Adding line-in to B-100R?

[velo-hobo]

Or Effects Return or Power Amp In, whatever you wanna call it.

I've had one of these for about 13 years and just picked up a second one because I like it so much. I want to have the option of stacking them as a few others here have done.

I've tried using the line out of one into the input of the other, and it works pretty well, but setting up the controls can be tricky. Also, I'd rather not buy a buffered A/B or DI box if it can be accomplished with <$5 worth of parts.

I have almost never used the headphone jack in all the time I've had this amp, so I am thinking one could convert that jack location to a line-in, which would seem much more useful (effects loop, slave amp, etc).

I'm not an expert on electronics, but I tinker with amps and such quite a bit and it seems like it would be pretty simple to implement. Looking at the attached schematic, the preamp is in the top half of page one. Could one add a switching jack (and any necessary accompanying resistors and/or caps) after C21 and just before the Master Vol (extreme right side of the preamp diagram)?

This seems to be the logical location as it is in the same place as the tap for the line-out, and would allow you to control the output level of the slave amp with its MV while making all the gain and EQ adjustments on the primary amp.

Before I go monkeying with my amp, anyone have any informed opinions to contribute?

BTW, I also have a V4B and Hartke 3500 that I run into a 410-HLF, but I love the tone of the B100R so much that I want the option of playing louder gigs with it. I often play shows without PA support so it's a relevant factor to consider.

 

[RickenBoogie]

This is a case of, if you have to ask, it's over your head. best to find a qualified amp technician near you, and have it done safely and correctly. Good idea though, best of luck.

 

[velo-hobo]

That's a reasonably cautionary reply, but with all due respect I don't personally find it helpful. I've done recap jobs and other minor repairs on tube amps and have overhauled solid state devices and power supplies plenty enough times to feel confident modifying my B100R. The amp is long out of warranty so that's not an issue either.

I'm hoping that this thread will serve as a useful reference for other DIY types who are interested in the amp's possibilities. It's often mentioned that this amp lacks a line-in so I would like to foster a discussion on the smartest and simplest way to implement one.

Sure, I could pay my tech $100-$200 to figure it out but the amp itself isn't worth too much more than that. If I felt the need to go that route I might as well just use that money to invest in a good A/B box, but that still wouldn't accomplish what a line-in would do for the functional versatility of the amp.

 

[anderbass]

Hey cool idea velo-hobo, I've gigged my pair of B100r combos and always ran into drawbacks just like you.

I cant offer any tech help but I agree this would be the best method of chaining a pair of these combos.

 

[velo-hobo]

I took another glance at the schematic just now and realized some minor work would need to be done around the headphone jack connections as well, since plugging in to it mutes the speaker.

Looks like it accomplishes this by opening up the speaker's connection to ground, so a small jumper would do the trick.

Another thing I am seeing is that one could add a level control to the line out by replacing R31 with a pot wired as a variable resistor, possibly with a resistor wired in series to provide a ceiling for the signal level. Don't know where that knob would end up - I suppose it could go where the headphone jack is instead of a line-in jack.

I'm pretty busy with other repair projects but when I get the chance to delve into this some more, I will report what I find. In the meantime I'm hoping some knowledgeable folks will chime in with their ideas.

 

[Shadi]

Subscribed!

 

[billfitzmaurice]

Could one add a switching jack (and any necessary accompanying resistors and/or caps) after C21 and just before the Master Vol (extreme right side of the preamp diagram)?

Yes. I'd put an output jack post C21 on one amp, the master, and a normally closed jack pre C21 on the second, the slave, so that with nothing inserted it operates normally, with a jack inserted it bypasses to pre and takes the signal from the master amp. You'd retain separate master volumes.

 

[velo-hobo]

Yes. I'd put an output jack post C21 on one amp, the master, and a normally closed jack pre C21 on the second, the slave, so that with nothing inserted it operates normally, with a jack inserted it bypasses to pre and takes the signal from the master amp. You'd retain separate master volumes.

Do you think the existing line out as wired would be insufficient as a feed for the slave amp? Just asking as R31 is in series with the hot side of the existing jack. I'm assuming Ampeg put this in as a means of setting the output level of the line out jack. [edit: ok, I see why putting this before R31 makes sense: you want the slave amp to see the same signal it would be expecting from its own preamp]

Also, what is the reasoning behind putting the line in jack before C21 on the slave (instead of after C21)? I'm not clear on the function of C21 so maybe you could elaborate.

 

[lowend1]

Radial Big Shot ABY - I use it with my B100R/B50R stacked(and a Yamaha NE-1 parametric), and it makes it all work. Have you tried using the attenuated input? When I use my tube preamp in front of the B100R, that's where I go in.

 

[velo-hobo]

So, unrelated to the idea of this thread, my older B100R decided to start blowing fuses. I'll need to figure out what is shorting or pulling too much current in there and do some repair work before proceeding with the mods we've been discussing here.

