Ampeg BA-108 Coffeeshop Micro Rig

[40 Hz]

First of all, these are great little amps. I have a pair of them that my kids and I have been doing experiments with as I teach them basic electronics. We don't use the effects send/return, so we wired those up as a speaker outputs.

We have a couple of small compact external cabs (ported Eminence S2010 loaded) that we hooked up. We wired two of them up in series for 16 ohms and it sounded REALLY nice, but if we could run those wired in parallel at 4 ohms for more volume it would be even better. We have also hooked the amp up a PA speaker, plugged in an iPod to the CD input, and rocked a birthday party (surprisingly loud!). If this amp could safely run at 4 ohms, I would seriously think about putting a Eminence Alpha 8A in it, stack the BA-108 on top of one of my external 10" cabs, and that would be all the kids would need to do battle against a small drum set.

Also, I think Woodstockz mentioned the schematic had the op-amp listed as a TL072, but he had a 4558. For what its worth, ours do have the TL072 in them. We socketed one and put in a 5532 that I had on hand. Since we have two of these amps we could do an actual side by side comparison. The 5532 eliminated some of the amp hiss that is noticeable at higher volumes and seemed to tighten or crisp up the sound slightly. We may try ordering some of the other op-amps mentioned and experiment with those.

Thanks also to everyone who mentioned gluing the seems. We did that on both amps and it definitely eliminated the cabinet rattle. We also put in some open-cell foam in to dampen the inside of the cabinet, and that seem to tighten up the low-end a little bit too. After these tweaks we have done, I am totally amazed at how good these little amps sound for so little $$$.

Also, we have been experimenting with an upgrade that make a remarkable difference in the sound of this amp for less that $5, and would take very little time to do (no soldering required!). Once we perfect that we will share our results with you guys, possibly with some audio A/B tests so you can hear the difference before you attempt it yourself. Thanks

[whitedk57]

Originally Posted by 40 Hz

Also, we have been experimenting with an upgrade that make a remarkable difference in the sound of this amp for less that $5, and would take very little time to do (no soldering required!). Once we perfect that we will share our results with you guys, possibly with some audio A/B tests so you can hear the difference before you attempt it yourself. Thanks

That's called "being a tease".

[Woodstockz]

Originally Posted by 40 Hz

First of all, these are great little amps. I have a pair of them that my kids and I have been doing experiments with as I teach them basic electronics. We don't use the effects send/return, so we wired those up as a speaker outputs.

We have a couple of small compact external cabs (ported Eminence S2010 loaded) that we hooked up. We wired two of them up in series for 16 ohms and it sounded REALLY nice, but if we could run those wired in parallel at 4 ohms for more volume it would be even better. We have also hooked the amp up a PA speaker, plugged in an iPod to the CD input, and rocked a birthday party (surprisingly loud!). If this amp could safely run at 4 ohms, I would seriously think about putting a Eminence Alpha 8A in it, stack the BA-108 on top of one of my external 10" cabs, and that would be all the kids would need to do battle against a small drum set.

Also, I think Woodstockz mentioned the schematic had the op-amp listed as a TL072, but he had a 4558. For what its worth, ours do have the TL072 in them. We socketed one and put in a 5532 that I had on hand. Since we have two of these amps we could do an actual side by side comparison. The 5532 eliminated some of the amp hiss that is noticeable at higher volumes and seemed to tighten or crisp up the sound slightly. We may try ordering some of the other op-amps mentioned and experiment with those.

Thanks also to everyone who mentioned gluing the seems. We did that on both amps and it definitely eliminated the cabinet rattle. We also put in some open-cell foam in to dampen the inside of the cabinet, and that seem to tighten up the low-end a little bit too. After these tweaks we have done, I am totally amazed at how good these little amps sound for so little $$$.

