Lowering the bass level: best place to start?

[bsaul]

I have an old amp that still passes too much bass, even when the bass knob is on zero.
The first half of the input 12ax7 uses the common 1.5k/25uf decoupling stage. (I could reduce the cap to 10uf or 4.7uf).
Then there is a .02 coupling cap before the tone stack. (I could reduce this to .01)
The second half of the first gain stage tube also has a 1.5k/25uf network.
Following this is a .0022 cap leading to the phase inverter. (I could drop this to .0015 or .001).
Could someone with experience please recommend the best place to start.

[Structo]

Try the lower bypass caps first.
The coupling caps won't be as effective at lowering the bass as the bypass but you can make both work together.

I would try 10 uF bypasss caps on the first two stages to see what that brings.
If not enough bass is removed, try a 5uF in the first stage.

[Bob-I]

Best place to start? Depends, what amp is it? bypass caps can help, mods to the tone stack, coupling caps etc but if we don't know the amp it's hard to discuss.

[PCollen]

Best place to start? Depends, what amp is it? bypass caps can help, mods to the tone stack, coupling caps etc but if we don't know the amp it's hard to discuss.

+1....the devil is in the details; please be specific. Have you tried new power tubes ? Are the power tubes cathode biased or grid biased ?

[tubeswell]

For a geetar, you might not notice much bass roll-off difference until you get to around 2.2uF or 1uF Ck on V1

[Drumslinger]

maybe it's not the bass but the mids and treble not coming through enough. Just trying to look at the other side of things.

[rdjones]

For a geetar, you might not notice much bass roll-off difference until you get to around 2.2uF or 1uF Ck on V1

Some amps drop the V1 cathode cap all the way down to .68 for a "bright" channel.

rd

[bsaul]

Thank you to everyone who was kind enough to reply.

[Gaz]

If you've played the amp in a band context it should be somewhat easy to to tell whether it's a matter of 'too much bass' or 'not enough treble'. If you're not playing with a band, it's a matter of taste unless the amp is making your speaker crap out in the low end (depends how 'tight' the speaker is, of course). It seems to me that the most effective place to cut bass is earlier on in the preamp. Changing the coupling cap going into the PI might be very subtle until you get down to 1000 pf, but like everyone else said depends on the amp...

[daydreamer]

i had this issue on a solid state princeton chorus (now sold, never did like it) but it was a combination of the guitar and amp. probably more the guitar than anything. If you are running heavy gauge strings, or a strat style guitar it won't be helping whatever issue the amp has. Have you run a gibson style (short scale, humbucking) guitar through it? could be the perfect combo. I find that some guitars just don't sound right through some amps, I could throw big words around (fundamental frequency response, e.g. ribbon mics will never sound like condensors ) but i wouldn't say either the amp or guitar is wrong, any more than I would say a 't-shirt' or 'winter' is wrong, it just better to move to where the weather suits your clothes!!

[daydreamer]

Also, bass is a prick for judging correctly in just about any enclosed space. depending where in the room you have the amp and the construction of the room you could have your head right where the bass frequencies are 'stacking', if you move 7 feet to one side you might moving into a 'null'. remember bass frequencies can be 14+ feet long between peaks and are the single greatest challenge to get right, either live or recorded. stand 20+ feet away from the amp in an outdoor setting and you may have the perfect festival amp on your hands!! An amp or two that I thought sounded great at home, were down right embarrassing live. bass tends to spread out in all directions from the amp, so at home you'll think you have plenty, live you can hear the crickets chirping in the uncomfortable silence that is your solo! sound guys tend to protect their front of house and roll bass out of guitars, so if you don't have some on stage, you won't have it at all! My advice, no matter what you do to cut the bass, make sure you can put it all back! tuning you amp to your room is what you are doing, which is fine if you never go out with the amp, i suppose.. If you don't gig live, lend it to someone who does, they may fall in love with it, sell it, buy 2 more that suit you with the profit!

(I'm only piping up with this advice, because I have no idea what you guys are talking about otherwise, though give me 6 months and I'll be thinking everything is solved with a set of capacitors and resistors! For the last 20 years I've been working around these sort of things, finally getting around to seeing the other -more technical- way of fixing them!)

[Structo]

All true scenarios.

Sometimes it is hard to distinguish the difference between too much low end and not enough top end.
Throw in a hand full of room acoustics and you have a recipe for trouble.

I have fallen prey to trying to tune an amp in a small room with the speaker cab on the floor, near a corner, etc.
But this is where I play the amp 99% of the time so there is that.

I f you do play in a band and use this amp, try not to make drastic changes.
But rather smaller ones, keep good notes and give each change a fair listen before reverting or changing another thing.

A lot of times, an amp that sounds good with the band and cuts through the mix well, does not sound so good by itself.

Try to avoid setting the tone of your amp to where it occupies the same spectrum as the bass (low mids and bass) and high mids (keyboards).

This is probably why Marshall amps have done so well over the years.
Because they can cut through the mix like nobody's business.