[LeonvB]

Ok, there are more owners of an Rudistor RPX33 on this board, but I bet none of them has what's beneath it: it's the new power amp RR20 build 2. Rudi made this one (serial #3) specificly to match the looks of the RPX33.

I already had the RPX33 (and the K701) for several weeks, and I was so impressed by the RPX I wanted it in my main rig too. I didn't like the looks of the RR20 however, and asked Rudi to make it black. After a few weeks, this is what he came up with. Not quite what I expected, it's likely he took my request a bit too literally (not that I'm complaining

).

Like the RPX33, it's all SS, in a dual mono setup. Output is 2x10W class A. The unit gets very, very hot: within a very short amount of time (2 min) it's at operational temperature. Build quality of RPX33 and RR20 are top notch, I must say the RR20 is a tiny bit better built. Can't comment on the sonic quality yet, as this unit has only just arrived, but if it's anything like the RPX I'll be very happy.

 

[mrarroyo]

That is one sharp looking amp. By the way I have a 1970 Ampeg SVT with 6 x 6550/KT88 power tubes. They installed a fan to help circulate some air and keep it a bit cooler. I wonder why more headphone amplifier manufacturers do not do the same.

 

[Carl]

I love the look of Rudi's modern-looking amps.

 

[cosmopragma]

The look is always a strong point of Rudi's amps.
I did own an Egmont and I sill own a RP 31.Both are looking and (way more important) sounding good.
2x10W isn't much though, you'd need fairly sensitive speakers.
I wonder how it sounds driving the K1000s.

 

[Patu]

Very nice. I'm waiting for your further impressions.

 

[LeonvB]

Quote:

They installed a fan to help circulate some air and keep it a bit cooler.

Rudi intentionally didn't increase cooling. You have to remember: this is SS. The components need to reach their operating temperature, and preferably as soon as possible. High temperatures are not that much of a problem, as most electronic components are available in versions that are rated up to 125 degrees celcius (this unit reaches 60-70).

Quote:

I wonder how it sounds driving the K1000s

Exactly my thoughts also, but I've yet to buy a DAC, and possibly new speakers. All that combined with this purchase should keep my wallet thin enough for quite some time...

 

[LeonvB]

Let's start with a short review of the RPX33:

Product description

The RPX-33 is a class A solid state dual mono headamp, which can also be used as a pre-amp. Do note you need to ask Rudi to add the pre-out, it's an option which doesn't cost much.
The amp delivers 600mW of power, so it should provide more than enough current to almost all headphones. I've personally never dared to go past the 6 o'clock position with my K701's in the low gain output (and that was with VERY quiet music).
For a headamp, it's quite big and heavy. This is a result of the extreme dual mono setup: Rudi even uses 2 transformers, which adds significantly to the size and weight of the unit.
Further info: http://www.rudistor.com/soundsystems/RPx33.htm

Connections

The amp has only a few connectors.
Rear: 2x RCA for In, 2x RCA for loop out, 1x 6.35 mm pre-out.
Front: 2x 6.35mm headphone out (one for low and one for high gain).
The choice of 6.35mm for the pre-out is a bit odd, but fortunatly Rudi can also deliver an excellent 6.35 - 2xRCA cable for a reasonable price.

Build quality

The build quality of the amp is very good. The finish itself is excellent, there are 2 improvements however to be made.
The most noticeable: hum. My unit was very noisy when it arrived. Rudi led the pre-out cable underneath the board, which caused the unit's enclosure to hum at an unacceptable level. After rerouting this cable OVER the board, hum was greatly reduced and can now only be noticed at quiet passages when you're within 1m (3ft) of the unit. I've informed Rudi of this problem, and I take it this shouldn't happen again.
The other problem is the loop-out: the loop out itself is excellent (i.e. the sound to f.i. an amp), but if you keep an amp connected a lot of noise is introduced into the circuit. This makes the loop-out rather useless: if you need to detach the cables, you could as well plug them in the component you're going to use next.

Sound quality

This is where the RPX33 really stands out: it is excellent. The sound is extremely rich and detailed, no matter at what range. Bass is fast and deep, the highs are right there, the midrange is equally excellent. Yet it's not agressive anywhere, and a real pleasure to listen to.
The coloration is slightly warm, which makes it sound non-SS in some respects. The speed of it's SS circuit however is very noticable with for instance synthesizer music, which suddenly sounds quite well (to my astonishment).
Being a dual mono amp, the channel separation is of course excellent. The soundstage of this amp is HUGE, esp. with the K701. In fact, some might find it quite artificial with the K701. Noise is non-existant (provided you don't use the loop out). Silence really is just that. Esp. important for classic.
I've listened to all sorts of music, from pop and rock to opera and orchestra music, even found some jazz in my collection to test this amp. No matter what I throw at it, there's absolutely no weak point I can find in the sonic performance of this amp. Of course it helps if the recordings are really excellent, but even with the lesser quality work I've played through this amp it doesn't sound that bad at all.

Strengths/Weaknesses

To sum things up:
+ Sounds extremely well
+ Finish
+ Price reasonable for true dual mono
- Hum (likely only in this one)
- Loop out introduces noise
If sonic performance is your main concern you should definately look at this amp.