Also, we have been experimenting with an upgrade that make a remarkable difference in the sound of this amp for less that $5, and would take very little time to do (no soldering required!). Once we perfect that we will share our results with you guys, possibly with some audio A/B tests so you can hear the difference before you attempt it yourself. Thanks

Thanks to everyone for the renewed interest in this project.
It was a lot of fun for me. I have been working on a PF-350 and a PF-500 lately, I still use my BA-108 for jams and gig.
[But now I know that a PF-350, a stock Fender Squier, and a BP-102 in a DIY 1.5 cu FT cab make an AWESOME funk machine.]

Thanks for your post. It is good to see another BA-108 hacker. The extra information on what you are trying to do helps. It also helps to know that you know how to use a soldering iron.

I remember now about the Op-amps. The schematic says 4558. One of my amps had a 4558, and the other had a TL072.

For 4 Ohms, the quick answer is no, the long answer is yes.
As JimmyM mentioned, you could damage the circuit, and other things, but there is more. We are now getting into an area of one of the design weaknesses of combos, which is why I started working on seperate head/cab.

The Ampeg BA-108 and BA-110 have an enclosed electronics box. That brings up two issues.
The first is that the electronics box takes away from speaker enclosure volume. The rig would sound better if it used the whole cab for speaker volume.
The second issue is that all of the heat is enclosed inside the electronics box. If you go to 4 ohms, then you are basically doubling the current and doubling the heat that needs to be dissipated. And all of that heat will be bottled up inside the electronics box.

That said, I was working on a design to put the heatsink on the outside, like some of the larger Ampeg Combos. Then I could re-claim some speaker volume.
I redesigned the electronics box and got a heatsink from Heatsinks USA to mount on the back, but never finished the project. Now that I am thinking about it, and the PFs are working, I will go ahead and finish.

If you address the heat issue, then you might drive 4 Ohms.
You might be able to put in some vents, one low and one high. You might even add a small fan.
But First, before you go driving 4 Ohms, you should upgrade the circuit to handle the added current requirement.

Upgrade the transistors and the current limiting resistors.
The TIP41, is not a modern device, replace it with a MJE15028-35. [Post #73]
The protection circuit is pretty much just the current limiting resistors.
The original current limiting resistors were 3 Watts.
The upgraded limiting resistors are 5 Watt resistors.
They are the big, white rectangular resistors in the picture.

That's what I would do if I wanted to drive 4 Ohms. Ventilation/fan, Transistor, ceramic resistors. It would be a little bit of soldering work, but a cool project.
Let us know.

[Woodstockz]

Originally Posted by Woodstockz

Thanks to everyone for the renewed interest in this project.
It was a lot of fun for me. I have been working on a PF-350 and a PF-500 lately, I still use my BA-108 for jams and gig.
[But now I know that a PF-350, a stock Fender Squier, and a BP-102 in a DIY 1.5 cu FT cab make an AWESOME funk machine.]

Thanks for your post. It is good to see another BA-108 hacker. The extra information on what you are trying to do helps. It also helps to know that you know how to use a soldering iron.

I remember now about the Op-amps. The schematic says 4558. One of my amps had a 4558, and the other had a TL072.

For 4 Ohms, the quick answer is no, the long answer is yes.
As JimmyM mentioned, you could damage the circuit, and other things, but there is more. We are now getting into an area of one of the design weaknesses of combos, which is why I started working on seperate head/cab.

The Ampeg BA-108 and BA-110 have an enclosed electronics box. That brings up two issues.
The first is that the electronics box takes away from speaker enclosure volume. The rig would sound better if it used the whole cab for speaker volume.
The second issue is that all of the heat is enclosed inside the electronics box. If you go to 4 ohms, then you are basically doubling the current and doubling the heat that needs to be dissipated. And all of that heat will be bottled up inside the electronics box.

That said, I was working on a design to put the heatsink on the outside, like some of the larger Ampeg Combos. Then I could re-claim some speaker volume.
I redesigned the electronics box and got a heatsink from Heatsinks USA to mount on the back, but never finished the project. Now that I am thinking about it, and the PFs are working, I will go ahead and finish.

