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Messages - incurably_optimistic

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Amplifier Discussion / Re: Hartke B90 - disappearing sound
« on: November 23, 2016, 05:46:38 PM »
Turns out there's a problem with the preamp - I finally got it to cut off after more than an hour of injecting 440Hz, 1000Hz and 2000Hz sine wave, and also playing a guitar through a fuzz with the controls maxed out - I thought it was never going to shut off and that this problem can only be encountered while rehearsing, but the output cut off eventually. I had to attach a big heatsink to the 100W resistor and use a fan to avoid ovearheating and smoke (the transistors' heatsink barely got warm during the process).

I probed the pre-amp output and there was nothing there. To be absolutely sure, I plugged the guitar cord from the preamp out to another amp, and there was no sound.

I'll probe the whole audio path later, but the problem with troubleshooting this thing is that the pattern seems totally random - one day you can jam on the thing with the volume at full for 3 hours without breaking a sweat, the other day it shuts off after 15 minutes. I couldn't get it to shut off again after it happened once today, so I gave up for tonight.

Amplifier Discussion / Re: Hartke B90 - disappearing sound
« on: November 20, 2016, 10:57:50 AM » this is the best thing I could find about this oscilloscope.

Yeah, I've already used it many times - it's controls are so simple you don't really need a manual to figure out how this works.
Obviously it may not be the greatest oscilloscope out there, but I cannot afford a good digital oscilloscope (let alone the really cool ones I've been using at my university), and for audio purposes it covers most of my needs so it's all good.

Anyway, I'm waiting for the 100W resistor and I'll report back with measurements once I get it.
Oh, and my friend just gave me a messed up Fender Frontman 212R, so I guess I'll start another thread for this one :loco

Amplifier Discussion / Re: Hartke B90 - disappearing sound
« on: November 18, 2016, 06:07:00 PM »
Thank you!
I sourced the same resistor in another shop for around 2,50€, so it's even better. I thought it would be more expensive to be honest. Should be here on monday, so that's when I'll continue with this.

Should the clipping occur within the preamp or power amp? I have an old analog soviet oscilloscope, but I don't think it can handle 20V+ voltages on the input (I'm not sure, because the only user's manual I found online is in Russian, and I don't understand any of it!)

Amplifier Discussion / Re: Hartke B90 - disappearing sound
« on: November 15, 2016, 06:46:16 PM »
I live in Poland. Does it increase or decrease my chances of making it work again?  :duh

Amplifier Discussion / Hartke B90 - disappearing sound
« on: November 15, 2016, 02:40:06 PM »
Hello everyone,

Recently I've purchased the Hartke B90 from my friend for cheap and I used it at my rehearsal space. The sound was alright, but after some time a weird problem occured - one day, after 15 minutes of playing, the sound abruptly cut off and you couldn't hear anything. 5 seconds after turning off I've heard this "capacitor discharging" sound that was not there when I turned it off during normal operation.

If I turned on the amplifier after the discharge sound, it would work normally for 30 seconds or so, before shutting down again.

At first I thought that the power-amp was a chip-amp of some sort and what happened was some thermal protection shutdown, but when I touched the back of the chassis it didn't even get warm, and as you can see on the schematic, it is made of discrete components.

I also suspected a cold solder joint, but after I opened it up and took the PCB out, I couldn't find anything suspect. I did reflow most of the bigger solder joints, but the problem is still there.

I am new to amp troubleshooting, so I post here hoping that some of you could guide me or maybe someone more experienced has already seen something like this and knows what to do.

The problem with doing measurements is that the problem usually occurs after 5-15 minutes of loud playing, and for obvious reasons I cannot do this at home. I don't have any dummy load either.

The Newcomer's Forum / Re: HELP
« on: September 07, 2016, 07:15:16 AM »
that's because the pre-amp shouldn't be connected directly to a speaker - driving a speaker is a job of power-amp.

a lot of op-amps (especially TL072) aren't suitable for driving low impedance loads, I think that around 1k the TL07x start limiting the current, which results in distortion. At 8 ohms it's probably pretty awful.

If you want to keep it simple, you can add a simple LM386 straight-out-of-the-datasheet power amp after the pre-amp section. If you want more power than half a watt or so, you can use a more powerful chipamp like tda2040 or similar.

Schematics and Layouts / Re: Laney CD300 Mixer schematic
« on: September 07, 2016, 06:05:58 AM »
thanks!  <3)
I'm still tweaking this on a breadboard, but I'll make sure to post the schematic when I'm done with it in case anyone is interested.

Whoops, looks like I've derailed a thread about a Laney mixer  :loco sorry

Schematics and Layouts / Re: Laney CD300 Mixer schematic
« on: September 05, 2016, 01:15:42 PM » just note that I'm not really a guitar player and I didn't have any good recording equipment at hand, so the quality is not very good  :(

Schematics and Layouts / Re: Laney CD300 Mixer schematic
« on: September 05, 2016, 08:34:40 AM »
there's a mistake on the schematic in the 2399 section - obviously the regulator to pin1 of the 2399 should be a 78l05, not 78l15.

