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New DIY project in the works - Ampeg B-50R bass preamp

Deaj

Member
Messages
4,674
Hello all,

I've been out of circulation for a while. I've had precious little free time as of late and, feeling somewhat better (recently diagnosed with Psoriatic Arthritis), I've been spending more and more free time playing and less time breathing solder fumes. It's been good! I was starting to burn out on building pedals.

I've been thinking about building another guitar amp recently (specifically a 5E3 tweed Deluxe) though the cost of such a project has kept me from moving forward on it. Through other circumstances I got an idea for a more reasonably priced project - a solid state bass preamp with an old school sound. I've owned several great sounding bass amps over the last 15 or so years and my favorite too date has been the now out of production Ampeg 'Blue Diamond' series B-50R Rocket Bass 50watt 1x12 combo. It was voiced to sound like an old B-15N and it really covered that sound wonderfully.

Ii just sold my B-50R to help pay for a bass amp suitable for gigging / playing with a drummer (the B-50R, at 50w SS was never up to the task without solid sound reinforcement. I did have the opportunity to use my B-50R on a few gigs by running the line out to the effects return on more powerful bass amps and with excellent results. I've had to turn down quite a few requests to play bass for a jam due to not having an amp capable of being heard in the same room as a live dfummer. So away went my much beloved B-50R To make room for a new Markbass Jeff Berlin 1x15 300w combo.

A few days later I began to regret selling the Ampeg even though it was clearly not meeting my needs all around (plus I don't have sufficient space for two bass amps). It occurred to me last night that I definitely have room for a preamp and it's the preamp portion of the B-50R that I miss. Then I began to wonder how feasible it might to build the B-50R's preamp as a DIY project. Hmmmm.....

I called Ampeg this morning and asked if I could purchase a schematic for the now discontinued B-50R. The tech rep asked me for an email address and then asked me to check my inbox. Sure enough they sent a full schematic and for free!

The preamp is based around a TL074 quad op-amp IC and relatively simple. I found a Hammond transformer ideally suited for this project and I believe I've sorted out the power supply.

Next: circuit layout for a perf-board build. I love doing layouts! Aside from seeing/hearing a new build fire up and work for the first time the layout and diagram are my favorite part of these projects. I'll post links to the schematic and my initial preamp circuit layout (sans power supply - ran out of time tonight) in a few minutes. I'll be sure to post updates as I make progress.

Second revision preamp circuit board layout:


First revision power supply board layout:


Ampeg B-50R schematic (in .pdf format): http://home.centurytel.net/flanneldrawers/B50R_schematic.pdf
 
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TAVD

Guitar Player
Platinum Supporting Member
Messages
3,707
Cool. I might have to give that one a try as well.
 

Deaj

Member
Messages
4,674
Hi Tom,

I have all of the parts on order now and should have them by early next week. Once I have completed the build and verify that it works I'll post a Mouser parts list for the project. :)
 

jfromel

Member
Messages
1,127
That's a pretty cool circuit, clean layout on the pre, what does the VTL5C7 on the power amp side do? I haven't studied many SS amp schems but looks like there is some fun to be had in there. Perhaps split the op-amps up for swapping? You could use TL2272 which is rail to rail.

Would it be possible to run this with a 18v-24v wall wart, divide the rail so it has 9-12v on either side?
 

TAVD

Guitar Player
Platinum Supporting Member
Messages
3,707
You can try a max1044 set up for +/- 9v. It should still have enough headroom and can be powered from 9vdc. I also thought about splitting the opamps. You can also change that pseudo balancing to a Jensen transformer.
 
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Deaj

Member
Messages
4,674
Quick update: build on the power supply is completed and tests good.



Preaamp board is next.
 
Last edited:

Deaj

Member
Messages
4,674
Well, I've made a couple of mistakes so far. The first was easy to correct. When I did the layout for the preamp board I grabbed the wrong graphic for the IC (TL074 is DIP14 - I used a 16 pin template). I also ordered a 16 pin IC socket instead of the required 14 pin. I corrected the layout last night and I'll pick up the correct socket today. I'll go over it a couple more times before I build it but I believe it's good now. The second mistake is that I built the ower supply board without leaving space for stand-offs - oops! I believe I have a solution that will work (clamping the boardat the sides/corners) but it'll require fabricating non-conductive brackets. I'll correct this in the project files once it's finished.
 

sharpshooter

Senior Member
Messages
4,012
I play guitar, but a neighbor of mine, who I jam with, who is a bass player, was using some no name amp,,I could'nt stand the sound,,pulled-out my B-50R, for him to use, now my ears are much more happy.
 




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