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Messages - slimjohnny

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Amplifier Discussion / Re: Troubleshooting a 30W guitar amp i built
« on: April 15, 2020, 07:20:28 AM »
Thank you Phill, it does have two supply rails and I will isolate it.
But do you think that could be causing this problem?

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Amplifier Discussion / Troubleshooting a 30W guitar amp i built
« on: April 15, 2020, 05:54:55 AM »
I am having a big issue with the solid state guitar amp i built. The pre amplifier is from the dean markley k-20x and the power amp is the TDA2040 30W amplifier. I am reading 15.5 to 16 volts dc on the positive speaker output and -15.5 to -16 volts dc on the negative speaker output (those are my power supply voltages).
I have desoldered the jumper wire that connects the pre amplifier and power amplifier so i know the issue is there. I have also checked every single resistor and capacitor in the power amplifier and checked my board design again.
I noticed only the positive side TDA2040 appears to short and heat up and when i switched it for a new one and turned the amp on i was able to see the voltage quickly rise to those 15.5 volts on the oscilloscope(then it just stays on that value). Also when i desolder the shorted TDA only pins 4 and 5 (output and V+) check for continuity(these pins measure about 30M ohm on a brand new chip), and the rest of the pins seem okay. The negative side TDA2040 seems okay too.

I attached the power amp schematic below.

Id love to hear your opinion on this. This is for a final year project and im getting desperate.
I start to regret not having done a little arduino toy like the rest of the class instead of a real eletronics project.

P.S- I did not put any isolation between the chips and the heatsinks because I didnt think that would be a problem. Please tell me if it is. The two heatsinks are separate from each other and arent touching anything else.

Double P.S- Im using a 12-0-12V 80VA transformer with a BR356L rectifier and two 2200uF/25V capacitors as my power supply

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Schematics and Layouts / Re: Does A500 mean 500 ohms or 500k ohm
« on: October 11, 2019, 07:11:19 PM »
Thank you!

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Schematics and Layouts / Re: Does A500 mean 500 ohms or 500k ohm
« on: October 11, 2019, 01:50:15 PM »
Thank you for your advice.

So you think they meant 500 ohm in the scheamatic?

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Schematics and Layouts / Does A500 mean 500 ohms or 500k ohm
« on: October 11, 2019, 12:50:33 PM »
I found this cool preamp schematic that i would like to replicate

https://elektrotanya.com/dean_markley_k-20x_sch.pdf/download.html

But I don't know if the bass pot means 500 ohm or 500k because I didn't find 500 ohm log pots on ebay.
The mid and treble both have the K, so why wouldn't they put it in the bass one as well.

6
Thanks for the quick reply, how exactly would you move VR1 to the output?
And, although it may be unnecessary, how would you add the mid pot(i'm still unsure if I add it or not)

Edit: I just now noticed that this tone control system works differently than the marshall or fender ones, so never mind the mid pot

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I found this preamp circuit for a 30W solid state amp I want to build. The only problem is that it only has a 2 band tone control(bass and treble) and I would like to make it a 3 band tone control, the other problem is that it only has one gain knob,( they call it gain in the website but I'm not sure of they mean overdrive or just volume). Anyways I would like to have a volume and a distortion knob.

Here's the link to the circuit: http://www.zen22142.zen.co.uk/Circuits/Music/guitar_tc.htm



How would I make these changes?

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Preamps and Effects / Thanks
« on: September 11, 2019, 06:01:57 AM »
Yeah that makes sense, thank you for your reply it really cleared up things for me.

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Preamps and Effects / It's the Marshall mg15cdr
« on: September 11, 2019, 04:38:57 AM »
That's the preamp section of the amp, and to the right are the two ics.

Do all amps have this?, and why?

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Preamps and Effects / Do you need a low pass filter in your amp?
« on: September 10, 2019, 02:39:05 PM »
First off i'm a guitar (and amp for that matter) noob.

So i'm making a 30 watt solid state combo as my first amp and i've checked a lot of diy schematics and that gave me an idea on how mine is going to look like. All the schematics i saw were similar, preamp with tone controls and the poweramp. But then i started looking into schematics from marshall and the preamp had more two ICs than the other diy circuits so i did some research and those two IC's behave as a low pass filter.

Now that got me thinking: is the low pass filter really necessary when you already have controls over the frequecy(eq)?. Is it normal for amps to have this? And why did none of the diy schematics that i saw have this low pass filter?

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