If you address the heat issue, then you might drive 4 Ohms.
You might be able to put in some vents, one low and one high. You might even add a small fan.
But First, before you go driving 4 Ohms, you should upgrade the circuit to handle the added current requirement.

Upgrade the transistors and the current limiting resistors.
The TIP41, is not a modern device, replace it with a MJE15028-35. [Post #73]
The protection circuit is pretty much just the current limiting resistors.
The original current limiting resistors were 3 Watts.
The upgraded limiting resistors are 5 Watt resistors.
They are the big, white rectangular resistors in the picture.

That's what I would do if I wanted to drive 4 Ohms. Ventilation/fan, Transistor, ceramic resistors. It would be a little bit of soldering work, but a cool project.
Let us know.

Oh yeah. If you are going to do all of that, then you might as well separate it into head and cab, like those cool ones in post #147.

[Ben B]

Originally Posted by Woodstockz

If you address the heat issue, then you might drive 4 Ohms.
You might be able to put in some vents, one low and one high. You might even add a small fan.
But First, before you go driving 4 Ohms, you should upgrade the circuit to handle the added current requirement.

Thanks for this information. I have been wondering if I could run my Rumble 15 at 4 ohms. It uses TDA2050 which, at least in theory, can do 4 ohms. I don't think I will try it now.

[Woodstockz]

Originally Posted by Ben B

Thanks for this information. I have been wondering if I could run my Rumble 15 at 4 ohms. It uses TDA2050 which, at least in theory, can do 4 ohms. I don't think I will try it now.

When I was 14, I used to try to make a stereo with old radio parts. I added more speakers and it seemed to work. That was before I went to college and found out about impedance.

The designer of an amp circuit of a combo has a simpler task than a head designer because he knows what the load will be. If it is an 8 Ohm combo, he doesn't have to make as many allowances for short circuit protection, can skimp on over-current circuits, etc. He knows how much heat will be inside the box.

The designer of a head doesn't know what his load will be. He can only specify if it is 8 Ohms or 4 Ohms, or 8 & 4, or down to 2. He has to over-design the short circuit protection. He has to consider scenarios like "What if the user runs the speaker output into the headphone jack." He has to idiot proof his amp for situations what combos will not see. That is until we start taking them apart.

It you can duplicate the conditions of a working 4 Ohm TDA2050 design, you might be able to give it a shot.

[JimmyM]

Well you guys are way more adventurous with your $100 practice amps than I ended up being but I did add some more lining to the inside areas of my BA110 that weren't covered and reglued the seams (pretty sloppy) just to be sure, and that got rid of the last of my rattles. And I've used it on 8 or 9 gigs so far, including a stage volume gig for about 100 people on a casino ship and several outdoor gigs in front of a few thousand people with PA, and it is killing! Granted, it's not quite like an SVT/810, but it sure is Ampeggy and sounds killer and has enough for me to do what I need, whereas the BA108 would always come up short in those situations, though it was great for a living room rehearsal last night. Yeah, it's a little dirty at clean volumes, but in a good way, and you can't hear it while the band's playing anyway. BA110 steps it up in that respect, though. Doesn't sound as dirty till you start pushing it hard, which I don't.

So I think I'll just leave them alone and go with them as they are. Salut to those of you who are modding them, but if I need better sound, I'll just go with one of my better Ampeg rigs

[40 Hz]

Thanks for all that info on the transistor upgrade Woodstockz! I think that will be a project we will do at some point, but it will probably be a while before get around to it.

Separating the head from the cabinet has also got me thinking some more projects we can do. We actually have one of the amps disassembled right now and after looking at it, that would be very easy to do. The amp chassis has a back panel already drilled with three holes (line out/send/return) and a power cord hole. The top of the chassis already has tapped holes for mounting. I am not sure what other amp head Ampeg would have used the chassis for (Micro series?) but but most of the hard work is already done.

I am a multi-instumentalist and have the kids fooling around with guitar, bass, drums and keyboards to see if they find one that they want to master. I was trying to find a god multipurpose amp that would work well with all these instruments and stumbled upon the BA-108. Besides being a great little bass amp, we plug our iPods into the BA-108's line-inputs and run amp simulators apps (JamUp, Amplitube, AmpKit) and these amps double as a great sounding guitar amp.

