Stock Status – 2026.05.06
We have another batch of transformers coming this week. Sorry for the delays as our prior shipment included several pieces of iron we did not need, and we’re awaiting the correct parts.
Rackmount Power Amp Overview
Finally, the next in our wildly successful PA line of power amps is here! Available in either 100W or 50W, this is the perfect power amp to compliment your rack-based preamps, modelers, Ceres, Vesta, or any other preamp! Our goal for this product was to put the excellent power section first found in our amp heads, then into the PA50, and now into a rack format that’s still as compact and lightweight as possible. Weighing in at only 15 / 20 lbs (50W and 100W, respectively) and 8.75″ deep, it packs a huge punch in a compact 2U rack unit.
With the myriad of tone shaping controls the PA-100R / PA-50R will be right at home with any preamp, distortion pedal, or modeling unit. The HiFi / Guitar switch is the secret weapon for running your modeler, or if your preamp is particularly dark. The extensive set of NFB (negative feedback) controls allow for near limitless tone sculpting options, garnering both the best modern and vintage tones, especially given the variable Negative Feedback (NFB) knob.
New Features
Several exciting, never before seen, features are included in this power amp!
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- MIDI
Our first amp to come standard with MIDI since the Gemini! It recognizes PC (presets) and CC (direct control) messages. A front panel Store button allows for easy preset creation based on the currently selected functions.
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- Effects Loop
Being bypassable via TRS footswitch, MIDI, or the front panel, it allows for easy patching of external time based effects, or switching of preamp input signals.
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- Dual Master Volume
Having two Master Volumes allows for easy boosting or cutting of volume, bypassable via the TRS footswitch or MIDI.
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- Internal Load Box
An internal load box enables silent recording of the PA-50R / PA-100R, capturing all the tonal qualities and benefits without all the volume! This load automatically switches-on when no cabinet is connected, protecting the sensitive tube power section. The load can also be activated via the front panel switch or MIDI. When the load is activated, even with a cabinet plugged in, it is disconnected automatically.
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- Mute
A built-in MIDI recallable Mute function allows for seamless muting of the signal — useful for tuning, or multiple power amp selection for seamless “cabinet switching.”
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- Internal Color
The color can be set for each permutation of Loop on/off, Master Volume 1/2, Internal Load on/off, and Mute on/off. The Internal Color can even be controlled directly via MIDI CC message, allowing for light-show style automation.
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- Bias Monitor
Our next generation bias monitoring circuit allows you to select between a real-time and steady-state display mode. Some like the flashing real-time monitor, but some find it distracting.
Just as with the PA50, included right on the front panel are individual bias adjustments for each power tube. This allows for the use of slightly mis-matched tubes, as well as purposeful mis-matching to generate different harmonic content.
Demos
Coming soon! In the meantime, you can expect all the same tones as made famous by our PA50!
Power Amp Specifications
Controls: Top (presence), Bottom (resonance/depth), NFB (negative feedback), Master Volume 1, Master Volume 2, Line-out Level (on rear)
Switches: HiFi / Guitar source select, Effects Loop Enable, Internal Load Enable, Power, Standby
Buttons: Bias Display Mode, Internal Color, MIDI Store
Bias: Individual tube bias monitor and adjustment, all via the front panel.
LEDs from top-bottom: Good, High, Low. Fault LEDs above respective tube fuses.
Internal LED lighting color selectable via front panel button: Red, Green, Blue, Yellow, Purple, Cyan, White, or Off
Voltage Input: 115/230V, 50/60 Hz
Power Output: 100W RMS or 50W RMS
Power Tubes: 4x (or 2x) 6L6GC or EL34
Preamp Tube: 12AX7 phase inverter
Dimensions: 19″ wide, 3.5″ tall, 8.75″ deep (front face to rear rail ends — not including front handles, knobs, or switches)
Weight: 15 / 20 lbs (6.8 / 9 Kg)
Gene (verified owner) –
Being one of the first to recieve this unit has been fun, all my forum members are asking about it and using it with a Red Seven D100 pre amp has been fun as well, I’m sure these are going to sell like hotcakes in the coming weeks, I love this thing.
Anonymous (verified owner) –
Ken Snyder (verified owner) –
This amp is the perfect match with my Synergy preamps. Having it rack mounted with midi capabilities for solo boost is just an added bonus. Highly recommended the company makes great products and they are reliable.
Kurt T. (verified owner) –
This is just what I expected- double the power of the PA50 with added features in rackmount form. I own, and have owned, a lot of tube power amps, and this one is my favorite right out of the box. Plus, the sparkle purple finish gives it a Soldano vibe- love it. Thanks for the good work and great product!
Anonymous (verified owner) –
Pro: The Amp is good. Has more features than I would ever actually need to use. Professionally crafted. These guys know what they’re doing. Communication is also up there. I sent emails and got a response within a few hours to a business day the latest.
Con: The Power amp on the website claims to be lightweight 8lbs/16lbs. That’s not accurate. The amp is actually 20lbs. The PA100R is probably 26lbs or more I could imagine. So advertisement was a little false there.
