette.com/HeadphoneResistorNetworkCalculator.htm

 

[Nimzerz]

Ah, I see what you mean now, but then, it’s not one resistor now, is it?

 

[Articnoise]

Ah, I see what you mean now, but then, it’s not one resistor now, is it?

One resistor in parallel will do, if the the goal is to protect against if you turn on the tube speaker amp without anything connected.

With one i serie and one in parallel (the L-Pad) you will also get lower noise floor and less hum.

Both can have an negative effect on SQ, so better try if they are worth it.

 

[number1sixerfan]

Just sharing some thoughts on the PrimaLuna EVO 400 I picked up a few weeks ago. Will share in a few threads, since I've asked about speaker amps with each of my headphones in them. I’ve given it quite a bit of time and have done a lot of comparison against the Woo WA33 and HSA1b. Before providing some thoughts, most of the differences I’m describing are more subtle in nature. They’re a bit wider when comparing with the HSA-1b, but still not huge imho.

Edit* I'm using the Raal speaker interface box to the EVO 400. Using the Raal Sr1a -> conventional headphone adapter to connect TC/Susvara to the Raal interface.

TL;DR: the EVO 400 to my ears slightly outperforms the Woo, while doing so by a larger margin compared to the HSA-1b. The Susvara, TC and Raal all sound a bit fuller and more refined out of it. Vocals are also slightly improved. Bass is very slightly improved over the Woo in terms of impact, but is slightly behind the HSA in that regard and* quantity to a very small degree—but the bass is tighter and clearer which I didn’t expect out of a tube amp. Downsides: Amp is huge and gets hotter than the Woo or BHSE by far, which are two of the hottest running amps I’ve owned. It’s also a bit harder at times to fine tune the volume. Also suspect that another TOTL SS speaker amp could do even better with bass overall.

• EVO 400 vs. WA33
  • EVO 400 has a slightly fuller sound, has much more “tube magic” while still sounding really dynamic and punchy, which actually works really well with all of my headphones. There’s also an increase in perceived realism
  • The EVO 400 sounds a bit more open, there’s more separation in the music and overall it sounds a bit “bigger”
  • Very slightly harder hitting bass and slightly more in quantity than the WA33, but this is very subtle. I’m sure TOTL SS amps deliver more here, but also sure it would come with its own tradeoffs. (The larger difference in bass I saw with the Marantz amp and just knowing how SS traditionally sound are the reasons for this hunch)
  • Woo sounds quite a bit more neutral and less like a tube amp. I.E. the WA33 doesn’t sound like it has “color” or “warmth”
    • Susvara: more than any other headphone, the Susvara seemed to benefit the most from the EVO 400. It doesn’t transform it, but there is definitely a noticeable improvement over the Woo (and the HSA). It has a bigger sound, and sounds more refined. Sounds a bit more lush, but doesn’t sacrifice speed and dynamics, which is really important. Vocals feel a touch more thick, while soundstaging appears to be about the same. Definitely the biggest beneficiary of the speaker amp
    • TC: this was much closer, as the TC sounds really damn good out of the Woo. It adds just a bit of warmth to the TC, and actually compensates for the midrange recession quite a bit. Doesn’t eradicate it fully, but makes a decent difference. The WA33 again is a bit more neutral (HSA as well) and slightly relaxed, so the issue is more noticeable with the two of them
• EVO 400 vs. HSA-1b
  • EVO 400 is quite a bit more expansive in terms of soundstage, separation and layering within the music. Sounds much fuller and more refined in nature
  • Due to the above, the EVO 400 actually sounds more detailed as it’s easier to hear each aspect of the music across the highs, midrange and low end
  • There is more bass and it’s slightly harder hitting on the HSA-1b, but it’s less refined than the EVO 400, which was really interesting. At times, it sounded less controlled and accurate than the EVO. However, I do also enjoy the pros here with the HSA-1b
    • Sr1a: as detailed as the Sr1a is with the HSA-1b, the slight improvement in spaciousness and separation makes it sound even more so with the PL. The Sr1a also greatly benefits from the lusher, fuller sound. I was hoping for a major difference in bass, but that’s really just not the case. Again, the Raal hits just a bit harder with the HSA-1b, but the quality and tightness seems better with the PL. Each of these differences are apparent, but not major (but again, being transparent, I would’ve thought that the PL would have taken the cake in this area, so props to the HSA-1b). Overall, with the EVO 400, the Sr1a just sounds more refined
    • Susvara/TC: mainly the same as above in comparison to the WA33 (outside of bass), but just a bit bigger in difference. I don’t really find anything special with the HSA/TC pairing (although very sufficient), but I find it to be a bit better with the Susvara for some reason.

Rounding out these thoughts.. the speaker amp is very large, which isn’t a big issue for me, but the heat is definitely more annoying. It is considerable for sure. That said, the improvement I saw with the Susvara was pretty impressive, and to a slightly less degree the Raal and TC. I suspect that the Raal would have even better synergy bass wise with a TOTL SS amp, but the question is what you’d lose in comparison to the EVO 400 or any other superb tube amp. I’d love to find out, but I just don’t have to appetite to buy and sell more amps.. especially with how good what I’m hearing is. I have a home office I need a second amp for and I’d prefer to keep the Woo, but the HSA-1b’s versatility in being able to use the Sr1a in addition to the TC/Susvara almost makes me feel like the Woo has to go. TBD on that.