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

[Deaj]

Hello all,

I've been out of circulation for a while in the DIY community. 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/flanneldr..._schematic.pdf

[gerryjazzman]

Looks like a very cool little project. Since you are building it yourself you could do any mods that you want. One thing I noticed is the bridged-T network at the input to the second stage (C7, C9, R6, R41, R42) that should produce some mid-scoop. That's something that you could play around with a switching arrangement to switch it in and out and see how it sounds. Could provide a bit more versatility if you want. Also, if you wanted to you could run it off a pair of 9V batteries, package it really small and hang it off your belt or something. Instant availability to tonal shaping. In any case, should be able to drive any decent power amp nicely.

Reminds me of a project that's been sitting in my workshop for some years. I made a little 60 watt practice amp with an op-amp preamp (2 TL072's actually) that emulates (mostly) the Ampeg V4B / SVT tone shaping (Baxandall bass / treble, switchable mid boost at 300, 1000, 3000 Hz, and treble boost switch). I blew the power amp and haven't fixed it so it's been sitting. Got to dig that out and play around a bit.

[Passinwind]

Originally Posted by Deaj

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.

Thanks for posting this and linking the schematic. As it happens, I've been working on a new DIY preamp with a bit of an Ampeg-ish vibe. I still have to decide what midrange control circuit (if any) to use though. Right now it's just bass/treble, using a Baxandall stack.

This one uses the ESP Universal Preamp/Mixer project board, and a power regulator board from Welborne Labs. The rack case is from Par-Metal, and I had the power transformer kicking around in my junk box. I'll do my own thread with tested specs and sound clips as things progress a little further. But judging from how it sounded last night on the gig, I may call it done right now...



Lots of temporary wiring mess to clean up, but first I need to finalize the design.

[Chef]

I dunno; looks pretty well done from here mate...

[Deaj]

Originally Posted by gerryjazzman

Looks like a very cool little project. Since you are building it yourself you could do any mods that you want. One thing I noticed is the bridged-T network at the input to the second stage (C7, C9, R6, R41, R42) that should produce some mid-scoop. That's something that you could play around with a switching arrangement to switch it in and out and see how it sounds. Could provide a bit more versatility if you want. Also, if you wanted to you could run it off a pair of 9V batteries, package it really small and hang it off your belt or something. Instant availability to tonal shaping. In any case, should be able to drive any decent power amp nicely.

Reminds me of a project that's been sitting in my workshop for some years. I made a little 60 watt practice amp with an op-amp preamp (2 TL072's actually) that emulates (mostly) the Ampeg V4B / SVT tone shaping (Baxandall bass / treble, switchable mid boost at 300, 1000, 3000 Hz, and treble boost switch). I blew the power amp and haven't fixed it so it's been sitting. Got to dig that out and play around a bit.

That sounds like a cool project!

I do hope to be able to broaden it's tone shaping options once it's working.

Updates posted. Power supply layout rev1 complete.

[Deaj]

Originally Posted by Passinwind

Thanks for posting this and linking the schematic. As it happens, I've been working on a new DIY preamp with a bit of an Ampeg-ish vibe. I still have to decide what midrange control circuit (if any) to use though. Right now it's just bass/treble, using a Baxandall stack.

This one uses the ESP Universal Preamp/Mixer project board, and a power regulator board from Welborne Labs. The rack case is from Par-Metal, and I had the power transformer kicking around in my junk box. I'll do my own thread with tested specs and sound clips as things progress a little further. But judging from how it sounded last night on the gig, I may call it done right now...



Lots of temporary wiring mess to clean up, but first I need to finalize the design.

Very nice!!

[seanm]

Originally Posted by Deaj

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.

You are way more organized than I am. I just draw out the schematic on paper, get a strip board (or perf board for a simple pedal) and start soldering

Looking forward to seeing the updates.

[Passinwind]

Originally Posted by Deaj

Very nice!!

Thanks. As always, I mostly just see the flaws, but this time I'm reasonably happy with the sound at least.

Looking forward to seeing how yours progresses. I used to build lots of one-off projects with perfboard and the like, but I'm working up my CAD skills and hope to stay with PCBs as much as possible these days.

[Deaj]

Originally Posted by Passinwind

Thanks. As always, I mostly just see the flaws, but this time I'm reasonably happy with the sound at least.

Looking forward to seeing how yours progresses. I used to build lots of one-off projects with perfboard and the like, but I'm working up my CAD skills and hope to stay with PCBs as much as possible these days.

Thanks! I ordered the parts today so I imagine I'll get started building it early next week. If it sounds as good as the line out signal from the B-50R (it should as it's the same circuit) then it will have been well worth the effort.

More to come!

[Deaj]

Quick update: build on the power supply is completed and tests good.



Preamp board is next.

[Deaj]

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.

[barroso]

any update?