Hafler TRM12S manual TRM10S/12S FUNCTIONAL BLOCK DIAGRAMS, Qualified Service Personnel Only

TRM10S/12S FUNCTIONAL BLOCK DIAGRAMS

Input circuit

The stereo input signals are connected to the amplifier through balanced XLR connectors J8 and J1, or unbalanced RCA connector TP2. Unbalanced operation can be selected with switch DS1, which grounds the RCA shell through R37. Input buffers U1 and U10 provide a stable input impedance, dominated by R10, R4, R42, and R32. The left and right balanced summing amplifiers U4A and U3A sum the inverting and non-inverting signals to form unbalanced right and left channel outputs RCH and LCH. The Common Mode Rejection Ratio (CMRR) of each channel is optimized with trimpots R8 and R58.

		! Qualified Service Personnel Only
			INPUT CIRCUIT
RCH		NON-INV
INPUT
		BUFFER		RCH
J8
		U1A		BAL
TP2
				SUMMING
R10
		BAL / UNBAL		AMP
R4	DS1
				U4A	RCH
	R37
				R109, R110,
		INV
			CMRR	R111,R112
		BUFFER
			R8
		U1B
LCH		NON-INV		LCH	LCH
		BUFFER		BAL
INPUT
		U1OA		SUM
J1				AMP
TP2				U3A
R42				R64 , R61
R32				R104 , R62
		INV	CMRR
			R58
		BUFFER
		U1OB

Mono Sum/Gain Circuit

Left and right input signals LCH and RCH are summed to mono through R49 and R51. The mono signal is then attenuated in two stages with dual potentiometer RV1 which is accessible from the rear panel heatsink and serves as the gain control. R56 and R83 determine the maximum achievable attenuation level. R59 and R66 help to reduce the tracking errors of RV1 due to absolute resistance. Buffer U3B unloads the attenuators and provides 6dB of gain with R25 and R73.

	MONO SUM / GAIN CIRCUIT
		SUB ATTN	GAIN
		R59, R56
RCH	L/R SUM		U3B
		RV1B
LCH	R49, R51		R25
		R66, R83
			R73
		RV1A

Phase Control Circuit

The output signal of U3B goes directly to U4B if DS2 is left open

(0 degrees phase shift). If only DS2 is closed, the signal goes through 2 cascaded phase shift stages built around U6A and U6B, and experiences a 270 degree phase shift. Additionally closing DS3 causes the phase shift to be 180 degrees. Adding another closed switch DS4 results in only 90 degrees of phase shift. DS2, DS3, and DS4 are labeled 2,3, and 4 respectively on the rear panel heatsink.

Buffer/Gain Trim Circuit

U4B works as a buffer, and as a factory gain trim using trimpot R136. The voltage gain of the stage is (R74+R136)/R137.

Filter Circuits

TU112A and U112B form two cascaded 2nd order variable low pass crossover filters, for an overall 4th order 24dB/octave Linkwitz-Riley response. The quad potentiometer R29 is accessible from the rear panel heatsink and indicates the 40Hz to 140Hz range of the variable Low-Pass crossover. Following these circuits is a 2nd order subsonic High-Pass filter at U2A. The signal then connects to the Class-G amplifier.

PHASE CONTROL CIRCUIT			BUFFER / GAIN TRIM
			CIRCUIT
-180º PHASE	-90º PHASE	DS2	BUFFER/
SHIFT	SHIFT		GAIN TRIM
U6A	U6B, R113, R120,		U4B, R137,
R100, R107,	R114, R123,		R74, R136
R101, R132,	C89, C74,
C86, C73,
D53	D54

FILTER CIRCUITS
2ND ORDER VARIABLE LP	2ND ORDER VARIABLE LP
U112B	U112A
R29A, R85	R29C, R164
R29B, R98	R29D, R130
C64, C48	C46, C45
2ND ORDER
SUBSONIC HP	CLASS G AMPLIFIER
U2A
C36, C42
R44, R82

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