I have a new, primary bass amp in my GK Backline 210. I am thinking of gently disassembling my Johnson RepTone 15B practice amp. 15 watts through a 6.5" speaker. Not exactly loud, or booming with bottom end.

I was checking out a web site, and specifically this project:
http://diyaudioprojects.com/Speaker...Bass-Reflex/

It got me thinking I could do the same treatment to my RepTone.

Why? To see if I can do it. I don't have to make an mods to the electronics of the RepTone. And I just might be able to coax some more bottom end out of the tiny speaker.

Posted - 01/01/2010 :  09:39:53      

My son and I did something similar. There's a pic in my photo album. It was a lot of fun, so I'd recommend it.

Edited by - musekatcher on 01/01/2010 09:42:35

Posted - 01/01/2010 :  10:32:32  

Once I take the old RepTone apart, I should be able to find that info. The Johnson Guitar web site only lists the speaker wattage and size. Hopefully more info is written on the speaker inside.

Posted - 01/13/2010 :  12:02:08  

Okay, so here are my options.

I have the 15w practice amp. I would have to carefully remove all the components from the case, then reassemble them in a new box. Two main pieces and a wire that attaches the head to the speaker, shouldn't be difficult.

I also have an Optimus 20w PA mono amp that is no longer being used and a pair of speakers from a Sony bookshelf system (100 watts each). These speakers have a 6.25" woofer and a 1" tweeter. 70Hz to 20kHz range. The low-end cut-off won't be very useful for my 5-string bass, but maybe as a general amp for harmonica, guitar, vocal? Though, at only 20 watts, we are still not talking about a lot of low end thunder, but the tweeter allows for a more well-defined high. I could use my Bass EQ pedal to cut the really frequencies.

The speakers were free. I lose nothing, literally, for trying to build them into a new enclosure, which I may do first. I would rather mess up there, than a known-working amp. I can just sit the PA amp on top of the new enclosure and use the existing wire connects for this first experiment.

Now, to head to Lowes and see what kind of wood they have.

Edited by - caeman on 01/13/2010 12:03:50

Posted - 01/13/2010 :  17:17:12  

I decided to experiment with the sound of the Sony speaker before future experimentation, to have a reference.

Bass -> Bass EQ Pedal -> Optimus Amp -> 1 Sony Speaker

This setup did not like my B string, so I used the pedal to down the gain to -15db at 50Hz. That cleaned up the sound. Because of the high end being 20kHz with the tweeter, the sound wasn't bad for a practice-size wattage of amp.

I tested the volume knobs all maxed (amp and guitar) with +15db boost from the pedal. The sound was like that of a tube drive amp. It was positively horrendous for a bass sound.

But, with levels at more modest levels, it works as a practice amp. It would probably work better with a guitar, than a bass.

Posted - 01/22/2010 :  10:40:03  

I experimented with the PA amp as a guitar amp and I learned a valuable lesson: my active guitar electronics were sending too much gain to the PA amp too easily. :)

With the guitar on 11, the mic input on 5 and the master volume in 5 was the loudest I could get it. Sufficient for a practice amp, but totally lacking in any effects. I imagine if I scaled the guitar volume back to 3 or 5, I could get more volume from the PA amp.

So, looks like I have TWO amp rebuild projects.

I have two Sony speakers. Each is rated at 6 Ohms. What if I combined the two sets of speakers into the same cabinet? If I ran them in parallel, that would create a 3 Ohm system? Someone double-check me here. That serial vs. parallel stuff confuses me. The PA Amp has 4, 8 and 16 Ohm speaker connections.

Posted - 03/23/2010 :  16:26:19  

Ah, spring has sprung! I can now begin working on my garage again.

For the rebuilding of this amp, I am torn on what size to make the new cabinet:
1. 24x12x12 (h,w,d)
2. 36x12x12 (h,w,d)

The larger internal volume will accentuate the lower tones better (given a 6.25" speaker). But 24" high will be easier to tote and use less wood.

Of course, the only thing stopping me is the amount of wood I could buy and experiment with many different sizes.