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March 28, 2024, 08:53:20 AM

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#1
Amplifier Discussion / FM212r burnt resistor/distorti...
Last post by sd22 - March 27, 2024, 09:17:23 AM
I have a Fender 212r that isnt worth much, but I am trying to repair as a hobby. I am looking to get into projects after taking some previous circuits classes but I'm stumped. The amp works, but through the clean channel I have some background distortion. The distortion channels have separate tone and are fine/unnoticeable. The speakers seem to be fine too. This amp is usually pretty clean but doesn't have that same sound anymore.

I took it apart and found that R84 was on its way out, 470ohm resistor burning and increased in resistance to upper 500ohms. The increased resistance could be forcing more power into other portions causing that breakup but that might be completely wrong. I tried checking some of the transistors and diodes around to see if there was an issue surrounding that, but I didn't find anything conclusive. I'm hoping to get some advise on some places to double check for a source for the excess power flow since a bad resistor likely is due to something else going wrong. I plan to replace the resistor obviously along with any shorted transistors or whatever else I find.

Line diagram linked
https://pub.deadnet.se/Manuals/ciasteczkowypotwor/%23pro_audio/Inne/frontman_212r_sch.pdf
#2
Amplifier Discussion / Re: Heatsinks for your poweram...
Last post by JonnyDeth - March 26, 2024, 04:34:51 PM
I have a decent sized collection of heat sinks, but what I pulled out of my Beowolf projector that some criminal destroyed was a rather startling piece of salvage. It has a "heat pipe" too big to even adapt over to a CPU!
This for people that don't know, is a water cooled heat sink that's passive. The internal chambers and ducting use infinite distillation so the coolant rises to the outermost pipes from the core point where it's encountering the source of heat and was vaporized, is cooled quickly through the thermal process moving air, recondenses and runs back down to the core of the system again and whatever the device is that's generating all the heat.

The one out of that projector is absolutely massive so when I get a project that calls for it, I'm going to be all excited I discovered and saved it lol.
#3
Amplifier Discussion / Re: Watts vs Volume (db)
Last post by JonnyDeth - March 26, 2024, 04:22:59 PM
Quote from: saturated on March 26, 2024, 02:34:14 PM
Quote from: g1 on April 05, 2014, 01:37:52 PMIn car audio competitions you measure SPL.  Does a given system with a 200W amp sound twice as loud as the same system with a 100W amp?


I got tickled when I read this  :) as much as I groan when I hear them thumpers driving by I am intrigued by the idea of a contest which I presume the goal is to be the loudest?

If so I think I will keep an eye out for any local event like that it would be fun to watch
 8)

That question is why you really want to understand what VAR is, how to calculate the capacitor for your selected speaker, and then run tests using a sine wave @100 Hz to see how many VAR/Watts it actually sees from that amplifier, probably 10 Khz or at least around 6 to 7 too.

The kid that set the original world record that's since been broken used a specific series of pioneer subwoofer and that series of subwoofer amplifier. Pioneer spared no expense and recruited a degree bearing engineer and techs to design the entire line. They designed the amps so what they produced @1 Khz was also the same as they produced @100 Hz as well as all the way down to 25 Hz, this is why VAR is actually a critical detail when it comes to how much volume you can expect from the lows, mids and highs of a particular woofer and amplifier set, and what is the quality also going to be like.

A speaker whose resonance Q ranges down to 100Hz and still sees 75% of the VAR/watts it will see at 1 Khz will be an absolute monster, even if it's only rated for 90dB rather than 100. The dB sensitivity is still generated by 1-watt @1 meter, so it's not the critically defining feature to how much volume it's ultimately going to produce. It's just a test produce for reference when you're speaker shopping. If it's 110dB vs 95dB, but the 95dB speaker handles 5x the wattage, it's generally going to be louder than the one rated at 110dB when you max their wattage, but it won't be obscene when you compare them, and it's also likely to be better quality in sound fidelity.

I don't have extremely deep interest in car audio, but I do like having a competition class subwoofer in the trunk of my vehicle. My focus for audio engineering will always be focused on music equipment, but also when it comes to signal processing technology, that's going to include car too. I have some rather clever ideas for subwoofer crossovers that will give you brutal volume and thump out of a cheap ass subwoofer and amplifier that I've used in the past. When I finally moved to a competition subwoofer and much stronger power amplifier, it was significantly louder, but only about 20% with a significant amount of rumble. The cheapo was still only about $80 total investment excluding the enclosure I built, and the competition one setup was about $350! It was definitely worth it, but it also wasn't an obscenely dominating increase in performance. I've also been through 3 competitions subwoofers since that one after accidently frying it and having to buy 2 more is what was obscene.
#4
The Newcomer's Forum / Re: saturated's all encompassi...
Last post by saturated - March 26, 2024, 03:11:42 PM
Thank you sir.

Btw had to put up a sign

Sign sign... everywhere a sign

You cannot view this attachment.

 :P

Not sure what happens if I try to measure resistance on a live circuit  ::)
#5
Amplifier Discussion / Re: Watts vs Volume (db)
Last post by saturated - March 26, 2024, 02:34:14 PM
Quote from: g1 on April 05, 2014, 01:37:52 PMIn car audio competitions you measure SPL.  Does a given system with a 200W amp sound twice as loud as the same system with a 100W amp?


I got tickled when I read this  :) as much as I groan when I hear them thumpers driving by I am intrigued by the idea of a contest which I presume the goal is to be the loudest?

