Fender Bassbreaker 007 mods?

[Richard]

Has anyone around here modded one of these guys? I picked up a head and cab a few weeks ago and I like it but it's not quite there yet.

According to a schematic I found online (not from Fender), the amp has an input gain stage, gain control, 2 more gain stages, a TMB tone stack that is very similar to a 5F6-A Bassman except driven from a gain stage instead of a cathode follower, master volume, and a final gain stage to drive the single EL84. Preamp tubes are both 12AX7A. There is a footswitchable treble "boost" that unmutes the bypass capacitors for the first two gain stages. All cathodes have their own resistors and bypass caps.

I replaced the the stock 12" Celestion V-Type with a JBL MI-12 and that got me some high end sting that I couldn't get but now the bass response seems indistinct. The bass is there but it isn't as tight and defined as I'd like. The treble boost is now too intense, before, it was right on the edge of barely enough treble without, almost too much with. The cabinet has 2 3" x 6" oval ports, I'm going to experiment with plugging one or both of them or maybe taking the back off the cab. I may try a different speaker.

I have thought of making the boost only operate one bypass cap or maybe changing some values in the tone stack. I'll work a little more with the speaker and cabinet first.

I guess I should say that I have a Super Reverb Reissue that I love and that my main goal when buying this amp was to be able to get good breakup at non WMD levels. I actually really like it and want to tailor it to my use rather than try to turn it into a low power high gain Super Reverb.

[Helmholtz]

Here https://www.bonedo.de/artikel/einzel...ad-test/2.html is a (German) test report with nice sound clips of the head version into a 2x12 Celestion V30 cab.
Not a typical Super Reverb sound, at least partly due to Celestion speakers.
But obviously voiced for a little Marshall Bluesbreaker sound.

Please post schematic.

[Jazz P Bass]

This may be the proper schematic.

[Helmholtz]

This may be the proper schematic.

Thanks but the Bassbreaker 007 should be single-ended.

[Richard]

The schematic I found was one that someone did themselves, is it okay for me to share it? He did post it online for all to see and it has his name on it so I don't see why not but I also didn't want to assume. If people here say it's okay I'll gladly do it.

Hemholz, thanks for the link to the review. It sounds great butI think you can hear what I feel this amp is lacking in the first clip. It's a good sound but could use some more presence up top. He's also miked with an SM57 which I think excels at capturing that presence. Here's a GE Smith and the SNL band recording that has an example of that treble sting I crave.

https://youtu.be/h7T0VW85rVI?t=149

I thought about it a little more and given the similarities to the 5F6-A tone stack and the excellent sounds I've heard from Bassmen, I can leave the tone stack alone. The speaker and cabinet is where I will focus for now. The ports are about 4 times the size JBL recommends for the cabinet size so I'm going to try something there. After that I will look at different speakers. Once I'm done there, I think that I will look at controlling the second gain stage treble bypass with a panel mounted switch, keeping the first controlled by the footswitch, instead of having both on the footswitch.

As soon as someone says it's not a violation of etiquette to post the schematic, I will be happy to do so.

[Helmholtz]

The schematic I found was one that someone did themselves, is it okay for me to share it? He did post it online for all to see and it has his name on it so I don't see why not but I also didn't want to assume. If people here say it's okay I'll gladly do it.

If it's online, it's public. Patents don't protect against publishing schematics. Everyone who has the amp could draw a schematic and publish it. I don't see a risk to share the link.

Helmholtz, thanks for the link to the review. It sounds great butI think you can hear what I feel this amp is lacking in the first clip. It's a good sound but could use some more presence up top. He's also miked with an SM57 which I think excels at capturing that presence. Here's a GE Smith and the SNL band recording that has an example of that treble sting I crave[.

Nice record, btw.
But remember there's a lot you can do to guitar sound in a recording studio.

I don't think modifying the cab will change much.

[Richard]

If it's online, it's public. Patents don't protect against publishing schematics. Everyone who has the amp could draw a schematic and publish it. I don't see a risk to share the link.





Nice record, btw.
But remember there's a lot you can do to guitar sound in a recording studio.

I don't think modifying the cab will change much.

I didn't think there would be a problem but I wanted to make sure. He put his name on it so I'm not taking credit for his work.

I'd like to see what playing with the cab will do for the bass response, I've been curious about cabinet acoustics and this is an excellent opportunity to experiment. I don't think that any normal cabinet design has a significant effect on treble, at least not compared to the bass.

As far as the lack of treble from my amp, previously, with the V-Type, I was running the treble and the mids at 3 O'clock or higher and the bass at about 8:30. Reducing the mids allowed the treble to stand out more but I still would like to have a little more range usable. With the JBL I can set the treble to 12 O'clock. When I hear someone say that any setting of the EQ produced a good sound, I think that means that the EQ didn't have enough range. A little extra should be available, otherwise there are probably useful sounds just past the range. For reference, on my SRRI, I run the treble just below 5, the bass at about 4, the mids all the way up, the bright switch off, and the volume at 2. (on the knobs that start at 1)

The JBL may not be the right speaker for me and this amp but It was educational hearing what the extended top end would do. Much better for less distortion but not as good for more distortion. The V-Type is a good sounding speaker, although I actually thought it would sound better with an SM57 in front of it, which I've never said before. I usually prefer the sound of a Sennheiser e609 or a small diaphragm condenser for the smooth treble response. I now have two data points and know that the ideal lies in the middle. I've only had the amp for 3 weeks so I'm still getting to know it. The JBL has been in there for a week. I still feel that I have a decent handle on it, but with all the gain available and the master volume, it's a lot different than the Blackface style amps I know and love.

I've got a couple of guitars to rewire before I tear into the amp, 1 meg pots will probably help the treble response, maybe do something with the tone control for when I need less treble, and I need to make sure my soldering skills are sharp. It will be a little while before I start modding the amp. I am intrigued by the possibility of separating the switching for the gain stages, with a 3 position switch I could have the second stage on, off, or controlled by the footswitch.

Thanks for all the help, I'm sure I'll learn something useful and hopefully someone else will, too.

[Dave H]

The treble boost is now too intense,

Try adding a resistor (1k5?) in series with C27.
C27 boosts treble. C22 boosts all frequencies. Remove C22 for treble boost only.

[dmeek]

Here is the service manual

Bassbreaker 007 Service Manual.pdf

[Helmholtz]

Actually it's not quite clear to me what the OP wants to change.

More bass /less treble (not the same!) ?

I think the amp has a nice overdrive structure and modifying it might destroy that.

[vintagekiki]

He doesn't even know what he wants.
With amateur equipment, can't expect a studio recording.

[Richard]

What I want is more treble with the boost not engaged and a less dramatic boost.

[vintagekiki]

Treble boost is obtained by installing C1 and (or) C2 220pF - 470pF (optional) and (or) remove C34 6.8nF.
Bass boost is obtained by changing C19 and (or) C21 from 2.2nF to 10nF - 22nF (optional).

[Richard]

Thanks, I haven't even cracked the amp open to see what it looks like inside. I'm much more comfortable working inside handwired amps than PCB constructed amps.

[DrGonz78]

Thanks, I haven't even cracked the amp open to see what it looks like inside. I'm much more comfortable working inside handwired amps than PCB constructed amps.

If it’s anything like the other Bassbreaker series amps the layout could give you a serious case of fight or flight. Hopefully that version is easier to work.