In Barn for Review: A Grimm Audio System—PA1 Mono Amplifiers, PW1 Phono Preamplifier, MU2 Music Player

Soup to amplifiers.

If you haven’t heard, I love reviewing systems. Case in point—back in June of 2025 I reviewed the Grimm Audio LS1c Active Loudspeaker System (review) including the Grimm MU1 so in that in case we’re talking soup to nuts. Since that review, Grimm has released two products in the amplifier category including the PA1 Mono Amplifiers and the PW1 Phono Preamp.

“Would you be interested in reviewing the new PA1 monoblocks?”
“I would but I’d like to also include the MU2 as I don’t review separates.”
“OK. How about the new PW1 phono preamp?”
“While I don’t normally review analog gear, yes! I’d love to review the PW1 too.”

And here we are.

The Grimm PA1 monoblocks offer 100 Watts of output power into 8 Ohms and double that into 4 from its Class AB operation. But if you know anything about Grimm’s designs, this isn’t your uncle’s Class AB.

From the company:

One of the most striking design choices in the PA1 is found in the output power stage. It is a traditional ‘class AB’ type of design, but of a highly innovative kind. We created a fully symmetrical circuit, with no less than 96(!) small and fast power transistors to achieve a very high bandwidth. This unique technique became possible by using modern aluminium printed circuit board technology, that offers an extremely tight thermal coupling of all the power transistors. An ingenious output driver circuit, mounted on the very same aluminium printed circuit board, takes care of the quiescent current setting point of the output stage transistors.

The circuit is an evolution of an original design by the late Henk ten Pierick, dating back to 1985. His concept provides an extremely well defined power output stage setting point, through which the output stage impedance remains constant over the full cross-over region, resulting in the lowest possible distortion of dynamic signals. The tight thermal coupling of the output stage transistors with the driver stage ensures that this ideal setting point is maintained even when large (low-frequency) currents are delivered to the loudspeaker. The PA1 name refers to Henk’s genius, we call it the “Pierick Amp”.

The PA1 offers Manual or Auto operation with the flip of a toggle switch, a Gain switch for 16 dB or 26dB of amplifier gain to match your preamp’s output, and an Input select switch to choose between single-ended RCA or balanced XLR input options. A single pair of binding posts per side, power switch, and IEC inlet complete the backside.

The nearly 10″ square PA1 were designed by Michiel Uylings of MU1 and PW1 industrial design fame and each monoblock weighs in at 33 lbs. Think solid and I enjoy the subtle curves and side long heatsinks that remind me in a winking way of the classic Pass Aleph 3.

The Grimm PW1 Phono Preamplifier supports MM and MC cartridges and measures a chunky 4″ x 4″ x 9″ (in round numbers).

A subtle symphony of textures and offset angle are nice visual touches while the PW1’s 7.7 lbs provides reassuring heft.

Recessed MM and MC RCAs in and XLR out fill out the rear panel along with a ground terminal, power switch, and IEC inlet.

Hidden underneath is where you’ll find a sliding panel, held in place by knurled brass thumb screws (I appreciate that detail), that reveals cartridge load options. I recommend a trip to the PW1 manual for the nitty gritty.

I reviewed the Grimm MU2 Music Player back in May 2024 and concluded:

If you want to hear the best digital music reproduction I’ve heard by an obvious and distinct margin, you’ll need to find a Grimm MU2 to listen through.

I’ll point you to that review for the skinny on the MU2’s ins and outs and operation but in brief the MU2 can function as a Roon server, Roon endpoint, DAC, and preamplifier. All in one which is how I intend to use it here along with the PW1 and PA1s paired with a few pair of speakers including the Barn resident DeVore O/96.

the MU2 includes 2 pair of analog RCA inputs one of which will be receiving the output from the PW1

As regular readers know, I own a Grimm MU1 (review) which is part of my reference system, typically paired with the Imersiv D-1 DAC and I’ve been more than impressed with everything Grimm that’s come in for review as well as what I’ve heard in Grimm’s rooms at shows. Which goes along a long way in explaining why I responded with all those yeses when asked about all this Grimm Audio gear that’s begging to be played.

I shall happily oblige. Stay tuned.

Grimm Audio PA1 Mono Amplifiers: $26,500/pair
Grimm Audio PW1 Phono Preamplifier: $5650
Grimm Audio MU2 Music Player: starts at $20,000
Company Website: Grimm Audio

Grimm Audio PA1 Specifications

General:

Max. ambient temperature for operation: 40 °C.
Line voltage 100-120 VAC or 200-240 VAC.
Power Consumption, operation: 65 W ~ 600 W.
Power Consumption, low power mode: <5 W.
IEC C18 type line voltage connector (without safety earth pin). Class 2 isolation.
Fuse 230 V: T2.5AH250V, Littelfuse 021502.5MXP.
Weight: 15 kg.
Dimensions: w x d x h: 250 x 250 x 240 mm.

