Ok all you Marantz people (and others)
I've got a Marantz 16, a dual mono power amp soon to be on the bench for an overhaul/restoration - the 100w-100w version.
I'm concerned about the input section, it wasn't built with any type of balancing attenuator.
So if both of the monoblocks are a tad bit "off balance" from each other, a preamp balance adjustment must be done.
I want to add in a multi-turn trimmer on each amp so both amps are in perfect Db balance to avoid preamp adjusting.
I've come up with this (in schematic) - does anyone have an issue with this? - I want to have around a -3Db adjustment range that should be sufficient, eh?
I've got a Marantz 16, a dual mono power amp soon to be on the bench for an overhaul/restoration - the 100w-100w version.
I'm concerned about the input section, it wasn't built with any type of balancing attenuator.
So if both of the monoblocks are a tad bit "off balance" from each other, a preamp balance adjustment must be done.
I want to add in a multi-turn trimmer on each amp so both amps are in perfect Db balance to avoid preamp adjusting.
I've come up with this (in schematic) - does anyone have an issue with this? - I want to have around a -3Db adjustment range that should be sufficient, eh?
Hi wiseoldtech,
I believe your modifications should work fine. The only negative I can imagine is a slight rise in thermal noise due to the increased source impedance.
May suggest an alternate for your consideration: replace R3 and R5 with 1% (or better) tolerance resistors. Even if four 1% resistors combined for maximum mismatch, gain difference would be only about 0.34 dB.
Best,
Steve
I believe your modifications should work fine. The only negative I can imagine is a slight rise in thermal noise due to the increased source impedance.
May suggest an alternate for your consideration: replace R3 and R5 with 1% (or better) tolerance resistors. Even if four 1% resistors combined for maximum mismatch, gain difference would be only about 0.34 dB.
Best,
Steve
I really don't want to mess with R3/R5, I want to stay as original as possible, particularly around the DC Offset area.
I do, however, intend on replacing C19/C20 with a 47Uf bipolar.
I do, however, intend on replacing C19/C20 with a 47Uf bipolar.
What I believe Steve is saying is R3 and R5 feedback resistors set the gain of the amplifier and replacing those resistors with matched parts the gains will be closer. Use the same values but closer tolerance. This will be closer to original than your idea, though your plan still may be needed.
Craig
Craig
Just to clarify, I'm not suggesting changing their ratio, only their tolerance. But I think your design will work fine.
BSST, in the service manual, notice the circled (F) for those resistors.
It is mentioned in the manual that that represents Precision Film resistors.
Of course, I will check actual values, as I always do with something on my bench.
It is mentioned in the manual that that represents Precision Film resistors.
Of course, I will check actual values, as I always do with something on my bench.
I wondered if they might be 1%, but wasn't certain since they happened to be amongst 5% values. Maybe measurement will show gains are well matched at the outset.
Cheers!
Cheers!
BSST:
Those specific "F" resistors are all in the "critical" offset areas of the amp, not bad for a 1970-era Marantz.
However, they don't state the tolerence %, only wattage value. (1/2W)
Again, I will test them for any issues when I get the unit on my bench.
I'd just like to have an easy way to balance each amp without digging into that brick - the way it's made is unusual and tight.
Those specific "F" resistors are all in the "critical" offset areas of the amp, not bad for a 1970-era Marantz.
However, they don't state the tolerence %, only wattage value. (1/2W)
Again, I will test them for any issues when I get the unit on my bench.
I'd just like to have an easy way to balance each amp without digging into that brick - the way it's made is unusual and tight.