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SPECIFICATIONS
Product Release No.:PR 348 (This is not a model number)
Part Number:120V Version : 21-3300
240V Aust : 21-3330
230V UK : 21-3340
230V : 21-3360
100V : 21-3370
Preamp section
Input impedance:470k -„¦
Full power sensitivity:12.75mV
Tone controls:Treble: +/- 15dB @ 3kHz
Bass: +/- 15dB @ 40Hz
Graphic Equalizer:+/- 12dB @ 31.5Hz, 63Hz, 125Hz, 250Hz, 500Hz, 1kHz, 2kHz,
4kHz, 8kHz, 16kHz
Mid notch:-20dB @ 700Hz
Low boost:+10dB @ 40Hz
High boost:+10dB @ 6kHz
Power Amplifier Section
Power output:1200 Watts RMS into 2 -„¦ @ <0.2% THD
Sensitivity:1V RMS (0dBV)
Power Requirements:100V AC, 50/60 Hz, 1800W
120V AC, 60 Hz, 1800W
230V AC, 50 Hz, 1800W
Speaker Complement:Designed for use with the Sunn 410H or Sunn 215 Bass
Loudspeaker Enclosures
Dimensions:Height: 3.5" (8.9 cm)
Width: 19.0" (48.3 cm)
Depth: 15.0" (38.1 cm)
Weight:35 lbs (15.9 kg)
Product specifications are subject to change without notice
CIRCUIT DESCRIPTION
The Sunn 1200S Bass Amplifier employs many new technologies in various sections. This document is a
brief overview.
Preamp
The preamp section employs two 12AX7 tubes. Channel one (V1) is fairly conventional, while channel two (V2) uses a
second tube with additional op-amp gain (U2B) to provide a 60's style overdrive sound. The op-amp is used as
straight gain and is never allowed to become non-linear.
In typical operation, the drive channel and the clean channel are presented to the channel 1/2 mix control (R25) so that
a "blend" can be established. The channel select button (S7) on the front panel (or it's foot switch counterpart) selects
between this channel mix or channel one only. This selection employs JFETS Q1-Q4.
Signals are then presented to a second-order Sallen and Key filter set to F
0 of 36.6 Hz and a Q of 2.1. This filter
provides about 6.5dB of boost at 41 Hz.
The signal path is routed to U4B where low-boost (S2) , mid-notch (S4), and high-boost (S3) equalization switches can
be used. These circuits are followed by conventional Baxendall low (R67) and high (R70) equalization. The Baxendall
circuit output is then sent to a graphic equalizer which can be selected by the footswitch or graphic EQ button (S61) on
the front panel. The far-right graphic EQ slider (R660) is a +/- 10dB trim for graphic EQ gain compensation.
Next, the signal is presented to a second-order state-variable filter before being presented to the compressor circuit.
Said filter is set to 420 Hz. At the compressor, low-frequency compression ratio (R88) and high-frequency
compression ratio (R98) are adjustable to suit the user. Audio is presented to the "compressor EQ balance" (R107).
The compressor EQ balance controls the mix ratios of the compressor outputs. A compressor gain trim (R113) is
provided to compensate for the amount of amplification lost due to using the compressor. The compressor-gain trim
control is able to compensate for a compressed signal of up to 10dB.
The FETs Q5 and Q6 select between pre- and post-compressor via the front panel switch (S8) or footswitch. After
passing through op-amp U10B and master-gain control R116, the signal is sent to output jack J3, effects-loop send.
The signal input at J4, effects-loop return, goes to differential receiver U11B.
Signals are forwarded to power amp pass through amplifier U12B and on to J5. At these same nodes, the signal is
passed on to the 1200 W att class H power amplifier.
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Power Amplifier
The power amplifier employs class AB topology in the pre-driver circuit Q8-Q11. Quiescent current is established with
transistors Q12-Q13. Driver transistors Q16-Q17 provide drive for Q23-Q26, and Q31-Q34. Transistors Q19,Q21, and
Q27-Q30 provide positive on demand supply-rail boost. Transistors Q20, Q22, and Q35-Q38 provide the same
function for the negative rail.
Transistor Q18 provides charge depletion of Q23-Q26 and Q31-Q34. This allows for the suppression of common
mode current that can occur at high frequencies.
