1959slp Specific Question About The Four Inputs...

[Yugedrums]

Hi all, I recently purchased a 2000 1959SLP reissue and I'm really digging it. It's my first non-master volume amp and I've had fun playing around with it and I like the tones I'm getting out of it. I understand the "jumpering" method with the two channels and have been experimenting with doing that.

That being said, my specific question is this... and I've scoured the internet and these forums and haven't really seen this question answered exactly...

With "jumpering", you plug the guitar into an input (most typically the "high" input of the "high treble" channel), then connect a patch cable from the other input of that same channel (typically the "low" input of the "high treble" channel) to an input of the other channel (typically the "high" input of the "normal" channel). I understand that this takes the guitar signal from the channel the guitar is plugged into and "jumps" it over to the other channel, so that both channels will get signal from the guitar and can be "mixed" with the two volume controls. The way I've been "mixing" it is to start with the high treble volume, adjusting it to a level that's loud enough but not "destroy your ears with icepicks", since that seems to be this channels specialty... then I blend in the normal volume until the bass/treble balance is right to my ears. Coming from a master-volume background, this is a strange way to turn up the volume on an amp, but I actually like it and the sounds I'm getting are great.

Where my question gets specific is here....

If I plug the guitar into either channel, high or low... and I DON'T jumper it, I still get output from the high treble side and output from the normal side, the same way it behaves when jumpered and the "blending" of the two volumes acts the same. What I expected was to get zero output from the unused side if there was no input being jumpered to it (volume control would do nothing), but there seems to be no change in the behavior of the inputs/outputs nor the two volume controls whether jumpered or not.

One possibility I considered was that maybe the jumpered configuration doesn't actually change the way the inputs work/blend together, but maybe that the addition of the jumpered signal from the other channel increases the overall gain by doubling the input signal (makes sense), but I have read many arguments on forums about whether actual gain is added with jumpering or not.

Another possibility I've pondered... maybe there's something wrong with this amp....?

Anyway, that's pretty much it... why do I get output from both channels whether jumpered or not?

I'm anxious to hear from people who know more about these amps than I do since like I said, I've never had a non-master volume plexi-type amp before.

Thanks guys!

 

[Gunner64]

I' m not an expert on superleads by any means but maybe its internally jumpered already..just a thought..

 

[grainman]

it sounds like your channels are linked already... ..someone took care of that mod before you.....i'll leave it that way....

 

[Yugedrums]

Thanks guys, I had considered that too (modification), but the times I've been in it since I've had it, I didn't see anything obvious but I'll have to compare it to the schematic next time I'm in there.
But to any 4-input owners: if you plug into only one input, does the volume control of the other channel do anything at all when you turn it up, or only the volume you're plugged into? I need to know this since I've never owned one nor do I have another one to compare it to.
Thanks again!

 

[marshallmellowed]

Thanks guys, I had considered that too (modification), but the times I've been in it since I've had it, I didn't see anything obvious but I'll have to compare it to the schematic next time I'm in there.
But to any 4-input owners: if you plug into only one input, does the volume control of the other channel do anything at all when you turn it up, or only the volume you're plugged into? I need to know this since I've never owned one nor do I have another one to compare it to.
Thanks again!

There is a very small amount of "bleed" when the channels are not jumpered. If you turn the "Normal" channel volume up all the way when not jumpered this bleed can be heard, but that's it. I agree that it sounds like your channels have been internally jumped. Should be easy to reverse if you want it back to stock.

 

[Yugedrums]

There is a very small amount of "bleed" when the channels are not jumpered. If you turn the "Normal" channel volume up all the way when not jumpered this bleed can be heard, but that's it. I agree that it sounds like your channels have been internally jumped. Should be easy to reverse if you want it back to stock.

Hey thanks. Yeah, I'm about to retube it so I'll check the inputs out then. Another weird thing it does... when both volumes are all the way down, a little sound can be heard if I strum the guitar. It's not very loud, but it's not silent either. This is whether it's jumpered or not.

 

[Blueslicks]

Another weird thing it does... when both volumes are all the way down, a little sound can be heard if I strum the guitar. It's not very loud, but it's not silent either. This is whether it's jumpered or not.