We have also come up with a way to make the BA-108 also work as a keyboard and PA amp. With this simple modification I have even gotten a decent amplified tone out of it with my Taylor acoustic guitar. If someone told me about his modification I would have laughed at them, but we think it definitely make the amp much more useful (and even improves the tone when used just as a bass amp).

We have a working prototype that we are experimenting with to improve further. I will try to get my kids to make a recording, and if there is anyone who likes the sound of the modification maybe that will push us to take some pictures and do a write-up explaining how to do it.

I am thinking about getting two more of the BA-108's, as they are so versatile every room should have one! They actually qualify for those discount coupons MF is always offering. I got one of them new a while back for $75-80 after the discountt, which is unbelievable cheap for what you are getting.

[40 Hz]

Originally Posted by JimmyM

Well you guys are way more adventurous with your $100 practice amps than I ended up being but I did add some more lining to the inside areas of my BA110 that weren't covered and reglued the seams (pretty sloppy) just to be sure, and that got rid of the last of my rattles. And I've used it on 8 or 9 gigs so far, including a stage volume gig for about 100 people on a casino ship and several outdoor gigs in front of a few thousand people with PA, and it is killing! Granted, it's not quite like an SVT/810, but it sure is Ampeggy and sounds killer and has enough for me to do what I need, whereas the BA108 would always come up short in those situations, though it was great for a living room rehearsal last night. Yeah, it's a little dirty at clean volumes, but in a good way, and you can't hear it while the band's playing anyway. BA110 steps it up in that respect, though. Doesn't sound as dirty till you start pushing it hard, which I don't.

So I think I'll just leave them alone and go with them as they are. Salut to those of you who are modding them, but if I need better sound, I'll just go with one of my better Ampeg rigs

Are you using still using the factory speaker or did you upgrade? I agree that the tone has a hint of grit in it, and I like that too. I recently switched to flatwound strings (after years of roundwound with hi-fi modern amp tones) and I am really digging my new sound! I wouldn't be putting so much time in working on this amp if it wasn't for my kids, but I am really enjoying myself. It's like I am back in high school again, trying to get the "big" sound with very little money to spend.

[JimmyM]

Factory. Only mod I did was the extra foam in the BA110. Didn't really need it for sonic purposes but it did finally tame that last rattle. I know what you mean about high school...stuff like that is fun if you can do it. But really, I'm happy with them as they are, especially the BA110.

[Woodstockz]

Originally Posted by JimmyM

Well you guys are way more adventurous with your $100 practice amps than I ended up being

Hi JimmyM. This thread would never have grown the legs that it did if you and BenB had not suggested an alternative cost effective speaker upgrade.

I would love an SVT, but the dragon_lady/minister_of_finance/lovely_wife keeps an eye on expenditures. She is not a musician, I'm sure that she would not approve it.

However, she does approve of me puttering around in the garage fixing things.

Maybe, if I found a busted one that needed...

[Woodstockz]

Originally Posted by 40 Hz

Thanks for all that info on the transistor upgrade Woodstockz! I think that will be a project we will do at some point, but it will probably be a while before get around to it.

...Snip

I am thinking about getting two more of the BA-108's, as they are so versatile every room should have one! They actually qualify for those discount coupons MF is always offering. I got one of them new a while back for $75-80 after the discountt, which is unbelievable cheap for what you are getting.

No problem. I am anxious to see what other people come up with.

I thought about using the BA-108 to give some basic lessons.

[JimmyM]

Originally Posted by Woodstockz

Hi JimmyM. This thread would never have grown the legs that it did if you and BenB had not suggested an alternative cost effective speaker upgrade.

I do still get tempted to throw an Alpha 8a in the BA108...I'll admit. I'm just lazy and cheap

I would love an SVT, but the dragon_lady/minister_of_finance/lovely_wife keeps an eye on expenditures. She is not a musician, I'm sure that she would not approve it.

