RM100 Brain Surgery

So aside from the usual Input Coupler cap mods notated in Pete's forums, has anybody done any non-visual mods to their actual head unit?

My buddy Steve has....

We blew some resistors (and fuses) trying to play a bass through the head into a car subwoofer, so we had to open up the head and find out what was damaged. In the process of replacing the busted resistors with something that handled a bit more wattage, we decided to upgrade the capacitors on the tube board while we were at it!

Dear sweet Lord... An RM100 filled with SoZos... It's a beautiful thing, and it's barely had 20 hours of play on the caps yet

And the result?

See my last line in the post

The power tubes and a couple of preamp tubes were changed out, but it seems the caps smoothed the highs and gave the amp a bit more of a "mature" voice. Kinda like what upgrading the components of a stock module will do, only on a more subtle level.

Steve loves his treble (just like Fig), and usually his leads are piercing to me. Not any more!

We have the components to do the same thing to my amp when I'm ready and have the time Maybe after this weekend...

I did some similar tweaks to my RM4 I just sold, an RM100 I sold a while back (too bad cap changes couldn't shave 30lbs off that beast...) and my RT2/50. Big boy sounds are a good descriptions. I went with Orange Drops, Mallorys or a few MPW's I have around here. The stock stuff wasn't total crap or any different than the stuff in my Egnater M4, but nicer parts are always good.

Cool to hear that other people had the same things in mind! I'm gonna put SoZos in mine too, but I won't be doing all the caps in the FX loop section like Steve did. Plus, I've got an Audience Auricap for the input coupler. The theory is that each module has its on coupling cap (C3), so having a transparent input on the head will allow a greater disparity between different preamp voicings! Hopefully I didn't waste $13 xD

Could you make some pictures while you're in there?

I've been thinking of upgrading the caps in my RM4 to Wima's ..

Any advantage or difference between Wima, Orange drop and Sozo's?
Anthony has mentioned that he prefers Wima's for a lot, but I don't have any bearing on those boutique-ie ones (SoZo, Audience ?)

m0jo said:

Could you make some pictures while you're in there?

I've been thinking of upgrading the caps in my RM4 to Wima's ..

Any advantage or difference between Wima, Orange drop and Sozo's?
Anthony has mentioned that he prefers Wima's for a lot, but I don't have any bearing on those boutique-ie ones (SoZo, Audience ?)

Click to expand...

SoZos: I would guess more vintagey and a little more mature sounding.
Orange Drop: Like SoZo but a looser bottom end response. They can make an amp boomy in the input coupler when using the same value from what I've heard.
Wima: From what I can tell, tight and smooth lows and highs with a unique midrange to them.
Audience: Hi-fi cap. Super clear, very little coloration, and they make your wallet bleed a lot too...

Is there any more info or pics on changing out caps?

Not yet, Daryl. I haven't had the time to work on my amp yet. But I'll make sure to take a high res series of pictures chronicling my work.

As I said, there are about a half dozen aps in the FX loop that I probably won't be changing out that I'm sure can add something to the mix. I'm wondering if Maybe adding some Orange Drops in there would beef the sound up MORE when I crank the FX level knob... Like using the FX level as a variable "beef" control

So it looks like I might be interested in a mix of mostly SoZos and some Wimas for something "classic" and at the same time "just a bit off-color"

Interesting that Orange Drops would be "boomier" as I understood Orange Drops to drift into the "ice-picky" realm.

After the caps comes the MM Trannies (and choke!) surgery... :shock:

Zander said:

So it looks like I might be interested in a mix of mostly SoZos and some Wimas for something "classic" and at the same time "just a bit off-color"

Interesting that Orange Drops would be "boomier" as I understood Orange Drops to drift into the "ice-picky" realm.

After the caps comes the MM Trannies (and choke!) surgery... :shock:

Click to expand...

Yeah. I would probably try the SoZo in the Input coupler and try the Red Wimas elsewhere. I may end up using the SoZos I got for something else and sticking the Wimas in my power section for a bit more of that German flavor (supposedly ENGLs use Red Wimas a lot?)