Normal IME. A powerful amp waiting to unleash it's sonic fury.

 

[BanditPanda]

Thanks guys, I had considered that too (modification), but the times I've been in it since I've had it, I didn't see anything obvious but I'll have to compare it to the schematic next time I'm in there.
But to any 4-input owners: if you plug into only one input, does the volume control of the other channel do anything at all when you turn it up, or only the volume you're plugged into? I need to know this since I've never owned one nor do I have another one to compare it to.
Thanks again!

I don't own the amp but in readING about it I believe the answer to your question is yes.
One channel will affect the other even when it is not in use. Seems weird just the same.

 

[mixn4him]

IF they are jumpered internally than yes both volumes can be heard if only 1 input is used. Also though on Shared Cathode version which an SLP shouldn't be you will hear the second channel make changes as you adjust the knob on the first channel.

More than likely your is modded internally for linked..

 

[neikeel]

No you will always hear a little channel bleed, shared cathode or not. V2a onwards is common to the channels and the node where 470pF/470k and 470k mixer resistors meet is the reason.

 

[Yugedrums]

Hey thanks again guys! I also suspect an internal jumper mod, but am out of town until later today. I've got new tubes coming this week so I'll have it back out anyway, so I'll check it out and post the results. Even from the pictures I've already taken of the insides, I think I'm seeing a suspicious wire coming from one of the jacks. If it is an added wire, I will remove it since I'd rather have this amp be as it originally was, so I can experiment with the channels myself.

Normal IME. A powerful amp waiting to unleash it's sonic fury.

It's funny you should mention that because when I first got it and was experimenting wit it, just plugged straight into the front, at low volumes it was so clean... even as I started bumping it up slowly, I was like "this thing is going to be clean at all volumes, there's no way it's going to break up". Then once I got to around 3 and above, it broke up beautifully and sounded magical! It does get ungodly loud quickly though.

 

[Blueslicks]

No you will always hear a little channel bleed, shared cathode or not. V2a onwards is common to the channels and the node where 470pF/470k and 470k mixer resistors meet is the reason.

All of the many NMV 4 hole Marshalls I have owned had channel bleed and none of them had mods. As do the two un-modded 1987x heads I am currently playing. A subtle effect but audible nonetheless.

It is the nature of the beast IME.

 

[Blueslicks]

Hey thanks again guys! I also suspect an internal jumper mod, but am out of town until later today. I've got new tubes coming this week so I'll have it back out anyway, so I'll check it out and post the results. Even from the pictures I've already taken of the insides, I think I'm seeing a suspicious wire coming from one of the jacks. If it is an added wire, I will remove it since I'd rather have this amp be as it originally was, so I can experiment with the channels myself.

It's funny you should mention that because when I first got it and was experimenting wit it, just plugged straight into the front, at low volumes it was so clean... even as I started bumping it up slowly, I was like "this thing is going to be clean at all volumes, there's no way it's going to break up". Then once I got to around 3 and above, it broke up beautifully and sounded magical! It does get ungodly loud quickly though.

Use inefficient speakers in a 2x12 and attenuate a bit. It is manageable if you are sensible. The sweet spot is around 7-8 and then just use the guitar volume knob for cleaning it up.

 

[Yugedrums]

Thanks guys. Well, I took the chassis out tonight and put it on the bench, since new tubes are on the way anyway. I checked all the wiring at the inputs, compared them to the schematic and other references, pictures etc... and it is NOT modded. Everything is stock. I'll do another comparison with/without the jumper once it's all back together.
The other thing I noticed tonight was that after previously assuming the Marshall-branded ECC83's were possibly the original (17-year old) tubes, I noticed that two of them have a small "99" printed at the bottom and the other one has a "98" at the bottom. I'm assuming this could be the year codes...? The Marshall branding all wiped off when I was originally cleaning them (It was owned by a smoker and I could write a book at this point on de-stinking amps). I also noticed tonight, that the Svetlana EL34's all had "9951" stamped on them, which after some internet research I found that this is the build code for 51st week of 1999. It looks like this poor amp has it's original tubes... 17-year-old tubes! So, I'd say a retube is probably in order.

