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Author Topic: Velleman Kit 4001  (Read 1309 times)

flester

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« Last Edit: May 23, 2016, 01:24:05 PM by flester »
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phatt

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Re: Velleman Kit 4001
« Reply #1 on: May 24, 2016, 12:35:17 AM »

You need a higher supply voltage if you want more clean. :tu:
Phil.
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flester

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Re: Velleman Kit 4001
« Reply #2 on: May 24, 2016, 04:31:21 AM »

Thanks for that. It can take up to 18 v so will look for a new supply ti deliver that. Or 12 AA batteries. Would a 4 ohm speaker help?
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phatt

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Re: Velleman Kit 4001
« Reply #3 on: May 24, 2016, 09:56:11 AM »

4 ohms will be a bit louder but twice the current draw on your battery and it may or may not help the distortion.
You really need a bigger amp unit and a preamp will also help as raw guitar signal may be to much low frequency which adds to the distortion problem.
Phil.
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flester

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Re: Velleman Kit 4001
« Reply #4 on: May 25, 2016, 05:44:50 AM »

Think iIl just accept that i can have quiet and clean or loud and dirty.  For quiet and dirty i can use my overdrive pedal. Will be back for more ideas on my next build-possibly something tiny with a 2" speaker just for fun.
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mckayprod

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Re: Velleman Kit 4001
« Reply #5 on: May 25, 2016, 09:16:04 PM »

I'm using that chip for a similar project.  The cleanest sound I was able to achieve was using the +15v side of a regulated bipolar supply (Rod Elliot's board).  It sounded great, but the regulator got too hot to touch so I shut it down.  Velleman makes a really cheap 1a regulated, adjustable supply that I'd like to try in the future, but for now I have 4X9v batteries in series/parallel for a bit more than 18v.  It still breaks up too soon for my taste, but I put a 50k pot between the guitar and the input and that cleans it up at the expense of some volume.  I'm using an 8 ohm, 8-inch Peavey speaker (I think I like my Radio Shack closeout/ceiling PA 8" better).  No preamp, yet.  Glad to see someone else using this chip/board; keep us posted.
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flester

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Re: Velleman Kit 4001
« Reply #6 on: May 26, 2016, 06:19:59 PM »

Mackayprod, thats cool. Are you using the Velleman kit, or just the TDA2003 chip which is at the heart of it? I got kit from Maplins (the UK/Ireland equivalent of Radio Shack)

Been playing with it again and decided I like it (or am too lazy to modify). basically I play it quiet or else flat out (wakes the family if not the neighbours) and theres no in-between. One mod I heard of is to use a smaller resistor going in to the inverting input. this increases negative feedback thus reducing the gain. I based the enclosure design on the Pignose (imitation, flattery and all that) though its a bit smaller. I put a bit of effort to fit a DC input jack and also a headphone out jack, so I can always change the guts while keeping the enclosure (of which I'm quite proud). Mainly used with my homemade Lap Steel and a Hofner Shorty guitar. Actually sounds great as a Harmonica amp too.


Letting the battery run down gives more distortion anyway (sometimes in a good way...) as Brian May did with his Deacy amp. You can now buy a Deacy replica including a variable power supply to simulate a dying battery but wheres the fun in that?
« Last Edit: May 27, 2016, 06:00:58 AM by flester »
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flester

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Re: Velleman Kit 4001
« Reply #7 on: May 27, 2016, 06:09:41 AM »

Any suggestions for preamp design?
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mckayprod

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Re: Velleman Kit 4001
« Reply #8 on: May 27, 2016, 10:10:04 PM »

I'm using the Velleman kit.  I originally used it as a quick-n-dirty guitar amp for my daughter, who got a strat copy for Christmas.  I built it into an old RCA hi-fi speaker with an on-off switch and a 9v battery.  As I remember, it sounded better on those single-coil pickups than it does with my humbuckers.  I think the battery power supply lacks enough current to give the chip all the headroom we are looking for, or at least that's the theory I'm working from now.

I'm going to build the Rod Elliott P27 circuit and experiment with the diode "soft-clipping" system http://sound.westhost.com/project27.htm.

I've been looking at the TDA datasheet and would like to try to reduce the gain of that chip...better to do that than to pad the input?  If we can drive the amp into clipping with just a guitar pickup straight in, why use a preamp (other than for eq control, pickup loading impedance)?  I think that's done by varying R1/R2, but I'll try to figure it out and post.
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J M Fahey

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Re: Velleman Kit 4001
« Reply #9 on: May 29, 2016, 06:48:11 AM »

You can't reduce gain very much, I guess minimum is around 20X , because it becomes unstable.
So reduce R2/R1 ratio to about 20:1 but not less, any ectra reduction myst be input padding."Which is not all bad, you can add a passive tone conrol which will be lossy anyway.
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flester

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Re: Velleman Kit 4001
« Reply #10 on: December 02, 2017, 02:57:56 PM »

You can't reduce gain very much, I guess minimum is around 20X , because it becomes unstable.
So reduce R2/R1 ratio to about 20:1 but not less, any ectra reduction myst be input padding."Which is not all bad, you can add a passive tone conrol which will be lossy anyway.
OK here is plan B. I've been playing around with the Lm386 opamp and decided it might suit my little enclosure better than the TDA2003. I thought id use 2 of the TDA2003 modules with each one driving a 4" car  speaker in some sort of cabinet. Maybe shaped like the Roland Street Cube https://m.thomann.de/ie/roland_cube_street_bk.htm

Sent from my SM-G935F using Tapatalk

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