Ampeg BA-108 Coffeeshop Micro Rig

[Gintaras]

Glued the seams and batting. (could not get the staple gun into the box and the batting was floating around with just a few staples. Glued the edges down.) Installed the speaker and it was definitely worth the investment. Sounds more open and improved tone. I have not cranked it past 5. Even then it had more volume then I need. This is for bumping up the volume of my ABG.

I have been reading about the precision port and there website has a calculator for it.
Can anyone supply the info in this caculator. Out of my level of expertise.

http://www.psp-inc.com/tools.html

[mbelue]

Just checking in on your Woodstock, still feeling ok after your accident?

[Woodstockz]

Originally Posted by Gintaras

Glued the seams and batting. (could not get the staple gun into the box and the batting was floating around with just a few staples. Glued the edges down.) Installed the speaker and it was definitely worth the investment. Sounds more open and improved tone. I have not cranked it past 5. Even then it had more volume then I need. This is for bumping up the volume of my ABG.

I have been reading about the precision port and there website has a calculator for it.
Can anyone supply the info in this caculator. Out of my level of expertise.

http://www.psp-inc.com/tools.html

Hi,

It is great that your mod worked out. I hope that you will enjoy it.

That is the Precision Port calculator that I used for my port. I don't have any more information about the tool, but it worked out well for my project.

[Woodstockz]

Originally Posted by mbelue

Just checking in on your Woodstock, still feeling ok after your accident?

mbelue,

Thanks for asking. I'm doing OK. I had a headache at the time of the accident, and few headaches afterwards, but none recently. And I'm not as jumpy when driving as I was at first.

I did have time to think about some new projects. As I get better at playing, I need more volume. I just don't know which one to do next.

Thanks again...and tell us about your rig.

Woodstock

[Woodstockz]

Originally Posted by Gintaras

I have been reading about the precision port and there website has a calculator for it.
Can anyone supply the info in this caculator. Out of my level of expertise.

http://www.psp-inc.com/tools.html

This calculator tells you how long to make your port. You give it your internal box dimensions, tuning frequency, port diameter, and number of ports, and it will tell you how long to make the port.

I don't remember my numbers offhand, but for example:
1.5 cubic feet, 50 HZ, 3 inch port, 1 port and hit calculate.
That means that you need a 3.885339 inch long flared port.

[mbelue]

Originally Posted by Woodstockz

mbelue,

Thanks for asking. I'm doing OK. I had a headache at the time of the accident, and few headaches afterwards, but none recently. And I'm not as jumpy when driving as I was at first.

I did have time to think about some new projects. As I get better at playing, I need more volume. I just don't know which one to do next.

Thanks again...and tell us about your rig.

Woodstock

I know what you mean about the jitters I had an accident when I was younger that left me flinching for a year or better.
I don't have a BA-108 but I totally dig your approach to your upgrades. Really enjoy reading about it.

[xaxxat]

Originally Posted by Derek Balonek

Thanks for making this thread, it's an interesting thing to read. I'd like to do some of this myself on some gear. I recently found out that the Fender practice amp I picked up is through-hole, so it's going to get some mods; I will probably make it into a preamp and disconnect the power opamp.

Here's a couple of cool combo to head conversions.

http://www.sevenstring.org/forum/gea...-head-mod.html



http://www.sevenstring.org/forum/gea...-amp-head.html

[tayal01]

I just picked up a new BA108 as an exchange for a Christmas gift my lovely wife got me.

I've just ordered the Alpha 8a, TL072 and a pound of Acousta-Stuf Polyfill batting from Parts Express. The shipping to Australia costs more than the parts!

Can't wait to get started...

As soon as I'm done the Fender Rumble 150 is going to get listed.

[whitedk57]

Originally Posted by Woodstockz

I think that an upright playing through a BA-108 with an upgraded speaker, and Burr-Brown OPA2132 op-amp in the pre-amp would sound awesome.

Woodstockz, I was thinking about switching out the op-amp im my amp with the Burr-Brown OPA2132 that you mentioned. But looking online, I noticed that there are several variations of the chip. Can you tell me what the difference is between these?

• OPA2132
• OPA2132P
• OPA2132PA

I don't believe there is much difference in them, but I wanted to be sure not to get the wrong one.

