Low cut overdrive channel question...

ChrisCox1994

On amps with shared EQ between clean and overdrive channels I often find the overdrive channel in need of a bass cut. 

Whats the simplest way to have some kid of low cut maybe a pull pot on the gain or volume of the OD channel? 

Is there a simple bright cap style mod thats a bass cut instead? 

Winny_Pooh

In the amp internally you can have an extra coupling cap between the EQ section and phase inverter. This works best with a mini switch on the amp faceplace or chassis. 

Or in a more complex way if the gain channel uses an extra 12ax7 half you can tweak the electrolytic cathode bypass cap value on that 1/2 12ax7 for a treble boost.


The other alternative is to use a boost with Eq/eq in front of the amp.

Headphones

A treble booster...

ChrisCox1994

Headphones said:

A treble booster...

good one

ChrisCox1994

Winny_Pooh said:

In the amp internally you can have an extra coupling cap between the EQ section and phase inverter. This works best with a mini switch on the amp faceplace or chassis. 

Or in a more complex way if the gain channel uses an extra 12ax7 half you can tweak the electrolytic cathode bypass cap value on that 1/2 12ax7 for a treble boost.


The other alternative is to use a boost with Eq/eq in front of the amp.

thanks, I'll have a chat to my tech and see if he can implement one of these mods, a small switch at the back externally would be great. 

MattBanshee

Use a pedal with an EQ section, or get a two-channel amp.

Headphones

ChrisCox1994 said:

Headphones said:

A treble booster...

good one

Actually a serious answer!

The age old trick, as used by May, Blackmore, Gallagher, Iommi and many, many more.

ChrisCox1994

MattBanshee said:

Use a pedal with an EQ section, or get a two-channel amp.

Is it 2 channel but it's a shared eq section 

ChrisCox1994

Headphones said:

ChrisCox1994 said:

Headphones said:

A treble booster...

good one

Actually a serious answer!

The age old trick, as used by May, Blackmore, Gallagher, Iommi and many, many more.

But then I'd have to turn it off as treble boosters sound harsh and unpleasant on high headroom channels, I find. 

The point was cutting bass from the overdrive without having to do more tap dancing.

Unfortunately the kind of gigs I do require more range of sounds than May, Blackmore etc - and not at their volume! Haha

hywelg

Switching the coupling cap is probably the easiest way to cut bass. Best to do two options on a On-Off-On SPDT switch. Values will depend on whats already there and the circuit layout. 

ICBM

An actually serious answer - dial it in for the overdrive channel not the clean. Clean channels are often less fussy and you don’t notice the EQ as much. I do that even though I play clean most of the time.

Although it has to be said that I usually find *lack* of bass and treble, and excessive midrange, to be more of a problem than too much... I rarely run the bass below half on any amp. We may have very different tastes!

MattBanshee

ChrisCox1994 said:

MattBanshee said:

Use a pedal with an EQ section, or get a two-channel amp.

Is it 2 channel but it's a shared eq section 

If it's just an overdrive switch with no separate EQ, then really it's just a single channel amp with an overdrive switch.

ICBM

MattBanshee said:

If it's just an overdrive switch with no separate EQ, then really it's just a single channel amp with an overdrive switch.

This is actually a complicated issue, and not as straightforward as you may think.

You can have an amp with dedicated clean and overdrive audio paths using separate gain stages for each, which then run through a common EQ section - it's still a two-channel amp. You can even have that if there are only one set of gain and volume controls as well, if the overdrive mode adds extra gain stages.

Or you can have an amp with completely separate control networks, which appears to be a two-channel amp, but which in fact only has one set of gain stages and switches the controls - most people would think of it as a two-channel amp, but in fact it's actually a single channel with two presets.

Or any combination in between...

That might sound like splitting hairs, and from a user point of view it doesn't matter much - but it can do if you're trying to change something in the voicing of one channel and not the other.

hywelg

Would help to know what the amp is.

ICBM

hywelg said:

Would help to know what the amp is.

This should be a sticky at the top of this section.

Modulus_Amps

what is the amp? how high up is the gain knob setting?

a bright cap will boost high end only if the gain knob is not turned up full and its effect depends on the gain knob setting, so a pish idea really.

A smaller coupling cap early in the pre-amp will  roll off low end at -20dB/Decade slop, this will make your drive tones brighter and tighter.

A smaller bypass cap on an early stage will give a different bass cutting effect, rolls off at -20dB/Decade, but it is a shelved response between bypassed and unbypassed gain of the stage, this might be the best solution depending on the amp you have and what the cathode values are in the amp.

A good tech would be able to work up something for you on a mini toggle switch.

Saying that, watch you are not playing with too much bass on the clean setting, easy to do as it sounds good on its own, but sounds crap once a bass player joins you

ChrisCox1994

Sorry, should've said, its the Redplate Blues Machine 66 - it was initially for sale then I started using it again. 

The available controls are Gain, Volume and Tone on the clean channel then cascading into a Drive, Gain and Level control (with high cuts) for the overdrive section. 

kt66 (currently biased for and running 6L6s) power section and a vintage 30 speaker. 

exocet

ChrisCox1994 said:

Sorry, should've said, its the Redplate Blues Machine 66 - it was initially for sale then I started using it again. 

The available controls are Gain, Volume and Tone on the clean channel then cascading into a Drive, Gain and Level control (with high cuts) for the overdrive section. 

kt66 (currently biased for and running 6L6s) power section and a vintage 30 speaker. 

Those amps are often based on Dumble Amp designs. If that's the case, the cathode bypass caps are typically fairly large and could be reduced to 1uF or less. If it's like an Overdrive Special, the Overdrive stage is cascaded in when activated. You could just reduce the bypass cap(s) on that and it would only impact on the drive tone.

Likewise if it is based on a Dumble type design, you can lower the values of the coupling caps on the overdrive stage (Valve 2a and 2b) and this will only impact when the drive is engaged.

ChrisCox1994

exocet said:

ChrisCox1994 said:

Sorry, should've said, its the Redplate Blues Machine 66 - it was initially for sale then I started using it again. 

The available controls are Gain, Volume and Tone on the clean channel then cascading into a Drive, Gain and Level control (with high cuts) for the overdrive section. 

kt66 (currently biased for and running 6L6s) power section and a vintage 30 speaker. 

Those amps are often based on Dumble Amp designs. If that's the case, the cathode bypass caps are typically fairly large and could be reduced to 1uF or less. If it's like an Overdrive Special, the Overdrive stage is cascaded in when activated. You could just reduce the bypass cap(s) on that and it would only impact on the drive tone.

Likewise if it is based on a Dumble type design, you can lower the values of the coupling caps on the overdrive stage (Valve 2a and 2b) and this will only impact when the drive is engaged.

this sounds perfect! 

easily reversible too I suppose? 

hywelg

Email Henry and ask what he thinks would be the best thing to do. I think you'll find he's very hands on.

I'd bet he'll suggest a v2a cathode bypass cap swap, with the possibility of switching a different value in on a push-pull pot, (probably the Gain as Drive and Level are already push-pull doing something else).

ChrisCox1994

hywelg said:

Email Henry and ask what he thinks would be the best thing to do. I think you'll find he's very hands on.

I'd bet he'll suggest a v2a cathode bypass cap swap, with the possibility of switching a different value in on a push-pull pot, (probably the Gain as Drive and Level are already push-pull doing something else).

I've emailed Keith in the past, he's been pretty good at helping diagnose and solve issues in the past - I'll shoot them a message, thanks.