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January 28, 2021, 09:17:29 AM

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Amplifier Discussion / Re: Rocktron Rampage R80 - No Sound problem
« Last post by paolone on Today at 02:15:23 AM »

I’m waiting that the 1uf caps arrive from internet, so i can change them.

Which component is the colprit of the master volume’ low level?
Maybe some other caps?

@dmeek do you have the electric schematic of my amp please?


The Newcomer's Forum / Re: Marshall ValveState VS232 repair
« Last post by EddieH on January 27, 2021, 10:45:49 AM »
Thanks Enzo!!!    Sorry for the delayed response I was waiting on parts.

So the solution was the IC2 TDA2050 was leaking DC out Pin4.   Replaced that with one from amazon.  They are only 7.99 for 10 of them.  Thought I would have to replace both IC1 and IC2 to get a more matched sound since this is a stereo amp.   So far it sounds equal and balanced.  That fixed the problems with the Power Amp board. 

The zenor diode zd1 was shorted causing R38 to burn.    Replacing that fixed the amp.

Once I had good sound, I found that VR3 for the clean channel is broke.   I have one of those on order.   The reverb seems weak as in not having much verb.   I will dive in to that next and post if I find anything.

Hope this helps anyone else experiencing issues. 

Amplifier Discussion / Re: Ultra Chorus/Ultimate Chorus mod
« Last post by fallingfrog on January 24, 2021, 11:26:11 PM »
Edit:  the treble capacitor should be 1440pf, not 1250.  Then it has the same tonal fingerprint as the 250pf treble cap in a tube fender amp tone stack.
Schematics and Layouts / Re: Ibanez TSA30 Schematic and PCB Layout
« Last post by Diydidi on January 24, 2021, 03:07:16 AM »
Hey Bajaman!
Thank you for your detailed explanation of the mods you do.
I will give it a shot this coming week. Customer dropped off his amp and its buzzing like crazy.
Someone already installed the 2200uf cap. I tested the ESR of all the caps and they are very low indicating good caps generally.
Any idea as to why some of these amps are buzzing and others not?
Also as to the heater voltage for V1 and V2: Does it matter that they are at ±10V and not the nominal 12V as indicated on most datasheets fro 12AX7's????
My first post here. Thank you!!
Tubes and Hybrids / Re: Reduce signal from preamp.
« Last post by flester on January 23, 2021, 05:09:29 AM »
By the way it's all running at 12v dc and I have left out the tone pot.

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Tubes and Hybrids / Re: Reduce signal from preamp.
« Last post by flester on January 23, 2021, 05:07:14 AM »
Noise was worse when I wiggled the gain pot so I replaced that which seemed to solve the problem. The whole thing did work fine at first and the preamp and power amp each worked fine on their own so interested to know if the noise was due to the power amp getting too much signal or not.

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Tubes and Hybrids / Re: Reduce signal from preamp.
« Last post by flester on January 23, 2021, 04:55:13 AM »

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Preamps and Effects / Re: Old newb questions
« Last post by edvard on January 23, 2021, 02:05:12 AM »
Hey guys, haven’t been here in a while or played around with electronics and electric guitars for couple years. Been on an acoustic odyssey lol. Feel like I’m starting from scratch again. Dragged out my MIM strat and red knob superchamp..thats downstairs in the man cave and too loud for the living room.

I was wanting to build myself a small stereo coffee table guitar amp. I have seen plenty of cheap amp boards on ebay, pre soldered with surface mount components with stereo 3w output. That would do me, anything much louder would annoy the missus, and we don’t want that ;) and I don’t want make a real amp with power transformer..i don’t do AC.

I need a preamp...but before I get to that stage I have some really obvious things that I don’t know/ forgotten.

1. Could I just use an effects pedal as a pre?
My intuition says no because guitar amps have an input stage ( i remember that part)

As Loudthud said, it depends.  A chorus pedal?  No.  A 5- or 10-band EQ with boost?  Yes.  Some dirt boxes are full-fledged preamps in themselves, consisting of a gain control, multi-band tone control, and output volume.  That's about the bare minimum for what you'd want in a preamp, even a clean one.

