200Ohms is the only figure I see when I google for this amp and output impedance (from many retailers, not just here). SE output impedance should be half the balanced spec if the amp is designed properly.

Can I ask for examples of "designed properly" because most of the balanced amps I am familiar with have no specific correlation to the balanced output impedance due to various methods employed to output SE as well as balanced

Sorry, "designed properly" was poorly chosen. If it is balanced drive at all, then the balanced output impedance is almost always double what the SE is. Short story: generally speaking, if the output impedance of the SE side is there for a reason, it will necessarily also be there on the balanced out, which means the balanced out will have double the output impedance of the SE out.

Long story, output impedance is essentially the resistance to ground from the signal. In SE outputs, you get the output impedance from the one wire that has signal. In a balanced drive, there are two "signals"; you add the source impedance from both sides to get the output impedance. Assuming they didn't do anything really strange this is the same as doubling the output impedance of the SE output. I suppose it is still possible for an amp to have a "really strange" SE output (eg, SE shuts off when you plug in XLR and vice versa, high SE output impedance for no particular reason, etc), but all the balanced amps I've seen have output impedances that are twice the SE output. I am assuming SS in the above, if that makes a difference. I don't know if OTL tube amps are different and I don't care (and it wouldn't be relevant here anyway).

I have been thinking about buying this amp for some time, but as mentioned if this specification is correct, it will make it a poor match for the majority of the headphones that I use. The SE output impedance is not listed, but if it is as typical at 1/2 the balanced out, it is still way to high.

The interesting thing is that the one person on HeadFi that has bought one has had nothing but positives to say about the unit. He reports having good luck with several headphones, some of which are pretty low impedance.

So, I remain conflicted. I may have to wit until I read more from first hand users and see a few reviews, hopefully with actual test data. It is too much money for me to buy with this question in mind. I am hoping it is just a mistake in reporting the specifications. It would be real nice if there was a way to contact Gustard to ask the question. So far I have not found any way to do that.

Edit 2 (Undo my edit to retcon following comment after looking at the correct voltage source model of an amplifier which does have the voltage soirce in series with Rout in series with Rload which means original comment was not wrong): The output impedance cannot be 200 ohm. I did the power calculations in another post and it would dissipate insane amounts of heat at the maximum power specified to a 32 ohm load. Given the power specs my guess is it is less than an ohm.

Someone thought 200 could be the damping factor though that number is usually used in the context of load:source impedance (which would mean higher is better as 8~10 is the usual minimum people claim to want) but with respect to what load who knows.

I know this isn't how a lot of people think of it, but the headphone is in parallel with the output impedance. The current going through the headphone is not the same as what's going through the source resistance.

This is kind of a long read, but look at the schematic and his description. Note that the attenuator has an output impedance of 3.3 Ohms. Solderdude designs commercial headphone amplifiers (and also does headphone reviews/measurements), he knows his stuff.

Edit: False - Voltage source model of an amplifier has the source in series with Rout and Rload as I thought originally and it is the current source representation which has them in parallel.

Original comment: ~~True this comment is partially wrong and the other one needs to be rewritten. Not sure why I mixed up the amplifier representations.~~

I was recalling the quote from memory from December and forgot that the load was specified. Then I guess if it is an accurate interpretation it gives us the answer of 50/200 = 0.25 ohms.

> the headphone is in parallel with the output impedance. The current going through the headphone is not the same as what's going through the source resistance.

Maybe I'm missing something, but this statement seems to be quite simply wrong. Headphones are connected in series with output impedance.

> This is kind of a long read, but look at the schematic and his description. Note that the attenuator has an output impedance of 3.3 Ohms.

That's an attenuation adapter based on a simple voltage divider. The output impedance will typically be around 3 ohms (it depends on the output impedance of the amp as well as the values of the two resistors). However the output impedance of the attenuator is connected in series with the headphones, just as it is when connected directly to a headphone amp.

You are missing everything. Look at it again. The attenuator is 33Ohms in series with the headphones and 3.3Ohm output impedance in parallel. Obviously, if it were any other way, it wouldn't work as an attenuator.

> You are missing everything. Look at it again. The attenuator is 33Ohms in series with the headphones and 3.3Ohm output impedance in parallel.

I don't mean to be rude, but you clearly have no idea what you're talking about here. The 3.3 Ohm resistor is not the 'output impedance' as you seem to believe.

The primary purpose of the attenuator is to reduce voltage (and therefor power) to the headphones. Modification of the output impedance is just a byproduct of the voltage divider used to achieve this.

The output impedance of the attenuator is not determined solely by the 3.3 Ohm resistor but rather by the combination of the amps output impedance (call it AZ) and the two resistors (call them R1 and R2 for the 33 Ohm and 3.3 Ohm resistors respectively).

The output impedance of the attenuator can then be calculated with: ((AZ+R1) x R2) / (AZ+R1+R2)

Which is why the attenuator's output impedance will be around 3 Ohms with most headphone amps rather than 3.3 Ohms.

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