Yamaha score! Now I have a few questions...

Hi folks,

I think that I did really well with my latest acquisition but I'll let you be the judge of that.

Last night I picked up a Yamaha MX-630 power amp (135 wpc), a CX-630 preamp, a TX-350 tuner and a CDC-625 5 disc changer for an unbelievably low $125. I think that the amp alone is worth double that and the rest is just icing on the cake.

The gear is in good cosmetic condition with some minor scuffing on the front panels. The preamp is in the roughest condition - the bass adjustment knob has been replaced with a non-Yamaha part and the LED in the volume dial has burned out, assuming that there was one in the first place. My Yamaha HT receiver has one and it's just a couple of years newer than the preamp.

The first thing that I did upon bringing everything home was to perform a visual inspection of the amp and preamp. Nothing looked burned or out of place so I gave them a blast of canned air and closed 'em up. Next, I connected a multimeter to the speaker terminals and checked the amp's DC offset. I was pleased to see that it hovered around zero with the occasional run up to about 1.7 mV. Pretty good numbers as far as I can tell. I connected the preamp, amp and CD player together, crossed my fingers and powered the system up. Everything worked but there was a problem - the left channel was much weaker than the right channel. I powered everything off and checked all my connections. No problem found. I fired the system back up but the problem was still there. I fiddled with the knobs and switches on the preamp - nothing unexpected happened. Wait a minute - that Loudness pot is really scratchy! I opened up the preamp again and gave the pots a shot of Deoxit then worked them for a couple of minutes. Hooked everything back up and BINGO!! Sweet, punchy, rock and roll playing through my grateful HPMs.

It took all of ten seconds to hear the difference between the MX-630 and the SX-880. Is it the extra wattage doing that or is there something else going on here? I'll have to get to know this MX-630 better. I have to say, the HPMs love Yamaha amplifiers. They sounded fantastic with the RX-V870 and even at low volume, they sound amazing while connected to the MX-630. I had pretty low expectations for the CD player but it didn't do too badly either.

So now if you'll indulge me, I have a few questions:

1. How do you restore the exterior finish of these black Yamaha components? I'd like to eliminate the scuffs and small scratches, if possible. Would a touch of gentle car wax restore the shine once the scuffs are gone?
   
   
2. The power amp has level pots but the overall volume is largely determined by the preamp's gain. Is there any reason why I wouldn't want to leave the amp's levels at full and just use the preamp to adjust the volume? Are there any situations where I would need to reduce the output at the power amplifier?
   
   
3. My power-up sequence is preamp on first, power amp second and the reverse for shutdown - amp off first followed by the preamp. Am I doing this right?
   
   
4. As mentioned, the bass adjustment knob is not the original part. Those "VH889x00" knobs appear to be pretty common on Yamaha Natural Sound equipment. Might somebody have spares to sell or be able to tell me where to find a replacement?
   
   
5. I have already cleaned some pots with Deoxit. I hope that this was not a mistake! Is a follow-up with Faderlube recommended, unneccessary or something to avoid altogether?

Thanks for taking the time to read this long and windy post. As you can tell, I'm pretty excited about the new gear. I have always wanted separates and I have been a fan of Yamaha products for some time. Of course, it's nice to get a deal on equipment too! To have combined all of these things in one purchase is a real treat for me.

Cheers!

Concrats on the Yamaha gear.

Yes, more power does sound different. Usually it gives more clean dynamics and bass response, this of curse is only up to some point but at 60W vs. 135W the difference will be quite audible. A rule of thumb is that the amp shall be 2 x the rated power of the speakers and this is where the level pots on the amp come in to play, by turning the level down on the amp you get more "room" on the pre amp volume knob and safety for you’re speakers (if some jack as just cranks up the volume to 11 on the pre).

The power up sequence? If something goes haywire how will you detect/stop it? The only thing that really will do an impact is to start the power amp with the level turned all the way down and then go up to desired level but this will be a pain in the a.. In the long run if you don't run the level on full power all the time.

Lubing; if you ask a pro about using lubing in pots and faders they will look strangely at you, if you have a problem with a pot/fader you change it. If you have to clean it, no lube. In the long run the lube will act like a magnet on dirt.

rushfan said:

1. How do you restore the exterior finish of these black Yamaha components? I'd like to eliminate the scuffs and small scratches, if possible. Would a touch of gentle car wax restore the shine once the scuffs are gone?
   
   
2. The power amp has level pots but the overall volume is largely determined by the preamp's gain. Is there any reason why I wouldn't want to leave the amp's levels at full and just use the preamp to adjust the volume? Are there any situations where I would need to reduce the output at the power amplifier?
   
   
3. My power-up sequence is preamp on first, power amp second and the reverse for shutdown - amp off first followed by the preamp. Am I doing this right?

Click to expand...

1 Clean with a mild cleaner and cloth first, then wax. You could try a mild polish like Meguire's Crystal System-Step #2 if there are any scuffs still visible. Just be gentle around any lettering.

2 Those controls can be used to attenuate the max output to the speakers so you don't inadvertently blast the room. Also, should be set lower if your speakers are rated for less than your amp.

3 Plug the amp into the switched outlet on the pre-amp, and leave it turned on. Then just use the power switch on the pre-amp to turn on the system.

the-real-mandak said:

Lubing; if you ask a pro about using lubing in pots and faders they will look strangely at you, if you have a problem with a pot/fader you change it. If you have to clean it, no lube. In the long run the lube will act like a magnet on dirt.

Click to expand...

"markthefixer" recommended Faderlube for the pots in my SX-880 so I ordered some a few days ago. He seems to really know what he's talking about. I bought the 5% formula only so I feel confident that it won't gum up the pots. If it does for some reason, I'll flush them again.

I appreciate the advice given thus far. I'm gonna go grab some rags and start cleaning! I'd like to post a few pictures if the results are good.

I chickened out and didn't use the Faderlube. I did, however, give the pots and jacks another Deoxit treatment.

I used a bit of Meguire's Plast-X on the front panels of the amp and preamp and it did a nice job restoring the finish. It's intended for clear plastic so it's pretty gentle. This was preceeded by a good clean with mild soap and water with a nearly-dry cloth. I followed up with an Armor-All like product from Turtle Wax that was designed for plastics. It was well suited to the job. The remaining blemishes faded from view and the finish was a nice smooth, velvety black. Not too oily or shiny either.

I still have to tackle the tuner and CD changer and then the big job starts - moving components in and out of the cabinet to accomodate the new gear. I really wish that I had some decent interconnects but I have just one good one at the moment. I'm thinking about making some DIY interconnects but the version that I want to try requires a Woods brand cable that I can't find here in Canada. Perhaps I'll head over to the DIY forum to see what folks over there have done.

Deoxit D5 may be a problem with some pots because the thinning solvent can sometime dissolve the adhesive holding the carbon contacts on on inside. It is recommended to use 100% Deoxit in pots, followed by Caig Shield or Gold, followed by Faderlube: see attached scan of a Deoxit white paper. The solvent in the D5 can also dissolve the existing lubricant in the pots so the addition of Faderlube resolves this issue. Faderlube is designed for this purpose and won't create an attraction situation as described earlier in this thread. Just don't use oil or WD-40, which will attract gunk.

Bubba,

Thanks for the second opinion. I went with the Faderlube after all. I had already purchased the 5% spray so I went with what I had.

Everything is clean and installed in the cabinet. I was pleased to discover that the remote for my RX-V870 works with the CX-630 so that's one less purchase to worry about.

Now I just need to find an original tone adjustment knob to finish the job.