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Topics - Bakeacake08

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Amplifier Discussion / Frontman 15G Suddenly Died
« on: October 02, 2016, 12:35:25 PM »
I have a Fromtman 15G I've been using as a practice amp (and live a couple times) for about a year and never had a problem with it. Last night I was playing on it with my phone plugged into the auxiliary input. I played for a few minutes and heard a kind of popping/scratchy noise, like you'd hear if you moved a bum cable the wrong way. It happened once for about a half second and ten went back to normal. Then give or ten minutes later it made the noise again and the amp *s!!t* down--no noise, LED off, like it was unplugged. I opened it up and checked the fuse and continuity on the switch. Both were good, so now I'm out of ideas.

In typing this out I realized I should check the transformer secondary and make sure the IEC plug is working. Assuming those are okay, where should I look next?

Schematic here:

Tubes and Hybrids / Crackling noise from Peavey Valveking 100
« on: December 07, 2015, 12:57:22 AM »
My buddy asked me to repair his Peavey Valveking VK 100 amp head for him; he left the speaker cord in and the amp fell over, so now the jack needs to be replaced. He also asked me to try to figure out another issue he has been having since he's owned it (so before the damage), which is a sort of scratchy, crackling noise it makes. The noise is a little pop sorta like when you plug in a guitar cable while it's on. It's not very loud though, easily overpowered while playing. It does not come at regular intervals and can be anywhere from once every couple seconds to a couple every second. None of the pots seem to have an effect on it. It is considerably louder on the gain channel and faint (though still noticeable) on the clean channel. I tried hitting it a little to see if it was an obvious mechanical thing, but nothing changed. I played through the amp for about twenty minutes or so and afterward didn't notice it before I turned off the amp. I didn't have time to tell if it was totally gone or just taking a break. I haven't opened it up yet because I haven't had time to put together my light bulb limiter. Your thoughts?

Oh, and I have also had trouble finding a proper schematic for this amp. All my searches seem to point me towards either the Valveking combos or the new line of heads. Anyone know how to find one for this specific model?

Tubes and Hybrids / New Build Power Amp IC
« on: October 30, 2015, 04:13:28 AM »
A while back I was working on designing a hybrid amp with a tube preamp and SS power amp. I'm finally getting around to finding components for it, and it is my understanding that the TDA2050 is no longer commercially available. I guess my first question is is there In fact no more legitimate source for this part? If not, does anyone know where I could get (preferably) a kit for a power amp IC? My circuit has one 35VDC rail, and I've only been able to find kits for dual-supply operation. I just want it to make a small signal bigger, so I'm not too picky; any run-of-the-mill, standard, boring IC will do just fine. Thanks for any suggestions!

Amplifier Discussion / Pickup Placement
« on: February 28, 2015, 12:52:07 AM »
I'm currently building my 1-year-old son his own little guitar he can drag around and beat up since he shows much interest in my Taylor acoustic (which he cannot drag around and beat up). After I finish that project, I want to make one for myself. I have a humbucker pickup from an old Epiphone SG style body I acquired awhile back. These guitars only use three strings, so I was wondering of there would be anything beneficial to arranging the pickup so that more of the magnets are under the strings. That is to say, instead of setting it up in the normal fashion and only having half of it covered, I could angle it--or even turn it a full 90 degrees--so that the strings rest over all the magnets. What would this do for the signal? I'm inclined to think it would make it stronger. But I'm also inclined to think there could be some kind of phasing issue as well. But really, I have absolutely no clue, so I'm asking the experts.  :)  Your thoughts?

Amplifier Discussion / Practice Amp Suggestions?
« on: August 01, 2014, 02:52:47 AM »
I'm wondering if anyone has any recommendations for a good practice amp.

. . . electrical modification practice, that is.  8|

I've been looking at various second hand websites, and I've discovering that one can buy any number of entry lever guitar amps dirt cheap (<$20 US). I was thinking it would be fun/educational to pry one of these open and try to make some changes to it. Is there any particular amp(s) that stand out as being commonly modified to improve the sound a little? Not necessarily improve the sound, but make it somewhat at least noticeably different (e.g., doing something to reduce the hum). I figured I could work on my circuit skills, and worst case scenario I bought a bin of parts useful for twenty bucks.

Your thoughts?

Amplifier Discussion / How to choose a Topology
« on: July 18, 2014, 06:25:06 PM »
I have been re-reading @Teemuk's book "Solid-state Guitar Amplifiers," and it makes a lot more sense the second time around. Well, a lot more makes sense, that is. I don't have much time for projects, but I've been thinking of putting another one on the back burner: making a solid-state amp. I've been playing around with LTspice to test my understanding of theory, and it seems to be going pretty well (things mostly do what I expected them to do).

Anyway, the issue facing me right now is that I don't know how complex I should/need to go. After learning basic topologies, all the articles I read start talking about how to improve them, and it gets pretty complicated pretty quickly. I'm not against having difficult circuits to build, but what I'm wondering is at what point does it become so elaborate that it would make sense to just use an op-amp circuit instead? Or how simple can a circuit be made that is still serviceable? Put in different terms, if I were looking to build myself a car, I could make a hot rod and optimize the entire engine, but my '88 Tercel has all the basics and gets me around just fine. (And it got GREAT gas mileage. Too bad it was totaled a few years ago . . . )

I hope you understand what I'm getting at with my question. It seems that with tube amps (which is what I've been looking into mostly before now), there are only so many options, making it a little easier on beginners, but with solid-state designs, there are a thousand different ideas on how to put it all together, so I can't figure out what the "introductory" method might be.

