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A DIY 500 Watt Bass Head

#81
Passinwind said:
The parts stash in my hobby shop finally hit critical mass this winter and I decided to build myself an amp and try out a few circuit designs I've had kicking around in software models for a while now. I'm still pretty much of a rookie at printed circuit board design, so this was a good excuse to work on that skill set a little too. I want to say right up front: this particular project has great potential to fail spectacularly and I highly recommend not trying this at home! :p

... stuff snipped ...

Just have to wire up the preamp section and I should be making some noise in the next few days. Pics to follow as things progress...:cool:
Click to expand...

This is just plain beautiful. It is creative. It is a work of art.

Congratulations.
 
#83
Today I finally got around to doing some measurements on the preamp section to see how well reality stacks up with my models.

Modeled frequency response, all tone controls at noon and high pass filter full clockwise for least possible bass cut with the HPF still switched in:

PW8B_12_12_12_HPFdimed_model.jpg


Measured response, same settings:

PW8B_12_12_12_HPFdimed_measured.jpg


The curves are actually quite close, and I tried lots of different control settings and found good correlation to the model in every case. How close I got to aligning the knobs on the pot shafts (or not) accounts for the biggest error factor, I think. Once again, I find LTspice to be a great tool, and certainly even more so given that it's free.

FWIW, here is the model for flattest response, reflecting very subtle cuts of all three tone controls and HPF set a little above noon:

PW8B_nominallyflattest.jpg


I didn't have a way of modeling signal/noise and distortion with a high degree of confidence, although I did try to optimize them in my model as much as my limited skills allow. Going back to my last couple of preamp build measurements as benchmarks I was hoping to achieve at least a -96dB noise figure (think CD quality, more or less) and no worse than 0.02% THD.

Some quick and dirty measurements, to be refined at my friend's better equipped shop eventually:

PW8B_RMAA.jpg
 
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#90
#91
Gig Report:

Finally had a chance to try the rig pictured above at my buddy's cowboy open mike last night, in a pretty scary dive bar a few towns upriver from me. I've been in there enough times now to almost not get the full stranger stinkeye routine, but this place will never be in my comfort zone completely, I'm sure. I like that though -- good honest feedback rules. I'd have to say this was the best I've yet heard my EUB sound, especially for this old school country context where I was really trying to cop an authentic acoustic upright feel. Just one Tuesday night in a dive, but still pretty encouraging. :bassist:
 
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#94
Passinwind said:
Gig Report:

Finally had a chance to try the rig pictured above at my buddy's cowboy open mike last night, in a pretty scary dive bar a few towns upriver from me. I've been in there enough times now to almost not get the full stranger stinkeye routine, but this place will never be in my comfort zone completely, I'm sure. I like that though -- good honest feedback rules. I'd have to say this was the best I've yet heard my EUB sound, especially for this old school country context where I was really trying to cop an authentic acoustic upright feel. Just one Tuesday night in a dive, but still pretty encouraging. :bassist:
Click to expand...
Did it have chicken wire around the stage? If it didn't, it wasn't that scary.:smug:

Amp's looking great Charlie.
 
#99
agedhorse said:
The XR-20 is one of my all time favorite compact analog consoles Charlie.
Click to expand...

I remember you mentioning that before, and yeah, same here. I've had mine for quite a while, it's a pre-Peavey one. For these recordings I was just using the direct out on one channel, with EQ bypassed. Kind of overkill, but I haven't gotten around to doing a DIY mic preamp just yet...Link Removed

chienmort said:
Sounds great Charlie. A wonderful
Project.
Click to expand...

Thanks John. Really looking forward to seeing how your DIY amp project comes out when you're able to get back to it.
 
#100
And now, Round 2. Since it ain't broke, I'm just going to have to fix it anyway...

Got in the Rev 1.1 boards and stuffed the HPF daughter card this afternoon. This one should integrate more neatly with the preamp module and clean up some wiring clutter, and it also has a few different volume control config options to optimize gain staging. I tried a number of mods on my older standalone preamp and hope/expect to see a modest improvement in signal/noise ratio and distortion ratings as well. I will also be trying the PEQ out with a nominal frequency sweep range @ 200-2KHz this time.

HPFPEQ_1_1.jpg
 
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