MCS 3245 q-u-e-s-t-i-o-n-s-?
- Thread starter Billy Dio
- Start date
Hifirob2
NEC and Klipsch rock!
That Spokane commercial makes me wonder if it was trying to clearance those models out of their particular local stores. By 1982, the 3125, 6700, and 8228s should have been long gone. They weren't in the catalog. Maybe the commercial was from mid 1979 through 1981?
The 1977 commercial is great!
The 1977 commercial is great!
Racingh11
Super Member
I thought so too. It really has that 70s feel and lighting.
Racingh11
Super Member
I have several SAMS manuals in front of me at the moment and I'm looking over the power amp sections
3207 is a simple 5 transistor per channel(7 if you count darlingtons as 2). It does not have a differential input or a bias adjustment according to the schematic. It is a bootstrap design with darlington outputs. No speaker protection.
3230 has 9 transistors(11 counting darlingtons). It has a differential input pair with a resistor/capacitor voltage tail. Resistor/transistor set current VA stage with typical bias setting transistor. It has darlington outputs with a pair of current limiting transistors on the emitter resistors. Uses fuses for speaker protection.
3233 and 3235 are the same except the transformer voltage is higher on the 3235. They have 8 transistors per channel(or 9 if counting bias darlington). It has a differential input with a zener/capacitor voltage tail. And a bootstrap VA stage with typical transistor bias setting. It uses a typical emitter-follower driver and output stage with 1 pair of 2N2955/2N3055 per channel. The heat-sink includes the chassis and has thermal grease between the flange. Uses fuses for speaker protection
3835 has 7 transistors. It is the same basic design as the 3233 & 3235. It has a differential input with a zener/capacitor voltage tail. And a bootstrap VA stage. Except it uses a diode and potentiometer for bias control. That is worse for temperature compensation. Has 1 pair of output transistors and uses a relay for speaker protection.
3237 has 11 transistors. It has a differential transistor input with a diode/transistor current source tail and a diode/transistor current mirror on the collector side. It then goes to a diode/transistor current source paired VA stage and typical bias control and emitter-follower in drivers and output stage. Has 1 pair of output transistors and fuses for speaker protection.
3245-00 has 11 transistors per channel(12 with bias darlington). It has a differential pair input with zener/capacitor controlled voltage. It goes from there to a diode/transistor current sourced VA stage with typical bias control. It is then a typical emitter-follower driver and output stage with 1 pair of MJ1015/MJ15016 and a pair of current protection transistors driven from the emitter resistors. Runs on +/-38.5v. It uses a relay for speaker protection.
3245-10 has 12 transistors per channel(13 with bias darlington). It has a differential pair input with zener/capacitor controlled voltage. It adds a transistor to the circuit in the 3245-00 to make it a differential-current mirror VA stage with typical bias control. Then on to a typical emitter-follower driver and output stage with 1 pair of MJ1015/MJ15016 and a pair of current protection transistors driven from the emitter resistors. Runs on +/-42.5v. Uses circuit breakers for speaker protection.
3253 has 7 transistors. It is basically the same as the 3835 with higher wattage. It uses a differential input pair with a zener/capacitor controlled tail. It uses a bootstrap designed VA stage and typical emitter-follower driver and output stage. It uses 1 pair of 2SB618/2SD558 output transistors and has relay speaker protection.
3260 has 15 transistors. It uses a FET differential input and zener/capacitor voltage tail with DC offset potentiometer. It then goes to a second differential pair made from bipolar junction transistors. Then to a third differential pair for the voltage amp stage with a diode/transistor controlled current source. Uses a diode and potentiometer for bias control. The path then goes to a emitter-follower driver and output stage. It has two pairs of staggered current protection transistors on the output emitter resistors. It has 1 pair of output transistors and uses a relay for speaker protection.
3860 has 7 transistors and an IC. It uses an IC for input and voltage amp stage. It then goes into a emitter-follower driver stage with transistor/potentiometer bias control. Then to another emitter driver stage with thermistor bias protection and into a single transistor pair output. It uses relay speaker protection.
