Hi all, new to the board, new in general: I have diy Qs

Recording Techniques, People Skills, Gear, Recording Spaces, Computers, and DIY

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Tavvish
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Hi all, new to the board, new in general: I have diy Qs

Post by Tavvish » Tue Jan 24, 2012 11:21 pm

unnecessarily long introduction (questions below):
Hi everyone, I have been getting tape op for the last few years, it is an amazing mag even for a someone like me who is very slowly getting into recording, I have also lurked the board for long time and have found it very useful for info, for whatever reason I haven't joined until today.

I don't know much about electronics at all but over the years have been really interested in learning (especially since I have gear I want to mod and gear that needs fixing) I have done a little tinkering (I've made a couple slinky spring reverbs, adjusted trim pots on pedals, shorted circuits on radios/keyboards to make them do weird things) but basically I know nothing and have millions of questions (I'll ask only a few in this post). Recently I was lucky enough to get a job I am absolutely not qualified to do: build auto pilots/ other things for boats. My boss is basically taking me under his wing because he is awesome and probably considers it charity. I have only been working there for about a week but have already gotten a good amount of practice soldering.

Questions:

What does recapping do exactly? Why is this what most people do when they get older gear that needs or could use tinkering? I don't know how capacitors affect the sound of gear.

I have a couple old (and awesome) casio mini keyboards that would basically be considered toys ( I consider them beautiful instruments) all of them have distorted outputs and they are only getting worse (I have to keep the volume really low when sending the signal out) how do you remedy this? what component(s) are most likely failing?

I also have a couple of those old dbx compressors (119 and 117) They are both messed up (can barely hear the signal they have a BUNCH of hum not sure what is up with them)... I'm sure I'll ask how to fix them later. I have the manual for the 117 and it says to mod the compression ratio so it can go to infinity I would have to short out a resistor on the circuit board, the only shorting of circuits I have done is the find 2 solder points and put something metal in between them type of shorting. How do you short out just one component (in this case a resistor)? I realize this is probably a stupid question, I really know nothing.

Can anyone point me in the direction of good/actually cool beginners projects?

Words of wisdom?

That is all for now!
-Tavish

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RodC
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Post by RodC » Wed Jan 25, 2012 5:07 am

Welcome to the board.

Re-capping is replacing all the capacitors in a piece of equipment that tend to degrade over time, mostly the electrolytics. When they go bad in the powersupply, you get bad ripply DC that leads to 60Hz hum. If they go bad and are in the signal chain various other issues occur, loss signal in the lows sometimes highs, and even distortion.

Im not an expert on the keyboards, but I would start studying the output sections. Start by making sure the connection is good and that there are no bad solder joints around it. There is prob an IC that drives the output and maybe a coupling cap, I would suspect those first.

Comps can be fun to work on, my best advice is to learn how to use a signal tracer, use this to identify which portion of the circuit is causing the distortion.

Maybe others here have worked on these exact models and can throw in some advice.

Good luck, and start by learning some safety practices.
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ckeene
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Post by ckeene » Wed Jan 25, 2012 5:21 am

You can short out a resistor by soldering one leg of a single-pole/single throw switch to one side of the resistor, and soldering the other switch leg to the other side of the resistor.

When the switch is on, current will flow thru the switch: the path of least resistance. So that's a short circuit. Note that in electronics, a "short" can also mean a fault situation where current is flowing to ground unintentionally, and bypassing the rest of the circuit.

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Scodiddly
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Post by Scodiddly » Wed Jan 25, 2012 6:10 am

Safety first!

Electrolytic (and also tantalum) caps can go bad over time, often not in obvious ways. These are the can-shaped things, usually the ends are metal and one side is marked with a minus sign (they have to be connected correctly or they can blow up!).

Resistors can also go bad, though it's much less common in gear from the last 30-40 years. Old tube amps would be more likely for bad resistors, though it can happen even in modern gear due to abuse or poor design. If you put an ohmmeter on a resistor in circuit (never with the power on!), it can read lower than the actual value because of the other components around it. But since resistors almost always go bad by drifting higher in resistance, you can measure for resistors that measure higher than marked.

Tavvish
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Post by Tavvish » Wed Jan 25, 2012 3:38 pm

ckeene wrote:You can short out a resistor by soldering one leg of a single-pole/single throw switch to one side of the resistor, and soldering the other switch leg to the other side of the resistor.

When the switch is on, current will flow thru the switch: the path of least resistance. So that's a short circuit. Note that in electronics, a "short" can also mean a fault situation where current is flowing to ground unintentionally, and bypassing the rest of the circuit.
So basically you can solder a switch onto the two solder points of the resistor? How about a wire from one leg to the other? I wouldn't need an on off feature.

Tavvish
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Post by Tavvish » Wed Jan 25, 2012 3:47 pm

RodC wrote:Welcome to the board.

Re-capping is replacing all the capacitors in a piece of equipment that tend to degrade over time, mostly the electrolytics. When they go bad in the powersupply, you get bad ripply DC that leads to 60Hz hum. If they go bad and are in the signal chain various other issues occur, loss signal in the lows sometimes highs, and even distortion.
On my compressors I can hear a signal coming through but mainly it is just a loud hum. Is it possible that it could just be bad caps? I'm hoping all these need is a recap (probably isn't the case), I think I'm capable of doing that at this point, I know what the look like, I know how to identify which caps I need and by looking I'll know where the pos and negative belong. I should probably just do a recap and see if there is much a difference.

I already love being around the guts of electronic stuff, it's frustrating not knowing how it all works.

Tavvish
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Joined: Tue Jan 24, 2012 10:25 pm

Post by Tavvish » Wed Jan 25, 2012 3:54 pm

As for safety I'm definitely going to read up on it, and I'm definitely not plugging anything into a wall while I work on it till I know what I'm doing.

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RodC
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Post by RodC » Wed Jan 25, 2012 4:02 pm

Tavvish wrote:
RodC wrote:Welcome to the board.

Re-capping is replacing all the capacitors in a piece of equipment that tend to degrade over time, mostly the electrolytics. When they go bad in the powersupply, you get bad ripply DC that leads to 60Hz hum. If they go bad and are in the signal chain various other issues occur, loss signal in the lows sometimes highs, and even distortion.
On my compressors I can hear a signal coming through but mainly it is just a loud hum. Is it possible that it could just be bad caps? I'm hoping all these need is a recap (probably isn't the case), I think I'm capable of doing that at this point, I know what the look like, I know how to identify which caps I need and by looking I'll know where the pos and negative belong. I should probably just do a recap and see if there is much a difference.

I already love being around the guts of electronic stuff, it's frustrating not knowing how it all works.
Its possible, but I would suspect a bad connection. Its hard to diagnose over the interweb. You just have to start at the beginning and trace the signal through it.

What does it sound like if you push the bypass switch? If its true bypass, and it still doesn't pass signal, then check the jacks and the bypass switch.
'Well, I've been to one world fair, a picnic, and a rodeo, and that's the stupidest thing I ever heard come over a set of earphones'

http://www.beyondsanityproductions.com
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