BTW, I have been using the Aphex Xciter Aural Exciter and Optical Big Bottom Effects Pedal - instead of my SansAmp BDDI. I am able to crank the amp up more without distorting or farting out. I have come to the conclusion that the BDDI, along with my bass pre-amp, was too much signal for the BA108 when connected to the 0db input. I know - that input is for passive basses, but I wanted more volume than the -15db input can give.

Actually, I used my BA108 amp at church on Sunday. I basically wanted an on-stage monitor, since the bass was run through the house sound anyways. It performed admirably, and I was able to hear it without issue. Granted, the drummer was using a djembe and not drums.

[Woodstockz]

Originally Posted by tayal01

I just picked up a new BA108 as an exchange for a Christmas gift my lovely wife got me.

I've just ordered the Alpha 8a, TL072 and a pound of Acousta-Stuf Polyfill batting from Parts Express. The shipping to Australia costs more than the parts!

Can't wait to get started...

As soon as I'm done the Fender Rumble 150 is going to get listed.

Happy New Year! Congratulations on your BA-108! It is an underrated amp, I hope that you enjoy it.

This was a fun project. In miniaturizing, one inspiration that I had for this project was the Markbass MicroMark. I thought that it was amazing that they could get so much bass out such a tiny box. But it was too expensive... so I thought, let's see what I can do with a BA-108 for less than half the price for the project...

I replaced the stock TL072 preamp chips with Burr-Brown OPA2132 for higher slew rate and lower distortion. By lowering distortion, I wanted to get a few more Watts out. Some people prefer a little distortion, but generally it is tube distortion that they want. I wanted it as clean as possible, and figured that anyone that wants to change the tone will use pedals. I have since designed a tone circuit that I want to try, so I will make a stompbox to see how it sounds.

The Alpha 8a has a larger voice coil than the stock speaker. It is more efficient and handles more power than stock. You can crank it further without it farting out.

Good luck on your project. Let us know how it turns out.

[Woodstockz]

Originally Posted by whitedk57

Woodstockz, I was thinking about switching out the op-amp im my amp with the Burr-Brown OPA2132 that you mentioned. But looking online, I noticed that there are several variations of the chip. Can you tell me what the difference is between these?

• OPA2132
• OPA2132P
• OPA2132PA

I don't believe there is much difference in them, but I wanted to be sure not to get the wrong one.

BTW, I have been using the Aphex Xciter Aural Exciter and Optical Big Bottom Effects Pedal - instead of my SansAmp BDDI. I am able to crank the amp up more without distorting or farting out. I have come to the conclusion that the BDDI, along with my bass pre-amp, was too much signal for the BA108 when connected to the 0db input. I know - that input is for passive basses, but I wanted more volume than the -15db input can give.

Actually, I used my BA108 amp at church on Sunday. I basically wanted an on-stage monitor, since the bass was run through the house sound anyways. It performed admirably, and I was able to hear it without issue. Granted, the drummer was using a djembe and not drums.

I'm glad your BA108 is working for you. My trio is not a loud rock band. We use a percussionist with congas and djembes also. Djembes still can get loud on the bass stroke.

In choosing chips I was looking for FET input, High slew rate, Low noise, Low distortion. The OPA2132 and the AD823 stood out as my choices. The TL072 is OK, but not high slew rate.

If you go to Digikey web site, and put in OPA2132 for search keyword, then you will see a long list of variations. Most will be surface mount. You will want 'Through-hole' or 'DIP'. In all cases, there will be more characters after the OPA2132. The P is for plastic package, as opposed to ceramic. Just make sure that you get the DIP [Dual In-line Package].

Another chip to consider is the AD823. JFET input, High slew rate, Low noise, Low distortion. I have both, and both sound great. Easy to swap if you install a socket. The socket also prevents you from overheating the chip on installation.

Best regards and Happy New Year!

[LowEZ]

Originally Posted by Woodstockz

Another chip to consider is the AD823. JFET input, High slew rate, Low noise, Low distortion. I have both, and both sound great. Easy to swap if you install a socket. The socket also prevents you from overheating the chip on installation.

I've put AD823's in two of my preamps to replace some 4558's in critical areas (gain stages, effects loop buffers, etc.). I like them a lot!

