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[njutn]

Hi guys,
I am a german amp hobbyist. This is a very intersting site and I want to share my projects with you. Actuall I build a 50Watt SS-Guitaramp. It contains a Poweramp, a preamp and a equalizer. Mayby some of this modules are interessting for you, or they push on your own inventions

This is the Amp in the test phase:


I have a own site where I publish the development. There are also some sound samples.

http://xipix.de/elektro/gimos50.html

The next days i will start with the case and a DC-protect.

[J M Fahey]

Nice, keep posting, an keep contributing.
Welcome to the board.

[Trent]

Hi,

Been a while since I posted but I thought i'd let you guys know how my project went. Needless to say my teacher was impressed, I think he was glad to see someone actually build something with a bit of passion as opposed to everyone else who just wanted to do as little as possible to get a pass.

If you remember when I started the project I didn't even have an electric guitar. It was a good excuse to get one, so I ended up getting an Ibanez RG and just had the tremolo blocked (don't ask).

Anyway, to the amp, the tiny giant I built for the power amp worked really well. did everything it was supposed to and sounded pretty cool. However the K20-X preamp didn't work that well (managed to hide that from the TAFE teacher quite well  8|) in that the treble and mid adjustments don't do anything at all and the bass does nothing until right up the top when the sound suddenly changes to mud. I checked the schematics for ages but can't find what I did wrong :embarassed:

Anyway after TAFE I kinda just threw it in the wardrobe for a few months and was actually thinking about giving it away for the space, until Christmas where my soon-to-be-wife bought me a big muff pi (she has good taste), and out of curiousity I hooked it up the the tiny giant through the 10in cab I built and WOW! I'm impressed. Sounds fantastic!! So good infact that if I have to get rid of one, it won't be the one I built.

So here are some pics I took the other day.


Tiny Giant on the left, K20-X on the right





Holes I cut in the cab because as a sealed cab it sounded like poo.




Inside the K20-X - Sorry its not the best but I cbf undoing the pots to get the lid off.




Inside the tiny giant





I'm still not finished yet as I am going to have the cab and tiny giant painted. Then it will be complete!

Anyway thanks to all you guys for your help and advice. It has been a very educational build and well worth it. The next project is to take a 1/5 scale baja rc car and convert it from petrol to electric  :tu:

Thanks again!

[J M Fahey]

COOL !!!!!!  :dbtu: :dbtu: :tu:

[joecool85]

Sounds like for the K-20X you used linear pots instead of logarithmic.

[Trent]

Sounds like for the K-20X you used linear pots instead of logarithmic.

I believe I did. That would be the problem then aye?

[phatt]

It may make little difference what pots are used.
(I hope Joe cool understands I'm just trying to help build a better mouse trap. winky.)

I've taken some time to test the KX20 preamp concept and thought I'd share my findings.

There is substantial loss with this idea and this maybe some of the reason it did not work.

Note the 3 traces which should need little explanation.
The output of the opamp has 20Db gain but is lost by the diode clamping.
But then the signal gets an even bigger kick in the teeth.
So without another gain stage I doubt it will be worth the effort.
Overall loss is down 25 Db at 1kHz.

This (Tone after diode clippers) idea may work in some situations but without help it will be hit and miss when shoehorned into any circuit.
Phil.

[joecool85]

I wonder if the original K-20X does that or if it is just my rendition.

[phatt]

Hi Joe,,, Yep hard to know without setting the whole thing up to test it.

Here is another shot this time focus on the tone curves.

Note that most of the bass boosting is below 100 Hz.
Which tells me that unless the next thing in the signal path has MASSIVE bass cut it will sound like mud.

You could raise the treble cap too 5nF (Even 10nF) and see if that helps but as is,,, it's a hit an miss tone.

The screen shot shows all the extreme tone control positions.
Note; the drawing I have is rather blurred so I may have read the values wrong.

Lowering the value of coupling caps may help wipe excessive Bass response.

Cheers,,,Phil.

[joecool85]

Phil, here is a link to the original schematic: http://deanmarkley.com/Info/LegacyAmps/Schematics/D1515.pdf

As for it sounding muddy, I don't think my K-20X does and with it driving the stock 8" speaker you'd think it certainly would by what you are describing.  Maybe you do have the values wrong?  I didn't have time to check what you had.

[J M Fahey]

Agree that simulation, a *very* useful tool, tells only half the story.
The often forgotten speaker is the other 50% of the sound.
*NO* guitsar speaker I know is flat, all show some huge mid/high frequency peak.
This certaomly colors the sound a lot.

[joecool85]

Agree that simulation, a *very* useful tool, tells only half the story.
The often forgotten speaker is the other 50% of the sound.
*NO* guitsar speaker I know is flat, all show some huge mid/high frequency peak.
This certaomly colors the sound a lot.

Agreed, and regardless of what any simulation says, I know that my K-20X has a nice dynamic EQ and isn't muddy at all unless I crank the bass full and turn the mids and treble all the way down...which is what you would expect (and want).

[phatt]

Hi Joe,
       Great thanks for the link to the schematic.

Arrh HUH  :police:
Lets see how good My detective skills are working? 8|

Yes C12 is only 1uF and this to my understanding dramatically wipes low frequency from the signal. Hence it all balances out but as I mentioned it may not work so well when used with another power stage.

Most SS poweramps I've seen don't bother much and just let it run flat from about 10Hz BUT This is ONE place you can make a big impact on bass response. Below 5uF it really cuts deep,,, 10uF seems to be the most common for the average SSpower chip.
HiFi power stage might use 50uF or higher.


A point of interest that some might like to know;

If you care to research the response curves in some famous Valve Amps you might notice that the preamp stages have almost DC response (massive bass) BUT the power stages being cap coupled do wipe off a lot of lows. So the whole thing balances out as one.

Whereas most SS circuits the opposite is almost the norm ,,all the eqing is done in the preamps and the power stages tend to run hi fi flat response.

Some quality SS gear does play around with the power stage response but with most cheap guitar amps this would be very Rare.

LOL,, so you either have a rare quality unit or just a lucky mistake at the factory.

I agree with Mr Fahey's speaker comment but in this case my money is on C12.
Change that back to 10uF and you WILL instantly understand. winky.
Cheers,, Phil.