RM 100 CAPACITOR CHANGE THREAD

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Rilke

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Capacitor Change RM100
A thread about a complete capacitor change in the RM100 head.

I want to start this with a disclaimer, I'm neither a guitar amp tech or a man with thousands of hours of building amps or likewise. The reasoning behind changing capacitors in the RM100 stem from an honest curiousity and a problem (which might be specific to my RM100), which I had suspected was a capacitor problem, which indeed was rectified through the capacitor change. I also did not change the capacitors myself (had an amp tech do it), so in the nuts/solder/how-to-do-it department I must dissapoint.

Another thing worth mentioning is that there is great dispute as to what a capacitor change actually will accomplish. Some are on the train that if you exchange values exactly (which I more or less did), nothing will change, if the amp was in full working condition before/after. Some are of the opinion that the dialectric material and quality will matter in exchanging capacitors. IMO the capacitor change in my RM100 elicited a change, in many ways BUT one of my filter capacitors was in a bad way, so take this with a grain of salt. You can skip to the end of this post (”results”) if this is of your primary interest.

Process of thought/reasoning:
Filter caps:
I had noticed a filter capacitor bulging, which in elecotrolytic capacitors is generally a bad sign. So I was sure that a capacitor change for my amp was in order. The RM100 (mine atleast) was also born with Sus'con electrolytes, which is some forums is regarded as a 'bad cap', i.e. one liable to drift, break etc more easily than higher quality ones. Besides that the amp was 14 years old, which is a timeframe in which some electrolytic caps might need exchanging, again this is a topic of hot debate.
So regarding filter caps I thought I might aswell exchange all of these for ”higher quality” ones while one was being changed. After measuring dimensions of the capacitors used in the RM100 I opted for Nichicon and Würtz electrolytic capacitors for the power section and Elna Silmic electrolytes in the rest of the amp for electrolytes. You could of course do with other brands etc. this was just my choice for caps which would physically fit and was regarded to be of good quality for the application.
After consulting with Rob (Jaded Faith, whom I'll recommend any day for anything regarding amp work) whether or not this was ”safe”, I chose to up the values of the big 330uf, 350v filter caps to 390uf ones. This was the only actual value change in capaticance I chose to do with this installation.
Other caps:
The reasoning behind changing the other caps of the amp (including non-signal passing caps... Again an internet debate of giant proportions), was the thought, that since I was getting the filter caps replaced, I might aswell go all in, and replace the no-name brown drop 104's (0.1 uf) caps in the RM100, since I had no idea of the quality/composition of these.
Generally I opted for Orange Drop 6PS's to exchange the 104 brown drops, though I ended up picking up some MKT1813's aswell (among others). Since I don't know the composition of the original brown drops (polyester/polypropolyne/?), I can't tell for certain if I exchanged these with a similar type of cap. I went generally for polyester types since I like a great many different amps which rely on polyester types in signal paths. This is again a can of worms in regards to internet discussions.

Lastly I chose to replace all other caps, aswell (non signal passing etc). This was mainly due to OCD and giving myself the knowledge that I had done what I could. It could be over the top, and it might not be, just didn't wanna lose any sleep over it :)

Results:
As I have recorded this amp very much before the ”upgrade” (it's permanently attached to my recording studio i.e. Not a gigging amp), I had a very good baseline for judging the differences of the amp.
Immidiatly after upgrade the amp struck me as a lot more defined, especially in the low end/low mids.
I was worried the amp was TOO clear and bright in the midrange, but was also wondering whether some burn-in might elicit a change. Again burn-in of capacitors are a BIG discussion, with many arguments, but over time I did indeed notice an improvement.
I left the amp overnight for 2 days playing DI tracks of varying sorts through my cab, to see if any change was to be had. I am happy to report that the amp definitely DID become even better sounding. The brightness in the midrange settled somewhat down, and the amp developed a ”fuller” characteristic. Just to remove any suspicion of user-bias, I had recorded a before and after burn-in which were in line with my findings.

Overall the capacitor change made the amp both deeper/fuller sounding, and helped definition immensely, chord-definition in mid-to-high-gain is brillant, and the top end is less harsh, and somehow more chimy sounding. In one word, the amp sounds better than it ever has, while I have owned it.
Would I do it again; yeah, definitely. The cost of caps + tech could have been lower, if I had changed it myself and perhaps not opted to change EVERY single cap I could get my hands on haha. As with anything your milage might vary but for my particular RM100 it did make a hell of a lot of difference, and every single module I own (6 ranging from marshall plexi to over the top high gain), sounds better after.

I have linked the Mouser shopping list here. Again it is NOT necessary for you to exchange every single cap (as I did). I am very OCD about these things so I would recommend consulting the schematics with an amp tech to discuss where you'd get most bang for the bucks, in case you want to save some money:
1.
https://drive.google.com/open?id=1qz_MnKMQxSzvHv3eCYMgm87fB28Db-Bk
2.
https://drive.google.com/open?id=1Qm4fY4dTs_3cu9RQVqnPkwy1yuM_DCao

Last but not least this particular RM100 is now up for sale, this isn't a reflection of me being dissapointed with the amp, but a result of me needing to scrape together a lot of cash to buy a piece of gear I've gotten a great del on, even though it kinda tears me :(

Sorry for the long post,
Best regards Christian
 
Certainly can't hurt to replace those filter caps after 12-15 years and generally noticed quite a bit of change elsewhere in the amp by using Orange Drops.

Fun project! GLWS!
 
Thanks JKD! Yeah, it really hurts to let go of something which you've put this amount of love into haha :D But yes, IMO the amp sounded fuller and more balanced afterwards, so I'd do it again in a heartbeat.

General info:
The amp is now up in the Classified section (along with some modules)
 
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