I need impedance help. Rogue RH-5 to Solid State Amp.

The output impedance varied with both output and frequency. The unbalanced line output measured 0.5 ohm at 20kHz, 9 ohms at 1kHz, and 3.3k ohms at 20Hz, the last presumably due to a DC-blocking capacitor in series with the output. The balanced line-output impedances were twice these values, as expected.

https://www.stereophile.com/content/rogue-audio-rh-5-preamplifier-headphone-amplifier-measurements

Thank you. Are those 3 measurements for the 3 gain settings? So I would be able to use a 22k amp on the first two gain settings? 

@nickrobotron

Best to call Rogue for a chat - they’re friendly! Personally I would definitely be concerned by this bit "3.3k ohms at 20Hz" and this bit "the balanced line-output impedances were twice these values". That means 6.6K at 20Hz from the XLR outs?! That’s way WAY too high for a preamp IMO. Even if on paper it doesn’t look like a big dB loss in bass, and 20Hz seems far enough down, in my experience is you’ll be able to hear this as a leanness in sound.

And yeah, at least with prior models (Athena, Hera) the input impedance of the preamps changes with gain setting, so other stuff might change too.

Quite frankly if I had this unit I’d be tempted to try the headphone out (via adapters) as the preamp. The headphone out has VERY low output impedance. It probably makes some compromises to get that (e.g. lower quality coupling caps to achieve the low ESR), but I’d argue it’s probably less of a compromise than a 6.6K output impedance!

Also keep in mind Rogue's power amps often have a very high input impedance, 100K - 300K. That might work OK with the 6.6K, but when you use other amps...

I had this preamp and it is super clear and has amazing drive and dynamics.  Specs schmecs.  

my amp at the time had 23k input impedance and sounded fantastic.  

what amps are you considering?   

For a non-tube counterpart, I’ve been looking for something powerful that can handle 4 ohm speakers well. The Parasound A23+ is a contender. It and its big brother, the A21+, measure 33k (unbalanced) and 66k (balanced).

Open to suggestions on balanced amps that can handle the wild specs of the RH-5. I would prefer to use the balanced out if possible, but if the best option is unbalanced, that’s cool.

I know this is a “headphone amp”, but it does really feel like a design flaw to not be able to use the two different preamp outputs without careful system matching and potentially not with the same amp!

Mark at Rogue seemed surprised by the numbers I quoted him from the Stereophile review. He suggested bypassing a capacitor that he put in place to keep from sending DC power to the amp. Haha. So I’m not sure if he’s even confident in the design. I mean, do we sacrifice protection in the circuit so we can use off-the-shelf amps? With so many amplifiers at 20k, it’s strange to me. I do know that I will not be grabbing a soldering iron to bypass a capacitor in a $2500 preamp.

In the end he recommended an amplifier with an input impedance above 50k. Seems like I found that in the Parasound specs.

I am thoroughly impressed with the sound of these products and really believe in what Rogue is doing, but it’s far from user friendly.

It’s like how all of their unbalanced preamplifiers reverse polarity, but they don’t publish this anywhere. Not in the manual or on their website. You have to call and they say, “You’ll need to swap your polarity on the speaker end.” Umm. You did a really good job of explaining how to plug it into the wall and how to flip a rocker switch, but you left out a very non-intuitive instruction?

Doesn’t help that Stereophile’s measurements don’t align with Rogue’s. With the RP-1, is it just the phono with reverse polarity? Stereophile says yes. Rogue says it’s all the inputs. But only when you really dig.

@nickrobotron 

In that range check out the BelCanto e.One REF501S.  

Balanced connections, 95Kohm impedance but more importantly an ultra smooth midrange and treble that will go together with the RH-5.  The RH-5 is dead on neutral and sounds best with a smoother amplifier.    

I have the Parasound a21+ with a Cary Audio tube preamp and it sounds great but  the a21+ is just a touch too neutral for the RH-5.  

https://www.musicdirect.com/equipment/amplification/power-amp/bel-canto-e-one-ref501s-balanced-stereo-power-amplifier/ 

Thanks for the advice! Great to hear. Coming from the RP-1 to the RH-5, I believe there is a brighter, faster, more dynamic nature to the 5. The 1 is a great piece as well and has that warm, bloom that is so nice to be around. The 5 feels a bit more analytical and agile. 

Your write up confirms ears. So thank you! I will focus on a warm amp. The Cambridge is quite warm, honestly, just getting a little old at this point.