 

[Yugedrums]

So... today I received in the mail the new JJ EL34's and JJ ECC83S's that I ordered and I installed them. As I thought might be a possibility (as was the same thing with my 2203 reissues), the bias pot maxed out way before my desired 70% dissipation, so I changed out the stock 47k bias resistor with a 33k resistor and it biased up perfectly. I had also previously changed out all 6 potentiometers because they were all scratchy and cut in/out badly. I cleaned them out with Deoxit (usually does the trick), but they were still too far gone. This amp having solder-lug type pots and not PCB mounted pots made this process as easy as changing pots in a guitar. I used Alpha pots of the same values and they work great.

So, back to my original question about the inputs... Once I had it all back together and fired it up to play through it, I experimented with the four inputs. What I noticed was this...

When plugged into the High-Treble channel: I can turn the Normal channel all the way up and never hear it. Only the High Treble volume increases any volume.

When plugged into the Normal channel: When I turn up the High Treble volume, it definitely increases the screamy High Treble type sound, but not as loud as if I were plugged into the High Treble channel it'self.

When jumpered: Both volumes increase each channel simultaneously.

So either it was working differently before, or I just didn't notice the difference in volumes between jumpered and not jumpered. That High Treble channel definitely bleeds very much into the Normal channel though. I'm having trouble adjusting to the High Treble channel anyway, as it is SO ice-picky and screamy. I'e heard of some who just plug into the Normal channel and EQ it to taste, but I was really trying to utilize this whole classic 4-jack Plexi thing. When jumpered, I just bump the Treble channel up to a tolerable level, then mix the Normal side in until it sounds full and complete. The two volumes are like a treble knob and bass knob. I feel like I'm EQ'ing it instead of turning up the volume! It sounds fantastic though and I'm really digging it.

 

[SG~GUY]

-maybe the RR mod is worth a try-

 

[neikeel]

Get a Y-cord into both high inputs and retry

 

[danfrank]

Another possibility is that the old pots had so much smoke residue that the pots weren't zeroing out all the way when turned fully counter-clockwise.

I have a JTM45/100 build (shared cathode) that has bleed through and a SL build (split cathode) that only bleeds one way like yours, I can't remember which though. I even changed out the volume pots thinking it was a defect in one of them but same thing happened with the new ones I put in there. Neikeel and Blueslicks just confirmed this for me.

 

[Yugedrums]

-maybe the RR mod is worth a try-

I can see the allure of modding amps, since I have modded a couple of pedals and it was fun and rewarding, but with these amps, I'm really striving to "un-mod" them and get to know them as they were originally designed. I won't say "never" though.

Get a Y-cord into both high inputs and retry

I never thought of that. What would it do, tame the high-pitched shrill of that channel some?

Another possibility is that the old pots had so much smoke residue that the pots weren't zeroing out all the way when turned fully counter-clockwise.

I have a JTM45/100 build (shared cathode) that has bleed through and a SL build (split cathode) that only bleeds one way like yours, I can't remember which though. I even changed out the volume pots thinking it was a defect in one of them but same thing happened with the new ones I put in there. Neikeel and Blueslicks just confirmed this for me.

The smokey-pots thing is what I originally suspected, but I changed out ALL of the pots and everything was the same, except for the scratchy cutting in/out that most of them were doing, which is all better now. It was an easy replacement and only cost like $12, so I figured why not?

But even after changing all of the pots and a full re-tube/bias, the volume(s) still don't go all the way silent at zero and the High Treble channel can still be heard (well) in the Normal channel. The High Treble channel's volume also still goes from zero > pretty loud > balls loud, all within the first 1-2 of the knob. It is also extremely trebley (duh) and loud.

None of these things are deal-breakers for me... I suspected and wanted to confirm whether or not these were just common characteristics of these amps since I had no experience with these. Before this 1959SLP, all of the other Marshalls I've owned (from the 80's until present), were JCM800's and 900's... along with a 9200/JMP-1 rack setup.

Anyway, thanks again for all the replies. I love talking about this stuff and my wife is tired of hearing about it, haha!

 

[neikeel]

Seriously get the y cord and balance the two volume pots like EQ pots.
These RI SLPs are pretty notorious for this - they need cranking up to 7 or 8 on the dial before they smooth out. Definitely trickier to dial in than the originals which I find much smoother.