The delay circuit is actually pulled straight from the datasheet - one might change  the delay pot to 50k and tinker a bit with the filtering capacitors to achieve longer, but still useable delay times  8|
other than than PT2399 is one of my favourite chips - so many cool possibilities in one small dip package - you can get useable delay, chorus/vibrato, even reverb if you combine more than one of them, some weird pitch bending and much more  (I designed a 2399 circuit with an envelope-controlled delay time for some weird tape-like effects :duh )

it's C11 on this schematic:

in case you are asking about my layout for the preamp - yeah, I forgot to put it on the board, but it works fine as it is.

Amplifier Discussion / Re: How digital amps work
« on: July 03, 2016, 10:21:45 AM »
and speaking of construction - yes, there's probably one or more DSP chips in the preamp . It would be REALLY hard to build it (designing the PCB for that would be a nightmare, then soldering all the SMD stuff, not even to mention programming the chips - if you don't have any experience with DSP stuff then forget it). Arduino can be used to control some parameters, but not as a sound processor.

Speaking about sound quality - I agree with Phil, I don't like the digital reproduction of analog stuff too. But if you're not trying to replicate the sound of something else, then the DSPs become more interesting - there's some things you just cannot achieve with analog stuff, like really long/infinite delays, clean pitch-shifting by an arbitrary interval, some crazy reverbs and others. And the sound quality got really good over the years.

In short - if you like the sound and possibilities of some digital amp that you mentioned, just buy it. You won't be able to replicate it unfortunately.

Amplifier Discussion / Re: best build for 18V laptop supply
« on: June 30, 2016, 07:41:30 AM »
Regarding the TDA7492 - there are non-expensive complete boards out there that are actually just the application circuit from the datasheet, but I guess it's the not-cool, non-diy way to do it - considering the small difference in wattage between this chip and TDA2040 I guess I'll just settle for the latter and look for a high-efficiency speaker to go with it!
Thanks again.

Amplifier Discussion / Re: best build for 18V laptop supply
« on: June 29, 2016, 01:11:27 PM »
Please look at your specific situation.  SMPS are not generic, so to say "SMPS ARE ALL NOISY" is not fair.  How noisy is YOUR SMPS.  FInd out, you have it in front of you.
That's true, so I looked at it on my oscilloscope and it looked alright on a quick glance. Guess it will work fine.

Class D is a digital amp, the TDA7294 is a plain old bipolar amp in a chip.
Not TDA7294, but TDA7492 - confusing, I know, but those are two different chips. The datasheet claims it should provide ~15W into 8ohms or 25W into 4ohms with 1% THD. If true then I guess it would make an audible difference from 4W @ 8ohms or 9W into 8ohms for TDA2030 (and those are with 10%THD).

A single 18v supply is the same as +9 and -9 supplies.  SO at best about 6vAC into a load.  If I grant it 6v optimistically, then I get about 4.5 watts into 8 ohms.  The difference between 4.5w and your 5w is unhearable.  The difference between 5w and 10w is only 3 decibels, this half watt would not make a detectable difference from 5w.   Using an IC that is capable of more than that will not overcome that limit.  The power amp does not create power, it only controls power.  The power comes from the power supply.

Yeah, I was just wondering how much clean output I can squeeze out of that power supply, but if it's not worth the hassle then I guess I'll just build a Tiny Giany amp and call it a day (oh, this TDA2040 chip specs look fine!). Thanks for the reply!

Amplifier Discussion / best build for 18V laptop supply
« on: June 28, 2016, 12:45:21 PM »
hi everyone, it's me again - after building myself a "real" 3886 amplifier with the real power supply, I accidentally laid my hands on a 18.5V, 3.5A SMPS from a broken laptop. I figured I could use it to build a small chip power amp in the 5W-10W range so I have a few questions:
  • What chip would be the best for this application? I have or a LM1875 somewhere on my shelf, but while looking at the datasheet I found that this chip operating on a single 18V supply would provide even less  than 5W into 8ohms, so it's not ideal. Maybe using a chip designed for a low voltage single supply power supply would yield better results? Like one of those car chipamps (for example TDA2003) - do you have any suggestions which chip would work best in this situation? 
  • What about the class D amps? Take for example the TDA7492 - it should be able to provide more than 15W into 8ohms on 18V PS and 1%THD. Does anyone have any experience with them - are they any good?
  • And speaking of the laptop SMPS - I've read a lot about how noisy the switching power supplies are.  Would it really be a big problem in this build or will it work just fine?

Amplifier Discussion / Re: Quick question about this circuit
« on: June 12, 2016, 09:53:15 AM »
I was just about to ask that question - I thought that this resistor was supposed be connected to +9v to provide enough current to bring the diodes into conduction, but then I thought "hell, maybe it's some smart trick that I just don't understand" so I didn't say anything  :loco

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