(After 30+ years of harmonica playing, I came to believe that I really needed to give something useful back to the harp community that has been so generous to me. Hope this qualifies.)
The Excelsior: It looked really good. Classy retro design, big 15" speaker, old school circuitry, three inputs, 13 watts of tube power.
And it sucked. Big time. Clean, feedback prone, thin and trebly-sounding even with my beloved Shaker dynamic. Disappeared altogether in the band mix. Ugh.
Now, I bought my Excelsior used on Ebay because I knew I was going to change the tone control right off the bat. Goodby warranty. Add one "Dark Chocolate" tone control mod.
That helped some but not nearly enough. After an exasperating and exhaustive series of testing with different pedals, mics and configurations, I decided to go full on customize and dialed up my amp guru, Dale Murrow of Old School Amps and set up an appointment to see what we could make of this beast.
I took my Kalamazoo Model II and the Excelsior, played them both for him and asked simply, "How can we make the big one sound like the little one?"
While Dale poked around the innards, I installed a brand new 20 watt alnico speaker from Weber (I have their ten-inch version in my Kalamazoo) which helped but still didn't get us there. What follows is pure magic for me but all in a day's work for someone like Dale. I'm putting his technical notes below:
"In my opinion, the amp sounds rather thin for harp lacking bass response. Remember this is a guitar amp design and is optimized for the electric guitar. To improve this, I made a couple of changes in the amps preamp section. This means removing the chassis and the cover, to gain access to the circuit board.
5. To improve the amps bass response, and give it some balls, I changed the value of the Cathode Bypass capacitor (C18 on the schematic) for V1A from a 10uf/35V cap to a 47uf/50V electrolytic polarized capacitor. Please note the correct polarity of the cap. This fattens up the sound considerably.
6. To pass the improved bass response on to the power amp, I changed the Cathode Bypass capacitor (C7 on the schematic) for V1B from a 10uf/35V cap to a 22uf/25V electrolytic polarized capacitor. Sprague Atoms are my favorite for this, but I also use Nichicon branded caps. Avoid the cheaper caps, in my opinion.
Once these changes are made, reinstall the chassis cover and mount it back in the cabinet using the top screws. These changes improve the overall tone of the amp, for harp use, and I also think they improve the tone and response for a guitar player as well.
Mod to make the amp sound and play more like an early amp:
Brief explanation - As mentioned above, the power amp is running on very high B+, stretching the limits of the 6V6-GT power tubes. I hoped to change the bias of the Class A power tubes, by altering the value of the shared Cathode Resistor (R10 on the Schematic), however any change to this would result in over heating the tubes or exceeding their Voltage ratings.
So we are wise to leave the power amp alone. To achieve the same results, I decided to drop the plate voltage of the Preamp tube V1A and V1B plate voltage from 350V to about 225V. This change results in a softer overall sound of the amp and allows the preamp to compress somewhat, giving the amp some growl at a lower overall volume.
My inspiration for this change is the Kalamazoo Model One guitar amp, the best sounding old guitar amp that I have ever heard for harmonica. The Model One also uses a very low plate voltage on its preamp tube. To do this mod, you must remove the power amp chassis from the bottom of the cabinet.
7. Locate resistor (R12 on the schematic) on the board. Its stock value is 15K/1W. I clipped the leads leaving something to solder to on the top of the board. I replaced it with a 100K/1W metal oxide resistor, and reinstalled the chassis in the bottom of the cabinet.
I feel this change really changed the character of the amp, making it more responsive and much fatter sounding. The side effect of this change is you will lose a bit of volume.
Thats about it! Enjoy!"
Dale Murrow Old School Amps Olympia, WA info@oldschoolamps.com
Did it work? Oh, hell yeah! Fat, ballsy, loud, breaks nicely BUT still feedback problems. The solution to that final problem is an old standard; the Boss GE-7 EQ pedal. I sent mine to Modest Mike's Mods in Arkansas for a complete workover and couldn't be happier with the results. (It performs far better than when it was new!)
With the 16k slider set all the way down, feedback disappears even with the amp's tone control set well into treble range. This rig alone is worth the price of admission but wait, there's more.
I run the mic through the guitar side of my VoiceLive Acoustic pedal for two reasons; effects (reverb, etc.) and the balanced xlr output of the VoiceLive. Nearly doubles the mic power, clean effects and no feedback. I run the VL output through an impedance matching transformer straight into the Excelsior. Wow!(The same rig works equally well on the Kalamazoo for small spaces.)
Does it sound like a Kalamazoo? Well, no. I can best describe it as having the same characteristics but with a more "grown up" sound. Clean at lower mic volumes but very fat and compressed with the mic on full volume. Thank you Shaker! Even my chromatics sound good through this thing.
A lot of money, a lot of time, a lot of patience. That's what it takes to tame the wild Excelsior. It's worth it!
Interesting article glad it had a good outcome.As an aside i have to agree that using a EQ pedal is a very good way to combat feedback and a hell of a lot cheaper than the Harp centric feedback controllers.Sometimes as little as a few mill will work.
@Sarge, great to see you too! @Cliffy, I've got an a/b switch on the way so I can compare the Kalamazoo with the Excelsior using the same setup. I'll post results then.
Okay, got the video up comparing the modified Excelsior to a stock Kalamazoo. My first video! https://www.youtube.com/watch?v=v7PFZ3UrJh0&feature=youtu.be
hi just ordered the Boss GE 7 from Modest Mike Where in your chain did you put the pedal? and or did u try effects loop with it? and is it the last knob b4 volume u turned down? u said 16000 htz May use it to boost volume for leads in the effects loop
So My comping volume would be down enough not to feedback then step on pedal for volume boost and cut 16000 htz
may get a volume pedal and put in effects loop?? money
And could u post b4 and after volume ,feedback etc with the pedal-if not I understand -makin videos is a pain in the postereior Thanks very much
Snoman, I put the Boss GE-7 first in the chain (after the wireless receiver) with the 1600k knob (third from the right) all the way down. There is a volume boost on the pedal and I have used that gently with the Kalamazoo. Not needed the Excelsior. Normally I set the amp in a room with mic on full and turn up the volume until I get feedback. (Even the Boss can't do it all!) That's plenty loud. Then I roll off the volume on the mic control and enjoy the evening. And you're right, it may be a while before I can post the pre/post effects of the pedal. I'll look for an opportunity.
I just got a Ge-7 and will be using it for the first time this weekend. You mentioned that you set the 16k slider all the way down. Where do you set the other frequencies? This will be an outdoor gig and I need a lot of volume!
I had one and I did mods and tube swaps still had no headroom. It also sounded muddy when cranked. 1X15 speakers are not good for harp (there's a few exceptions though). I personally don't like them for Bass or guitar either, I just find them muddy sounding. I could get good tone but lots of feedback. I saw someone convert one into a 1x12 and it helped with the feedback
