circuit modifications in amps

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usernamename

New member
I want to mod an amp (toobs!). But I dont know what I'm doing and dont feel like taking an EE course.

I'm not touching the power amp, only the pre-amp.
I know not to touch things while the amp is on without covers (High voltage)
Is it safe to add/remove resistors and capacitors at random and not damage anything. Or are there rules to follow?
Antying else I should know to stop the deadly sound of sudden silence?
 
usernamename said:
Is it safe to add/remove resistors and capacitors at random and not damage anything. Or are there rules to follow?
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If you're trying to remove resistors and capacitors at random, you're going to run into some problems. There are of course rules to follow.

Some weirdo made a post a while ago with an introduction to tube preamp design, that may have some useful information for you. But perhaps if you could let us know what it is you're trying to accomplish, someone may be able to point you in the right direction.
 
Sounds like you want to circuit bend, but without any true aim as to what you want to achieve?

I'd at least source a schematic so you can tell which component belongs to which part of the circuit (eq, drive, volume, etc...) so you can swap caps to change filtering or the things that cause clipping.
 
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usernamename said:
Is it safe to add/remove resistors and capacitors at random and not damage anything. Or are there rules to follow?
Antying else I should know to stop the deadly sound of sudden silence?
Click to expand...
It isn’t safe and yes there is rules to follow. And there’s just plenty to know.

First amp I modded did good for 6 months, but went dead after fail in bias circuit which caused tubes to run too hot. There was first heat damage followed by socket arcing on pcb caused by tube failure. The amp sound was amazing just before failure. But back then I was just starting to understand circuit blocks and their function. Lesson learned!

1. Understand schematic and its relation to the build: https://robrobinette.com/Reading_Tube_Amp_Schematics.htm
2. Dive into understanding how amps work: https://robrobinette.com/How_Amps_Work.htm
3. Figure out what you want.
4. Look into possible tweaks: https://robrobinette.com/Generic_Tube_Amp_Mods.htm
5. Do all over again and then apply mods needed.
6. You have just one life, don’t electrocute yourself. It’s not cool.
 
Yeah, you have to have some sort of cursory understanding of the building blocks of a circuit in order to make meaningful modifications without it feeling like throwing darts blindfolded. Look up Wampler's course, he has some videos on youtube and his book is online for free download. It's enough to point you in the right direction without having to understand too much.
 
JohnnyCreepy said:
It isn’t safe and yes there is rules to follow. And there’s just plenty to know.

First amp I modded did good for 6 months, but went dead after fail in bias circuit which caused tubes to run too hot. There was first heat damage followed by socket arcing on pcb caused by tube failure. The amp sound was amazing just before failure. But back then I was just starting to understand circuit blocks and their function. Lesson learned!

1. Understand schematic and its relation to the build: https://robrobinette.com/Reading_Tube_Amp_Schematics.htm
2. Dive into understanding how amps work: https://robrobinette.com/How_Amps_Work.htm
3. Figure out what you want.
4. Look into possible tweaks: https://robrobinette.com/Generic_Tube_Amp_Mods.htm
5. Do all over again and then apply mods needed.
6. You have just one life, don’t electrocute yourself. It’s not cool.
Click to expand...
Daaaammnn a whole light show.
 
usernamename said:
The main thing i need to know are things "not to do".
What are the things that will damage components or get me into trouble some other way.
Click to expand...
bro.

please read the advice and explore the links provided. this is not something either of us can answer in a single sentence or paragraph.

as @JohnnyCreepy has linked, this website is no joke:

How Amps Work

How Tube Guitar Amplifiers Work
robrobinette.com
if you take the time to read and comprehend this, you may be able to begin to answer your query of knowing not only what not to do, but also how to effectively achieve whatever goals you have with regards to your modding endeavours.

having said that, if you do have a specific mod in mind, or something you are trying to do with a particular amp, it would probably be useful to elaborate on that.
 
usernamename said:
I want to mod an amp (toobs!). But I dont know what I'm doing and dont feel like taking an EE course.

I'm not touching the power amp, only the pre-amp.
I know not to touch things while the amp is on without covers (High voltage)
Is it safe to add/remove resistors and capacitors at random and not damage anything. Or are there rules to follow?
Antying else I should know to stop the deadly sound of sudden silence?
Click to expand...
Advice: don't.

You have no business being near lethal voltages.

It's clear you don't have a basic grasp of electronics, let alone the safety basics that prevent you, or anybody else who uses the amp down the track, from dying.

Tube preamps have the same lethal voltages that power amps do, and just turning the switch off isn't enough to guarantee your (or anybody elses) safety).
 
I quote drew.spriggs, don't try doing something you don't even understand . And if the amp is a tube one it can even kill you, and I'm not joking or exaggerating, there are hundreds of volts going on there, even when it's switched off sometimes.
 
Always wet your finger before touching the top of the first filter cap in series, it’s tradition.

If you don’t know what it means please don’t open an amp.

The not do list is massive. It can go from small bad smell to coffin pretty fast with all the shades of arcing and fuzzy insides in between very fast.
 
usernamename said:
The main thing i need to know are things "not to do".
Click to expand...
A quick summary:

1) Don't rush. You seem to be in a hurry to get in there and start poking around, and I think that is what is scaring people. "Tube amps can kill you" is not hyperbole. You can actually feasibly die.

We're not trying to gatekeep, obviously you can't learn how to work on amps if you never try working on amps, but if your goal is just to jump in and start circuit bending, I think the risks far outweigh the possible rewards.
 
vigilante398 said:
We're not trying to gatekeep, obviously you can't learn how to work on amps if you never try working on amps, but if your goal is just to jump in and start circuit bending, I think the risks far outweigh the possible rewards.
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This. There are quite a few kit and I would recommend starting with one. It doesn’t have some thing you never use, but building a kit while trying to understand signal / supply chains is a great way to get into it. As a bonus you’ll get a functioning amp at the end on top of the know how.

We are a few here that can help get you started slowly and somewhat safely. Rushing in blending blocks you don’t understand is not the way.
 
So BillM used to mod PCB boards on Fender Blues Jr amps all the time with a lot of success. He loved that amp for some reason (it's an awesome amp, but the squeeze maybe isn't worth the juice at the end of the day). Big difference with him is that he had a schematic of that amp and he understood what he was looking at and had a good understanding of the changes he wanted to make and what their effect would be on the amp itself. You can mod your own amp, but if you look at the schematic and don't know what it's doing, you will be lost ... and without a functioning amp. An amp circuit is like a cat's cradle, every component has downstream effects on other components. You can do this, but first you should do a mountain of research. What amp are you wanting to mod?
 
usernamename said:
The main thing i need to know are things "not to do".
Click to expand...
The biggest thing that can stop you from discovering new things is being afraid of the unknown. Everyone has different tastes in modifying circuits and will tell you not to do this or not to do that, based on their preferences and experience. The truth is you just have to try things out until you find what you like
 
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