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Messages - joecool85

Pages: [1] 2 3 ... 142
1
Schematics and Layouts / Re: signal tracing
« on: December 09, 2019, 01:57:35 PM »
Trying to repair a fender FM15 DSP that blows the F2 fuse. Trying to use an audio probe but can't read schematics. very well. Need to trace signal from input to out put. Can anyone help me? I also think the problem could be in the DSP board but not sure the schematic even shows it. Would like to know how to bypass it if possible.  This is a learning project for me so don't need to buy another amp Thanks.I

It shows the plug going to DSP.  I believe you can unplug this and use the amp without any DSP.  It's been a while since I've been inside my 25 DSP, but I think this is the case.

2
Amplifier Discussion / Re: Kay 708 amp repair
« on: August 19, 2019, 09:23:47 AM »
For some reason, your images were causing the threads to break.  SMF didn't agree with them.  I have removed the images causing the issue and turned on some features in SMF that should prevent this from happening again.  Sorry for the trouble, but welcome aboard!

3
Amplifier Discussion / Re: What Op Amp for 20W+ Busking Amp?
« on: August 12, 2019, 04:10:14 PM »
Thanks.  The OEP30w appears to be an excellent choice.   :tu:

It looks like at 12v you will only be getting 10w @ 8 ohm and 12w @ 4 ohm.  Still probably plenty, but beware.

4
Amplifier Discussion / Re: AMPEG B2R Problems-Help Please!
« on: August 12, 2019, 04:07:46 PM »
One time I was working on a Crate GX130c guitar amp and it was acting strange. Just as your amp it would turn on okay and then get a weird volume or crackle even then it would  start to drop the signal. Eventually it would shut down and turn back on by itself... All this happened within about 2 minutes. This would happen every time you turned on the amp. What I found was a 120 ohm 10 watt wire wound resistor was cooking up so hot that it was getting loose from trace or something. I don't think wire wound resistors typically get intermittent but this was the issue possibly. The wire wound cement was cracking and even though it read around 120 ohm cold it was heating up and loosing the battle, then the amp would shut off. Now these resistors on this amp would heat up anyhow, but after years of use it was toasted. I replaced all the wire wounds on the amp and it stopped that problem. The amp lives on now!

In your case this might not be what is happening exactly, but what is happening (very probable) is that some component is heating up too much. Each time it heats up something is loose inside and at that point the amp becomes unstable. When it starts to break up and act funny does tapping on the amp have any effect to bring the signal back momentarily? A cold solder joint is hard to detect but chopsticks help.

I had a very similar issue on a Vox I got cheap a while back.  Turned out the cement resistor had broken a leg (dropped amp?).  Sometimes it worked, sometimes it didn't.  I found the break and, being cheap, I soldered it to itself rather than replace.  It worked fine for a few years, then I sold the amp.  Still working as far as I know.

Regardless, sounds like a mechanical issue.

5
Amplifier Discussion / Re: Unicord Stage 65b Output Transistors
« on: June 13, 2019, 12:45:09 PM »
Ok mounted to chassis and so far so good. :dbtu:

Glad to hear it!  :tu:

6
Preamps and Effects / Re: Noisy EFF board from a Roland JC-120G
« on: April 16, 2019, 01:58:30 PM »
Sounds like the effects board is picking up and amplifying stray RF signals.  Is the board properly grounded?

7
Software / Re: DIY Layout Creator
« on: April 03, 2019, 10:42:52 AM »
Bringing this topic back from the dead as I just revived the software myself on my Linux box.  It still works great!  Thanks Bancika!

8
Amplifier Discussion / Re: Crate gx900h
« on: April 01, 2019, 03:04:18 PM »
Welcome aboard!  Regarding making it more reliable, not a whole lot you can do unless it is really old.  If that is the case, verify that grounding from the mains power input is there and is making a good contact.  You can also replace aging electrolytic power supply caps if they are very old.  Honestly though, it would have to be 30+ years old before I would consider recapping unless you were having issues with it.

Mostly, just enjoy!

9
Amplifier Discussion / Re: Help with Gallien-Krueger 200GT guitar amp
« on: February 28, 2019, 11:22:07 AM »
I have worked on this GK 200GT for a little too long and believe the 1976 "boat anchor" output transformer is bad. Rather than searching for a replacement, I would  like to replace the whole power amp board with a chip amp, either class AB or D. The problem I have, if it is actually a problem?, is that the preamp section which I like a lot, except for the "Current Limiter" pot, has a negative -8.7 vdc signal wire to the power amp board. Is that too much voltage and needing to be changed to a positive voltage before using a chip amp power board? I believe the preamp is working correctly but I am not sure because the schemo is hard for me to read and not sure if the signal from R85, the reverse 10k pot called "Current Limiter" is showing a negative voltage feed to the power amp? Review of the Owner's Manual shows that the Current Limiter function is to change the power output of the amp (I would just as soon remove it). Would anyone care to look at this and offer suggestions?  thanks

There shouldn't be any DC going to the power amp on the signal line.  If there is, something is wrong upstream.

