Tuning bass on the OD channel

[greiswig]

So now that I got the partially-broken lead to the bass pot fixed on my build, and have the bass I was looking for on the clean channel, I find that my neck pickups in particular start to sound flabby on the OD channel.

There are two primary ways I'm aware of to fine tune the bass in OD, and I'm interested in some discussion on the pros and cons of each.

First, you can control how much bass gets into V2 in the first place. It's common for D'Lite owners to put an additional .02uF coupling cap in before V2 to help tame the bass, as I did.

Second, you can play with the cathode bypass caps. My guess is that this is where I need to focus, since I think I put in larger ones (10uF?) when I was trying to get more bass overall, before I found the real issue. #124 uses 5uF, and mine is a low plate.

I'm guessing that both have their place, but I'm curious about some things. For example, how is the slope of the cutoff affected with each method? And usually when you put in a low-cut filter, there is a bump right above the knee; can this be used and fine tuned to give a little more oomph to low mids in just the right area? What kinds of ways have you builders used to fine tune this, or is it just trial and error?

[Structo]

Maybe try a 1uF on V2a or V2b.
I think I may have my D'lite modded that way. But it's been awhile since I was inside.

Unfortunately, this is the bane of the non HRM.
You get the V1 sounding great then the OD isn't so great.
Since the cascade and there is no tone control for V2.
I wonder if a person could wire in a tone control for V2?

One thing I noticed about the 100w amp is the tone controls actually do something.
On my D'lite it seems they are much more subtle in their operation.

I was very surprised with how much more I like the 100.
Totally different beast.

[talbany]

I personally don't care for the 1uf in the OD side!!...I have better luck controlling the low end content with different cap types and values.. You may find the NTE (Thin brown caps) in certian spots provide a tighter bass response like in the PI or bass cap..Also a higher gain tube will help.. Raising the preamp voltages a bit will also help..
Just a few other/different suggestions

Tony

[greiswig]

I am aware that I can lower the bypass caps and get somewhere, I'm more interested in how treating the bass in different parts of the circuit changes things. For example, you could have a lower bypass cap on V1a than on V1b... or vice versa. Or you could size both "right" according to the rule of thumb for that cathode resistor, and change the coupling cap.

Tony, I like the bass I have on the clean side, so I'm reluctant to change the PI or other things that will affect the whole.

[TheHandsomeOrk]

You could try lowering the out cap on V2a from .01uF to .005 and see how it sounds.

[greiswig]

You could try lowering the out cap on V2a from .01uF to .005 and see how it sounds.

I might try that. I'm less after practical solutions to my specific problem than I am a discussion about the merits and effects of the various ways of coping with it. In this case, you're talking about playing with the input coupler to V2b, but how does this differ from lowering the coupling cap into V2a even more?

Another example: it is common for D'Lite owners, at least, to add a .02uF cap in series with the .05uF coupler already there, to try to tame the bass a bit. My build, no matter whether it was high plate or low, never sounded good without that. So that's a total coupling cap value of around .015uF. Yet #124 used only .05uF! What's the difference?

Thanks for the thoughts!

[Structo]

I had the same issues with my D'lite going in circles.
I eventually came around to about the same values I had early on.
The 101 non HRM schematic is pretty much where I ended up.

What output transformer did you end up with on yours?

A trick I have seen guys use and is what was suggested is to let the big signal come in, then funnel it down a bit on the way out with the smaller coupling cap. Sometimes that can lead to too much compression but in some cases is just what the doctor ordered.

You are probably talking about the tone at gig level right?

Because I probably tweak my amps for a little lower volume since I am not currently playing out.
But everything the guys said about the 100w being bigger in every way is true. More girth and tone.
Plus loud as hell!

Heck I may even end up selling my D'lite down the road.

[greiswig]

Tom,

Keep in mind I have 100k/1.5k pairs all around. 101 uses higher values, doesn't it? So the recommended cathode bypass caps are going to be correspondingly smaller?

Still, maybe getting Fender-ish cleans by having 100k plates and big bypass caps on V1 while preserving the OD is simply too tall an order.

I'm using one of Brandon's Twin OT's.

[erwin_ve]

Something that helped me is: not looking at the bass content but rather look at the lack of high freq.
Raising the GNFB resistor to 10K was my solution and measuring the entire range of caps in the amp. I replaced 4 caps that were off spec.

[TheHandsomeOrk]

greiswig,
my suggestion was a bandaid that worked for a particular build, a highplate 50w and it did the trick as I was pushed for time so it might not be the best for low plate 100w.
All things come into play, is it a combo? have you tried another speaker cab?
For instance I have a 50w highplate that won't give it up (bloom) with an EV or Altec but will at whisper volumes with a red,white, blue speaker which I don't like the sound of.
Upping the GNFB will give you more highs but will also give you more highs in the clean channel, you may or may not won't more in that channel.
Are you running 100k/1.5k on the OD plates? Have you tried 180k and 120k ( I liked it on another build )
What mid cap .05 or .01?
I'm learning what others have mentioned many times before about it being a system and changes (upstream or downstream) affect the outcome good/bad.
I hope others will pipe in with more experience.

[Structo]

Yeah, 101 is high plate.

Erwin does have a point. Sometimes it is a matter of balance.

[dave g]

You could try lowering the out cap on V2a from .01uF to .005 and see how it sounds.

I personally prefer this over adding the extra series cap to the OD input network.

Keep the 5uF cathode bypass cap on both OD stages...

[TheHandsomeOrk]

Another example: it is common for D'Lite owners, at least, to add a .02uF cap in series with the .05uF coupler already there, to try to tame the bass a bit. My build, no matter whether it was high plate or low, never sounded good without that. So that's a total coupling cap value of around .015uF. Yet #124 used only .05uF! What's the difference?

Thanks for the thoughts![/quote]

Which brings up this question.
By having series caps to reduce bass does the bass get totally shaved off and dumped or highs go through first, arrive first at the listeners ear giving the impression of less bass? So if you had a problem with bass freq's messing up the OD section causing fuzz ect. would the problem still be there but not as noticeable with series caps?

[vibratoking]

By having series caps to reduce bass does the bass get totally shaved off and dumped or highs go through first, arrive first at the listeners ear giving the impression of less bass?

Then bass frequencies are filtered and not passed to the next stage. The idea of some frequencies arriving before or after others is called group delay. Group delay is normally applied to circuits as far as I know. It can be calculated for a given circuit topology. A delay of frequencies can also occur after the amplifier output due to speaker cable, speakers, etc...

[talbany]

Oops!! I thought you were talking the entire amp..

If we look at the entire OD circuit and take the various places that effect low frequency content just for the OD channel we have..

Drive and Level pot values.. Upping these to say 250k like 124 and or 183 adds low end so these are out..
the 100k 150k level and drive feeder resistors.. Going up in value will cut some lows however will also effect gain and mid content and tone so these are out..
So that pretty much leaves bypass caps and coupling caps..
One other thing to think about may be to lower the OD trim pot from 100k to 70k or 50k and set it about half way will also help with the low end..
Sometimes different types of bypass caps can help..For instance a 50v TVA Black Sprague will give you tighter lows than say a 50v Nichicon will..
In some cases it depends on the brand and voltage rating on the bypass cap..The higher voltage rated ones usually yield tighter lows.. I have good luck with the Spragues TVA 50v Black ones though expensive..If your looking at tightening the lows this is a good place.. If there is just way too much low end you almost have to go to a smaller value or smaller coupling cap..You also have the balancing act of cutting lows for the neck PUP also thins the bridge..
Hope this helps this time..

Tony