Overload bass on my 2204 ...Little help!

[massimo]

Hi there
I built my first Marshall replica 2204 last year. It is very great amp but I've always felt too much bass tone especially on power chords or palm mute .
To be more precise when I play 5th and 6th strings gain seems to be drop and the tone tend to be deep.
I try to recheck all resistors and caps value but they seem to be ok with scheme/layout that I followed :

http://www.dreamtone.org/pdf/NEW2204Lay ... amTone.pdf

Usually most 2204 have the opposite with too much High treble tone.

Have you any Ideas?
Could be a NFB issue? I have 4ohm / 100 K
Thanks for you help
Cheers
Massimo

PS These are the Transformers / choke specs :

Power T. 178 Va - 0 220/230V - 345/0/345V 200mA - 3,15/0/3,15 6A
Output T. 3,6 KOhm - 50Wrms - 120mA - 44/19000 Hz - 13 Henry
Choke : 10Henry +/- 10% IND 10H15

[catalin gramada]

Hi
At first glance,from what you presented here,this is what I consider responsable for you particulary tone.in order:
1. - you OT seems to not be one for guitar amp aplication
2. - you did not tell us nothin regards filtering in power stage -but hope you work with original values
3.- the "choke" is also a important element in tone shaping so you have to check yours even change it with an equivalent DC resistance power resistor.
ciao

[danman]

I recently built a 2204 and I wasn't happy with the flabby bass when using the high input. I started with NFB at 4ohm/100k and tried dropping down to 4ohm/27k which did tighten the bass up slightly. The thing that worked best for me was to insert a .0047 capacitor between the impedance selector and purple NFB wire. This really tightened things up and took away the overbearing bass I was experiencing. I also placed a .47cap across v2a cathode which really brought the mids forward and seemed to increase sustain. These couple of tweaks really brought the amp to life and it's so much nicer to play now.

[massimo]

hello
thanks for your reply!
Regarding filters I use 50+50 u in Main screens and preamp. I've d always considered that my OT wasn't correct for 2204 and You seem to confirm me.
At this moment I'll try to make some mods as danman suggestions. Unfortunatly I have not other OT and choke to make some tests.
I try to change 100k/4 ohm with one 47k (I have not a 27K in my stock) and also insert a .0047 capacitor between the impedance selector and purple NFB wire, and I'll let you know
Many Thanks
Ciao

[catalin gramada]

No worries
...then,you should try to change the PI output coupling caps first. experiment yourself with some into 2.2-4.7nF range.
...and maybe modify the slope resistor in tone controls from 33k to 47k or so.
You will not be able to recover the 2204 original tone but both will be effective in your bass reponse.
You can try to switch the nfb resistor for a lower value after changes,if you feel

[Thiez]

Probably you use the amp on high gain settings? The brightcap isn't working at that moment, i've got the same problem with a superlead. With the gain on max, it's quiet boomy and muddy.

[danman]

Installing that fixed resonance cap in the NFB circuit helped get rid of the boomy bass quite well. The amp has a nice tight thump now that I really enjoy! The .0047uf cap seemed to work perfectly but you can experiment with different values to increase or lower the response.

[catalin gramada]

yes, think those OT passed way to much bass so have to tame a little, better as far to the end of signal chain. both solutions are viable: modifing the high pass filter (change output filter caps to smaler values) with price to rise amplification in PI stage. or more selective feedback in frequency of interest (through a cap from output) with price to decrease the signal. worth to try both to choose which one works better.

[massimo]

Hi There
Thanks for your Help!!
Finally I'm going to play in Studio this evening. I've tried to change NFB resistor 4ohm/47K with cap .0047uF as danman suggested an I'll Let you Know...
I also received some couples of caps 0,0022uF , 0,0033uF and 0,0047uF to try to change the PI output coupling caps.
After this evening I'll try to change them if still necessary
Many Thanks

Massimo

[danman]

I hope you like the results! My amp sounded much tighter on high gain stuff and the bass control seemed much more responsive afterwards. You can raise the value to reduce the bass even more or lower the value for more thump. I'm really digging the added .47uf bypass cap on the v2a cathode. It gave the amp a nice midrange boost and really increased the sustain of the amp.

[massimo]

Hey the tone seems to be better now, with NFB resistor mod !! Many Thanks!!

I'll probably try to reduce resistor NFB to 27kohm to listen other differences.

I hope you like the results! My amp sounded much tighter on high gain stuff and the bass control seemed much more responsive afterwards. You can raise the value to reduce the bass even more or lower the value for more thump. I'm really digging the added .47uf bypass cap on the v2a cathode. It gave the amp a nice midrange boost and really increased the sustain of the amp.

The v2a cathode mod is a 47uf cap accross V2 Pin 3 - 8 ?
Many Thanks
Cheers

Massimo

[danman]

With that mod all you need to do is solder a cap across the 820ohm cathode resistor on v2a. I used alligator clips on mine to try various values (.33/.47/.68uf) before deciding on the .47 in the end. This gives the amp a strong mid boost which you can tailor up or down depending on the value you choose.

[stef]

The 47uf should not be confused with .47uf! I like the stock SUper Lead value of .68uf, but 1uf electrolytic 50v is fine to. Bigger values like 25uf, 47uf, 250, 330uf, 470uf etc are way too much in V2a IME - the bass gets overbearing

[Thiez]

sorry to up this older topic, but i have the 2204 and it is quiet boomy. What i don't get is how the fixed resonance would fix this...? Fixed resonance capacitors takes away the NFB for low freqs, zo less low will be canceled out sow you will get even more lows? Or am i wrong on this one?