SV20 - Bright Cap Mod is Worth it

[gush]

I just picked up the SV20H and I feel it is too bright for my taste. I will be doing this cap mod for sure. Thanks for the info!

 

[Point 2 Point]

Like I posted I changed my cap to a 2700 but am putting the original back.

 

[Brett Holden]

Hi all -

I’ve been a Studio Vintage SV20 owner for a couple of years now. While I quite love the amp I’ve never truly been able to love the bright channel as much as I’d like to. I felt like the normal channel was too dark and the bright channel was too bright, and when cranking the bright channel I just got more gain than I wanted, and when mixing the channels I couldn’t get a balance I was happy with without it being too bright.

I’m not a metal guy, not really into the 80’s hot rodded plexi sound, I was going for more of a 70’s classic Marshall crunch, which is why I picked the SV20 over the SC20. I wanted to be able to play Jimi Hendrix, Zeppelin, AC/DC etc., and at the time the SV20 was a lot more affordable than a 1987X. I picked it up when it was $1,300 new.

I think that I was hesitant to make a mod to it because of how many people claim that the Plexi is supposed to sound like that and if it doesn’t sound good you’re not running it right. I spent a lot of time with this amp. I ran the amp volume high and rolled off the guitar volume etc, etc, and frankly these 20W models don’t sound like a 50W/100W model. The small transformers are likely part of the reason, as well as the low plate voltage running the tubes cold to keep the output at 20W.

Anyway… Today, I finally ended up changing the bright cap from the stock 4.7nF down to 100pF, and I must say I’m honestly impressed with how much better the amp feels. I first removed the cap and ran 2 wires from the pcb, and used alligator clips to try about 7 diffferent values ranging from no cap to 4.7nF (stock). I ended up going with 100pF because it gave back some of the clarity and air without feeling like the top end was falling apart.

Clipping the cap definitely felt too dark to me. It’s still brighter than the normal channel because of the 470pF cap on the channel mixing resistor, but with it completely removed it definitely felt like it lost a little magic.

I am running the amp head through an Origin 2x12 vertical cab which I replaced the stock Seventy-Eighty speakers (junk) with modern day G12-M Greenbacks. It now has the thick creamy bluesy overdrive that I was wanting. It does the AC/DC thing, Zeppelin riffs sound incredible as well, I run the High Treble volume on about 6-8, and it’s awesome. The 20W seems to move enough air to make me feel the magic without pissing off the neighbors.

If you’re an SV20 owner who feels the same way I did about your amp, I highly suggest you try the mod. You simply replace C101 on the control panel PCB. The whole PCB comes off by removing nuts from the pots, and pulling a couple of wire connectors.

I documented the whole process with photos if anyone is interested in a walkthrough. If you’re savvy, you’ve probably already done this, if you’re at all handy with a solder iron, it’ll be a breeze!

Just wanted share my thanks to everyone for sharing their their knowledge and insight on this post. I have had the studio vintage for over a year now and like the OP, had struggled to get the creamy blues rock tones I wanted from it, to the point where I was considering trying to mic my Yamaha THR10 practice amp and sell the SV20 (because the Yamaha was putting the Marshall to shame!) I was also hesitant to mod it due to how many others loved the amp (“perhaps you just don’t like the sound of a plexi”). Anyway I plucked up the courage, the instructions provided were spot on and my amp is singing like a champ now. I went with the 100pf too btw.

Many thanks, this post stopped me selling my SV20!

 

[ckaudio]

Just wanted share my thanks to everyone for sharing their their knowledge and insight on this post. I have had the studio vintage for over a year now and like the OP, had struggled to get the creamy blues rock tones I wanted from it, to the point where I was considering trying to mic my Yamaha THR10 practice amp and sell the SV20 (because the Yamaha was putting the Marshall to shame!) I was also hesitant to mod it due to how many others loved the amp (“perhaps you just don’t like the sound of a plexi”). Anyway I plucked up the courage, the instructions provided were spot on and my amp is singing like a champ now. I went with the 100pf too btw.

Many thanks, this post stopped me selling my SV20!

That’s awesome! This was my experience as well, and I’m glad you tried it before selling!

 

[Les59]

With respect,I have a mxr 10 band eq in the effects loop and dial it to whatever I want.Thank God for effects loops.
Killer amp man.

 

[SquidVicious]

Hi all -

I’ve been a Studio Vintage SV20 owner for a couple of years now. While I quite love the amp I’ve never truly been able to love the bright channel as much as I’d like to. I felt like the normal channel was too dark and the bright channel was too bright, and when cranking the bright channel I just got more gain than I wanted, and when mixing the channels I couldn’t get a balance I was happy with without it being too bright.

