5F6-A More bass

[Toneseeker]

Hi Guys,

what's the best way to get a little more bass out of my 5F6-A HRDLX conversion? I'm not looking for anything radical, just a tone stack change maybe. I'm really pleased with the amp but it would be perfect if I could get just a little bit more bottom from it.

Pete

[ziess]

Not having enough bass is rarely a description used for the 5F6-A circuit. In the one I build I increased the size of the preamp stage filter cap (from 8mF to 16mF) to tame the bass response a bit.

You're running some kind of Celestion Neo, right? Perhaps another speaker would do the trick.

Tommy.

[cdw2000]

Just looking at the 5F6-A schematic -

There is a 56K resistor coming off the 12AX7 plate and connected between the 250pF Treble stack capacitor and the 0.02uF Bass stack capacitor.

Lowering this resistor value can bring up the bass a bit. You can do this experimentally without altering your amp by temporarily connecting resistors in parallel with the 56K resistor. A 270K resistor in parallel will result in about 47K total. An 82K resistor in parallel will result in about 33K total.

In case you don't know, the formula is:

Rparallel = 1 / (1/R1 + 1/R2)

Where R1 is your 56K resistor and R2 is the value of whatever resistor you use in parallel.

If you come up with a combination you like, there's no reason you can't just permanently solder the parallel resistor in. That way you can always reverse the mod later.

[Toneseeker]

Originally posted by Ziess:

You're running some kind of Celestion Neo, right? Perhaps another speaker would do the trick.

Hi Tommy, a speaker change is not on the cards, that Celestion G12 Century cost me £80. I was kinda hoping a cap change might do the trick. This bass thing is just a minor itch and it's still a great sounding amp. I'm just trying to sqeeze a little more out of it.

cdw: that's the slope resistor you're describing. I 've already got a 100k resistor in there with another resistor on a switch to give me 100k or 56k. The 56k sounds better. However my understanding is that lowering that further will also shift the treble response down a bit. I may be wrong on that though.

Pete

[NTBluesGuitar]

You're running this circuit in a re-built Hot Rod, right? What cathode bypass cap did you run off of V1? The original calls for a 250uF, but for guitarists, I put in a 25uF. You'd want the 250uF.

[cdw2000]

Based on the original 5F6A schematic, 56K is what is supposed to be in there, the 100K value you have would explain why you would want more bass from the Bassman.

Here the schematic I was looking at:

http://www.schematicheaven.com/fende...5f6a_schem.pdf

All the values in the tone stack are somewhat interactive, but the slope resistor shouldn't affect the treble response that much.

Have you ever tried the Duncan's Amp Pages' Tone Stack Calculator? This will help you play with values and visualize the results. Looking at the schematic above, the Bassman topology more closely resembles the Marshall rather than the Fender as depicted in the Calculator. The difference is in how the Midrange pot is connected. Just modifiy the Marshall values with those in your amp to see how the curve changes.

http://www.duncanamps.com/tsc/index.html

[Toneseeker]

TJ, I am using a 250uF bypass cap in there.

CDW, I know the standard resistor is 56K thats why I put a switch in there to parallel another resistor with the 100k to give 56k. The 56k sounds better than the 100k I think. 100k was recommended to me by someone but I wasn't convinced so I fitted the switch. I think it's a Marshall tone stack thing. I'll try lowerng the value of the slope resistor and see if that helps.

Thanks for the pointer to the Tone Stack Calculator.

Pete

Edited: Had a look at that Tone Stack calculator. Looks like a 33k slope resistor is a move in the right direction.

Thanks for your help guys and have a good weekend.

Pete

[Toneseeker]

OK...I swapped the 100k slope resistor for 56k and wired in a 82k resistor in parallel on the switch to give me the choice of 56k or 33k (approx). Yep that did it...strum a cord and let it ring, flick the switch and you can hear the difference. I'm happy with that. Thanks for the advice guys.

Pete

[NTBluesGuitar]

Glad you got what you wanted!

Although, lots of times, guitarists want LESS bass from a Bassman, so I was surprised you wanted MORE. Especially in a normally boomy Hot Rod cab (assuming you're still using that).

[yankeerob]

Well yer all right - it's amazing how we could all put an amp together and come up with something slightly different... glad yer still pleased with the amp Pete - those neo's can be a little bass light - but it seems you've found the solution with as little pain as poss - and we all learned a little from all the conjecture - win/win

[Toneseeker]

Originally posted by NTBluesGuitar:

Although, lots of times, guitarists want LESS bass from a Bassman, so I was surprised you wanted MORE.

TJ, I there's just a few songs that I do where I use the neck pickup on my Epiphone Sheraton to get a nice deep bluesy kinda tone. I was trying to deepen that a bit. That's why I've got the switch in place. When I want a brighter tone I just flick the switch back to 56k. It's nice to have the flexibility. I've also got a bright boost switch in there a' la JTM45, which is handy sometimes.

Rob: You're probably right about the G12 being a little light on bass, Ziess mentioned that as well but it's such a good speaker in other respects and swapping it was not an option as it was quite expensive.
I think that's just about all the tone I'm going to get out of this amp. Next step will have to be another build. Errrmm..maybe not.

Pete

[cdw2000]

Glad it worked out for you, TS.

Building my own little 4-1/2 watt 6V6 amp using bits and pieces of old Fender designs, I discovered there is some tweaking to be done in the tone control to voice the amp properly with the speaker and OT (or at least properly to my ears).

In my case my OT was a little oversized and my speaker was a little strong in the bass. Initially I was trying to tailor the bass with one of the AC coupling capacitors, but found that was just not giving me the desired effect. But increasing the slope resistor did the job nicely.

Hmm, maybe I will add a "Deep" or "Blues" switch to cut it back to the original value when I want the extra bass ...