[Woodstockz]

Originally Posted by LowEZ

I've put AD823's in two of my preamps to replace some 4558's in critical areas (gain stages, effects loop buffers, etc.). I like them a lot!

I upgraded both my BA108 and BA110.

Funny, the schematics said that they were TL072s, but when I pulled the parts, they were 4558's.

[whitedk57]

Originally Posted by Woodstockz

Easy to swap if you install a socket. The socket also prevents you from overheating the chip on installation.

I haven't looked at the circuit board yet, but are you saying there are no sockets already installed on it? I thought I saw a close-up pic of the circuit on this board somewhere, and I thought I saw a socket. But my mind deceives me maybe.

So are there sockets already on the circuit board, and how many of these TL072s are there and need to be replaced?

[Woodstockz]

Originally Posted by whitedk57

I haven't looked at the circuit board yet, but are you saying there are no sockets already installed on it? I thought I saw a close-up pic of the circuit on this board somewhere, and I thought I saw a socket. But my mind deceives me maybe.

So are there sockets already on the circuit board, and how many of these TL072s are there and need to be replaced?

The circuit boards come stock with the 8 pin op-amp soldered in. There is only one op-amp and are no sockets in the factory circuit board.

The 8 pin op-amp has two amplifier sections. One section is used for pre-amp gain, the second section is used for the tone stack.

After de-soldering the factory 4558 opamp, [which was listed on the schematic as a TL072], I installed an 8 pin empty socket. Post number five shows the empty socked after it was soldered in, and the new op-amp is just pushed in after that. That way, it is easy to change op-amps, and you won't over heat the new op-amp when soldering.

The op-amp is also shown in post number 73. It is behind the volume pot. The dot from a sharpie is on the circuit board indicating pin #1. The op-amp has a circle at pin one which is adjacent to the dot on the circuit board.

You might consider the AD823. LowEZ mentions that he has replaced 4558's with AD823's and likes them as well.

[Woodstockz]

Originally Posted by Woodstockz

...

After de-soldering the factory 4558 opamp, [which was listed on the schematic as a TL072], I installed an 8 pin empty socket. Post number five shows the empty socked after it was soldered in, and the new op-amp is just pushed in after that. That way, it is easy to change op-amps, and you won't over heat the new op-amp when soldering.

...Snip

Correction. I just looked at the schematic. The schematic for the BA108 showed 4558's. Sorry Ampeg.

[tayal01]

Originally Posted by Woodstockz

The circuit boards come stock with the 8 pin op-amp soldered in. There is only one op-amp and are no sockets in the factory circuit board.

The 8 pin op-amp has two amplifier sections. One section is used for pre-amp gain, the second section is used for the tone stack.

After de-soldering the factory 4558 opamp, [which was listed on the schematic as a TL072], I installed an 8 pin empty socket. Post number five shows the empty socked after it was soldered in, and the new op-amp is just pushed in after that. That way, it is easy to change op-amps, and you won't over heat the new op-amp when soldering.

The op-amp is also shown in post number 73. It is behind the volume pot. The dot from a sharpie is on the circuit board indicating pin #1. The op-amp has a circle at pin one which is adjacent to the dot on the circuit board.

You might consider the AD823. LowEZ mentions that he has replaced 4558's with AD823's and likes them as well.

Ok. AD823 on order...

[40 Hz]

Does anyone know if there is a safe way to determine if this amp can be run at 4 ohms? I would like to hook up a different speaker to it, but don't want to stress the amp and burn up the output section if it isn't safe . Thanks.

[Woodstockz]

Originally Posted by 40 Hz

Does anyone know if there is a safe way to determine if this amp can be run at 4 ohms? I would like to hook up a different speaker to it, but don't want to stress the amp and burn up the output section if it isn't safe . Thanks.

Why do you want to go to 4 Ohms? Do you already have the speaker?

[JimmyM]

Originally Posted by 40 Hz

Does anyone know if there is a safe way to determine if this amp can be run at 4 ohms? I would like to hook up a different speaker to it, but don't want to stress the amp and burn up the output section if it isn't safe . Thanks.

That's exactly what will happen unless the protection circuit comes on and shuts you down entirely. If they could be safely run at 4 ohms, Ampeg would let you do it and tell you it's OK because that is a feature. So don't