3275 has 11 transistors (uses 2 pair of outputs). It is almost the same design as the 3245 except it uses a resistor/capacitor current tail on the input pair. This is a step down below zener controlled source. Both are worse than a transistor current source. Also has diodes instead of transistor for bias control(inferior temperature compensation), and does not have a pair of transistors to control output current. It uses 2 pairs of 2SB618/2SD588 output transistors. It uses relay speaker protection.
3285 has 23 transistors. It uses a FET differential pair with a zener/transistor current tail and a pair of transistors for current mirror legs. It then goes to a differential pair with resistors for legs and tail. Then on to a differential pair VA stage with diode/transistor current mirror. The output side of the last differential stage has one transistor cascaded with it for linearizion, voltage handling, and has a zener to keep it from overload. It uses two diodes and a potentiometer for bias. Then to two emitter-follower driver and one output stages. The second higher current driver stage has an adjustable current mirror between them and the base resistors for the output.(unusual) It also has two pairs of cascaded transistors driven from the output emitter resistors and a thermistor for current protection with thermal tracking. There are parallel resistor/capacitors on every base of the drivers and output. It uses relay speaker protection.
3125 has 22 transistors. It has a FET differential input pair with zener/capacitor collector legs and a diode/transistor current source tail. Tail has DC offset potentiometer. Path then goes to a bipolar junction transistor differential pair with resistors for legs and tail. This goes to a third differential pair VA stage with a transistor/transistor current mirror. It uses a pair of diodes and a potentiometer for bias control and a transistor cascaded with one of the last differential pair and appears for linearizion and voltage handling and has a couple of diodes to keep it from overload. Then it has two emitter-follower driver stages and one output stage of a single pair of transistors. It uses no capacitors in the base paths and no resistors at all on the second driver bases. It has six transistors driven from the output emitter resistors and are used for current protection. Two pairs are cascaded into the other pair and one has a thermistor in the base circuit. It appears they might have two different cut rates and thermal compensation on one. The one with thermistor cuts right at the max power level, hard cut. The other pair cuts at about 1/3 power, but needs to charge a capacitor first and average power, or soft cut. The 3285 and 3125 are similar but I would say the 3285 has a better input differential stage, but everything a little worse than the 3125 after that.
These are some of the basic attributes I noticed. There are many small details as well. They all have different resistor and capacitor sizes even if the schematic design is basically the same. Dominant pole capacitor roll-off, negative feedback curve, gain, and values that effect slew rate could all be examined further. I'm open to schematics or comments to add.
3207 is a simple 5 transistor per channel(7 if you count darlingtons as 2). It does not have a differential input or a bias adjustment according to the schematic. It is a bootstrap design with darlington outputs. No speaker protection.
3230 has 9 transistors(11 counting darlingtons). It has a differential input pair with a resistor/capacitor voltage tail. Resistor/transistor set current VA stage with typical bias setting transistor. It has darlington outputs with a pair of current limiting transistors on the emitter resistors. Uses fuses for speaker protection.
3233 and 3235 are the same except the transformer voltage is higher on the 3235. They have 8 transistors per channel(or 9 if counting bias darlington). It has a differential input with a zener/capacitor voltage tail. And a bootstrap VA stage with typical transistor bias setting. It uses a typical emitter-follower driver and output stage with 1 pair of 2N2955/2N3055 per channel. The heat-sink includes the chassis and has thermal grease between the flange. Uses fuses for speaker protection
3835 has 7 transistors. It is the same basic design as the 3233 & 3235. It has a differential input with a zener/capacitor voltage tail. And a bootstrap VA stage. Except it uses a diode and potentiometer for bias control. That is worse for temperature compensation. Has 1 pair of output transistors and uses a relay for speaker protection.
3237 has 11 transistors. It has a differential transistor input with a diode/transistor current source tail and a diode/transistor current mirror on the collector side. It then goes to a diode/transistor current source paired VA stage and typical bias control and emitter-follower in drivers and output stage. Has 1 pair of output transistors and fuses for speaker protection.