However, she does approve of me puttering around in the garage fixing things.

Maybe, if I found a busted one that needed...

Hey, they're out there

[tayal01]

I've just completed the preparations for stage one while I wait for delivery of the Alpha 8 and AD823.

I have to say I wasn't expecting quite so much disassembly. I pretty much pulled the whole thing to bits to get at the op amp to desolder it and install the socket. It's been about 3 decades since I last did any desoldering. I think a solder pump might be an improvement over my old soderwick!

It looked to me like the seams were all glued just fine but I applied a bead of PVA glue as recommended anyway.

The batting is unattached around the edges and about 2 or 3 inches of it is hanging free and needed to be glued. I'll be adding more batting.

My primary aim is to limit buzzing and rattles to the minimum possible but I'm eager to see how the new speaker and op-amp improve the tone.

Thanks for the fun project!

[JimmyM]

That Nu-Foam is great for extra batting.

[Gintaras]

Originally Posted by Woodstockz

I have read many internet builds in the past, but this is my first. I hope that this helps someone out there.

Notice that the new speaker is very close to the port. So the strategy is to plug the port, and go to a rear port.

I am reproducing what you did with putting the port in the back. I just got the precision port and it came with 2 adapters and a 12" tube. Did you cut down the tube or just not use it and hook the 2 flares together with one of the adapters

[Woodstockz]

Originally Posted by Gintaras

I am reproducing what you did with putting the port in the back. I just got the precision port and it came with 2 adapters and a 12" tube. Did you cut down the tube or just not use it and hook the 2 flares together with one of the adapters

I have become a fan of flared ports. Precision ports advertise that you can average 3 dB increase.

If you don't use both rings and some tubing between, then the port will be too short, and your tuning frequency too high.

Precision ports has a tool on their website to help you in determining the length.

I used the 3 inch port with the 2 adapters. I cut a piece of the tube about 2" long to fit between them. I used a hacksaw to make the cut.

[throbgod13]

and no one thought to recap the PCB with better filter/audio caps??

[tayal01]

Glued Seams, Check. Upgrade batting, Check. Eminence Alpha-8A, Check. AD832 Op Amp, Check it out!



Rolled out the stock TL072 and rolled in the AD832 and I can confirm that it's a nice, warm sounding, tube tone. The amp sounds better both through the speaker and the headphones.

Less distortion even at full volume unless you're really pounding on the strings, but who ever does that?

I'm still waiting for the Burr Brown to arrive and I'll report back.

[Woodstockz]

Originally Posted by tayal01

Glued Seams, Check. Upgrade batting, Check. Eminence Alpha-8A, Check. AD832 Op Amp, Check it out!

Attachment 315697

Rolled out the stock TL072 and rolled in the AD832 and I can confirm that it's a nice, warm sounding, tube tone. The amp sounds better both through the speaker and the headphones.

Less distortion even at full volume unless you're really pounding on the strings, but who ever does that?

I'm still waiting for the Burr Brown to arrive and I'll report back.

Awesome! I am glad that you are making good progress.

I started with the BurrBrown, and then went to the AD832. I like them both. Cleaner sound for the cost of a burger.

The BA108 is a surprisingly good platform in stock form, and a great platform for mods, especially since the circuitboard is through hole and not surface mount. I'm glad that you like the mods so far.

I started my BA108 project because I was very surprised by the way the Markbass MicroMark sounded - how could they get so much sound from such a small amp. I wanted it, but it cost too much. I figured that I would DIY on a BA108. I've performed the mods on my BA108 first to proof them out, them repeat them on my BA110.

I thought that I was through with modding the BA108, but now I have some new ideas, so I'm still not done. Now I want to give my BA110 some love. I will reverse the process by modding the BA110 first, then migrating the mods to the BA108. In addition, I have other projects in work that I have to prioritize, like cabs for my PF350 and PF500, and also my Ibanez Troubadour. But I just wanted to say that the BA108 is still in development.