If so I think I will keep an eye out for any local event like that it would be fun to watch
 8)
#6
Preamps and Effects / Re: what exactly is a preamp
Last post by JonnyDeth - March 26, 2024, 01:53:15 PM
The best way to regard a preamp is as a SSA; Small Signal Amplifier which is the technical term. It gives a small amount of amplification to the device used to directly produce sound, and has some amount of control over altering the signal, even if it's just a single knob.

In reality, every pedal on a pedal board is a preamp and then your guitar amplifier itself will have a preamp with a power amplifier in it. They pre-amplify the signal before being sent to a power amplifier. They are also conditioning your signal in such a way that it will potentially be in much better condition for the power amp to have stability and evenness in it's performance of power amplification.
It may even only provide unity gain, which means a factor of 1x, and balance impedance for the sound source it is specifically designed for.
A preamp is also regarded as an "addition/subtraction" stage of signal amplification; features of the signal directly created by the sound source are both added and taken away.
#7
Preamps and Effects / Re: Solid state preamp with to...
Last post by JonnyDeth - March 26, 2024, 01:45:37 PM
The Dr Boogey is probably exactly what you're after. It's someone's solid state pedal version of a Mesa Boogie which are generally wicked metal amps, and you can choose from a variety of general stomp boxes to stick in front of it and "sludge" it up.
https://www.taydaelectronics.com/pcb/diy-guitar-effects/mesa-boogie-distortion-diy-pcb-guitar-effect.html

My bet is the Big Muff Pi or even a tube screamer coupled with the flexibility of the Dr. Boogey will do just about any sound you're after. If not one of those pedals in front, something sludgy and truly "awful" but notoriously popular would be a fuzz face, but fuzz faces are low impedance input and biased completely wrong, so they're a crude form of a Class A-B circuit stealing input bias voltage from your guitars signal, and don't always do so well stacked with other boxes. Now with all that said, they do however give you a very rich, high gain and sludgy fuzz style distortion and can be modded easily enough to be more flexible.

#8
Amplifier Discussion / Re: Watts vs Volume (db)
Last post by JonnyDeth - March 25, 2024, 04:22:02 PM
Quote from: g1 on March 20, 2024, 08:39:30 PM
Quote from: JonnyDeth on March 20, 2024, 02:56:58 PMWell, looks like I wasted all that time going to college for electrical engineering, thanks for the clarification  ::)
If you can't apply it, I guess you did.
Amplifiers are rated into resistive loads to take reactive power out of the equation. 
Note that I specified amplifiers in my earlier comment to exclude what you said about speakers.

When one walks into a new room, it's best not to have the flamethrower on and start out with the idea that everyone else has it wrong.

Get a grip, you're the one being rude. The thread is about wattage, dB and output of a combined devices and how they relate to one another.
What I said is absolutely critical, and I was simply offering some factual information that is helpful based on the entire purpose of the thread from the OP. I wasn't rude, and I wasn't condescending, I just made a point, and you had an immature reaction twice over now. You literally tried to crybully me and I'm not interested. I'm under the impression I already need to be prepared to block you after that immature harassment.

VAR is what truly matters unless you're operating at a single frequency. Not all companies test their amplifiers the same way, but those that do it correctly will test it into an RLC tank circuit, or at least, an LC circuit. If they have built something truly special, they will test it with an LC circuit for 100 Hz, 1000 Hz and 10,000 Hz and they will also test it with sweep going from 100 Hz to 10,000 Hz.

So, any given amplifiers selected at random won't necessarily perform as well at 100 Hz as they do at 1 Khz.

Typically, the further you stray from a 1000 Hz sine wave in frequency, the worse the amplifier will perform in it's production of VAR, and for general purposes, we can use the 3 fixed frequency points defined by factors/divisors of 10 in the >< connotation of 1000 Hz, and regard VAR as watts.
An amp screaming loud with 100 watts @1 Khz may only push 20 watts at 100 Hz, and thus the owner is grossly dissatisfied with it's performance. Now a lot of amp manufacturers will produce a design that is so effective, but there are some out there that will produce nearly the same wattage at 100 Hz as they do at 1 Khz and 10 Khz. These are often used in the subwoofer competition industry and when a brand really wants to make an impact, they will produce test data for those 3 frequency points, design a speaker specifically for a selected frequency point, and that amp and speaker in combination will be at resonance producing the spec'd wattage because the manufacturer took a lot of pride in it's design.

You can always do the math using your desired speaker and run the tests yourself after calculating the necessary capacitor value to see what you get at 100, 1000 and 10,000 Hz.
#9
Amplifier Discussion / Re: SZ13C zener replacement fo...
Last post by saturated - March 25, 2024, 01:52:22 PM
That is some very nice work congrats  8)

Beautiful amp thanks for the pics  :)
#10
Amplifier Discussion / Re: Acoustic 134 reverb
Last post by Pete - March 25, 2024, 01:10:34 PM
Thanks, really appreciate the input and suggestions. I'm not trying to keep the amp close to original. Just want it to be working and useful.

Some comments/questions on your suggestions:

1. Why so important to keep the power resistors so close to PCB/power transistors? Will moving them 10" away, with robust conductors, really cause a problem?

2. The 4 output transistors mounted on the chassis (2N3055) don't seem to get very hot, so not sure if I need to move them. (It's the 40410 transistor and the 2 power resistors that seem to be generating most of the heat.)

3. What's the advantage of putting a speed control on vent fan? Maybe just a 120v disc thermostat?