The Stax thread (New) - Page 56

I imagine anywhere between 10 and 40 would suffice. The Sigma is harder to drrive because the drivers are further away from your ears which is why Carl was wary of the t-amps output. I thinkk it'll do it but a little more powah can't hurt.

I think I know where I might be able to acquire/purchase a SRD-7 Pro. If only I had my vintage Marantz receiver with me. That thing's speaker and headphone outs are awesome in my opinion.

We'll see how it works out. The SRM-1 MKII is coming in about a week, and I'm going to try them with Jason's Lambda. I'll probably sell the SRM-1 MKII since I don't have a normal bias Stax anyways (unless I acquire one for some unforeseen reason in the near future). That'll let me get my first taste of Stax (other than the OII) before my Sigma Pro and SRM-3 arrive in a couple of weeks. Maybe by that time I'll have thought things through.

Are you referring to the one that is ending in a bit under three hours? The thing is that I've already talked to someone a little while ago regarding acquiring his SRD-7 Pro if the need ever arises. I think I'll need to talk to him again soon.

Hehe, I see that one now. Oh hmmm, a MKII has both a pro and a normal bias output. That might be useful.

Let's see what happens in 9 hours.

I've been fiddling with numbers of this sort a lot lately investigating my transformer box project so I figured I'd run the numbers here. Hopefully I won't stuff it up...

From basic electronics theory we have P=IV and I=V/R
Combining the two we get P=V*V/R
We can then re-arrange to get V=sqrt(P*R)

Now for a 10W speaker amp we know P=10W and assuming this is 10W into 8 ohms then we also know R...R=8. Running the numbers we get...
V=sqrt(10*8)
V=8.94 Volts
This is the rms voltage swing generated by the amp when it's providing the full 10 Watts of power. Now assuming this is fed into a Stax transformer box with a ratio of 1:24 (which apparently the SRD-7 Pro and MK2 are) then we multiply the voltage by 24 which gives 215 Volts RMS. This would be the maximum swing provided to the stators.

Now of course this doesn't say anything about the quality of the sound signal but based on the amp specs spritzer posted this voltage is well on the low side and I expect would limit the dynamics that the headphones could portray. Whether this would bother you is another matter but it does suggest that ideally you want a higher wattage amplifier.

Note that an amp providing 10W into 16 ohms or into 4 ohms changes things significantly. For 16 ohms we get 304V RMS (okay) and for 4ohms we get 152V RMS (too low).

The equations assume ideal conditions where the output voltage level can be sustained as required. The damping factor is only going to reduce the actual voltage even more in real world applications.

Reduce? Not based on my understanding of damping factor.

A 30 to 50 watt amp (rated into 8 ohms) is just fine for driving the SRD-7. If you plan to use a tube amp (with a output transformer) I would connect it to the 8 ohm tap. The SRD-7 has a falling impedence with frequency. You want to make sure that there isn't any roll off at high frequencies.

AudioD

We could post about numbers all day long and never reach any real world conclusions. I will tell you this though. ON paper my 30w amp running to the SRD-7 Pro isn't a whole lot more powerful than a SRM-313 (If at all really). And there is absolutely no contest. The amp/tranformer combo has so much more power, it's as said above no contest. The 313 from my experience cannot drive the OII to decent levels at all IMO. I'm really starting to wonder if in fact there is just more to it ,and were all figuring something wrong or ???
Any ideas ?