I think I am being misunderstood here. I am merely pointing out that if someone wants to use a dedicated headphone amp, and does not want to do a lot of soldering then it is a good mod. You say op-amps are a must, if so then removing the HDAM will improve it and costs NOTHING. I will not post again and spoil the club!
It costs nothing but without other mods it's going to be a downgrade in my opinion. I remember when my main player was a cd63ki I did the HDAM bypass and it DID improve the sound. Veils were lifted and all such goodness but it does also make the sound thinner. That's not something I'd want unless the op-amps behind it were good and some power supply work had been done too. I'd also not do it before re-clocking as with that hazy, fuzzy jittery sound it would be better to have some weight behind it, even if it lacks distinction and clarity.... but this is me and I very much favour a rich sound over an "accurate" or anaemic one.
Brent's mods list is by far the most comprehensive collection of mods, though it doesn't include instructions!!!
http://www.fidelityaudio.co.uk/rmcdmodlist.pdf
http://www.fidelityaudio.co.uk/rmcdmodlist.pdf
If it's a cd63 the best mod is probably regulating the servo drivers, along with re-clocking the servo and the DAC. Those two/three mods are your key ones. The output stage is perhaps a matter of taste more than fidelity. I've tried op-amps, op-amps + HDAM, Lundahl transformers, Lundahls + op-amp and finally discrete stage. The discrete one is the truest one, the others are just differing levels of lower-fi.
The easy fix for the output is just to change the op-amps for better ones, usually done with LM4562 as they're exceptionally neutral-sounding - very similar to the discrete output stage (DOS as often called). On top of this you can keep the HDAM (less open, more weighty) or bypass it (more open and decluttered but less foreceful and warm). A MUST-do mod is bypassing the DC blocking caps as, generally speaking, they achieve nothing and corrupt the sound (particularly the bass I found) a lot.
It's also exceptionally important to add some additional voltage regulators to the other circuits: DAC, decoder, servo chip etc. The more you add the clearer the sound gets, simple as that really.
Simon
The easy fix for the output is just to change the op-amps for better ones, usually done with LM4562 as they're exceptionally neutral-sounding - very similar to the discrete output stage (DOS as often called). On top of this you can keep the HDAM (less open, more weighty) or bypass it (more open and decluttered but less foreceful and warm). A MUST-do mod is bypassing the DC blocking caps as, generally speaking, they achieve nothing and corrupt the sound (particularly the bass I found) a lot.
It's also exceptionally important to add some additional voltage regulators to the other circuits: DAC, decoder, servo chip etc. The more you add the clearer the sound gets, simple as that really.
Simon
Just as an aside: I compared my player (just before this latest upgrade) to a stock 63' that I am now listening to, and a Teac something from a few years ago. The 63 sounded rather mechanical and veiled. The Teac with an outboard Musical Fidelity V-dac, sounded very pleasent but still lacked the definition of my 67. I suspect now the differences will be a lot greater. The Teac surprises though...It is time to address the rather dismal esthetics of the Marantz. I can't do much about the front but I will put nice thick wooden cheeks and a plexi top. Man's gotta do what a man's gotta do.
What do you mean by shorting out? And how would that make a difference? Aren't the fuses important to protect the whole circuit from a short circuit?
ahh now there's a question! and one that can raise the dead and the not so dead from their graves. This is an ancient tweak dating back to the 80's at least. I don't want to hear howls of fury from our flat earth friends and I don't have the tech savvy to explain this, but the el-cheapo fuses holders and fuses in general are bottle-necks. Unless you are really ham-fisted or have some dire surge in your electrics, the fuses are useless. It's a simple mod and can be tried out before making permenant. As a tweak it is on a par with removing the zip-cord and installing a proper power cord. It's not vital but it is free and it works. I haven't has any fuses in mine for 15 years and it works a treat.
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Okay, I'll check it out
Also, any instructions for regulating the servo driver chips?
Is that a tongue I see wagging in your cheeks Simon? Funny you should mention this. The Teac has long pointy feet built-in. I removed the rubber ones on my M. and use ebony cones.
Yeh, buy some 7808 and 7908 regulators (3 of each) and tap power from the +-10V rails that previously supplied the servo drivers to supply each chip (there's a resistor on each supply you can lift to isolate it) with its own regulated rail. Have a good gander at the service manual and come back with any questions.
The fuse only protects one part of the player and it's the most power-hungry part which, particularly in vanilla-grade models, is supplied with a barely-adequate supply. The fuse is resistive so it's just a little tweek to lift the ability of the supply.
The fuse only protects one part of the player and it's the most power-hungry part which, particularly in vanilla-grade models, is supplied with a barely-adequate supply. The fuse is resistive so it's just a little tweek to lift the ability of the supply.
"Okay, I'll check it out
Also, any instructions for regulating the servo driver chips?" I'm afraid I am out of my element there but you will be answered shortly. Regarding the fuse issue: bypassing the fuse means either; soldering a piece of decent solid core wire across the two halves of the holder (minus the fuses!) or desoldering the fuse holders altogether (from underneath) and soldering a piece of wire connecting the now opened holes in its place. The first option is easy if you sand down a bit the holder, but you risk getting solder in the holder and rendering it pretty useless. The second requires getting access to the underside of the board. I will leave you to invisage what that entails. Not exactly for the faint-hearted. Yet a third option is splashing out 40£ or so for audiophile grade fuses. But this is not going to be as good as number 2. Jeez I'm wordy today...
Also, any instructions for regulating the servo driver chips?" I'm afraid I am out of my element there but you will be answered shortly. Regarding the fuse issue: bypassing the fuse means either; soldering a piece of decent solid core wire across the two halves of the holder (minus the fuses!) or desoldering the fuse holders altogether (from underneath) and soldering a piece of wire connecting the now opened holes in its place. The first option is easy if you sand down a bit the holder, but you risk getting solder in the holder and rendering it pretty useless. The second requires getting access to the underside of the board. I will leave you to invisage what that entails. Not exactly for the faint-hearted. Yet a third option is splashing out 40£ or so for audiophile grade fuses. But this is not going to be as good as number 2. Jeez I'm wordy today...
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A better option, IMO, is to solder across the holder on the outside, thus not rendering the holder unusable in the future. Why on earth you'd change it I don't know, but it leaves the option.
Shep - I didn't remember you already had good cones! I only suggested metal ones as they'd match the gold writing / details on the front of the unit.
Shep - I didn't remember you already had good cones! I only suggested metal ones as they'd match the gold writing / details on the front of the unit.