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PostPosted: 09 May 2011, 21:00 
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Joined: 09 May 2011, 20:48
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Hello everyone!

I'm on a quest. I'm not sure if I'm in the right place for guitar amps but I hope someone could help! Maybe you've heard of the Ruby amp, which is based off of the LM386 DIP-8 amp chip. They have some mods like the Fender Bassman mod which is a really cool concept, as the Bassmans have some truly amazing vintage sound!

Now, I doubt that a $0.90 chipamp can be made to sound like a true tube, but for the hell of it, I thought I'd ask if anyone had any input.I will be following the Bassman mod, http://www.runoffgroove.com/ruby.html

I plan on using vintage carbon composition resistors (the big brown ones), Wima Polypropylene, Bourns conductive plastic pot (for volume), and Panasonic electrolytics (FM and FC mainly). Now, I'm not an owner of an old amp like a Bassman, so I'm not THAT familiar with them.

But, does anyone have any hints or possible ideas on how to tube-ify a cheap chip amp like this, (without going too overboard!)? I know it's not exactly the best of ideas, but I'm crunched for cash and I can't really step up to a TDA2020 or the like, as I'm already pushing my budget with this one! I'm buying a vintage Weber 6" x 9" speaker, which are proclaimed to be awesome for vintage equipment. That speaker is $25.

Can I change the value of any of the parts, or change the type of part. (Like exchange electrolytic for film etc). Since I don't really feel like using a battery for this amp, and because I want more headroom, I'm going to build a small PSU that will output a clean 15VDC. Any suggestions for the PSU etc?

Thanks!


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PostPosted: 10 May 2011, 19:10 
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Hi there,

i'm also not very familiar with vintage guitar amps but i think i can clear up a thing or two.

It is surely possible to get some kind of "tube sound" from a solid state or OpAmp circuit.
Tube sound is not always related to tubes themself. It is more a relation of even harmonics and distortions.
Circuits like the Ruby or the Bassman mod provide their tube sound or overdrive by adding this harmonics and distortions.
The trick is just the gain of the chip, the volume (signal power level) at the input of the chip and some
components (signal conditioner) at the input. The distorted and soft overdrive sound starts, when the chip
starts to saturate. Whether the chip itself (internally by the gain or feedback) or already at the mosfet buffer stage.
Changing some values will allow the circuit to distort earlier or later. "Overdrive" sound slightly is the effect of high distortions.

When i'm right now, the speaker has about 30Watts?
The LM386 pushes about 1 Watt depending on the model and power supply. I think you can not expect
very much if you want this project as an amp for practicing. Something like a TDA2003 would be more useful
and it allows more headroom and a higher volume level (only my 2c). The costs are not very much more.

The power supply can be built of anything you can afford. A small 12VAC transformer + rectifiers and filter caps,
a wall wart (12 to 15W AC or DC) + some filtering, switch mode supply or smps wall wart and some filtering.
That's not the real big problem.

Now - if you think 800mW to 1W could be enough for you - the 386 would OK for a start. IMO - the project is easily manageable.

_________________
Cheers,
Tom.

Some of my projects: TDA2050 Chip Amp, the LM3886 Gainclone Thread and the Szekeres Headamp Thread.


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PostPosted: 10 May 2011, 20:48 
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Joined: 09 May 2011, 20:48
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Well, I've played a 1W Fender Twin Mini and it was decently loud, but nothing much.

I suppose a TDA2003 would be much better. TDA2003 is EOL if I recall. Is there a "better" option at this point? A similar 7-10W class A/B chip? Mouser still has a few in stock, so maybe I'll grab one or two.

Does anyone have a simple layout/schematic that might be viable for TDA2003?

Thanks Mr. Bethe!


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PostPosted: 11 May 2011, 12:23 
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Location: Winnipeg, CANADA
FenderBender wrote:
Does anyone have a simple layout/schematic that might be viable for TDA2003?

Take a look at this tda2030 amp forum thread for ideas.
Cheers

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PostPosted: 11 May 2011, 17:25 
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Location: Duesseldorf, Germany
Hi again ;-).

Gio's idea to switch to the 2030 for the amplifier stage also is nice. It's not that far away from the 2003.

I had one more other idea today. What about building a Little Gem - respective Ruby - (with bassman mod and some little tweaks)
which can be used as preamp for a power stage later? This will help you to keep the things very easy and cheapo at the beginning.
I've played through all the possible stuff today, but reached a point where the power supplies started to be pricey!

The Gem is an amp which can be powered from a simple cheap wall wart - where i'ld go for a 12VDC supply.
The other things would need some more power and thus some more bucks (started with the 2003).

I can do a 2003 or 2030 based schematic for you. Including gain, volume and tone control (highs). It could take a while
because i would prefer to test it then first. You can also find a basic schematic on the 2003 datasheet (the test circuit).

Do you have an idea on how many volts your pickup/s provide?

_________________
Cheers,
Tom.

Some of my projects: TDA2050 Chip Amp, the LM3886 Gainclone Thread and the Szekeres Headamp Thread.