Connections:

XLR input impedance: 33 kΩ.
RCA input impedance: 16 kΩ.\
4mm ‘banana’ style binding posts.

Performance:

Gain: 26 dB or 18 dB (selectable).
Power: >100 W in 8 Ω.
Power: >200 W in 4 Ω.
Output impedance: <10 mΩ.
Damping Factor: >800 re 8 Ω.
SNR: 96 dB (1 W, 8 Ω).
THD+N: -96 dB (1 W, 8 Ω).
THD: <0.0001 %.

Grimm Audio PW1 Specifications

General:

Max. ambient temperature for operation: 45 °C.
Internally set line voltage 100/115 V or 230 V.
IEC C18 type line voltage connector (without safety earth pin). Class 2 isolation.\
Fuse 115 V: 315 mA TT, Littelfuse 0215.315MXP.
Fuse 230 V: 200 mA TT, Littelfuse 0215.200MXP.
Weight: 3.3 kg.
Dimensions: w x d x h: 100 x 250 x 100 mm.
Package dimensions: 265 x 350 x 220 mm.

Connections:

MM/RIAA gain: 37 dB ±1 dB. Sensitivity: typical 5 mV.
MC gain: MM/RIAA gain plus 20 or 30 dB. Sensitivity: typical 500 μV (20 dB gain) or 160 μV (30 dB gain).
Optional output boost: +10 dB.
Output impedance: 100 Ω (RCA and XLR).
Recommended output load impedance: > 10 kΩ.

Input impedance:

MM resistive: 47 kΩ
MM capacitive: 47 pF, plus optional 47 pF, 100 pF, and/or 220 pF in parallel.
MC resistive: 47 kΩ, plus optional 33 Ω, 100 Ω, 330 Ω and/or 1 kΩ in parallel.
MC capacitive: 330 pF, plus optional 330 pF and/or 680 pF in parallel.

Performance:

THD+N: MM ≤ -45 dB (1 kHz, 5 mV); MC ≤ -45 dB (1 kHz, 500 μV).
SNR CCIR-2k: MM ≥ 80 dB (+0 dB position, ref. 5 mV); MC ≥ 76 dB (+20 dB position, ref. 500 μV); ≥ 80 dB (+30 dB position, ref. 500 μV).
Overload margin: MM 24 dB (1 kHz, 5 mV); MC 24 dB (1 kHz, 500 μV).
RIAA precision: ±0.5 dB 20 Hz – 20 kHz.
Channel imbalance: ≤ 0.5 dB.
Crosstalk: MM ≥ 90 dB (1 kHz, 5 mV); MC ≥ 86 dB (1 kHz, 500 μV).

Grimm Audio MU2 Specifications

General:

Max. ambient temperature for operation: 35 °C.
Fuse (worldwide): 1 A fast blow (F).
Weight: 4.5 kg.
Dimensions: width x depth x height:
355 x 295 x 100 mm or 14” x 11.6” x 3.9”.
Package dimensions: 536 x 392 x 219 mm.

Clock specifications:

Internal intrinsic clock jitter < 0.6 ps RMS (> 10 Hz).
Can slave to 44.1 kHz and 48 kHz based digital sources of 1FS, 2FS and 4FS within a +/- 50ppm range. De-jittering with FLL topology.

Major DAC

128FS oversampling with proprietary “Pure Nyquist” filter.
Bit perfect 11th order 1.5 bit Noise Shaper at 512FS.
Max 12 dBu output for 0 dBFS digital input signal.
Harmonic Distortion: < -120 dB, < 0.0001%.
SNR: 107 dB.

Analog outputs:

XLR output 12 dBu nominal max *, 100 Ohm (impedance balanced).
RCA output 12 dBu nominal max *, 50 Ohm.
Max. output voltage: 18 dBu.
Headphone max output 40 mW in 30 Ohm, 55 mW in 600 Ohm.
Relay based volume control from -79 dB to +8 dB in 1 dB steps (0 dB is the recommended maximum position, positive gain is for soft sources
and may cause internal clipping on loud sources). *) nominal values listed are with 0dB volume setting.

Analog inputs:

XLR input, 100 kOhm input impedance, 18 dBu max in (balanced).
RCA input, 50 kOhm input impedance, 13 dBu max in.

Power supply: