Atma-Sphere
M-60 Mk. 3.3 OTL Monoblock
Introduced 1980$7,950 MSRP
Atma-Sphere Music Systems is a small, hand-assembly manufacturer based in Saint Paul, Minnesota, best known for pioneering output-transformerless (OTL) tube amplifier designs sold in small numbers directly and through a limited specialty-dealer network; the M-60 Mk.3.3 is the smallest monoblock in Atma-Sphere's OTL range, sharing the topology of its larger, more expensive siblings.
MSRP
$7,950
Used market · Good
$5,900
-26% vs MSRP
as of Sep 1, 2026MSRP to used market
From $7,950 at launch to $5,900 today.
Specifications
- THD
- Typically 1% at full power
- Price
- $7,950/pair, Mk.3.3
- Inputs
- RCA and true-balanced XLR
- Weight
- 30 lbs (13.6kg) per chassis, without tubes
- Topology
- All-triode, Class A / Class-A2, direct-coupled OTL (no output transformer)
- Warranty
- 3-year general coverage; 1-year on output tubes
- Dimensions
- 13"D x 17"W x 8"H per chassis
- Output power
- 60W/ch into 8Ω; 45W/ch into 4Ω; 80W/ch into 16Ω
- Tube complement
- 8x 6AS7G output tubes + 4x 6SN7 driver tubes per channel
- Frequency response
- 1Hz–200kHz within 3dB
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