On my D'Lite 44 (6L6) when playing at gigging volume, if I turn on the PAB in OD there is way tooo much bass.
Even with the bass pot at 0.
This is with both my humbucker strat and single coil strat.
I use a 2x12 open back cab with one V30 and one Classic Lead.
When I built the amp (kit) I included what Norm calls the bass mod.
Which I pictured below.
Will wiring the bass pot the Dumble way do anything for the bass when the PAB is turned on?
I haven't added the pre OD cap yet either.
Currently I have a 4.7 uf bypass cap on V1a but still have a 10 uf cap on V1b.
V2a and B2b have 4.7 uf bypass caps.
I haven't changed the values of the bypass resistors on either preamp tubes.
NFB resistor is still at 6K2.
The only other changes from the stock layout is a 330pf treble cap, 120K/ 110K PI plates, a 330R choke, on the power tubes (6L6) 470R screen resistors and 3K3 on the grids.
Any thoughts to tame the bass would be great.
Too Much Bass With PAB
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Too Much Bass With PAB
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Tom
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Re: Too Much Bass With PAB
A few thoughts:Structo wrote:On my D'Lite 44 (6L6) when playing at gigging volume, if I turn on the PAB in OD there is way tooo much bass.
Even with the bass pot at 0.
This is with both my humbucker strat and single coil strat.
I use a 2x12 open back cab with one V30 and one Classic Lead.
When I built the amp (kit) I included what Norm calls the bass mod.
Which I pictured below.
Will wiring the bass pot the Dumble way do anything for the bass when the PAB is turned on?
I haven't added the pre OD cap yet either.
Currently I have a 4.7 uf bypass cap on V1a but still have a 10 uf cap on V1b.
V2a and B2b have 4.7 uf bypass caps.
I haven't changed the values of the bypass resistors on either preamp tubes.
NFB resistor is still at 6K2.
The only other changes from the stock layout is a 330pf treble cap, 120K/ 110K PI plates, a 330R choke, on the power tubes (6L6) 470R screen resistors and 3K3 on the grids.
Any thoughts to tame the bass would be great.
1. You seem to have 2/3 of the Skyliner mod, based on your pots values. Some of us prefer the Dumble-approved 250KA middle pot when using the 500KA//.001uF bass arrangement and the 250KB treble pot. The 100KB pot you have there was the one used on the classic stack, with 250KB pots for treble and bass. But, this is just an observation. And by the way, Dumble connected the pots exactly as shown by you on the Skyliner amps.
2. Depending on your PAB scheme, the bass pot -- or bass cap for that matter -- may or may not have any effects whatsoever. Looking at your pictorial, it seems that your PAB is achieved by disconnecting the treble pot from the bass pot and the bass pot's wiper from the CCW lug. If that is the case, and your amp is wired correctly, you will have to look at reducing cap sizes (coupling and or cathode bypass) to get rid of some bass.
3. If you lift the tone stack with your PAB, which would not agree with your pictorial, then that'd be another story. The so called "mega boost" has way too much bass (and treble) in my opinion.
4. What size treble cap are you using? For the pot values shown, you have something like .002uF on the board and 390pF at the switch, or 330pF if there is no mid switch (which I suspect based upon what you wrote). When in existence, with the "MID" switch up you may feel there is too much lower midrange (I wouldn't call it "bass" per se). If you don't have a MID switch, ignore this part.
Do this test: do any of your tone controls work with PAB? IF so, then there is something wrong with your wiring, unless Norm is implementing something I am not aware of in your amp.
Good luck,
Gil
Re: Too Much Bass With PAB
Lower your feedback resistor to 4.7K and make sure the presence control is fixed. No grounding of the pot like the layout! It reduces NFB and adds raw bottom.
Not saying this is the issue, but it will help overall.
Not saying this is the issue, but it will help overall.
Re: Too Much Bass With PAB
Thanks guys.
Yes the PAB works as designed, that is, none of the controls function when PAB is turned on.
The bass, middle and treble pots are 500KA, 100KA and 250KB respectively.
No mid switch on this amp.
330pf treble cap. (changed from 270pf)
If I understand the layout I have a 0.1uf bass coupling cap on the board where the bass pot wire goes to the board.
The mid cap is at .05uf.
My slope resistor is at 150R.
Would changing V1b bypass from 10uf to 4.7uf help cut the bass?
The presence pot is wired as shown on #124.
How does changing the NFB resistor from 6K2 to 4K7 affect the tone?
Yes the PAB works as designed, that is, none of the controls function when PAB is turned on.
The bass, middle and treble pots are 500KA, 100KA and 250KB respectively.
No mid switch on this amp.
330pf treble cap. (changed from 270pf)
If I understand the layout I have a 0.1uf bass coupling cap on the board where the bass pot wire goes to the board.
The mid cap is at .05uf.
My slope resistor is at 150R.
Would changing V1b bypass from 10uf to 4.7uf help cut the bass?
The presence pot is wired as shown on #124.
How does changing the NFB resistor from 6K2 to 4K7 affect the tone?
Tom
Don't let that smoke out!
Don't let that smoke out!
Re: Too Much Bass With PAB
Would changing the bass pot wiring to this way help any?
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Tom
Don't let that smoke out!
Don't let that smoke out!
Re: Too Much Bass With PAB
If your slope resistor is really 150R instead of 150K, that would give you a huge bass hump.
Changing the feedback resistor from 6.2k to 4.7k will allow more negative feedback into the PI. This tends to flatten and extend the frequency response. Too much and the amp will seem lifeless, too little and it will sound scooped with emphasis on highs and lows. Actually, amps without negative feedback sound pretty cool to me.
