Weird problem - pedals + new amp

[ghostsauce]

So I bought a JCM900 4100 (DR) a few days ago, and the tone is heavenly! But anyways, it sounds really bad when I use my dr boogey and especially my (byoc) big muff triangle through it. The DB has these weird almost 8-bit noises in it, like something is being pushed too hard I guess, and the muff is even weirder.. it is all bottom end and all the mids and highs are just gone, and the same weird noises occur. Has this happened to any of you guys?  I'm running the pedals in front of the amp.. might try them in the loop.

Truth be told I likely won't use many pedals now that my amp sounds this amazing.. but still!

[newfish]

It's surprising how bad a good amp can sound if the pedal is clipping your signal - then the amp cliips the remainder.

I've had this, and have ended up using 'overdrive' pedals as 'gritty boost', to avoid the over-compressed 'mush' that happens.

Have you thought of checking output / input impedance also?

[Astronaurt]

I second the input/output impedance issue. It comes up all the time when trying to pair Home-built effects with commercial stompboxes, for example my Octavio just WOULD NOT WORK when placed in a chain before my old Boss SD-2. The only word I can think of to describe it was "Poop." So following some recommendations and hunches, I put a simple JFET output buffer onto the end of the Octavio to get the Impedance down, and it wasn't poop anymore!

As far as audio electronics goes, you generally want the output impedance of your pedal to be around 10 times lower than the input impedance of whatever it has after it, be it pedal or amp. If the Output impedance is higher than it's following input impedance, then you're generally looking at gross amounts of signal loss, particularly in the high frequencies, and if it's bad enough into Mid range, which seems to be what you're describing!

I know I've played a Big Muff I've made into an Old Marshall and it sounded amazing, but I think the newer ones have a vastly different input structure than the older ones with much much lower input Z than they used to. so I'd look into that possibility. Perhaps you can look up online what the input Impedance for your amp is so you can have an idea of what to shoot for?

[DavenPaget]

Perhaps you can look up online what the input Impedance for your amp is so you can have an idea of what to shoot for?

I attempted that for him and failed :\
It seems nobody knows the input impedance of that damn thing , even marshall's datasheets doesn't state that .

[anchovie]

It seems nobody knows the input impedance of that damn thing , even marshall's datasheets doesn't state that .

There's way more to this issue than impedance - just search for a schematic of the preamp!

The 4100 doesn't contain as much "tube action" in its preamp as some people think. You've got a bunch of opamp gain stages at the front, followed by diode clipping, then a 12AX7 gain stage and a cathode follower which doesn't make it too dissimilar to the Valvestate models that followed it. The second 12AX7 is used in the recovery stages after the FX loop and reverb and the final one is the phase splitter for the power amp (with opamps sandwiched between them).

It looks to me like the Dual Reverb models were designed to be self-contained "clean & dirty" solutions, not to have high-gain dirt boxes running into them.

[petemoore]

   Those are nice amps though, More or Less 'push' at the front end of the amp should make it easy to control the amount of distortion: more or less !
    Clean boost might be similar to turning the guitar volume up/down [if the VC doesn't dull the signal much] with the amp cranked up to 'more'...but a 'touch of dirt' type booster might sneak just enough non-linearity to trigger a harder-yet-still nice-distortion tone in the amp. Perhaps see what 'the others' do with the amp to make greater of distortions with increased volume control.  It might be as easy as grabbing a chunk-o-perfboard and foolin' around with measured Jfets [see Fetzer Valve].

[ghostsauce]

Yeah, I researched the 4100 a lot before I bought it, but it really does sound amazing. And if you jumper the fx send & return and crank the associated pot you snag the V2 tube bag into the signal for a big tone difference.

But anyway, impedance?! Man.. very strange. Funny though that I had been running an AVT150h with these same pedals before this without issue. Thanks for the info.. I'll keep messing with it.

Oh.. also the schematics can be found here: http://www.drtube.com/marshall.htm#JCM900
(mine is the 4100 JCM900 Dual Reverb, 100W head)

[anchovie]

Funny though that I had been running an AVT150h with these same pedals before this without issue.

The clean channel on those is a lot simpler - a couple of opamps and no diode limiting. The 4100 has diode arrangements on both channels.

[ghostsauce]

I see. I didn't get much time to play with it after church on Sunday, so I may not have thought to switch it over to the clean channel.. or may have had the gain cranked on it from when I was testing earlier. I don't have the foot switch for it but it's in the mail, so I was pretty much just leaving it on the lead channel. I'll do a bunch more testing when it gets here and finally finish setting it all up to my liking. Thanks!

[petemoore]

  A compressor was used once put and stayed on an Artist30 [similarities?] only to 'boost' when in bypass mode...the 'effect' was pretty useful because the comp'd keep the signal hot-long-enough and then the amp sounded like the amp when volume boosted [bypassing the compressor with volume setting for -attenuate]...may sound 'reversed' but actually very effective for getting 'over' [boost] and 'under' [attenutating] an amps tone.
 That Was before I did guitar volume pot inpections/work, but it did help retain note definition while getting the signal volume down lower but not dieing off or becoming dull.
 Buffer test is generally as easy as bypassing a 'factory effect that has a power supply', most have input and output buffers/switching.

[ghostsauce]

Heh.. yeah so I was definitely using it on the higher gain channel when using these pedals. I was in a bit of a rush so I must've forgot to switch it (don't have a footswitch yet) - anyways, they sound amazing through this amp on the clean channel! I can't get over how much more ass the dr boogey kicks through this amp. The muff is back to muffing properly as well..  so all is well. Thanks for the info and input. You guys are always so knowledgeable.