RockStarNick
Active member
So last year, I scored a mint Bogner Metropolis 30W. I've been playing it for the past year, and while it's an amazing amp, there was something about the tone that I wasn't completely bonding with. Even after many tube swaps and EQ changes, I still couldn't dial it in exactly to my liking. So, I did what anyone would do. RIP IT OPEN and take a look under the hood. 
Here's what I found:
The Bogner Metropolis is an interesting juxtaposition of super-tidy, super sturdy PCB work (typical Bogner high quality), combined with some really wacky, flying PTP components (like a Matchless). In particular, the 5 position "Schizo" switch. It's described as Bogner as a tone-shaping circuit. From what I can see, is that it selects one of 5 capacitors, or capacitor/resistor combinations, to alter the EQ curve. (I'm not an amp tech, by any means, but from my experience working on Randall/Egnater modules, I can assume that it's some sort of coupling cap).
The COOL part is that the flying PTP stuff makes it really easy to work on it. No need to disassemble the amp, or take out the circuit board, or work in a cramped space. The PTP portion is right up front, and wide open.
The combinations have changed somewhat over the years, according to Bogner. In the past, the capacitors just increased in size, adding more bass. The more recent Trops have cap/resistor combos, which do more EQ filtering. I appreciate the EQ filtering, but I felt that the amp was lacking a "normal" sound. Just a straight up, straight thru cap with a typical midrange and bass response. And my assumptions proved correct, when I realized there wasn't any .0022 "straight thru" cap. (Pardon my incomplete drawing - I'm no electrical engineer, I just drew out what was visible to me upon inspecting the inside. There's some missing pieces, but the bulk of what I needed was there.)
Well, now, onto my testing and conclusions: The cool part about having the 5-way switch in there, was that it provided a platform to do real-time, back-to-back comparisons between caps of different constructions and values. So for giggles, I soldered in three .0022 caps: a Silver mica, an Orange Drop 716, and a Mojo Dijon.
I know it sounds ridiculous, but there was a huge difference in sound between the two. The Orange Drop was harder, more hard trebles, bigger bass. But just kind of offensive sounding. Way too aggressive - at least in this amp. I hate to use all the typical Gear Page buzz words, but The Mojo was sweeter, less extreme EQ. dare I say woodier. Sounds a lot closer to my friend's Dr Z Maz 18, which is precisely what I was going for.
The Mojo just fits this amp so much better, makes it more pleasing to the ear, and it's much more enjoyable to play now. Really cops the Brad Paisley tone now. Now instead of the useless Position 1, which was 100pf thin screetchy crap, and position 2 which was a super hollow scooped tone, I now just have my choice between a a .001uF and .0022uF Mojo Dijon cap, to tailor the bass response, but still sound similar. Much, much more useable tones now.
I showed my findings to a good friend who is a very respected amp builder, and he said "It's important to stress, in your findings, that you were really hearing the difference in cap CONSTRUCTION, not brand. In this case, a Polypropylene OD vs a Polyester Mojo. Had you compared the PP OD's to another brand of PP caps, you would have heard much less of a difference between the two. Comparing composition & hearing a difference....valid & legit. Comparing "trade names" & hearing a difference...slippery slope." I think he's 100% spot on in this.
It's kinda crazy how one $1 component can change the character of an amp this much. It's also incredible how that first cap makes such a big difference. kinda like the first preamp tube in an amp.
The moral of the story: a little bit of research, and $2-3 worth of capacitors, can transform an amplifier, and tweak it to your exact needs.
Here's what I found:
The Bogner Metropolis is an interesting juxtaposition of super-tidy, super sturdy PCB work (typical Bogner high quality), combined with some really wacky, flying PTP components (like a Matchless). In particular, the 5 position "Schizo" switch. It's described as Bogner as a tone-shaping circuit. From what I can see, is that it selects one of 5 capacitors, or capacitor/resistor combinations, to alter the EQ curve. (I'm not an amp tech, by any means, but from my experience working on Randall/Egnater modules, I can assume that it's some sort of coupling cap).
The COOL part is that the flying PTP stuff makes it really easy to work on it. No need to disassemble the amp, or take out the circuit board, or work in a cramped space. The PTP portion is right up front, and wide open.
The combinations have changed somewhat over the years, according to Bogner. In the past, the capacitors just increased in size, adding more bass. The more recent Trops have cap/resistor combos, which do more EQ filtering. I appreciate the EQ filtering, but I felt that the amp was lacking a "normal" sound. Just a straight up, straight thru cap with a typical midrange and bass response. And my assumptions proved correct, when I realized there wasn't any .0022 "straight thru" cap. (Pardon my incomplete drawing - I'm no electrical engineer, I just drew out what was visible to me upon inspecting the inside. There's some missing pieces, but the bulk of what I needed was there.)
Well, now, onto my testing and conclusions: The cool part about having the 5-way switch in there, was that it provided a platform to do real-time, back-to-back comparisons between caps of different constructions and values. So for giggles, I soldered in three .0022 caps: a Silver mica, an Orange Drop 716, and a Mojo Dijon.
I know it sounds ridiculous, but there was a huge difference in sound between the two. The Orange Drop was harder, more hard trebles, bigger bass. But just kind of offensive sounding. Way too aggressive - at least in this amp. I hate to use all the typical Gear Page buzz words, but The Mojo was sweeter, less extreme EQ. dare I say woodier. Sounds a lot closer to my friend's Dr Z Maz 18, which is precisely what I was going for.
The Mojo just fits this amp so much better, makes it more pleasing to the ear, and it's much more enjoyable to play now. Really cops the Brad Paisley tone now. Now instead of the useless Position 1, which was 100pf thin screetchy crap, and position 2 which was a super hollow scooped tone, I now just have my choice between a a .001uF and .0022uF Mojo Dijon cap, to tailor the bass response, but still sound similar. Much, much more useable tones now.
I showed my findings to a good friend who is a very respected amp builder, and he said "It's important to stress, in your findings, that you were really hearing the difference in cap CONSTRUCTION, not brand. In this case, a Polypropylene OD vs a Polyester Mojo. Had you compared the PP OD's to another brand of PP caps, you would have heard much less of a difference between the two. Comparing composition & hearing a difference....valid & legit. Comparing "trade names" & hearing a difference...slippery slope." I think he's 100% spot on in this.
It's kinda crazy how one $1 component can change the character of an amp this much. It's also incredible how that first cap makes such a big difference. kinda like the first preamp tube in an amp.
The moral of the story: a little bit of research, and $2-3 worth of capacitors, can transform an amplifier, and tweak it to your exact needs.
