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Bogen chb100 input conversion suggestions

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Hi all. New to the board. Great site.

I just purchased a Bogen chb100. After I go through the amp in terms of maint, I was wanting to change the inputs to accomodate a harp, 1/4' speaker jacks, 1/4" instrument jacks and a line out to run a signal into another head to run monitors.

What would be your suggestions on this? I am going to use this head to run my mains at smaller gigs BUT I would also like to use it for harp (I am not planning to modify it in any way for harp so input considerations only) AND vocals at the same time if possible.

Just some background on me. I have built several tube amps-just never worked around a PA head before. So far, they look extremely similar BUT I also know that there are always secrets for every application.


Thanks in advance.
 
Thanks for the reply. MANY artists played harp through these exact type PA's so that was my thought.

I am more concerned with the line out or line ins than I am about the harp.

I am not quite sure about what you mean "treat it like a Twin". This is not going to be a harp amp or guitar amp. I want it to be a PA head for mains and two mics-one for vocals and one for harp. I want a line out to run a signal into another powered mixer to run the monitors.

Am I crazy to think this set up will work or ???

Thanks
 
Not doing a full-blown conversion to a harp or guitar amp is a waste of a good CHB in my opinion. 1/4" jacks are easy, drill out the rivets and desolder the old jacks, then mount the new 1/4" jacks (insulate them from the chassis) and solder the old wires to the jacks. Your "line out" seems like a waste of time because you're not going to be able to run this amp without a speaker load anyway. I have a schematic for this amp and it's a very uncomplicated circuit that suits a full-blown guitar conversion very well, and not a whole lot else.

I'd suggest something like a seperate preamp and power amp, it would work a lot better for your purposes. Actually, I've been considering a CHB for my next guitar amp project (I've done a Bogen M60A), I could give you some cash for it and you could buy something more suited to your needs.

-Darren
 
Thanks for the reply.

I guess I am not understanding your waste of time comments. This is a PA amp as designed right? As well, these old amps, as stock, were thhe foundation of MANY old harp players. A line out is absolutely necessary for doing what I want to do...unless you think there is not enough power in this unit to run a set of mains.

More thoughts please..

Thx
 
I understand a load is required. A line out, in my opinion, is NOT the same as a speaker extension-which seems to be what is continually being mentioned.

I would like, if possible, to have a lineout, as in preamplication, to go to another mixer. If not, at least a line in that is padded to accept a line out from another mixer.

I really do not care which way I hook up the two PA heads.

Am I just not being clear on my thoughte here or ????

Thanks.
 
You would have to stuff a whole new stage in the head to get your line out option. We continue to describe things as speaker extension because that is what you will get, and you don't want that obviously. The pre-amp stage is after the volume pot, hence your problem. It isn't as simple as moving a few wires around.

You can drive it just fine from a mixer. Nothing mods necessary. Between the volume pot on the head, and the fader on the mixer, no need to fuss with padding anything.

You are being very clear, we are just not so successful in convincing you that you can't get what you describe. Anyway, you will be happy driving the head from a mixer.
 
OK. Thank you for the clarity.

So, are you saying that I need to create a 1/4" input jack, insulated from the chassis, that ties in directly to the Bogen's Master volume pot-much like the Aux 1 and Aux 2 are wired i.e. utilizing that stock Aux input section of the schematic, by passing the pre amp stage that the mic channels utilize, running a patch from the other mixer/amp's line out to the newly created input on the Bogen.

Is that accurate? No considerations to deal with on the input jack for the Bogen in terms of reistors or anything else?

If so, that is great and very easy. As well, it allow me to also create an input for harp from one of the mic channels.

Here is a schem by the way for reference:

http://www.bogen.com/support/discontinued/pdfs/CHB100m.PDF

Thank you
 
My BOGEN CHB100

Hi, I'm new to this site as well...

So... my father passed away not too long ago..
I recently had a chance to go through some of his old stuff.

I found this Bogen Amplifier at his house in the basement the other day.
it's really beat up, and dirty! but curious, I brought it home and took apart
the chassis and decided to take a few pics.. Any ideas? I figure this will be a
good project to try my hand at fixing up an old amp (since it's already old and
busted anyway!) and perhaps maybe it'll be a nice unit (if I do decide to fix it up),
but will also have some kind of sentimental value too.


SLIDESHOW LINK
http://Bogen%20Tube%20Amp/?action=view&current=7355f81e.pbw

PDF MANUAL
http://www.bogen.com/support/discontinued/pdfs/CHB100m.PDF

SCHEMATIC
http://www.diycustomamps.com/images/schematics/Bogen_chb100.gif
 
For a line out,couldn't you just use a resistor divider right off of the speaker output?
Set the resistor values so that you get about 2Vpp at a "loud volume" and go with it ?

Tube amps don't like to be run without a load,as mentioned,so you will need a speaker,or a dummy load (aka a "powersoak" IIRC) connected to the output anyways.

The Bogen M-120 (?) I have had a similar setup for a "tape out" connection..just a voltage divider on the output.

As a rough start,try a 47k and 470k resistor in series,from output to ground.Take the "line out" from teh center of he two resistors,and ground. This will give you a 10:1 reduction in output.

Edit: I should add the 470K resistor goes to the speaker output to the center of the two resistors,then the 47K goes from the center to ground. the 47K resistor will set your line-output impedance at 47K,which is fairly standard.

Something similar is shown in the schematic above:
http://www.diycustomamps.com/images/schematics/Bogen_chb100.gif
Note the 39K and 10K resistors on the output.
 
HEy guys. I have this amp and tried revamping it a bit. A basic recap, and adding 1/4" connectors. Unfortunately I am color blind and got a resistor value wrong for one that was broken, so I had to put it away awhile until I got the right resistors. I didn't take a pic, and I lost track of what went where!

Schematic

Now it's a bit of a mess. I found some schematic online, but it's a bit blurry, and I think it's a little different anyway. Mine has a couple 100 uf caps in the power supply, and the schematic I have doesn't. I've seen pics of someone elses too that has 100s.

pics

Does anyone here have a schematic for this version of it, or maybe some closeup high res pics of the PSU section I could look at? Thanks!
 
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