10
Amplifier Discussion / Re: Trace Elliot Tramp 40w more gain in preamp mod?
« on: February 27, 2019, 03:18:49 PM »
I used a OD808 clone as a boost (with volume full and drive at min)

maybe if I stack another OD, like de OCD, or another mid or high gain, as boost too.
It could help to distort de amp?

thanks for replay! :tu:

Try winding up the drive on that OD808, I think you will be pleasantly surprised what it sounds like.

11
Amplifier Discussion / Re: Power transformer questions
« on: February 22, 2019, 02:09:23 PM »
I'd like to build a power amp somewhere in the range of 30-100 Watts running an 8 ohm cab. When it comes to building a +/- dual rail power supply, I am thinking I will need a center tapped secondary on the transformer.. (or is dual secondary coils better?? if so why?)

Does this transformer seem adequate? Under powered? Overkill??
What would be the maximum wattage amp one could safely build using this transformer?
https://www.digikey.ca/products/en?keywords=166M72

What models of transformers are others using for their power supplies, and what sort of wattages are they achieving??

I havn't messed around with transformers at all since a few labs 15+ years ago in college..  Know enough to not get myself killed, but don't want to waste a ton of money on the wrong transformers either..

I like to have 2x the VA rating as compared to the wattage at RMS.  IE, for your situation you would need a 60-200VA transformer.  The one you linked should be fine.  In this case, other than size and price, there isn't a problem with going larger.

12
The Newcomer's Forum / Re: Gear Suggestions
« on: January 15, 2019, 10:44:16 AM »
I suggest getting a Weller WLC100 station.  They are fantastic, reliable, inexpensive units and are used commercially in labs all around.  Typically they sell for $40 USD or so.  Regarding multimeter, I suggest a digital multimeter (referred to as a DMM).  I don't care for the "auto sensing" type, I like to adjust myself.  Brand isn't super important.  The one I use is a Craftsman because Sears had one on hand years ago and it fit the bill.  Higher end brands like Klein and Fluke are great if you can afford it, but not necessary.  Here is the cheap Craftsman I used for almost everything: https://www.amazon.com/Craftsman-34-82141-Digital-Multimeter-Functions/dp/B000X5TSUA

$20 and it gets the job done very well.

Past that the next thing I recommend is a "third hand" type of gizmo.  I use mine regularly and it's a real help.  You can get them all over the internet from very basic to very fancy.  I use this $5 one: http://smallbear-electronics.mybigcommerce.com/third-hand/

A silicone soldering matte is something I have been considering as it would keep my station clean.  I have one at work that I use mostly for keeping screws in place while tearing down laptops and such.  For $14, it's well worth it: https://www.amazon.com/SEASWAL-Soldering-Resistant-Electronics-Workbench/dp/B075F3C6J3

EDIT:
I forgot to add, make sure to get quality lead solder (I like Kester 60/40 in 0.031") and also some desoldering braid (sometimes called desoldering wick).  Thicker solder is harder to work with and mostly unnecessary for the small joints you will be working on.  I use leaded because it flows so well and withstands the test of time.  I do have lead free silver solder, and it works, but requires more heat and doesn't flow as cleanly.

Good luck!

13
Amplifier Discussion / Re: Happy New Year!
« on: January 10, 2019, 08:51:19 AM »
I'm glad to hear you are enjoying the site !  :tu:

14
Amplifier Discussion / Re: Hotone Nano Amp Heads
« on: January 08, 2019, 12:38:25 PM »
In which case they may sound a bit like my diy tda2003 amp so probably not worth my buying one. Looking for something to feed my diy 1x12 cab. At rhe moment I'm using various pedals with my diy amps and happy with that for now. I also play a lapsteel BTW.

Sent from my SM-G935F using Tapatalk

Just because they use a TDA2003 does not mean it will sound anything like your amp at all.  By definition, chip amps do not color the sound.  The "sound" of the amp is defined by the preamp.

15
Amplifier Discussion / Re: Grounding techniques
« on: January 02, 2019, 09:39:21 AM »
If you are having noise issues with the amplifier, I would look into why.

The power pack itself may be the issue, noise wise.

I agree, most likely it is the power pack that is causing the noise.  Sometimes this can be filtered by adding power caps inside the amp.

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