Need less bass from my Marshall 1986 clone

SlyStrat

Silver Supporting Member
Messages
4,497
I love my Rockitt Retro 1986. But I want to cut some of the lowest bass. On middle and neck pickups of Les Paul or Strat the low E string sounds like a bass guitar.
Go to split cathode or some other change?
 

ROKY

Member
Messages
7,217
Coupling cap values could be changed .. not sure what's in your particular amp, though

My bass circuit amps are Traynor YBA-1As and they already have .022 uf caps but were still a little woofy through most of my cabs .

It's manageable but sometimes I still wanted want less bass ,, the ultimate trick for me was a shallower depth cab of 10.5 - 11" max .
Now when I turn the bass down on those amps it's very balanced and if I want I can add bass back in .. so yeah more control, now .
 

SlyStrat

Silver Supporting Member
Messages
4,497
I have the bass on 0.
It would be nice to actually be able to use the bass control.
 

big mike

Cathode biased
Platinum Supporting Member
Messages
12,995
Change the PHASE inverter plate caps to .022

Changing first stage .022 to .0022 is just going to boost highs.
 

fusionbear

exquirentibus veritatem
Platinum Supporting Member
Messages
10,923
Change the PHASE inverter plate caps to .022

Changing first stage .022 to .0022 is just going to boost highs.

Mike is correct IMO. Personally I hate the .0022, even on a Super Lead.
 

Carol-AnnAmps

Member
Messages
4,855
Change the PHASE inverter plate caps to .022

Changing first stage .022 to .0022 is just going to boost highs.
There's a better way Mike. Changing the PI caps means all that bass BS is just being attenuated at the end of the preamp chain, by which point its already made a bassy mess through the gain stages which REALLY compromises the tightness of the overdriven tone when the amp is pushed in to overdrive. Leave the PI caps alone. I use 0.1uF in all the CA's and they are not bassy at all because the preceding gain stages are correctly frequency balanced.

You have to make changes to multiple stage to keep things balanced so the overdrive tone is nice.

Assuming its pretty much a clone of a 1986 model Marshall......

1. Drop any stupidly massive cathode bypass capacitor in the first stage down to 1uF in the first stage. The original marshall value is 320uF and is the main source of issue with that circuit

2. Drop the 1st to 2nd stage coupling capacitor to 0.01uF or 0.005uF. 0.002uF is too low and will make the amp 'appear' too bright, especially if he intends to pedal it clean. 0.002uF doesn't boost the highs, that's physically impossible. 0.02uf is letting though some more lower frequencies because its Q point is lower. Taking away bass always gives the PERCEPTION of more mids and highs, but in reality there are no more. To create a 'boost' requires an RC circuit where a capacitor bypasses a series signal chain resistor. The 470k/500pF network is an example of this.

3. Change the coupling cap to the entrance of the PI to 0.01uF.

4. Leave the three 0.1uF capacitors on the PI well alone, that's part of a great drive circuit for the power tubes !!!! 2000+ CA's aren't wrong !!!! :)

This way you have removed bass by reasonable amounts at 3 stages, not just boat loads at one after its already crapped up the previous stages. Plus by keeping the 0.1uF caps in the PI you are letting more bass harmonics generated in the PI in to the power tubes (a good thing) and also remember that one of those caps is part of the -ve feedback loop. Dropping its value has the opposite effect, giving lower frequencies more 'open loop' gain if the amp has a reasonable amount of -ve feedback.

Creating correct frequency response and harmonic generation and balance is a fine art that requires small changes in multiple areas that all work together. Obviously the values I've given can be changed to taste and also don't take in to account some important specifics about the amplifier.

Hope that helps.

Regards, Alan.
 
Last edited:

fusionbear

exquirentibus veritatem
Platinum Supporting Member
Messages
10,923
Alan is truly a master. I am going to have to try his reco's. I owned an OD2. Not bass heavy in the slightest. It was perfectly balanced... miss that amp!

Alan's recommendations might cost you a few bucks in parts and an hour max of labor!
 

Carol-AnnAmps

Member
Messages
4,855
Knowing how he intends to use the amp, pushed hard into overdrive, with an attenuator or as a pedal platform really defines the exact component requirements. Also the feedback circuit itself is important. Because its a clone, someone may have taken liberties to change a few things, like some 1986 models had their feedback tied to the speaker jack and this changed the character of the amp depending on the impedance of the speaker cab being used. If you were building your own, you should commit to one tap and design your feedback around that to keep things consistent. For a 50W Marshall output stage with the 0.1's in the PI, I like a non standard arrangement of 33k feedback resistor from the 4 ohm tap with a 5K presence pot. This keeps the output stage pretty flat. If its a high gain amp with more cascading gain stages that require a lot more bass attenuation through the stages, like the Triptik, I'll use an RC network before the feedback resistor to allow more bass to go open loop. This helps acheive that thump you hear with a modern high gain amp.
 

big mike

Cathode biased
Platinum Supporting Member
Messages
12,995
kevin's amps seem to be note for note clones (very cleanly wired) of the Metroamp layouts. So it's pretty accurarte 1986 spec, but with bridge recto on the wall of the chassis to address a quick and easy solid state recto.
Down to the fused neutral instead of fused hot wire.

So any era correct changes would likely apply.
 

DrainBamage

Member
Messages
2,395
I cant even use the normal channel on my 1987 clone. If you are only trying to cut bass with out adding gain or really changing the character of the amp start with splitting the V1 cathode with the .68 cap. Then do the .0022 cap if it still has to much bass. Replace the .1 caps last and probably the least effective by this point.
 

SlyStrat

Silver Supporting Member
Messages
4,497
Celestion Heritage G12-65's.
I have the volume on 10 with Alex attenuator on -6dB.
 

coldengray

Member
Messages
1,799
+1 on reducing that 330 cap. Easy and cheap to start there, you can move on to other components if that doesn't get you to where you want to be.
 

SlyStrat

Silver Supporting Member
Messages
4,497
This?
"1. Drop any stupidly massive cathode bypass capacitor in the first stage down to 1uF in the first stage. The original marshall value is 320uF and is the main source of issue with that circuit"
 

coldengray

Member
Messages
1,799
Yes....V1 cathode cap, left side of the board, the first cap on there. Should be 320 or 330 in stock form, lower that sucker.
 




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