How to "spread" the mids

[aro]

The Marshall JCMs (and others) are famous for their mids, but when I play my 2204 and then my Trinity TMB through the same cab, the 18 watt sounds even more mids-heavy, almost box-ey. It sounds like the TMB accentuates a certain range of mids, while on the 2204 the range of mids is wider.

I'm comparing them at the same volume, at the edge of breakup, trying to make it as much as possible an apples to apples comparison.

Is there any way to "open up" more mids on the TMB, or are the EL84s the limiting factor?

[Crabman]

The tone stack is almost the same on both. The TMB has a 56K slope resistor which produces a more pronounced mid cut at 550 Hz. The 2204 has a 33K slope resistor that produces less mid cut at about 660 Hz.

You are probably hearing differences that are influenced by other parts of the circuit. The 2204 has 3 gain stages with different topology vs 2 in the TMB, a different power section and negative feedback which I imagine would have an impact on the broader frequency response.

It is possible that one of your components is incorrect in your tone stack so it would be worth looking it over.

[aro]

Actually, I modified my 2204 with a switch that can take out V1a. It basically makes it a 2 gain stage Plexi preamp, very similar to the TMB. I also decreased the NFB resistor, so my 2204 with the switch on is closer to a Plexi than a 2204.

Maybe I'll experiment on the TMB with cathode resistors and caps closer to the big guy values. I don't really want more gain... I'm just curious how it will impact the frequency response. It will be brighter, but will it be less box-ey...? I'll find out.

The tone stack follows exactly the Trinity TMB schematic, except the slope resistor. I'll try a 33k. Other than that, as you said, different power section and negative feedback.

I don't really want the TMB to sound like a Plexi/JCM. I just want to open up those mids a little more. It might not work... but I'll report back if there is any meaningful change in mids.

[Crabman]

Looks as though you already considered the differences ..

How does the normal channel compare?

I also have a Trinity 18 watt. I'm starting to think I prefer the normal channel to the TMB. Perhaps a bit more clarity but I wouldn't say it's less mids than the TMB .. just less congested. Plan on doing some changes to the TMB side to see if I can improve things a bit.

[JMPGuitars]

You guys should play around with the Tone Stack Calculator and see what the curves look like for comparison between the circuits.

https://www.duncanamps.com/tsc/index.html

[aro]

This is the only 18 Watt I played through, so I'm by no means an expert, but I also prefer the normal channel a little more. Years ago I went through a high gain phase, where I actually added a gain stage to my 2204 clone (and modified a few more things for even more gain). That was then... now I like my amps well behaved.

I haven't opened up the TMB yet but from what I start to remember, I think I have .68 caps on both V1a and b. Yeah, I'll take those off and start experimenting from there.

Thanks for the tone stack calculator suggestion. I used to play with it in the past. Looks like I'll have to fire up my Windows machine for that, they don't have a Linux download for my daily computer.

[JMPGuitars]

This is the only 18 Watt I played through, so I'm by no means an expert, but I also prefer the normal channel a little more. Years ago I went through a high gain phase, where I actually added a gain stage to my 2204 clone (and modified a few more things for even more gain). That was then... now I like my amps well behaved.

I haven't opened up the TMB yet but from what I start to remember, I think I have .68 caps on both V1a and b. Yeah, I'll take those off and start experimenting from there.

Thanks for the tone stack calculator suggestion. I used to play with it in the past. Looks like I'll have to fire up my Windows machine for that, they don't have a Linux download for my daily computer.

There's not really such a thing as being an expert when talking about personal taste. You're hopefully an expert on what your taste is.

You can use the web version of the tone stack calculator instead.

[aro]

Thank you! The web version is great.