Hey good lookin'! 😀
I have a Randall amp head that's in a less-than-solid state as the preamp circuit board's gotten itself some ugly burns (totally not my fault btw) and the traces no longer lead up to the tube sockets
I'm eager to learn and, since I'm building a preamp as part of my Music Tech assignment at uni, I thought I might as well get ahead of the game 😛
But I'm a newbie. So my first question is, will I have to mimic the previous circuit completely? Or in other words, how much personalization am I allowed to apply to it?
-Basti
I have a Randall amp head that's in a less-than-solid state as the preamp circuit board's gotten itself some ugly burns (totally not my fault btw) and the traces no longer lead up to the tube sockets
I'm eager to learn and, since I'm building a preamp as part of my Music Tech assignment at uni, I thought I might as well get ahead of the game 😛 But I'm a newbie. So my first question is, will I have to mimic the previous circuit completely? Or in other words, how much personalization am I allowed to apply to it?
-Basti
I think the easiest way would be to fix it first to working state and then you could modify it, if your not satisfied with sound.
I totally agree. This is where many inexperienced members go wrong. It's important to first get it working correctly before trying modifications. If problems crop up, and they quite often do, you won't know where you went wrong or how to sort them out. Planning and patience are the keys to success.
Once everything is back in working order, if you want to try some modification, it's important to do only one thing at a time, and document what you did. That way if or when something doesn't work as expected, you'll know what it was and how to fix it.
Mike
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I guess I didn't explain it properly...it's not working because the PCB itself got damaged rendering all of the connections to the 9 pins of the tube useless. I've contacted Randall but they don't have that board anymore so I figured I might as well do what I've been wanting to do and make my own (whether its a kit etc will be decided at a later date)
Okay, I'll post pictures as soon as I can. The question in my original post still stands though, if nothing else then just out of curiosity...
I think the OP wants to make a new one as part of his project, if I'm not mistaken. You should consider if you want to mod it later or not. If so, I would recommend not using a mass produced style board similar to the one in your Randall. It is much more challenging to solder on one of these, easier to burn the connection. Then you have the same problem you have now. See if you can find a mod-friendly board using turrets, eyelets or the like. Or at least a more robust trace board. If you can't find one, consider installing sockets for the op amps, ICs etc. Then you can change these without re-soldering. Remember,, if you use a mass produced style board, modding a discreet part requires three heatings of the connection, at the beginning, un-soldering and re-soldering the new part. Quite challenging for someone who is new at it. You will need to practice your soldering skills ahead of time.
The project will be separate. I'm conscious of the fact that I don't exactly know enough to build a preamp out of nothing so I'm going to humbly follow my course and learn from that. What I'd like to know is how much leighway I'd have (aside from the specifics of whether I want to make my own simple preamp, get a kit or what have you) given a pre-existing power amp and EQ circuit, to deviate from the original Randall preamp and all its components.
My take is that the previous advice is good. Build the preamp as it is designed and get that working. Then make one change at a time to see what it does, like increasing the plate resistor for more headroom or more distortion depending on what you want to do. Then make one more change if desired and see what it does. If you make many changes at the very beginning, it will be hard to figure out what is wrong if it doesn't perform how you want or if it doesn't work at all. If you follow this process then you will eventually be able to deviate quite a bit if you want.
Do you know how to make good layout? How to make grounding (star, bus, ground loops)? Potential problem with heaters hum? Proper decoupling etc. If you don´t know this, then get someone who knows or get some well documented preamp kit.
I know, yes, I'm a total noob but again, I didn't explain myself. Because I'm a total noob I'm more interested in the theory here. Would it be theoretically possible to build a separate preamp circuit and place it in an amp such as this one?
Theoretically, you could put almost any preamp on your amp that has the same wattage output tubes. For instance, if your amp has 6L6s then you could put almost any front end on it that has 6L6 or EL34 output tubes. The reason being you need enough signal gain to drive those tubes to full output(and beyond for power amp grind). Choose an amp who's sound you like with the same wattage output tubes and use that preamp. Of course, this is just a general guideline with many other possibilities, but it will get you in the ballpark.
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