Help with SC20H

[Smh79]

Hi All,

Long time lurker here! I have recently bought an SC20H and must admit to being a little underwhelmed. Having read various posts on here and watched multiple youtube videos, I thought this amp was for me. However having played it for a few weeks, I'm beginning to think there is something wrong with it.

I have to admit I probably had some misconceptions about the amp before buying - I hadn't appreciated how much the interaction between the Master and Preamp affected the gain and tone of the amp. Prior to owning the SC20 I've had a JCM2000 DSL401, DSL40CR, Fender Bassbreaker, Blackstar HT5R, and various practice amps.

I know the SC20 isnt high gain, but mine is really lacking in the gain dept, and is either thin, bright and harsh with the preamp at lower settings or becomes increasingly muffled with the preamp at higher settings.I know lots of people use boosts/ODs to seemingly great effect, but when I use mine (Boss Sd1/Tubescreamer/EHX Glove/EHX Soul Food/MXR Custom Badass OD) the amp becomes even harsher, and sounds like a cheap SS amp.

With no pedals, I would say the 'best' tone I can get is something like Love Removal Machine by The Cult. I can get close to a GNR tone with the Soul Food and an EQ in the loop, but boosting the 1k slider more than a hair results in a harsh clipping in the mids. The low input is very aneamic and dull and doesnt play well with any of my pedals.

I had a microphonic preamp tube which I swapped out, and have rolled a different preamp tubes, and also swapped the power tubes to no avail.

I took the amp to a tech (not one I have used before) as a guy I have been to before has a long waiting list. The tech seemed pretty uninterested tbh, and when I picked the amp up all I got from him was that he'd checked the voltages which were all ok, but the bias was a little on the cold side ( I thought these were self biasing?).

I have also noticed the amp is quite noisy, and there is the occasional fluttering static noise when idling. I also noticed that the high input jack occasionally makes noise when plugging in.

I know the Marshall EQs are infamous for having little effect, but the mid control in particular has almost no effect.

This is one of the clips I mean. Doesn’t sound like it’s been subject to any production



I know one cant rely on Youtube videos, but the clip used above seems like it should be pretty representative of the amp(?). Mine doesn’t have the same amount of gain

If I had hair, I'd have pulled it out, as this is really frustrating me - am I exepecting the wrong things from this amp? I cant believe that I am from all the posts on here raving about this.

For reference, I generally play with the MV between 4-6 and preamp around 6-7. My main guitar is a Les Paul Studio with Slash pickups, and the amp is going into an Orange 2x12 with V30s.

Any advice appreciated!

 

[PelliX]

I know the SC20 isnt high gain, but mine is really lacking in the gain dept, and is either thin, bright and harsh with the preamp at lower settings or becomes increasingly muffled with the preamp at higher settings.

This is "normal" to a degree; the gain sweep lacks bottom end through the first half and all the way up the low end is very dominant. You can compensate for this with the EQ controls, but its' "practical range" for me is between about 12 o'clock and maybe 5 o'clock on the high input. On the low input I tend to dime the gain and regulate a bit with the guitar or overall signal volume before hitting the amp. This is not necessarily "defective" but more a characteristic...

I know lots of people use boosts/ODs to seemingly great effect, but when I use mine (Boss Sd1/Tubescreamer/EHX Glove/EHX Soul Food/MXR Custom Badass OD) the amp becomes even harsher, and sounds like a cheap SS amp.

Try the gain arond 7 on the dial and hit it with a pedal. I have an SD1 (effectively) and a TS - that's roughly how I use those with it.

The low input is very aneamic and dull and doesnt play well with any of my pedals.

Maybe our tastes differ a bit, but I find it takes 'dirt' well on the low input. A TS will typically cut the low end so much that it won't sound very good on its own 'in the room' unless you crank the gain to reinstate the low end.

I had a microphonic preamp tube which I swapped out, and have rolled a different preamp tubes, and also swapped the power tubes to no avail.

While it won't turn the amp into a totally different beast, I find bigger glass gives it 'bigger tone'. I'm running KT88's in there and many here on the forum will back me up on that notion... if you have a pair, give them a shot, maybe or something like a pair of 6550's? Just thinking outloud here..

up all I got from him was that he'd checked the voltages which were all ok, but the bias was a little on the cold side ( I thought these were self biasing?).

