Hello, I finally got a copy of the schematic for my amp scanned...here is a piece of it:
What I want to do is replace the auxillary volume pot with just a normal 1 meg pot and use an aux input as a separate channel. Next I want to put the master volume just after the plate of V1B. Would the master volume pot be the same? and would I just connect the mic volume output to the grid of V1B? Any suggestions would be helpful
What I want to do is replace the auxillary volume pot with just a normal 1 meg pot and use an aux input as a separate channel. Next I want to put the master volume just after the plate of V1B. Would the master volume pot be the same? and would I just connect the mic volume output to the grid of V1B? Any suggestions would be helpful
yeah, it is a Bogen CHB20A...do you have any suggestions about the stuff I proposed in the first post of the thread?
any suggestions abaout my proposed modifications? will my ideas work or are there any major flaws with my ideas? I dont want to start cutting and soldering only to find out I messed something up...
Hi 9am53,
What are you trying to accomplish? You need the extra gain V1a gives you for the mic. Are you trying to make a mixer?
From what you have said, I'd use the circuit as is. You can replace the AUX pot with a single 1Meg if you don't like the way it works now.
-Chris
What are you trying to accomplish? You need the extra gain V1a gives you for the mic. Are you trying to make a mixer?
From what you have said, I'd use the circuit as is. You can replace the AUX pot with a single 1Meg if you don't like the way it works now.
-Chris
Ok, I guess I could be more specific...I would just like to make a simple guitar amp...not a mixer of any sort. I was thinking I could use the mic channel as a "hotter" channel, and the aux channel as a quieter channel...but I have never done this before, so I have no clue if I can use the aux channel as a guitar channel...let alone what it would sound like. I dont really need the second channel at all, so I think I will start off with just the mic channel. Also, I read in an article "converting PA amps into Guitar amps" that the master volume should go after the second amp stage, that is why I want to move the master volume.
Hi 9am53,
You need high gain for both the mic and pickup. You do not want to move the master behind the tube because you are driving the tone control ciruit from there. It looks like you need to add a tube stage before that point.
-Chris
You need high gain for both the mic and pickup. You do not want to move the master behind the tube because you are driving the tone control ciruit from there. It looks like you need to add a tube stage before that point.
-Chris
Ohh I see, so I need a tube section before every individual circuit...ie, I cant have the tone circuit and a volume control next to each other without a tube section in between. Cool, thats not a problem at all. So from the sounds of it I just need to change my tone stack to be more suitable for guitar... Can I use the mic volume as a pre-amp volume? Speaking of which, can I keep the 1 Meg pots for the volume controls, or will I have to replace them? thanks for all your patience and help
Hi 9am53,
The best thing for you do do is check out a bunch of Fender schematics, Hiwatt or Marshall. Whatever. After looking at these I thing you'll have a very good idea on how to do this. You are on the right track. I forsee success in your future.
-Chris
The best thing for you do do is check out a bunch of Fender schematics, Hiwatt or Marshall. Whatever. After looking at these I thing you'll have a very good idea on how to do this. You are on the right track. I forsee success in your future.
-Chris
HAHA! Thank you oracle of anatech! I think I will take your advice, I will just look at some old champ and ga-5 schematics to get an idea of what they were like, they all had 3 tubes just like this amp, so I think I will be able to mimic what they did easily.
ok, I have been looking at some old schems, and some have the volume and tone between the 12ax7 stages, some have the tone after and volume between, does the placement of the volume and tone circuits have a big difference in tone? or should I just experiment and find out for myself? secondly the numbers associated with the pots are confusing. they have the resistance value along with other numbers and letters, are these parts numbers, or do they have electrical meanings?
Hi 9am53,
It depends on what else is going on in the circuit. The control represents a load. The output from the control is a variable impedance and it may be high mid way (linear pot).
Controls used were normally audio taper, reverse audio taper, log and linear. Some were tapped on top of that.
Volume or level controls were audio taper for the most part. Tone controls and mixing controls would be expected to be linear.
As with any circuit, try different ideas unless you are cloneing an amp.
-Chris
It depends on what else is going on in the circuit. The control represents a load. The output from the control is a variable impedance and it may be high mid way (linear pot).
Controls used were normally audio taper, reverse audio taper, log and linear. Some were tapped on top of that.
Volume or level controls were audio taper for the most part. Tone controls and mixing controls would be expected to be linear.
As with any circuit, try different ideas unless you are cloneing an amp.
-Chris
whats wrong with my circuit?
ok, so I did some recon work, and decided upon a simple arrangement, or so I thought. Here's what I did (to the cicuit whose schem is posted earlier). I completely got rid of the aux inputs and volume, and I got rid of the mic volume, so the signal went from the C2 capacitor through the R3/C3 pair and into the master volume. This didnt work, so I got rid of the R3/C3 and went straight from the C2 to the master volume. I have it hooked up to a turntable, and all I am getting is th same amount of volume that the turntable produces by itself, so its like its not amplifying at all, can anyone see any problems?😕
ok, so I did some recon work, and decided upon a simple arrangement, or so I thought. Here's what I did (to the cicuit whose schem is posted earlier). I completely got rid of the aux inputs and volume, and I got rid of the mic volume, so the signal went from the C2 capacitor through the R3/C3 pair and into the master volume. This didnt work, so I got rid of the R3/C3 and went straight from the C2 to the master volume. I have it hooked up to a turntable, and all I am getting is th same amount of volume that the turntable produces by itself, so its like its not amplifying at all, can anyone see any problems?😕
A lot of the signal gain in V1B is lost in the tone control circuit. You need to run through V1A as well. The aux inputs were high level on Bogen. It is possible you have a problem further along too.
-Chris
-Chris
yeah, I pluigged my turntyable into the auxilliary inputs before I did anything to see if it actaully worked, and it worked fine, it was just kind of quiet. I am running through the "mic" input, so the signal is going through V1A and B with just the cap and master volume in between...
thats the problem you see, as I mentioned before I am getting no volume, its the same volume that the turnbtable puts out on its own...can you see any problems with what I have done? should I change any components? or could it just be me messing something stupid up...?
or, could there be a problem with the V1A itself? does it ever happen that 1/2 a tube works and the other doesnt? I have checked it a number of times and I have all my grounds to ground, and my solder joints are ugly, but good...I cant think of any reason it wouldnt work...could it be that since I have eliminated some of the load between V1A and B I need a bigger resistor somewhere? I have no clue...grrr again😡 😡
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