3245-00 has 11 transistors per channel(12 with bias darlington). It has a differential pair input with zener/capacitor controlled voltage. It goes from there to a diode/transistor current sourced VA stage with typical bias control. It is then a typical emitter-follower driver and output stage with 1 pair of MJ1015/MJ15016 and a pair of current protection transistors driven from the emitter resistors. Runs on +/-38.5v. It uses a relay for speaker protection.
3245-10 has 12 transistors per channel(13 with bias darlington). It has a differential pair input with zener/capacitor controlled voltage. It adds a transistor to the circuit in the 3245-00 to make it a differential-current mirror VA stage with typical bias control. Then on to a typical emitter-follower driver and output stage with 1 pair of MJ1015/MJ15016 and a pair of current protection transistors driven from the emitter resistors. Runs on +/-42.5v. Uses circuit breakers for speaker protection.
3253 has 7 transistors. It is basically the same as the 3835 with higher wattage. It uses a differential input pair with a zener/capacitor controlled tail. It uses a bootstrap designed VA stage and typical emitter-follower driver and output stage. It uses 1 pair of 2SB618/2SD558 output transistors and has relay speaker protection.
3260 has 15 transistors. It uses a FET differential input and zener/capacitor voltage tail with DC offset potentiometer. It then goes to a second differential pair made from bipolar junction transistors. Then to a third differential pair for the voltage amp stage with a diode/transistor controlled current source. Uses a diode and potentiometer for bias control. The path then goes to a emitter-follower driver and output stage. It has two pairs of staggered current protection transistors on the output emitter resistors. It has 1 pair of output transistors and uses a relay for speaker protection.
3860 has 7 transistors and an IC. It uses an IC for input and voltage amp stage. It then goes into a emitter-follower driver stage with transistor/potentiometer bias control. Then to another emitter driver stage with thermistor bias protection and into a single transistor pair output. It uses relay speaker protection.
3275 has 11 transistors (uses 2 pair of outputs). It is almost the same design as the 3245 except it uses a resistor/capacitor current tail on the input pair. This is a step down below zener controlled source. Both are worse than a transistor current source. Also has diodes instead of transistor for bias control(inferior temperature compensation), and does not have a pair of transistors to control output current. It uses 2 pairs of 2SB618/2SD588 output transistors. It uses relay speaker protection.
3285 has 23 transistors. It uses a FET differential pair with a zener/transistor current tail and a pair of transistors for current mirror legs. It then goes to a differential pair with resistors for legs and tail. Then on to a differential pair VA stage with diode/transistor current mirror. The output side of the last differential stage has one transistor cascaded with it for linearizion, voltage handling, and has a zener to keep it from overload. It uses two diodes and a potentiometer for bias. Then to two emitter-follower driver and one output stages. The second higher current driver stage has an adjustable current mirror between them and the base resistors for the output.(unusual) It also has two pairs of cascaded transistors driven from the output emitter resistors and a thermistor for current protection with thermal tracking. There are parallel resistor/capacitors on every base of the drivers and output. It uses relay speaker protection.
3125 has 22 transistors. It has a FET differential input pair with zener/capacitor collector legs and a diode/transistor current source tail. Tail has DC offset potentiometer. Path then goes to a bipolar junction transistor differential pair with resistors for legs and tail. This goes to a third differential pair VA stage with a transistor/transistor current mirror. It uses a pair of diodes and a potentiometer for bias control and a transistor cascaded with one of the last differential pair and appears for linearizion and voltage handling and has a couple of diodes to keep it from overload. Then it has two emitter-follower driver stages and one output stage of a single pair of transistors. It uses no capacitors in the base paths and no resistors at all on the second driver bases. It has six transistors driven from the output emitter resistors and are used for current protection. Two pairs are cascaded into the other pair and one has a thermistor in the base circuit. It appears they might have two different cut rates and thermal compensation on one. The one with thermistor cuts right at the max power level, hard cut. The other pair cuts at about 1/3 power, but needs to charge a capacitor first and average power, or soft cut. The 3285 and 3125 are similar but I would say the 3285 has a better input differential stage, but everything a little worse than the 3125 after that.