2. Would pedals work directly into a line level inout if i placed a DI box between pedal and amp? What would it sound like? Would a cabsim pedal or amp in a box work?

You don't need a DI between a pedal and a line input.  One thing that pedals are very good at is taking your high-impedance guitar input and producing a low-impedance output, which more-or-less is compatible with line level inputs.  A standalone cabsim would work well after your preamp if you want some color to the sound that more resembles a "real" amp, or you could get one of the Tech21 "Character" series or Joyo pedals that simulate amps.  They are a preamp and cabsim all in one.

3. Is there a schematic on here or elsewhere that gives a simple clean channel, with maybe basic tone controls that you could point me to, that may be suitable for these ebay amps. Fetzer valve was one i used in the past and I remember Phil(Phat) had some great preamp designs floating around here. Would there be a way to modify one of those to work with the ebay amp?

Any preamp with at least 2-band tone controls (bass & treble) and a volume or output control will work.  The only mod you may need is to make sure the output is low-impedance, but I don't think that's a problem with most schematics you can find here and elsewhere.  You can message Phatt, he's still around; I'm sure he won't mind at all sharing anything that might help.

4. Should I stay away from those chinese prepopulated boards on ebay, and build a proper deigned practice amp? If the latter option, Which one?

Use what works for you.  I'd say if you get a small stereo amp or kit that you plan to run regular hi-fi speakers with, then definitely a cabsim as mentioned before will help the sound, especially with headphones.  The same stereo power amp hooked up to a bona fide guitar speaker is not all that different from any production Solid State guitar amp.

5. If it was Ok to have a preamp board ( that i would perf) and the ebay amp side by side in a box, and i didn’t need a D/I circuit in between, could I use a single 9/12v wall wart to power both boards, or would I need a seperate supply for both pre and power amp?

As long as the power supply has enough juice to run the power amp and then some, you'll be fine.  Say you have a circuit or amp module that's 10 watts; you'd need something that was at least between 10 and 15 watts, and some will even say don't run the amp with anything less than 2X the power demands of your amplifier.

Am i barking up the wrong tree with the D/I box..i just remember having a need for a DI box when plugging into my mixer years ago..sounded terrible without it, and it had line level inputs. When it comes to electronics I know enough to be dangerous. I can solder ok and use a dmm. I used to build pedals 10 years ago, then had sporadic forays back into electronics but only limited understanding. Sorry for the dumb questions, and rambling in advance

A D/I box would be useful if you are simply plugging your guitar into something low-impedance with no pedals or preamps at all.  If you know how to build pedals, you already know all you need to tackle this one, it's just a bigger box with a speaker.  I don't think your questions are dumb at all.

Looking for your input
Amplifier Discussion / Re: Simple 3W amp IC? (for 4ohm speaker)
« Last post by edvard on January 22, 2021, 10:10:02 PM »
I’m using this TDA1517 stereo amp kit in one of my audio electronics classes. I built and tested it over Christmas and it is stable at 4 ohms. For $12 (Jameco, $27 on Amazon) it might be worth a try for your application. The output power will depend on the supply voltage and current capabilities.


- Will

I second the vote for TDA1517; 2 channels, 6 watts per, though they recommend heat sinking if you try to bridge it.  I used to have a habit of finding old ISA soundcards that are loaded with TDA1517 chips, or TEA2025B for the lower-power ones.  Also check the Craigslist "Free" ads or any friends with old broken computer speakers or one of those cheap mass-produced stereos from the '90s; they often have usable power chips hiding inside. 
Or go for broke and get a handful of LM1875s.  They are rated for 20 watts, but that's edge case; at 12 volts with an 8Ω speaker you'll get more like 6-8 watts.

JoeCool85's suggestion to go with a Class D chip is solid though, much less heat to deal with.
Tubes and Hybrids / Re: Reduce signal from preamp.
« Last post by Den. on January 22, 2021, 06:16:17 PM »
Heres the noise which comes in as I increase the volume.  https://drive.google.com/file/d/1KL_uZ8kQ9_aCp2k0lP7rCePaSFM_Zxf0/view?usp=drivesdk

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