bass boost

[HiGain]

Inspired by the idea of paralleling tubes to increase bass, I had a question about increasing the bass response of the express...

What if you used the second tirode of the second tube in parallel with the third gain stage. Connect the grid to grid and cathode to cathode. Now, connect the plate of the "new" triode to the plate of the third stage triode via a 100K resistor. This means there is a total of 200K to B+ for the plate of the new triode, as well as 100K series resistance from the output of the new triode to the PI. Last, place something like a .0047 cap from the plate of the new triode to the PS node.

The idea is to implement a parallel stage to boost bass with few parts. Do you think this would work?

Thanks,

Jake

[Darkbluemurder]

Inspired by the idea of paralleling tubes to increase bass, I had a question about increasing the bass response of the express...

What if you used the second tirode of the second tube in parallel with the third gain stage. Connect the grid to grid and cathode to cathode. Now, connect the plate of the "new" triode to the plate of the third stage triode via a 100K resistor. This means there is a total of 200K to B+ for the plate of the new triode, as well as 100K series resistance from the output of the new triode to the PI. Last, place something like a .0047 cap from the plate of the new triode to the PS node.

The idea is to implement a parallel stage to boost bass with few parts. Do you think this would work?

Thanks,

Jake

Jake,

I am not clear whether I am really with you. In other amps I found that increasing the plate resistors increases bass since it interacts with the coupling cap that follows the plate. If I used the dual triode for the 3rd stage I would probably tie the plates together and start with a 47k plate resistor and a 4k7 cathode resistor (that would make it close to the 100k/10k combo on a single triode section). I would expect if you now increase the plate load resistor from 47k to say 100k that the clipping of this stage would be less than before due to the shift of the operating point (I believe this is why 'umble went from 100k/1k5 to 220k/3k3 in his later amps - this made any amp cleaner and fuller I tried it on). It sure wouldn't hurt to try and see whether you like it.

In amps with much preamp gain I've had good experience by increasing the bass late in the amp, e.g. use 0.1uF PI caps and high value PI input caps. It probably wouldn't hurt to increase the coupling cap to 4700pF as you suggested.

Good luck!

[Richie]

The one i have been playing has plenty of bass..and with the LP i use the bright switch..you could do a few things.. like fender does in the bass boost of the bassmans with a switch..you could do a couple things in the feedback circuit for a bass boost or resonance control,or a switch to put a cap into the feedback circuit for a more bass boost.
If you go messing with adding things to the unused tube section..then the voltages will change a bit in the amp,which i think is part of the other mojo of the amp. But always worth a try,you never know..just some ideas of other ways to get a bass boost.

Richie

[Mark]

Dear Jake

A technique that Ken Fischer used to alter the bass response is to attentuate the high frequency response by putting a cap across the second pre-amp plate resistor.

I have experiment with this circuit after seeing a version of a Trainwreck in the circuits at Blueguitar. There was a 0.001uF coupling cap with a 0.0022uF cap across the second plate resistor. I was quite curious how this could possibly work, once I had carried this out the effect was an increase in bass response.

Perhaps what you could try is putting a 0.0047uF cap in series with a 100K pot across the second plate resistor and see if this works for you?

Good luck with your build.

[HiGain]

Thanks for the responses, guys. Since I read at Komet's site that the new KF amp uses an extra stage for bass boost, I just surmised that a parallel stage ahead of the PI was used. If you think about it, you could balance how much of the "bass triode" gets mixed in, so that the same feel, midrange punch, and clarity is there, plus some extra bass at the bottom.

Someday I will give it a try.

Jake

[ODwan]

Remember that too much bass before the clipping parts of a circuit can make it sound mushy!
Another use for triode would be as a gyrator aka simulated inductor which could be used to suck bass frequencies out of the NFB loop thus creating a boost at this frequencies.
This technique is actally used in Diezel amps, though Peter Diezel uses actual inductances (one of the reasons that his amps are so high priced).

Timo

[Funkalicousgroove]

perhaps try scaling the bass control differently, use a .033 cap or.047 cap for the bass and try a 500K pot

[ODwan]

I also found that taming the high end with a Vox-like Cut control results in a subjectivly bigger bass response.

Timo