These are some of the basic attributes I noticed. There are many small details as well. They all have different resistor and capacitor sizes even if the schematic design is basically the same. Dominant pole capacitor roll-off, negative feedback curve, gain, and values that effect slew rate could all be examined further. I'm open to schematics or comments to add.
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Racingh11
Super Member
Keep in mind, these are only power amp sections being discussed, the preamp and tone controls can be completely different between these models. I base what I consider to be a good design off of known tests from amp design books which show the effects of one change in the design and tests to compare in isolation. It gives me a good idea of what is good for distortion, noise, slew, power supply rejection, etc. Doesn't mean it's a sure thing, but I look for patterns and compare to real life opinions and it seems to hold up.
Racingh11
Super Member
I think the 3125 would have been even better if the second differential pair was properly current mirrored and sourced. All of the other sections are better isolated from the power supply. It would also help it slew faster. I personally would have only used one pair of transistors for current protection in the output and used the other transistors to setup that week point in the second diff. pair.
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Racingh11
Super Member
Update to this information:
3223 is the same power amp as the 3233 and 3235, except run at a lower voltage and has a few transistors that are the same model, but the lower voltage rated version. The tuner is the same as the 3233 & 3235. The preamp is a little different and tone board is different since it does not have midrange control like the other two. The 3223 appears to be the little brother of 3233 with less options.
Racingh11
Super Member
Update: 3865 has 11 transistors (uses 2 pairs of outputs). It has a bjt differential input with a resistor capacitor tail getting power from zenor/transistor regulated power supply. This goes to a second differential pair with tail powered by same reg. source as input, and legs with a current mirror voltage stage with potemtiometer/diode bias. Then to a typical emmiter-follower driver stage and then to a pair of parallel output transistors, 2SD587 & 2SB617 It uses relay protection. It is the same as the 3275, except with dual power supplies and regulated supply. And similar audio circuit to the 3245-10
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Racingh11
Super Member
There are a few differences in the design between the 3865, 3275 power amp section and 3245-10 power amp section even though they are very similar. (not talking pre-amp or tone control circuits). They are well designed amps that keep the transistor count low. The 3865 runs about the same no load voltage as the 3245, but since it is a dual mono-block, it has a transformer for each channel to give it 65 watts per channel at 8 ohm vs. 45 watt of the 3245 single transformer. The 3865 also runs 4x 10,000uF 50v caps vs. 2x 10,000uF 50v for 3275, and 2x 6,800 50v in the 3245. The 3865 also runs the differential input at a regulated 84V from end to end compared to about 54V in the 3245. The 3275 is unregulated at 93V. This should give the 3865 a slight advantage in input slewing over the 3245 and less noise than 3275. The voltage-amp stage is also supplied by the regulated power on the 3865, vs. the 3245 and 3275 which draw from the main power supply caps. This may give it a better s/n ratio in the that stage, but could slow VA slewing if regulation lags at all. The 3865/3275 uses 2 diodes and a potentiometer for bias which is not as good for thermal tracking as a transistor/pot setup like the 3245. The 3865 and 3275 use identical values and varies from what the 3245 has. Partly because of the different wattage and because they use different transistors that have different junction capacitance. And because different designers had different ideas about what works best. Difficult to say without reverse-engineering the whole thing. Both of these amps would be improved with a better differential input circuit. Put an actual controlled current source on the tail for sure plus a current mirror for the legs if someone really wants it good. The resistor tails require more current load and linearity from the transistors vs. an active current source that relieves them of most of those issues. Also there are no current protection transistors on the emitter resistors of the 3865 or 3275. This should open up the headroom a bit for transient sonics that could be cut off with current limit circuit. The 3865/3275 run the speaker protection relay circuit from the resistors instead.
Just wanted to add some information so people could know if or why something sounds better and what they actually have.
Just wanted to add some information so people could know if or why something sounds better and what they actually have.
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Racingh11
Super Member
I just tested THD+N on a recapped 3235. The numbers are hard to believe since it is rated at 0.3% THD. Both channels driven at rated power into 8 ohm loads.
