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Single C12N doesn't sound good

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6/12/2005 9:32 AM

Single C12N doesn't sound good

I bought a Pignose G40 some years ago.
After much modding I ended rebuilding everything and now the circuit is like a Fender Vibrolux except I have a 470 ohm resistor instead of a choke. Voltages are 420 on plates and 410 on screens. Everything around BF Vibrolux schem values.
Builded an open back cab with a new Jensen C12N for it and put the amp in a separate head.
It sounds ok and I've been gigging a lot with it without a problem but still, to me, it sound like it lacks some sweetness, some harmonics ?
I don't know. I play an Aria FA-80 archtop and play clean rockabilly with just an analog ibanez echo in front of it.
So, clean sound it's ok but more Hi-Fi than rich Fender clean I expected. Pushed vol to 5 or 6 or higher (normally I get plenty loud on 3 for gigs) the distortion doesn't sound good: unpleasent highs and boomy bass.
A couple days ago I connected the original speaker (Pignose 10 inches) in parallel to the same 8 ohm output (both spker 8 ohms so a little mismatched) and overdrive sound seems to improve but still missed harmonics.
So, as I haven't heard good fender amps is this normal ? isn't one single C12N enough ? Some ideas?
I tried different idle currents for the 6l6 and different 6l6 too without great differences.
Good preamp tubes made a difference in clean clarity but not in "richer sound"
Thanks and I'm sorry for the long story.
Scotty
www.geocities.com/hillbillyswing

6/12/2005 12:08 PM

"still, to me, it sound like it lacks some sweetness, some harmonics ?"

You can try doubling the value of the negative feedback resistor. This will add alot of spice and may improve overdrive a little.

"Pushed vol to 5 or 6 or higher (normally I get plenty loud on 3 for gigs) the distortion doesn't sound good: unpleasent highs and boomy bass."

If your dialed for a dynamic clean or semi distorted sound you will get mushy raspy distortion if you don't change your EQ settings when you crank it up. At 5 or 6 you still have alot of effect from the "bright" switch. If your using it, shut it off for the overdrive tones. Also the bass will need to be lowered alot. Some guys dump the bass to 0 when they're cranking BF amps. A larger mid pot can help with overdrive tones too. A 25k pot in place of the 10k pot will give you all the tones you have now but anything above about 4 or 5 will be a midrange boost which can help you get a thicker distortion tone.

A favorite BF mod of mine is to change the first gain stage cathode capacitor to 3.3uf and change the second gain stage cathode capacitor to 1uf. This seems to take out the boomy bass and improve distortion. It will change the clean tone though. If you lose too much bass, change the second stage back to the original capacitor value (22uf/25uf). Also, change the phase inverter plate decoupling caps from .1 to .022. This helps reduce boominess too (is that a word?).

HTH

Chuck

6/12/2005 2:33 PM

Thanks a lot.
I will clarify that when I told Vibrolux I meant Tremolux.
And one channel only with no reverb.
I took normal BF channel preamp with 0,047 uF, 220k/220k voltage divider before 500 pF to PI. BF PI and Power amp, too but with 0,047 uF instead of 0,1 at the output of the PI.
Your advice still apply to this being a BF I suppose.
I took the negative fb from the 4 ohm tap of the OT and connect spkr to the 8 ohm output.
I will first try increasing the negative feedback resistor to 1,5 k (I think that is the nearest value to 2x860) and then try the preamp cathode caps too.
I don't have a mids pot, maybe I should try that 25k too.
Still wonder why sounded better connecting the Pignose speaker. Probably its poorer eficiency hides some of those highs and bass.
Thanks again.
I tell what happens as soon as I try it.
Scotty
http://www.geocities.com/hillbillyswing/

6/13/2005 8:58 PM
Chuck	Not sure whay it sounds better through the 10" stocker. Maybe to your ears the tighter focus and rolloffs are the ticket. Maybe a 2x10" cab If you like the mid scoop clean tone of the BF type amps then you can put the 25k mid resistor on a push/pull pot and switch between the 6.8k stock value and the 25k. That way your not stuck in mid boost when you want to play a nice clean tone. Chuck

6/21/2005 10:04 PM

I did not like my jensen C12N when it was new. The distortion at higher volumes was raspy. so I put it away for awhile. latter when i came back I decided to push it up louder. certain high volum chords it would maks this buzzing sound. so I just turned it up more and decided to punish it. after about a half an hour of loud garage rock n roll, the buzzing went away. now the high end is clear and smoother and it is one of my favorite speakers in my Fender amps.

6/22/2005 7:50 PM
Chuck	I love it when that happens. Does't happen that often though. Usually I find that if I put the screws to something because it's pissing me off... I do manage to blow it up But there is the odd occasion when the punishment reveals something and you can then fix the problem. Chuck

7/13/2005 2:00 PM

I had the same initial experience with a C12N RI in my SFDR, more or less. At first I loved it because of the extended high end, which at the volumes I was playing was more like chime than rasp. I had never heard any of that from the POC (Oxford?) that came with it. Well, actually a parody of chime, it was so exaggerated that it pretty quickly fatigued me. My solution was to send it back and get a Weber C12N. End of story. They are really very diferent speakers, and if excessive highs is your beef, the Weber will take care of it without muddying up. But it is not a high gain type speaker--too much bottom.

Ben

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