[VRacer-111]

Isn't the input to the SRD-7 from the amplifier the grey wires and the output from the SRD-7, the red and black to the speakers? So either you use the headphone or the speakers but not both simultaneously?

Yes, which is what I said in my post.

Selector switch on the front of the STAX SRD-7 allows you to choose between socket outputs and speakers. Mjolnir SRD-7 has no such option.

 

[VRacer-111]

What is the load impedance of the SRD-7 to the speaker amp?

I just measured 3.6 ohms resistance from both L and R channels.

 

[wuwhere]

I just measured 3.6 ohms resistance from both L and R channels.

So if I have a tube amp should I use the 4 Ohm output? That 3.6 Ohms does not tell at what frequency.

 

[JimL11]

I just measured 3.6 ohms resistance from both L and R channels.

So if I have a tube amp should I use the 4 Ohm output? That 3.6 Ohms does not tell at what frequency.

The 3.6 ohms resistance is probably the DC resistance. According to spritzer, Stax used 1:25 step-up transformers, which means the impedance is reduced by a ratio of 1:625. Since the headphone load is largely capacitative, nominally around 100 pf, the impedance ranges from around 80 megohms at 20 Hz to 80 kilohms at 20 kHz, so through the transformer, the amp sees an impedance between 128 kilohms and 128 ohms - this means the tap you use is non-critical. Another way of looking at it is that the amp sees a capacitor of around 63 nf. You need an amp that is stable driving a capacitative load - most tube amps qualify. Stax recommends a maximum input of 30 watts (presumably into 8 ohms), so pretty much any amp will work. Note that this will produce nearly 1100 volts peak-to-peak into the headphones, or nearly 112 dB SPL at 1 kHz given the common rating of 100 dB output for 100 VRMS. If you don't want to exceed the max rating, you could choose the tap depending on the amp power rating. For example, for a 15 watt amp you could use the 16 ohm tap, for 30 watts use the 8 ohm tap, and for a 60 watt amp, you could use the 4 ohm tap.

 

[VRacer-111]

Thanks for the explanation JimL11, I knew I wasn't measuring the impedance which is why I stated resistance, more of a mechanical, not electrical guy. All I know is Birgir said the NAD C 275BEE (150 watt @ 8/4 ohm continous, 250/410/600 watt @ 8/4/2 ohm dynamic) would not be a concern for use with his SRD-7, which is the reservation I had. He puts protective circuitry on its input and output - main reason I went with the Mjolnir SRD-7.

 

[Ali-Pacha]

Too damn hot here to listen to headphones with (fake) leather pads, let alone with a BHSE cooking the atmosphere a bit more

Ali

 

[Whitigir]

Easy, bring them all to the pool! Lol

 

[Pahani]

Ahh, the joys of Central Air on a hot summer day!

*props up my feet and leans back in my chair*

Kinda boggles my mind that A/C is so rare in Canada and Europe.

 

[Hi-Fi-Apricity]

Stat amps are really just space heaters in disguise! Why not heat your entire house while listening to music? Double whammy!

 

[SeaWo|f]

The Megatron will probably heat a small room pretty effectively.

 

[Whitigir]

T2 is doing plenty of that. You can cook eggs and serve with warmed bread slices

 

[JimL11]

Stat amps are really just space heaters in disguise! Why not heat your entire house while listening to music? Double whammy!

More than a grain of truth here. BHSE consumes 160 watts, T2 over 200 watts, Megatron probably another 30-40 watts due to the filaments of four additional EL34s. GG probably close to BHSE. Not sure about the KGSSHV and Carbon, but can subtract 40 watts because you don't have the EL34 filaments. All to put 1 watt peak into a Stax headphone. OTOH AnakChan likes to use the MacIntosh MC275 for his Susvaras, and that draws 170 watts at idle.

By contrast, the Stax amps draw 30 (SRM-353X) to 58 (SRM-T8000) watts. The SRX Plus draws about 60 watts.

 

[Hi-Fi-Apricity]

More than a grain of truth here. BHSE consumes 160 watts, T2 over 200 watts, Megatron probably another 30-40 watts due to the filaments of four additional EL34s. GG probably close to BHSE. Not sure about the KGSSHV and Carbon, but can subtract 40 watts because you don't have the EL34 filaments. All to put 1 watt peak into a Stax headphone. OTOH AnakChan likes to use the MacIntosh MC275 for his Susvaras, and that draws 170 watts at idle.

By contrast, the Stax amps draw 30 (SRM-353X) to 58 (SRM-T8000) watts. The SRX Plus draws about 60 watts.

Yea I only have a 353X and it still runs pretty toasty. One day ill graduate to a KG amp I tell you! Day is not today but I have plenty of time

 

[VRacer-111]

Space heater is definitely an accurate description for stereo amps....the NAD C275BEE uses nearly 100watts doing nothing and 300+ watts during nominal use - noticeably heats up the room. Have A/C but window unit... have to turn it off to really listen to music.

 

[SeaWo|f]

I've actually been pleasantly surprised at the temp my bhse runs despite being in my cabinet.