And again, I can't recommend Teemuk's book enough. It's been a tremendous help so far on this journey, and I haven't begun to understand even half of it yet.

Amplifier Discussion / Transformer Selection
« on: June 29, 2014, 03:01:00 PM »
I've been designing a tube/SS hybrid amp. I based the power supply on running at 50 volts max as per my device limitations. At 50 volts of rectified DC, I was going to need a transformer with about a 35 volt RMS secondary (50V pk/1.414=35V RMS). So I designed in a 36 volt transformer, but I didn't really understand how the 50 volts was going to get there; I thought that it would be running at the RMS value and somehow I had to just know that the peak value was going to be higher and I had to keep it in mind when choosing components. Then I built a simple string of LEDs for my coat closet because our doorbell transformer sticks out of the wall in there and was begging to be more useful. After running some experiments to figure out voltages with a diode rectifier wired in, I realized that the peak voltage BECOMES the DC output when rectified, and the AC voltage goes away (save for a little bit of ripple voltage). So after I put a rectifier and the proper capacitor in, the system will be running off the PEAK voltage of the secondary, not the RMS voltage.

I don't know how common that misunderstanding is, but I went through it so I thought I'd explain how I figured it in case that helped someone else starting out figure out how to design a power supply. My biggest advice (which others repeat constantly) is to actually build the circuits so you can see how the theory/math actually works and if it doesn't, you can start to figure out why not.

Anyway, that was the helpful part of my post; now on to my actual questions.  :)

I decided for now that I'm just going to stick to the 35V design instead of re-figure out all the other components. I actually found a 25.2V transformer at Radio Shack that would be cheaper than buying one online with shipping and everything. My question is about VA rating: through my reading I have learned that the DC amps drawn by the circuit will actually draw more AC amps from the secondary (by a factor of about 1.6, as I understand it). So if I expect my circuit to draw 500 mA, I should actually make sure my transformer is rated for 500mA x 1.6 = 800 mA. Am I understanding this correctly?

My second question is more theoretical, but the transformer in question is center tapped so each side of the CT is at 12.6V. That got me to thinking: Is there any reason one couldn't wire up the center tap as some sort of reference voltage? I was thinking maybe there's a way to make a bridge diode between the two outside leads and one between the "ground" lead and the center tap or something like that. My gut tells me that there's some obvious reason why it wouldn't work, but it also seems like it *should* so I thought I'd ask people who actually know what they're doing.

Tubes and Hybrids / My Attempt at a Hybrid Design
« on: December 20, 2013, 06:41:39 PM »
I started out wanting to build an all-tube amp from the, but I was still learning about electricity and circuitry, so the high voltages made me a little nervous, which led me to research solid-state amp design. Then I found out that you could make a pedal using tubes, so I thought it might be cool to have a solid state clean channel and a tube crunch channel. That seemed rather complex for my first design attempt (at this point I had decided that I wanted to try to design something myself), so I settled on building a hybrid amp, which leads me to this post. I have come up with the attached schematic and I was hoping to inquire of people with actual knowledge and experience in the hopes of not killing myself of those around me with my first amp project.

I have a few specific questions, but I would also love to hear any overall comments anyone might have as well.

1) C17 is used as a reservoir cap. I estimated there will be a quiescent current somewhere around 3-400mA. Is this enough capacitance? Too much?

2) For the heater circuit, I saw somewhere online about using a zener diode to drop the voltage inside the operating range of a 12V voltage regulator. Then I added an 80R resistor to supply the required 150mA. Is this the same current that will be going through the zener as well? Also, does this idea even make any sense? I was hoping to be able to use the same (relatively cheap) transformer instead of having to get one just for the heater supply. (*crosses his fingers*)

3) I'm not super familiar with how to choose/implement fuses, so any comments on my current scheme would be great.

4) C2 and C4 are cathode bypass caps. Does 10uF seem like a reasonable value? I know there is such a thing as partially bypassed and fully bypassed, but I don't know how different capacitor values will affect the sound.

5) The tone section is a passive James/Baxandall type circuit. I know that there will be some insertion loss; will scaling down the resistor values by, say, a factor of 10 (and scaling up the caps accordingly) affect this loss at all? From what I understand, this could at least cut down on the Johnson noise, but I'm not very familiar with the concept of insertion loss.

General comments on the design: I chose the TDA2050 because I looked up the schematic for the Marshall 15DFX I used to have and that's what it used, so I figured it would work. That chip has a max voltage rating of 50 volts, so I picked at 36V RMS transformer, which will put out 35 volts after losing 1V in the bridge rectifier. All resistors will be .5W unless otherwise noted. I've read thousands of pages of electrical theory in the past few months, but this is the first non-9V-battery project I'm attempting, so I hope I'm at least on the right track with this.

I greatly appreciate any feedback I you have for me.

(You know, to reduce the amount of distorted ideas I might be throwing out. Waka waka.)


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