L R
20khz .037 .031
10khz .040 .030
1khz .022 .029
20hz .009 .012
I will probably go back and test IMD and slew-rate and rise-time when I get a chance.
L R
20khz .037 .031
10khz .040 .030
1khz .022 .029
20hz .009 .012
I will probably go back and test IMD and slew-rate and rise-time when I get a chance.
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Billy Dio
Well-Known Member
It's cool to see all this info and testing being added to the post as it can help someone at some point. The older these things get, the more important it is.
I'm still running my recapped 3233 daily, almost 24/7. Using it with a center channel (Matrix +L and +R to a center + and - to get the matrix effect on a mono speaker that compliments left and right stereo usage) and left/right stereo. Run it for PC/Streaming usage and gaming. Never push it hard though (like 10% or less of rated if I had to guess) which helps with heat as the stock heatsink is pathetic and needs a fan or fins brazed on or upgraded to a modern heatsink alternative. Works great for what it is. And doesn't have that flat and compressed sound like other units.
Keep them at sane power levels at 8 ohm (3233 and probably 3223 and 3235 if similar) and at least the 3233 runs forever. Beat the tar out of the one I had in HS and only thing it'd do is pop a speaker fuse if pushed excessively hard playing early 90's rap +6 bass w/ loudness on at/near clipping for extended periods. And even at those volumes, it held the sound together nicely whereas cheaper units started breaking up.
I'm still running my recapped 3233 daily, almost 24/7. Using it with a center channel (Matrix +L and +R to a center + and - to get the matrix effect on a mono speaker that compliments left and right stereo usage) and left/right stereo. Run it for PC/Streaming usage and gaming. Never push it hard though (like 10% or less of rated if I had to guess) which helps with heat as the stock heatsink is pathetic and needs a fan or fins brazed on or upgraded to a modern heatsink alternative. Works great for what it is. And doesn't have that flat and compressed sound like other units.
Keep them at sane power levels at 8 ohm (3233 and probably 3223 and 3235 if similar) and at least the 3233 runs forever. Beat the tar out of the one I had in HS and only thing it'd do is pop a speaker fuse if pushed excessively hard playing early 90's rap +6 bass w/ loudness on at/near clipping for extended periods. And even at those volumes, it held the sound together nicely whereas cheaper units started breaking up.
Billy Dio
Well-Known Member
Also, from what I remember with my 3245, the amp board layout is roughly the same. They even use the woefully inadequate heatsink of the 3233, or one that appears virtually identical. Given they are overburdened on the 33 wpc amps, pushing hard at 45 wpc is probably a bad idea, especially with original thermal paste.
Interesting thread as I am currently the owner of a fairly new to me MCS 3842. It is definitely Technics and appears to be from the same lineage as the 3840 and 3860. I use it in my main system to drive four speakers and it does well and doesn't get too hot. It does seem that MCS was a bit all over the place when it came to who built their stuff. My unit is from early 1982 I believe.
Racingh11
Super Member
The 3233 and 3235 are basically the same. The heatsink is better than it looks. It uses the whole chassis as a heatsink. It's a good idea to reapply the thermal grease between the heatsink and the chassis. The 3245 is a different type of amp design and uses a bigger finned aluminum heatsink.
The first pic is a 3235 and the second is a 3245.
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Racingh11
Super Member
I have had a 3842, 3860, and still have a 3840 and some matching tuners. I like the tuners look and layout. Nice looking and not too busy or flashy. I'm still not sure what the difference is between 3840 and 3842 amps, or 3760 and 3762 tuners.
The 3860 is interesting because it has a type of class G circuit that switches windings on the power supply depending on speaker resistance. It seems to be a static resistance checking circuit and not a dynamic power sensing one like a true class G or H.
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Nice information. I made a mistake as to the manufacture date of the 3842. It is November 1983. I think it's funny that they had both a 3840 and 3842. Two watts difference in power? In fact I currently see a 3840 for sale with a date code of June 1983 so maybe that was just a slightly earlier model. Also the 3860 I see for sale has a date code of June 1982. The 3842 must have come slightly later to the party.