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PostPosted: 11 May 2011, 20:04 
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TDA2003 seemed nice to me because I'd only need a 12V/1A supply, minimal parts, and I could do a simple JFET preamp (like a Tillman) that costs $5. The price would still be $50+, but still not a bad deal. TDA2030 is similar, but I think it has higher working voltages (correct me if I'm wrong), or atleast it want's more power. What's the point of getting a better chip if I don't want to pay for a transformer that can handle it.

LM386 doesn't seem terrible either, but <1W is a bit small for some things, though it might be viable...

My pickups. I honestly have no idea. They are AlNiCo Humbuckers. They came stock on the Epiphone Les Paul Special II. Cheap guitar, but sounds good.

If you really want to make a schematic/layout, I'd surely appreciate it. I still play mainly acoustic, and I don't need this urgently. In fact, I wouldn't care if I built this 9 months from now. I'm also very busy myself, so I understand. That's only if you want.

Just some theoretical questions. I hear a lot of buzz about component selection etc. Just out of curiosity, if I used "vintage" components, would it aid in achieving vintage sound (even though I'd be using chipamp?) So if I used Carbon comp resistors, a lot of poly film caps (in all places that require <10uF) etc...Would it help?

Thanks for the quick replies and for the help!


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PostPosted: 11 May 2011, 21:39 
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Somtimes I don't like the test circuits from the datasheets. Like on some linear regulators, they suggest like a 1uF filter cap....Now, I'm no electrical engineer, but I think 1uF might be a tad small. I use like 5600uF, just sayin. It seriously only costs like $0.75 more anyway. I guess if you were mass producing, but still...


But I guess it would be alright.

If you don't feel up to making a schematic (and maybe you better off, since who knows, I might not even get around to ever making it), I might just take Velleman's schematic, throw in a volume pot with that, and throw in a JFET preamp onboard. That would probably work too...Where would I put the gain control? On the preamp?


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PostPosted: 12 May 2011, 16:05 
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Sounds good so far. Nothing speaks against a 2003 and the circuit is easy to do. A pre amplifier stage is a must as the pickup
voltage may vary from type to type. Your humbuckers should have an higher output compared to single coils. That's one more
big advantage on humbuckers. The dual coil system eliminates hum and double coils also means double the power, which helps
a lot to push the circuit into overdrive sound ;-). So, the preamp will be integrated, which will provide a further advantage.
Quote:
I hear a lot of buzz about component selection etc. Just out of curiosity, if I used "vintage" components, would it aid in achieving vintage sound (even though I'd be using chipamp?) So if I used Carbon comp resistors, a lot of poly film caps (in all places that require <10uF) etc...Would it help?
Rather not. I doubt that someone can hear a difference from resistors. The only thing that might happen is the thermal noise if the resistors are bad quality (cheapo carbon resistors).

Vintage components IMO can not be used to achieve Vintage sound. That's a myth, really.
The coloration of sound heavily depends on the circuit design. Not mainly on the used components.
As mentined before - the harmonics and distortions play the role. Even order harmonics give a warm touch
on the tones, while odd harmonics sound horrible. Polypropylene film capacitors can help to make a circuit
sound Vintage - when they are on the right place. I like to use the "Orange drops". It is not 100% proved,
but they sound a little bit warm. Maybe due to a little cut off at the highs. I dunno, but i like them...

The gain control would be placed where it makes sense. Right at the chip's inverting input (pin2) instead of R1 / R2.
This should allow to adjust the gain of the amp stage and the distortion level from clean to heavy.

_________________
Cheers,
Tom.

Some of my projects: TDA2050 Chip Amp, the LM3886 Gainclone Thread and the Szekeres Headamp Thread.


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PostPosted: 12 May 2011, 18:33 
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Using high quality components can be helpful but usually isn't all that important, for sound.


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PostPosted: 12 May 2011, 19:19 
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Thanks Tom! I figured that the type of circuit would be more important than actual components. I'm sure that using ceramics vs polypropylene would indeed have an impact, but going nuts over components probably would be dumb, eh? However, carbon comps are pretty much the same price as Metal Film. After doing some research, I've heard that carbon comps have better tone but are noisier, while metal films are harsher but are less noisy. I find this to be kind of BS, but what do I know. I have nothing to judge against it. I know I probably won't tell the difference either way, though those carbon films might actually make it sound like junk...Since they are pretty much the same price, what would be your choice?

Orange drops it is then? Sounds good. No pun intended. Can you compare to Wimas or Panasonic?

I'll integrate a Tillman preamp right onto the amp board, but I'll put the PSU close to the AC recepticle to reduce any AC noise from getting into the amp circuit. I'm thinking maybe 2x 4700uF 25V and a simple bridge. 12VAC transformer. Should it be regulated at 15V perhaps? Since the power draw of a TDA2003 shouldn't exceed 1A, perhaps I could slap a low dropout regulator on there. No?

The potentiometer for the gain. Is 10K audio taper alright? I happen to have a nice Bourns one...But if not, what do you suggest?

Thanks a lot! I appreciate it.


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