I’m not a metal guy, not really into the 80’s hot rodded plexi sound, I was going for more of a 70’s classic Marshall crunch, which is why I picked the SV20 over the SC20. I wanted to be able to play Jimi Hendrix, Zeppelin, AC/DC etc., and at the time the SV20 was a lot more affordable than a 1987X. I picked it up when it was $1,300 new.

I think that I was hesitant to make a mod to it because of how many people claim that the Plexi is supposed to sound like that and if it doesn’t sound good you’re not running it right. I spent a lot of time with this amp. I ran the amp volume high and rolled off the guitar volume etc, etc, and frankly these 20W models don’t sound like a 50W/100W model. The small transformers are likely part of the reason, as well as the low plate voltage running the tubes cold to keep the output at 20W.

Anyway… Today, I finally ended up changing the bright cap from the stock 4.7nF down to 100pF, and I must say I’m honestly impressed with how much better the amp feels. I first removed the cap and ran 2 wires from the pcb, and used alligator clips to try about 7 diffferent values ranging from no cap to 4.7nF (stock). I ended up going with 100pF because it gave back some of the clarity and air without feeling like the top end was falling apart.

Clipping the cap definitely felt too dark to me. It’s still brighter than the normal channel because of the 470pF cap on the channel mixing resistor, but with it completely removed it definitely felt like it lost a little magic.

I am running the amp head through an Origin 2x12 vertical cab which I replaced the stock Seventy-Eighty speakers (junk) with modern day G12-M Greenbacks. It now has the thick creamy bluesy overdrive that I was wanting. It does the AC/DC thing, Zeppelin riffs sound incredible as well, I run the High Treble volume on about 6-8, and it’s awesome. The 20W seems to move enough air to make me feel the magic without pissing off the neighbors.

If you’re an SV20 owner who feels the same way I did about your amp, I highly suggest you try the mod. You simply replace C101 on the control panel PCB. The whole PCB comes off by removing nuts from the pots, and pulling a couple of wire connectors.

I documented the whole process with photos if anyone is interested in a walkthrough. If you’re savvy, you’ve probably already done this, if you’re at all handy with a solder iron, it’ll be a breeze!

This is a fantastic description of the mod. Thank you!

 

[SquidVicious]

That’s pretty awesome! Good to know! Kinda like how I use my Torpedo Captor X to try different speaker IRs to figure out what speakers I like for my amps 😂 technology has come along way.

That's a great idea. Just picked up a captor x. I'll do that to confuct a shootout to replace the 70-80s in my Marshall 2x12 vertical cab. As the original post author said... totally suck for my purpose

 

[taylodl]

With respect,I have a mxr 10 band eq in the effects loop and dial it to whatever I want.Thank God for effects loops.
Killer amp man.

Yeah, I would have tried this first before modding an amp! An EQ pedal can do wonders.

 

[DesolationBlvd]

I haven't felt the need to reduce the bright cap on my SV20H, between always having the inputs jumpered and leaving the normal volume on 4-5 (rolling that off once the high treble is up past 7), and using vented G12T-75s which seem to be darker and more "JCM800" sounding than Greenbacks. The only mod I did was the "one wire mod", which I reverted as I preferred using an overdrive for when I wanted metal out of it.

That said, OP's video on page 2 sounded pretty good and like what he was going for in his description.

 

[wizard1325]

can someone post a link to the 100PF

 

[ckaudio]

One of these will do fine, just choose the 100pf option

Silver Mica Capacitor

 

[wizard1325]

Thank you man theirs different types ceramic and silver mica

Looks like i will need another one for me JTM20ST since its the same board.

 

[ckaudio]

No problem. I have nothing against ceramic but they can tend to be microphonic so I usually opt for the silver mica.

Happy modding!

 

[ken361]

I haven't felt the need to reduce the bright cap on my SV20H, between always having the inputs jumpered and leaving the normal volume on 4-5 (rolling that off once the high treble is up past 7), and using vented G12T-75s which seem to be darker and more "JCM800" sounding than Greenbacks. The only mod I did was the "one wire mod", which I reverted as I preferred using an overdrive for when I wanted metal out of it.

That said, OP's video on page 2 sounded pretty good and like what he was going for in his description.

Some people might have higher voltage at home I run my amps through a voltage regulator APC it tames it some. Never found the amp bright I now run the EQ at 10 it really opens the amp up jumpered. EH power tubes have a vintage vibe. I play it loud straight up it so great.