Adding Midrange pot to a Bassman

[WRGKMC]

I bought a 10K pot and knob for my Blackface. Adding a midrange knob is super simple. There's a 6.8K resistor on the back of the bass pot and you simply wire in a 10K pot to take its place.

You can use a 25K instead and get a boosted mid tone but I'll go with the 10K first just to see how it sounds.

 

You can do it as a reversible mod by removing the double input jacks and using only one input, then using the other hole for the mid pot.

I used to have a presence control installed 25 years ago which I later removed then covered the hole in. I'm going to use that spot which is next to the bass knob.

The order will be treble bass and mid instead of treble mid bass but that's not that big a deal. It wont be labeled anyway but its placement looks like it belongs there.

 

That's the only thing about the Bassman I've never liked. They had great bass and treble control but no midrange. Midrange is fixed. The pot allows that range to be adjusted like the Tweeds were.

[WRGKMC]

Well I finally got the parts in and found the time to install the midrange control. It was a very simple operation. I had the hole drilled already so I only had to remove the plug I had covering it. Soldering it took no time at all. I left the old midrange resistor soldered in place in case I ever wanted to use it again.

 

The pot works flawlessly. It works in conjunction with the other EQ controls smoothly and has a broad Q which scoops/boosts what I'd call lower midrange frequencies with a center I'd guess around 700Hz just using my ears. I'll have to use it awhile to determine if this works for me. I was hoping to have something up around 2~3K as a midrange boost/cut which is typical for guitar amps and is great for getting speakers to drive. It still may be fine however. The Bassman has a really wide frequency response and it neither lacks for top or bottom end. The amp takes pedals extremely well and leaving the mids up and cutting the highs and lows should make it sound like a smaller amp.

 

The cab is the original Bassman cut in half. I did some horse trading back in the 70's and traded the amp for an Ampeg V2 with a 4X12 cab for awhile. The guy who had the cab cut it in half and made two 2X12" cabs out of it. I got it back as a runt. I need ti change the grill cloth to match the head. I removed the two Weber speakers I had in the cab and installed am old Eminence and a 60W Peavey speaker in it. The Peavey was out of one of those newer peavey modeling amps so it has a wide and flat frequency response. It wound up being a good match with the older black magnet Eminance. The Peavey has a slightly higher SPL but its not enough to be a problem.

 

I did a complete tube and cap change recently so this amp is really sounding good now.

This amp and I are old friends and seen countless gigs. I bought it when I was 10 years old back in 67.

It was due for some extra TLC. The mid knob is a minor mod that is highly beneficial as a guitar amp.