Well, I guess he didn't find a fault, so not much to report. They're actually cathode biased, which is 'self biasing' in a way. It means that the circuit adjusts the bias based on the properties of the valve. This however in turn means that one pair may bias themselves fairly high, another pair perhaps a bit low.

I have also noticed the amp is quite noisy, and there is the occasional fluttering static noise when idling. I also noticed that the high input jack occasionally makes noise when plugging in.

That's not right, there should be no 'random noises', unless it's picking up interference from something.

For reference, I generally play with the MV between 4-6 and preamp around 6-7. My main guitar is a Les Paul Studio with Slash pickups, and the amp is going into an Orange 2x12 with V30s.

Sounds like you should have enough signal to push the amp hard enough. You mentioned one valve had gone microphonic and you replaced it. I take it V1-3 are all ECC83/12AX7's?

 

[79 2203]

The clip sounds pretty close to every vintage 2203(79,80,82) 4104(82 x2) and Ceriatone 2203 I owned when the Pre is on 7/MV on 2-3 and going straight in with a LP, just a little more compressed.

Maybe his black box thingy is adding something and YT videos are more compressed than real life. Plus IME loud volumes will sound cleaner than very low volumes.

Also, keep in mind the SC is a simple amp, and simple circuits are more responsive to playing dynamics. It could be that you’re simply not attacking the strings like the guy in the video.

 

[Smh79]

This is "normal" to a degree; the gain sweep lacks bottom end through the first half and all the way up the low end is very dominant. You can compensate for this with the EQ controls, but its' "practical range" for me is between about 12 o'clock and maybe 5 o'clock on the high input. On the low input I tend to dime the gain and regulate a bit with the guitar or overall signal volume before hitting the amp. This is not necessarily "defective" but more a characteristic...



Try the gain arond 7 on the dial and hit it with a pedal. I have an SD1 (effectively) and a TS - that's roughly how I use those with it.



Maybe our tastes differ a bit, but I find it takes 'dirt' well on the low input. A TS will typically cut the low end so much that it won't sound very good on its own 'in the room' unless you crank the gain to reinstate the low end.



While it won't turn the amp into a totally different beast, I find bigger glass gives it 'bigger tone'. I'm running KT88's in there and many here on the forum will back me up on that notion... if you have a pair, give them a shot, maybe or something like a pair of 6550's? Just thinking outloud here..



Well, I guess he didn't find a fault, so not much to report. They're actually cathode biased, which is 'self biasing' in a way. It means that the circuit adjusts the bias based on the properties of the valve. This however in turn means that one pair may bias themselves fairly high, another pair perhaps a bit low.



That's not right, there should be no 'random noises', unless it's picking up interference from something.



Sounds like you should have enough signal to push the amp hard enough. You mentioned one valve had gone microphonic and you replaced it. I take it V1-3 are all ECC83/12AX7's?

Thanks for such a comprehensive reply! I’ll certainly have a look at at maybe replacing all the preamp tubes- yes they’re all ECC83s but with the exception of one, they are all a few years old and maybe not operating as well as they could.
I’ll check the cables etc but I’m pretty sure there’s no interference- I do get some if my laptop is nearby or I leave my phone near them.
I’m also wondering if the room I play in is having an effect? Its quite small and all hard surfaces so possible getting some high end reflections and possibly just standing too close. Just thinking when I sold my dsl40cr- it was always a bit fizzy-when I sold it the guy tested it on pickup but in my hallway and it sounded less fizzy. I’ll see about trying it one of the spare bedrooms over the weekend and then try some new tubes.
I really want to make this work- sometimes I think I’m getting there then the next day it sounds crap again!

 

[Smh79]

The clip sounds pretty close to every vintage 2203(79,80,82) 4104(82 x2) and Ceriatone 2203 I owned when the Pre is on 7/MV on 2-3 and going straight in with a LP, just a little more compressed.

Maybe his black box thingy is adding something and YT videos are more compressed than real life. Plus IME loud volumes will sound cleaner than very low volumes.

Also, keep in mind the SC is a simple amp, and simple circuits are more responsive to playing dynamics. It could be that you’re simply not attacking the strings like the guy in the video.

Hi, I tend to be pretty heavy handed- I was actually thinking that was contributing to the problem somehow. I have seen some comments on how this amp doesn’t give you anywhere to hide regarding technique and I have certainly noticed that!