Con 2: They don’t advertise that these are custom items. The website does mention custom items will take longer. Understandable. Although they give you the option to make them custom (black on black is not custom in my opinion) I do believe they should have an estimated wait time on them on their page. Like “Ships within 3 months” kind of situation or something similar as I waited 2 months for mine.
Finally, I’m very impressed with the design. I like the added knick knacks even if I won’t use them right now doesn’t mean I won’t use them in the future. The cooling system on this thing is also top notch. After 2 hours of being on and heavily played it stays warm and not burning hot.
Jarrett H. (verified owner) –
This is one of my favorite gear purchases yet! My Quad Cortex tones have never sounded so rich and present. Very happy with KSR as always!
DANIEL (verified owner) –
Hands down the best power amp I have ever played through.
Donald Gorst (verified owner) –
Kyle is amazing! He really went out of his way to make things happen for me. Amazingly easy to deal with, super company, super people, super product. This power amp is built like a tank and is the secret sauce to my tone, it looks as good as it sounds and it sounds killer!! I couldn’t be any more happy! KSR for life.
diogo freitas (verified owner) –
I absolutely love this thing! I am beyond impressed, with built quality and how it sounds, it brought my Axe Fx to life! I wanted to say thank you to KSR for their professionalism and attending to my requests. Great customer service.
Austin Livingston (verified owner) –
I have not received any tracking info or update on my item yet. Once I do and receive the power amp, I’ll leave another review!
Oeyvind (verified owner) –
Jingtao F. (verified owner) –
Kyle and his team did a great job with my order
Gary L. (verified owner) –
I don’t even need this because I already have the PA50 Compact. But I had to have it. Just gives me a ton of versatility venue to venue. I can do my own on-stage monitoring, or go full blast, or just not bring it at all and run totally off of my board with DI and CabSims. I’m sure I can find more stuff to cram into a rack with this thing. (Like my own IEM transmitter.)
I don’t know what the future will be, but I do know there’s more of a push for silent stage, IEM rigs, and then there’s that venue you still need your 4x12s and full head and anywhere in between. Simplify, simplify and simplify while still being versatile and flexible.
Nothing more annoying that lugging a 50-75lb head a block and half through a city only to use the DI on it.
Ceres, or Vesta (I use either depending), into a Rockboard MOD5 with DI Out and programmable CabSim right on my pedal board. Parallel out to a power amp feeding as many cabs as I need for the venue or as little as I need for onstage monitoring.
Absolute MUST for session musicians and last minute fill ins. Throw this in a rack with your own IEM rig, and you can fit right in with just about any band, at any venue.
Steve Schwartz (verified owner) –
Hi, the amp is great, love the controls, tone, and power. My only feedback is that due to the orientation of the power plug, you can’t use any of the right angle power cables, due to the orientation, as the cable coming out of the right angle faces down, and doesn’t work when racked. I want to do this so I can use a 1ft low profile right angle power plug to go from the amp into the Forman power module, like I do with all the rest of my rack gear that has a more typical horizontally oriented power plug instead of vertical.
Timothy Holden (verified owner) –
This is THE power amp as far as I’m concerned. I own a PS100 as well and I purchased this power amp to replace my PA50 that was stolen. The quality of the craftsmanship is equally as amazing as the tone. I ordered mine with an anodized purple face plate and flat black chassis, black metal knobs, and the footswitch. Opinions vary but I can honestly say there is no equivalent alternative. Lastly, Kyle and KSR in general do good business and provide excellent customer service. I will say if you’re in the fence about it go with the 100R. The 50R is plenty loud enough but if your playing gigs and you need the piece of mind to know you can volume match the rest of the band and have the headroom needed when you need ti push some serious volume just pay the extra couple hundred dollars and get the 100R. But if you’re just jamming at the house moonlighting as a bedroom/basement rockstar then the 50R is plenty kind enough. I will be purchasing a secondary PA as a redundant backup… that’s how much I love this heavenly piece of gear. Thank you Kyle, Benji, and the rest of the KSR team!
Jeff Lachelt (verified owner) –
Amazing EL34 powered rack amp! If you use Synergy or other preamp pedals this will get you that Menacing Bombastic growl without the earache!
Joshua McMahon (verified owner) –
I love my PA-50R! I have it paired with a Rocktron VooDu Valve as the preamp and a Rocktron Intellipitch in the effects loop , plus a Boss SD1 in front of everything. I can not express enough how much I love my tone now!! The Top and Bottom knobs are great, but the NFB knob is where the magic is at. A lot of other gear goes directly from silent to loud as you turn the volume up, so as a bedroom player, I am super stoked that the entire range of the volume knobs are actually useful. And maybe this is silly, but I chose Pink Sparkle for my faceplate. I love my hair metal and I smile every time I look at my rack now. Thanks KSR!
Michael O. (verified owner) –
This amp is awesome. Wonderful replacement of a powerstage. My quad cortex works perfectly with it.
Anonymous (verified owner) –
KSR make the best gear.