 

[leonid05]

Thanks for this short review.

Your impressions of the rpx-33 are exactly what I expected when I thought about buying this amp a while ago.

Considering the prize I went for the rp5.1 instead.
I have no comparison of these two amps, but I certainly like the rp5.1 a lot.

I wish RudiStor had a bit more feedback around here, those amps certainly deserve it!

 

[Patu]

Quote:

Originally Posted by leonid05 Considering the prize I went for the rp5.1 instead. I have no comparison of these two amps, but I certainly like the rp5.1 a lot. I wish RudiStor had a bit more feedback around here, those amps certainly deserve it!

I did some comparison between these two a while ago. I would've got RPX33 as used for a nice price. Well as you can see I ended up keeping my RP5.1.

I had 6DJ8 Amperex tubes in my RP5.1 and tube dampers on them. Stock unit has 6922 Electro Harmonix tubes and no dampers.

Differencies were smaller than I expected. RPX33 had slightly faster sound with slightly more bass. What surprised me most was that RPX33 was actually little bit warmer sounding than RP5.1 + Amperex. In soundstage I couldn't hear much differencies. Overall I liked RPX33 more but I would've lost so much money in the process that I decided to keep RP5.1. And there's always the possibility of tuberolling with RP5.1.

Now I'm enjoying my new ECC88 Mullard tubes with RP5.1.

 

[Colhd]

Hi,

When I first got my RPX-33 it worked very well but seemed to lack a little in terms of emotional impact compared to my valve amp, an Earmax Anniversary. It did most of the hifi things better eg tighter bass, greater definition etc but all in all it lacked something compared to the EA. My system at the time was an iMac/Apogee Mini-Dac/amp/Qualia.

I had decided to upgrade my valve amp but after getting some advice here (thanks JJCHA) I listened to and then purchased a Chord Dac64 to replace the Apogee. This sounded better with the EA but I then tried it with the RPX-33 and was REALLY surprised at the sound. The end result was that with the Dac64 in the system I preferred the RPX-33 to the EA, something I was definitely not expecting.

What this brought home to me was the old adage that it is the whole system that counts, not just the amp or the 'phones or the source but the whole package. For a while I was convinced that valves were the way ahead for me. I still like valve gear but having heard how wonderful the RPX-33 sounds I am no longer limiting myself to a valve amp - I'll let you know how the RP010 sounds when it arrives.

Cheers,

Col

 

[leonid05]

@ Patu:

Thanks for your interesting comparison and experiences.

I`ve got some questions about the rp5.1, sent you a PM
(not to hijack this thread).

Thanks in advance, and a little bump for this thread!

 

[LeonvB]

Quote:

I'll let you know how the RP010 sounds when it arrives.

I for one would certainly like to know how it sounds. Which one did you order? Classic or balanced?

Also some first impressions of the RR20:
It weighs a ton for a "simple" 2x10W amp. The finish of the unit is EXCELLENT. Build quality of the unit is EXCELLENT. It doesn't have any perceptible hum. During the warmup phase there's noise in the output, but that's totally gone within the first minute. After that, there's no noise, period.

Regarding the speakers: I won't need more efficient speakers, I'll likely need lower efficiency. 2x10W of real power is way too much. I almost can't turn up the volume knob on the RPX33, the output of the RR20 is LOUD. I've not pushed it past the 9 o'clock rating, in fact even at 8 it's usually to loud.
Quite surprising, given the fact that I turned up the power on my old 2x130W amp to 40% most of the time (and still found it lacking impact).

Even with only a few hours on it detail, bass, treble and highs are incredibly impressive. Of course the rest of the system was "well burned in" (or perhaps better put worn out: most parts are 10+ years old), but it's an amazing difference this amp/pre-amp combo makes.

More later...

 

[Colhd]

Hi,

I ordered the Classic on advice from Rudi as opposed to the balanced. He tells me that the Qualia benefits little from balanced drive as opposed to a headphone like the Senn 650 which benefits a lot (I tend to believe a manufacturer who tells me to buy the less expensive model!). Time will tell whether it was worth it over the RX-33. Hopefully it will be here by Tuesday.

Cheers,

Col

 

[LeonvB]

Ok, I'm putting this thread back to life.

Since my last post, I've sent both the RPX33 and the RR20 back to Rudi for repair/upgrade.
Hum in RPX33 is now gone, it was indeed only my unit that suffered from it, but not the way I initially thought: thanks to the guys at Fed-ex, one of the components was out of place inside. Must have taken them quite some effort given the way it was packed, but seems you can always rely on them to mess things up

The RR20 got a repair plus a bit of an upgrade: Rudi fitted it with 2 temperature sensors (one for each channel) to shutdown the amp if it's overheating, plus he removed the noise. It now sounds a bit thin when warming up, but there's totally no noise: background is as black as it can be, just like on the RPX33. I guess you can now consider books open for what should be called a RR20 build 2"i"

Both amps are now "perfect" by my book, and highly recommended. The service Rudi provides is really top notch, also for the "more difficult" customer (and believe me, I am).

@Col:

I'm quite certain you now have that RP010. Can you give some impressions?