Relay K1 and associated components reduce output-stage current gain to unity during power-up and over-temperature
events as monitored by thermistor RT1 on the main heatsink.
Power supply
Primary circuit inrush limiting is accomplished by TH1, a negative temperature coefficient thermistor.
The power supply employs a toroidal power transformer with only one tapped-main secondary. Two large bridge
rectifiers are used to obtain +/-47VDC and +/- 94VDC.
High voltage (356VDC) for vacuum tube sections is generated by half-wave multiplier comprised of CR92-CR95,
C125-C128.
Low voltage (+/-22VDC) and (+10~ +28VDC variable fan) is supplied by the synchronous rectifier system located on
the power supply break-away board. This synchronous system observes the input sine and allows Q81, Q85, and Q88
to be forced on until the input sine wave reaches the correct level as observed by Q83, Q87, and Q90. References
Q84 (variably controlled by RT2) CR811 and CR818 are employed. Regulators U21 and U22 reduce the +/-22V lines
to +/-16VDC
Heater voltage (24VDC for 2 series-connected 12AX7s in the preamp) is derived from the 32VDC supply (+/-
16VDC).. Excess voltage is dropped across across paralleled ballast resistors, R354-R356, on the preamp PCB.
PARTS LIST
NOTE: SHADED ITEMS ARE FOR REFERENCE ONLY
PRINTED CIRCUIT BOARD ASSEMBLY
QTY PART # DESCRIPTION REFERENCE DESIGNATION
2 0052047000 BRIDGE RECT 35A 800V BR1 BR2
9 0048451000 BUTTON PUSH OFF W HITE
2 0053930000 CABLE RIBBON 3 CKT 3 in P1A P5A
1 0048914000 CABLE RIBBON 8 CKT 7 in P4A
1 0054388000 CABLE RIBBON 8 CKT 9 in P8A
2 0033606003 CAP AE RDL .47UF 50V 20% C116 C640
3 0028494000 CAP AE RDL 1000uF 35V 20% C802 C805 C809
2 0028476003 CAP AE RDL 100UF 50V 20% C806 C810
6 0028463003 CAP AE RDL 10UF 50V 20% C39 C43 C46 C50 C55 C59
1 0028458003 CAP AE RDL 1UF 50V 20% C53
10 0028459003 CAP AE RDL 2.2UF 50V 20% C24 C34-35 C52 C57 C81-83 C85 C88
2 0054204000 CAP AE RDL 22UF 450V 20% C130-131
37 0028467003 CAP AE RDL 22UF 50V 20% C1-2 C7 C19 C23 C40 C48 C51 C56
C61 C64-66 C69 C72-74 C76 C105
C134 C137 C601 C603-613 C634 C636
C638-639
4 0028460003 CAP AE RDL 4.7UF 50V 20% C12-13 C28 C161
2 0053955003 CAP AE RDL 47UF 160V 20% C92-93
4 0054206000 CAP AE RDL 47UF 350V 20% C125-128
1 0054205000 CAP AE RDL 47UF 450V 20% C129
6 0047195003 CAP AE RDL 47UF 63V 20% C4 C86 C98-99 C803 C807
2 0037182000 CAP AE RDL 6800UF 63V 20% C121-122
2 0053915000 CAP AE100V10000uF 20% C123-124
1 0039261001 CAP CA 330PF 100V C80
34 0034788003 CAP CD .1UF 50V 20% .15"CUT C644-649 C94-95 C132-133 C135-136
C139-160
3 0051457003 CAP CD 100pF 500V 5% C100-101 C637
2 0051960003 CAP CD 180 PF 500V 10% C14 C20
9 0051406003 CAP CD 220PF 500V 10% C25 C45 C62-63 C67-68 C70-71 C641
4 0051445003 CAP CD 22PF 500V 5% C18 C49 C54 C58
3 0051409003 CAP CD 68pF 500V 5% C16 C60 C89
2 0027255003 CAP MPF .001UF 100V C5 C11
3 0027257003 CAP MPF .0022UF 100V C44 C47 C87
1 0027260003 CAP MPF .0039UF 100V C79
5 0027261003 CAP MPF .0047UF 100V C38 C84 C96-97 C162
2 0027262003 CAP MPF .0068UF 100V C41-42
2 0027264003 CAP MPF .01UF 100V C602 C635
