Trainwreck Express Filter Capacitors

[Littlewyan]

I've been pondering changing the main filter cap can in my TW Express. Its currently a JJ 50uF x 50uF and I was wondering if it should be 32uF x 32uF to be closer to the original spec. I was also wondering what difference changing to a F&T Cap Can would make. I've heard some people say that JJ Filter Capacitors sound a bit sterile.

I think my Express sounds a bit stiff compared to Glenn's Express in his demo videos. I know the Power Supply for the power valves isn't supposed to sag like old Marshalls but Glenn's Express has a bit of softness on the notes compared to mine which are quite sharp.

Anyone experimented with this?

[martin manning]

Maybe you could do a quick experiment by disconnecting half of that 50-50 cap? The brand of cap may make some audible difference, but the size is going to be much more noticeable. Have you measured it? You may have well over 100uF now.

[Littlewyan]

That's a good idea. I haven't measured it no so that's another thing to try. I'm actually building myself a JTM50 at the moment and have a F&T 32uF + 32uf Filter Cap on its way to me, so I could stick that in as a test. I remember reading that Glenn tried different filter caps in his Express clone and heard a big audible difference. I also remember reading that due to the impedance in filter caps they will affect certain frequencies differently. Not sure if that's right.

[martin manning]

The tolerance on those is huge, and I wonder if that isn't the biggest part of what people are hearing when they compare two different brands with the same marked capacitance.

[Bob S]

Well worth measuring the filter caps for all nodes.
Some state -20/+50% but in reality they are mostly +20 to 25%.
I used to think big for the reservoir (and keep a tight leash on the power valves drive signal), then adjust to suit further down the food chain.
Nowadays I'm not so sure...
I'll be interested in your findings.
Edit:
Particularly for an Express because the onset of distortion runs backwards through the amp.

[rp]

I think my Express sounds a bit stiff compared to Glenn's Express in his demo videos.

How old are Glenn's caps? The sound loosens up and darkens as the years go by. Start off green, ripen, then rot like fruit

[Littlewyan]

The JJ Caps are -10% and +30% whereas the F&T Caps just state +20%. Hopefully I'll get a chance to experiment at the weekend when I can turn it up loud.

[katopan]

The first filter cap sag in an Express is significant, so yes a higher value capacitance will effect the amp's response quite noticeably.

[Roe]

I really like the bc vishay 450v caps in expresses (33+47uf;33uf;22uf;22uf;22uf)

[geetarpicker]

You could source some actual Mallory electrolytics like Ken used. That is what I did in my two clones. Are you simply playing the amp loud or using an Attenuator or other? I've found attenuators vary in high end smoothness. I will mentioned I owned an Airbrake (among others) but the high end was the harshest with it. It had other good qualities but not in that regard. Currently I'm happier with my Alex Attenuator, which also preserves the amps ability to clean up with less volume loss than other such devices. Speakers also play a big part and my old Greenbacks definately have a natural compression in the highs that is part of why I prefer them.

Glen

[guitarmike2107]

Glens right, Speakers make a huge difference, probably way more than a small filter cap change. what speakers are you running through?

I tried switching in a filter cap on a previous build, going from 50uf to 100uf and hardly noticed a difference, I suspect there is an optimal value where you will start to really notice the power section compressing, I imagine that if you go to far and it will go to mush..??

[Littlewyan]

I'm currently using Eminence GB12 Speakers in a 2x12 Cab. I've heard they are very similar to Greenbacks but I've never played through Greenbacks before (that I know of) so can't compare them.

I've tried to achieve this tone by valve swapping or messing with the EQ but I find that when I find a good tone for single notes where the tone isn't too thin I also lose a lot of clarity and open chords start to sound like mush.

There is one thing I've yet to try. I replaced my JJ ECC83S in V2 for a JJ ECC83 MG which improved the tone tenfold. The JJ ECC83 MG is more open sounding and has more upper mid range than the JJ ECC83S. I'm using a EH12AX7 in V1 which is very balanced and can be thin. I wondered if I stuck a JJ ECC83 MG in V1 as well as V2 if I'd tame the top end enough to get the tone but keep the clarity. I tried the JJ ECC803S but it had way too much top end.

Anyone else used the JJ ECC83 MG?

[stretch2011]

Spend the money, get better speakers. I wish I could test a alnico blue or gold before I flip out my wallet.

[Littlewyan]

Can't have Greenbacks in a 2x12 Cab, the Express will probably turn them to dust! Anyway the Eminence GB12s are decent speakers. I replaced my Celestion G12T-75s with them. The G12T-75s aren't bad speakers but were too mid scooped for my liking. I suspect my speakers are still not fully broken in. Only once have I been able to run the Express through them without an attenuator and that was only for 5 minutes before I got shouted at!

Anyway I think it probably comes down to every Express sounding different. Maybe I need to try a few more pre amp valves.

[guitarmike2107]

How loud are you able to play before been shouted at, I think Glens recordings were at full tilt and speakers just respond different when they are pushed. I am surprised I don't have the police here often and that only pushing out 10 watts cranked, so I assume you must be attenuating the amp allot?

I would run the amp through two 25w G12M greenbacks, especially if you are attenuating it and with the low sensitivity of the speaker it will help you turn up the attenuator a bit. there are very few venues in the UK where you will be able to crank that amp properly... maybe outdoor gigs...

If you don't want the G12M speaker go for the 30w G12H, it has loads more bottom end, but once broken in the highs are much smoother compared to a vintage 30 say.