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FDP Forum / Amp Mods, Repairs, and Projects / Blues Jr mid cap mods

Tele Vince

United States

Dec 5th, 2016 12:20 PM   Edit   Profile  

Has anyone experimented with changing the mid tone cap at all?

I’ve changed my bass cap from 0.022uF to 0.1uF. Happy with that change.

However, I also changed the mid cap from 0.022uF to 0.015uF, per BillM’s specs. Now, I find the mids to be muddy (too many 150-400Hz, not enough 700-1,000Hz).

Would it make sense to put the 0.022uF mid cap back in? Or maybe go all the way up to the 0.047uF that many Fender amps use? I'm worried 0.022uF wouldn't change it much, and I'm worried 0.047uF would not allow mids to be turned up enough.


(This message was last edited by Tele Vince at 02:22 PM, Dec 5th, 2016)


United States

Dec 5th, 2016 12:44 PM   Edit   Profile  

I love my blues jr, it's stock all the way through and I've never had an issue with it. Do you have the tolex or tweed version? The speaker will make a difference.

Tele Vince

United States

Dec 5th, 2016 01:48 PM   Edit   Profile  

I have the tweed NOS.

Swapped the Jensen C12N for an Eminence GA-SC64. It reduced some of the harshness of over-driven leads, while still being voiced like a vintage'60s Fender speaker.


United States

Dec 5th, 2016 02:04 PM   Edit   Profile  

There's your sign. I've actually tried the GA-SC64 in my Blues Jr, if you're looking for fender sparkle I think you'll prefer the C12N. Just food for thought, I've personally A/B'd both, and the C12N sounded better to my ears.

Tele Vince

United States

Dec 5th, 2016 02:34 PM   Edit   Profile  

I'm pretty happy with the level of presence and treble I'm getting (which are the frequencies I'd usually consider to be sparkle). I didn't really like the way overdrive would sound on the C12N - kind of harsh (or what I've seen described as "ice-picky").

The speaker swap likely is contributing to the increased low mids and decreased high mids though, but I think the fact I switched the mid cap from .022 to .015 is the bigger factor. That changed the center bottom of the mid-range curve from around 700Hz up to 1000Hz. The center with the .047 would be about 500Hz, but it also drops that entire mid-range by 2-4 dBs.

Just curious to see if anyone has tried out the .047 mid cap in the Blues Jr along while having the 0.1 bass cap. I'd like to know if it reduces the mids too much and makes the amp sound too thin.

(This message was last edited by Tele Vince at 04:38 PM, Dec 5th, 2016)


United States

Dec 5th, 2016 03:47 PM   Edit   Profile  

Well different horses for different courses. I do know these amps are sensative to guitar input, but heres a short clip of my blues jr. Its all stock, and though they're mistakes the sound is pretty on point imo. Maybe you could post a demo clip as well so we can hear what your hearing.

Blues Jr

(This message was last edited by NHILL1 at 05:48 PM, Dec 5th, 2016)

Tele Vince

United States

Dec 6th, 2016 09:22 AM   Edit   Profile  

First five song clips here are with the Blues Jr NOS stock:

It was a little thin sounding, so I had those BillM mods and speaker swap done to make it sound a bit fuller/bigger. Happy with the results to the low and high end. Just want to un-"muddy" those mids now.

Don't have footage yet since making the mods.

(This message was last edited by Tele Vince at 11:24 AM, Dec 6th, 2016)

Tele Vince

United States

Dec 9th, 2016 08:44 AM   Edit   Profile  

Put the 0.022 mid cap back in. Seems to have removed the muddiness. (Yay!) I do understand though why BillM recommends the 0.015. That definitely sounded fuller when clean. So, it's a trade-off between fullness and mud. Since I play more overdriven than clean songs, the less muddiness was a larger priority. If I was playing mostly cleans, I'd leave the 0.015 cap in.

Either way, increasing the bass cap was still the way to go. I'm happy with the 0.1 I have in now, but I bet a 0.047 could be a good choice compared to the stock 0.022 too.

(This message was last edited by Tele Vince at 10:47 AM, Dec 9th, 2016)

FDP Forum / Amp Mods, Repairs, and Projects / Blues Jr mid cap mods

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