ODs can bring the ice pick too. From what I've read, the way they're built doesn't handle low frequencies very (I think under 200hz?), so there's more distortion from the capacitors in the low frequencies that contribute to that growly, wooly low end we're used to from Dual Rectos. Hence why my modules I've modded with Orange Drops have a different low end character than say something with Wimas or SoZos.

So are you planning on flipping the chassis over and open, cutting out the caps, solder-sucking the holes and just dropping the new ones in place?

fyi caps designed for hi-fi use will probably be ice picky

fender uses orange drops

Zander said:

So are you planning on flipping the chassis over and open, cutting out the caps, solder-sucking the holes and just dropping the new ones in place?

Click to expand...

Essentially. Actually Steve and I removed the board altogether and sucked the solder from the leads to pull them out and put new ones in.

nomad100 said:

fyi caps designed for hi-fi use will probably be ice picky

fender uses orange drops

Click to expand...

That's why I only got one :lol: I'll get a Sozo or something to replace it if I don't care for it.

At last, UPDATES! I cracked open my head with a drill and...

Wait a sec, this sounds bad :lol:

I got into my Randall today and looked around. I have a couple of resistors to replace, and I'll have to get a better pic of them once I remove the beard. They're suspended off of the board nearly the entire length of their leads :lol:

Here's the underside of the shell-less head.


Here's what I noticed first: The Negative Feedback section! I popped out the presence and density knobs and their board to see what was up... I saw there was a cap that I had a replacement for! Didn't get a pic of the top, but the bottom looked atrocious (the only thing I did was suck some solder off the pads relating to the big cap. The rest looked funky from the beginning)



After replacing this cap, however, I found that I may have done something to the presence pot (it was the presence cap that I changed). All of a sudden the pot is scratchy as a swarm of fire ants! The presence shift sounds so smooth now though

Now, on to the caps I INTENDED ON replacing, but didn't get around to. I need to replace a couple of resistors that were mildly fried in an incident involving a bass guitar... Those can be seen in the first pic, next to the two huge fuses, to the right of the black and white cables, bottom-left of center.

But the amp still works



That lil red cap under the wires and in front of the power resistor, dead center of the pic is one of my targets. I have four juicy SoZo caps waiting to go in their slots But I'll wait until I can get replacements for the resistors so I can get it all in one swoop.

One last thing... The input coupling cap!
The Audience Auricap I got... was a big waste of $13. The braided copper leads (oooh, snazzy!) were too thick to go through the PCB =/ So I got one of the SoZos meant for the FX loop section of the power tube board (less interested in replacing those atm)

The board before I changed anything


The board with the awkwardly placed new SoZo! Yes, it's the correct value. They're just that huge!


Now, nice and tucked away in the head again

Keep going man...this is excellent fun! 8)

I will when I get a couple of 3 watt metal oxide resistors (overspeccing because I can ) Expect the next update in the next week or so.

And to the pro modders out there: How am I doing? I'm still new to using super long caps in small spaces...

Shinozoku said:

I will when I get a couple of 3 watt metal oxide resistors (overspeccing because I can ) Expect the next update in the next week or so.

And to the pro modders out there: How am I doing? I'm still new to using super long caps in small spaces...

Click to expand...

Use a bit of caution putting larger parts in there. If there is added noise it's probably an issue with a part or lead being too close to something else.

So the noise in the pot could be from the lead? Should I maybe get an old piece of wire and pull the covering off, undo the offending lead and cover it with that? Or maybe just a bit of electrical tape?

My previous question about the noisy presence pot still stands, however I have an update!

Yeah I know, it took a while

I put the Auricap in my Input's C4C position. I had taken some old leads that were clipped off and soldered them to the leads of the capacitor to make them fit!

The thing is, after hearing it...



See, while it DOES what I wanted it to when it comes to creating greater disparity between modules... It adds some fizz. Like, Mesa Boogie or old Peavey VTM kinda fizz.

I'll have to play with it for a while.


Rob: Not sure if you were referring to the resistors I'm needing to get when you spoke of using larger components, but they fit quite easily in my friend Steve's RM100. The resistors in there are 2 watts from what I can tell.