SV20 - Bright Cap Mod is Worth it

[ckaudio]

Cheers ck, I'll discuss with it my chap. He'll source the schematic and then we'll take it from there. Undoubtedly it'll be more problematic working with a PCB than handwired. Used to have all sorts of fun and games many years ago dealing with the '80s M solid state amps, dry joints etc were rife

Cheers! Yes handwired are usually much easier to work on! From what I could tell while I was in there, the PCBs are really good quality and assembled well (probably because they’re UK made?) definitely better quality than the solid state Marshall’s that I’ve had my hands on 😂

 

[goldtop0]

Cheers! Yes handwired are usually much easier to work on! From what I could tell while I was in there, the PCBs are really good quality and assembled well (probably because they’re UK made?) definitely better quality than the solid state Marshall’s that I’ve had my hands on 😂

Cheers again, yes those old JCM800(if you could call them that) solid state amps were sometimes shockers and sold by the truckload here in NZ due to them being cheaper than their valve counterparts.
A good learning curve for me.

 

[mpv1504]

Is the bright cap completely bypassed when the volume pot is dimed ?
Some claim that it still produced a slight effect, but I don't see how.

 

[tidbit]

Just did this mod to my SV20, tried a couple of different values just for safety but yes, 100pF was sounding good - didn't try even lower values since I didn't have them on hand. Sounds very good right now, compared to stock cap it's so strange I could tolerate it for so long - that brightness was glaring.

Thank you for the instructions! That demo sounds awesome.

I just did the same finally this week. I absolutely love how the amp sounds like now. The painful brightness at low to moderate volume is gone.

 

[goldtop0]

I just did the same finally this week. I absolutely love how the amp sounds like now. The painful brightness at low to moderate volume is gone.

This is going to be the standard mod for the SV.
Mine's gone to my amp guru today.

 

[ckaudio]

I just did the same finally this week. I absolutely love how the amp sounds like now. The painful brightness at low to moderate volume is gone.

Glad you liked the result! It gave me exactly the sound I wanted out of my amp!

 

[ckaudio]

This is going to be the standard mod for the SV.
Mine's gone to my amp guru today.

Sweet! Be sure to share your thoughts of the mod afterwards 🤘🏼

 

[goldtop0]

Sweet! Be sure to share your thoughts of the mod afterwards 🤘🏼

When he looked at the schematic he said it was 'overkill ' to have the 4.7nf cap there

 

[ckaudio]

When he looked at the schematic he said it was 'overkill ' to have the 4.7nf resistor there

Do you know what value he is going to put in?

 

[goldtop0]

Do you know what value he is going to put in?

As per your posts the 100pf.
He's seen a lot of old Marshalls etc over the years and Fenders and the bright caps have mostly gone or been changed as we're discussing.

 

[ckaudio]

As per your posts the 100pf.
He's seen a lot of old Marshalls etc over the years and Fenders and the bright caps have mostly gone or been changed as we're discussing.

Nice! Looking forward to hearing your thoughts after you get it back 🤘🏼

 

[goldtop0]

Nice! Looking forward to hearing your thoughts after you get it back 🤘🏼

Here's what happened.
I tried KT66s in it and this is how it formed up.
I don't know all the ins and outs with changing tubes etc, the voltage differences on the plate and so on, other than my man saying that it's running too hot or whatever and so 'this and that' change is necessary. What I know is that when I put the KTs in it at home, the sound was less piercing compared to the EL 34s.
Got it back today and as you can see on the attachment, with the KTs installed. The High Treble channel is appreciably quieter(useable) and the overall output volume is slightly down.
I'll be playing it more tomorrow so will give it a good thorough workout, might even try the ELs back in it for a few minutes and see where that takes me.

 

[goldtop0]

Having played it for a few days now I thnk it's tonally the most versatile M amp that I've ever owned.
The change to the 100pf bright cap is essential and changing the cathode resistor to 180R is good ensuring that I can swap the tubes in and out without worries of shortening the KT66s life.
My guy said that the SV was made for EL34s specifically and changing between the two pairs doesn't show any real difference in tone that I can ascertain at this stage.

 

[ckaudio]

Having played it for a few days now I thnk it's tonally the most versatile M amp that I've ever owned.
The change to the 100pf bright cap resistor is essential and changing the cathode resistor to 180R is good ensuring that I can swap the tubes in and out without worries of shortening the KT66s life.
My guy said that the SV was made for EL34s specifically and changing between the two pairs doesn't show any real difference in tone that I can ascertain at this stage.

Very cool! Definitely a very versatile amp for sure! So safe to say, you like it after the mod more than before??

 

[goldtop0]

Very cool! Definitely a very versatile amp for sure! So safe to say, you like it after the mod more than before??

Yes, it's not an in your face over the top screechy treble monster. It's a manageable amp now with great tone, controlled from your guitar. Cheers ck.

 

[playloud]

Here's what happened.
I tried KT66s in it and this is how it formed up.
I don't know all the ins and outs with changing tubes etc, the voltage differences on the plate and so on, other than my man saying that it's running too hot or whatever and so 'this and that' change is necessary. What I know is that when I put the KTs in it at home, the sound was less piercing compared to the EL 34s.
Got it back today and as you can see on the attachment, with the KTs installed. The High Treble channel is appreciably quieter(useable) and the overall output volume is slightly down.
I'll be playing it more tomorrow so will give it a good thorough workout, might even try the ELs back in it for a few minutes and see where that takes me.

I recognize that handwriting!

Good to see you're in good hands.

 

[goldtop0]

I recognize that handwriting!

Good to see you're in good hands.

Met Clarry in the early '90s when I was selling Sovtek 5881s and we went from there, just a great guy, a real amp guru if ever there was one.
Are you in Auckland?

 

[playloud]

Met Clarry in the early '90s when I was selling Sovtek 5881s and we went from there, just a great guy, a real amp guru if ever there was one.
Are you in Auckland?

Yep - and definitely agree on that.

 

[Matthew124241]

Thanks for this post. I owned a 1971 superlead in the past, and noticed that the sv20, while amazing, is lacking some bass / umph. I fiddled 100pf, 500pf, and 4700pf. If you like AC/DC / van Halen, I suggest sticking with 4700pf. The “bite” goes away, even with 500pf and you cant get it back with presence and tone. If you like lower gain at 4 or so with no jumpered channels then maybe play with bright cap.

I ended up with 4700pf but it’s a ceramic disk. Not sure if the ceramic improved the tone over the stock one, could be placebo, but I swear its a bit warmer.
Anyhow, if you’ve owned a real superlead, dont expect to dial the sv20 in the same way. It needs the bass to be higher, like 7-8 and the treble a little lower. Amazing little amp and I’m thankful to have my old plexi tone in a bedroom with an attenuator.

 

[gush]

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!