 

[billfitzmaurice]

Also, what is the reasoning behind putting the line in jack before C21 on the slave (instead of after C21)? I'm not clear on the function of C21 so maybe you could elaborate.

C21 is an interstage coupling cap, to prevent DC flow to the next stage. If you put the insert post C21 you'd want to do so with a cap, the same size as C21, to serve the same function.

 

[beans-on-toast]

I've tried using the line out of one into the input of the other, and it works pretty well, but setting up the controls can be tricky. Also, I'd rather not buy a buffered A/B or DI box if it can be accomplished with <$5 worth of parts.

Rather than run the line out to the input of the other amp, you can use an instrument cable and run from the -15db input on the amp you are plugging your instrument into to the 0db input of the second (slave) amp. Set the tone controls the same on both amps. Adjust the volumes to balance. Worth a try since no modifications are involved to see how it sounds.

 

[velo-hobo]

Bit of a Zombie Thread here, but I started it originally and I finally got my broken B100R fixed up and did the line-in mod, so I feel reviving this one is appropriate. Sorry for the long delay if you were following the thread, it's been a busy year for me and this wasn't a front-burner project.

On the slave amp, I took out the headphone jack and put a jumper across the upper two solder pads (normally the speaker ground runs through a switch on the phone jack - plugging into the jack breaks the speaker ground connection).

The new jack in the photo is actually a transfer switch (that's all my local electronics supplier had in stock at the time) but a regular tip-shunt jack like a switchcraft 12A is all that is required. I am not using the normally open terminal on the tip switch in this mod.

The tip switch is located between C21 and the MV.

I took C21 off the board, soldered it in series with the normally-closed side of the tip shunt, and ran the green wire back to the solder pad where the pre-amp side of that coupling cap would normally be. The red wire goes from the jack tip to the outer lug of the MV pot.

So when nothing is plugged into the slave/line-in jack, the amp circuit works normally. Plugging in disconnects the preamp from the power amp.

I did this because I also had tried simply connecting the line-out jacks of both amps, but the slave amp sounded dull and muffled - I think due to the preamp circuit loading down the signal (allowing high frequencies to bleed to ground through the pots etc.)

I left the master amp alone, and it seems to work very well this way. Each amp retains separate Master Volume controls, but the gain and tone controls are confined to the master amp panel. There is a 1K resistor on the stock line-out, but I don't notice any real difference in signal quality or level between the master and slave.

[If it was an issue, I could install another jack on the master which would bypass this, or replace the resistor with a pot wired as a variable resistor for setting the line-out level. That could go in the headphone jack location on the chassis - possibly another useful mod for other applications.]

The two amps definitely sound bigger and fatter together than a single B100R, yet they still retain their presence and punchy quality. I would say this is better than a B200R, which I've also owned. Same overall power, but with tighter cabs and two 15s for moving more air! Another advantage is the bottom one can couple to the floor and the top one cuts across for better projection/stage monitoring.

I've been rehearsing and gigging with this setup for about a week and it seems pretty solid and useful. I'm about to go on tour and am planning on using this rig. The advantage I see over bringing one bigger amp is that I can use a single amp in smaller rooms, or in places that have big PA support, plus I have a backup should one of them burn up on the road.

 

[anderbass]

Cool mod, nice job!

 

[velo-hobo]

Wanted to re-awaken the zombie with one last update. The slave mod held up perfectly for a recent month-long tour which included 4 days recording a full-length album.

The amps did great in the studio, as we were able to use two different (yet complimentary) mics on the two cabs, found a nice balance and just printed them as one track to simplify mixing (we recorded to tape on a console with no automation).

In venues with no monitors, I was able to turn one amp slightly towards the drummer to give him some side fill, but keep the other facing frontwards for projection out into the audience.

Another thing which worked out really well was that we played 3 or 4 impromptu gigs with no PA support whatsoever, so we just used one of my amps as a vocal amp. The EQ was versatile enough to dial in a loud-enough and useful vocal tone in a bunch of different kinds of rooms.

 

[anderbass]

Awesome, I've never once used headphones with either of my B100R's, but I'd imagine some people do.

I think Ampeg shoulda offered a choice/option between having a line-in jack like yours instead of a headphone jack. Or better yet, It prolly would of only added a few bucks to the original purchase price to of installed both at the factory...

If Ampeg ever re-issues this very cool little combo, (like they should!) I think they should just go ahead and instal an effects-loop, + a headphone jack.

 

[SJamon]

Hi there,

I'm reviving this old thread because I'd like to do something similar although a little different, and you guys might be able to help.

Basically instead of using the line out on the master amp I'd modify it too to pick-up the signal post master. That would leave me the possibility to daisy chain the amps and use the line out at the same time, plus I'd control the volume of both amps with a single master pot.
Of course on the slave amp I'd input the signal post master.

Is it as simple as wiring jack sockets in parallel to the original signal chain post master on both amps (with a switching jack on the slave amp to decouple it's own preamp), or is there more to it ?