Changing the feedback resistor from 6.2k to 4.7k will allow more negative feedback into the PI. This tends to flatten and extend the frequency response. Too much and the amp will seem lifeless, too little and it will sound scooped with emphasis on highs and lows. Actually, amps without negative feedback sound pretty cool to me.
Re: Too Much Bass With PAB
Is it non hrm? --if so one cure is to load the .005 output cap from OD2,
before the 150k cap to the level pot, to signal ground. Usually a resistor 180k to 680k will do the trick, you might try a pot in here to find the value that works. It won't alter much except the bass. HAD even did this on some non hrm amps-I've seen pix w/180k, and 270k load resistors. Of course the other thing is to put a series cap in line before the OD 1 entrance network. Might take some experimentation to find a value that works but doesn't change the tone.Keep in mind that the OD stages create more low harmonics than went in, and I hate that swampy bass sound, it's not that bad w/a bridge humbucker, but sucks if you're a neck PU player.
before the 150k cap to the level pot, to signal ground. Usually a resistor 180k to 680k will do the trick, you might try a pot in here to find the value that works. It won't alter much except the bass. HAD even did this on some non hrm amps-I've seen pix w/180k, and 270k load resistors. Of course the other thing is to put a series cap in line before the OD 1 entrance network. Might take some experimentation to find a value that works but doesn't change the tone.Keep in mind that the OD stages create more low harmonics than went in, and I hate that swampy bass sound, it's not that bad w/a bridge humbucker, but sucks if you're a neck PU player.
Last edited by butwhatif on Fri Jan 25, 2008 3:14 am, edited 2 times in total.
Re: Too Much Bass With PAB
Standard Dumble PAB rolls the bass at 500hz!! If you get more bass when PABBING, then me thinks you have a miswire or incorrect component. Sure of it.
Re: Too Much Bass With PAB
I was wondering the same thing.... The PAB circuit as seen in the D'Lite will cut out a great deal of fat from the tone. It should do the theoretical opposite of your experience.
67:1
Re: Too Much Bass With PAB
I was thinking the same thing: I've been putting together a relay to bring back some of the bass when PAB is engaged.dogears wrote:Standard Dumble PAB rolls the bass at 500hz!! If you get more bass when PABBING, then me thinks you have a miswire or incorrect component. Sure of it.
-g
Re: Too Much Bass With PAB
Thanks guys.
Yes Norm, typo on the slope, it is 150K.
I'll try the 4K7 on the NFB.
Well, I'm pretty sure I have the PAB wired according to the D'Lite layout.
But I'll double check.
I also plan on putting in the footswitch relays this weekend.
butwhatif, When I have the chassis out tomorrow I'll tack a resistor in there and see what it does for me.
Also, would changing the bypass cap on V1b from 10 to 4.7uf help tame the bass?
V1a is already at 4.7.
Yes Norm, typo on the slope, it is 150K.
I'll try the 4K7 on the NFB.
Well, I'm pretty sure I have the PAB wired according to the D'Lite layout.
But I'll double check.
I also plan on putting in the footswitch relays this weekend.
butwhatif, When I have the chassis out tomorrow I'll tack a resistor in there and see what it does for me.
Also, would changing the bypass cap on V1b from 10 to 4.7uf help tame the bass?
V1a is already at 4.7.
Tom
Don't let that smoke out!
Don't let that smoke out!
Re: Too Much Bass With PAB
Try a pot in there and adjust to taste. Otherwise start hi-maybe 470k. If you can put the amp on the bench w/an 800hz sine wave, you can see how much bass it's affecting- 4.7 at V1b might change it some, probably not much, the tradeoff might be the bass in clean.
Re: Too Much Bass With PAB
Well no scope and no signal generator.
I'll have to do it the old fashioned way.
The thing about this amp is it has always been bass heavy.
Aways is a relative term since the amp has only been together for a couple months.
But given the speakers ( V30 & Classic Lead) in an open backed 2x12 cab and although it sits on the carpeted floor, I don't think the speakers are the culprit as they both tend to be on the bright side. They are relatively new also, with less than 40 hours on them.
Heavily doped too so, too much bass is the amp pretty sure.
So the cap you are talking about is the .005uf on the OD2 plate?
It has a 180K in series as per D'Lite right now.
So you are saying take out that and put a pot there as a variable resistor and go up in value to taste?
Something I noticed when I rewired the presence control to the #124 schem that there isn't a lot of noticeable difference in adjustment until the last 1/4 of rotation clockwise.
The pot is 2KB and I have a tant 1uf off leg 1 to buss.
Legs 1 & 2 jumpered and the resistor to buss on leg 3.
The wire to the board on leg 3.
I hope that is right.
I'll have to do it the old fashioned way.
The thing about this amp is it has always been bass heavy.
Aways is a relative term since the amp has only been together for a couple months.
But given the speakers ( V30 & Classic Lead) in an open backed 2x12 cab and although it sits on the carpeted floor, I don't think the speakers are the culprit as they both tend to be on the bright side. They are relatively new also, with less than 40 hours on them.
Heavily doped too so, too much bass is the amp pretty sure.
So the cap you are talking about is the .005uf on the OD2 plate?
It has a 180K in series as per D'Lite right now.
So you are saying take out that and put a pot there as a variable resistor and go up in value to taste?
Something I noticed when I rewired the presence control to the #124 schem that there isn't a lot of noticeable difference in adjustment until the last 1/4 of rotation clockwise.
The pot is 2KB and I have a tant 1uf off leg 1 to buss.
Legs 1 & 2 jumpered and the resistor to buss on leg 3.
The wire to the board on leg 3.
I hope that is right.
Tom
Don't let that smoke out!
Don't let that smoke out!
Re: Too Much Bass With PAB
Don't disconnect anything, I sent u a pm with the print-