 

[PelliX]

I’ll check the cables etc but I’m pretty sure there’s no interference- I do get some if my laptop is nearby or I leave my phone near them.

Doesn't have to be cables. In fact, if you're hearing "noises" from the amp, the first thing to do is to unplug anything from the input to narrow it down. Just sayin'.

I’m also wondering if the room I play in is having an effect? Its quite small and all hard surfaces so possible getting some high end reflections and possibly just standing too close. Just thinking when I sold my dsl40cr- it was always a bit fizzy-when I sold it the guy tested it on pickup but in my hallway and it sounded less fizzy. I’ll see about trying it one of the spare bedrooms over the weekend and then try some new tubes.

Yes, this can play a role - only way to confirm or reject the notion is to try it somewhere else. The cab does look a little "wedged" in...

I have seen some comments on how this amp doesn’t give you anywhere to hide regarding technique and I have certainly noticed that!

Weeeell..... try a plexi and you'll come running back to the cover of a JCM800

 

[Smh79]

Doesn't have to be cables. In fact, if you're hearing "noises" from the amp, the first thing to do is to unplug anything from the input to narrow it down. Just sayin'.



Yes, this can play a role - only way to confirm or reject the notion is to try it somewhere else. The cab does look a little "wedged" in...



Weeeell..... try a plexi and you'll come running back to the cover of a JCM800

Really? I’d best learn to play first then!

 

[ByrdmanFL]

@Smh79 You may have something wrong with your amp. I also have a SC20H and although I am not running V30 speakers, mine sounds very similar to the video you posted with the stock tubes. Also, these amps are pretty volume dependent with their tones, to get better tones at lower volumes, I will boost it with an SD1. I did it a lot more when I first got it, but now when practicing at bedroom volumes, I just deal with it sounding on the thinner side. Another also, how far away from the cab when you play it? Mine doesnt sound nearly as good close(thin) vs farther away(balls), so I have a 20' guitar cord and get away from it.

Where are you located? Maybe someone in your area has the same amp and can A/B yours and his to see. I know it's a long shot, but you may get lucky. If you are in Central FL, I'd be willing to meet up.

 

[Smh79]

Unfortunately, only one of my friends plays, and he’s got some tiny Laney from 1996. I live in Manchester, UK but thanks for the offer! There used to be loads of decent shops, but now there’s only one half decent one and their stock of Marshall’s isn’t that good. I actually went in recently and they had an SC20c which I tried but they don’t have a soundproofed playing room so couldn’t turn it up. I’ve actually spent the afternoon working from home and so spent a bit of time at lunch playing around with it turned up a bit and stood outside of the room and it sounded better, so I am thinking maybe the room size combined with a 2x12 is part of the issue. I’m looking at buying a 1x12 with a cream back for my Bassbreaker so if I do, I can doa comparison

 

[FrostyTheSnake]

My opinion is the same as yours. Can you send it back and get a SV20H?

Master volume should mean you can play it quiet and it will play great? That just ain’t the Marshall way. The MV amps still sound terrible IMHO with low volume. Gotta crank them. So why no go Plexi?

Also I will say my SC20H had literally no gain even cranked. Just ice pick top end. Everyone says my unit was borked. My SV20H cooks with a boost. As much gain as anyone can need.

 

[guitarbilly74]

If your amp is not sounding like the video you posted, there's something wrong with it. That video is the "normal" for a SC20H.

 

[Kuga]

I know the Marshall EQs are infamous for having little effect, but the mid control in particular has almost no effect.

Defently your amp has some issues. Mid control on mine have a big impact on tone. All EQ have a big impact on tone.

 

[Smh79]

My opinion is the same as yours. Can you send it back and get a SV20H?

Master volume should mean you can play it quiet and it will play great? That just ain’t the Marshall way. The MV amps still sound terrible IMHO with low volume. Gotta crank them. So why no go Plexi?

Also I will say my SC20H had literally no gain even cranked. Just ice pick top end. Everyone says my unit was borked. My SV20H cooks with a boost. As much gain as anyone can need.

I bought it on ebay a few months ago so can't return it unfortunately.

 

[Henrim]

Defently your amp has some issues. Mid control on mine have a big impact on tone. All EQ have a big impact on tone.

+1

The mid control is really sensitive on mine. Even a slight change can have a huge impact.