BAJA Hiwatt DR103 amplifier pedal 9v 120318  [documentation]

Original effects with schematics, layouts and instructions, freely contributed by members or found in publications. Cannot be used for commercial purposes without the consent of the owners of the copyright.
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Ben N
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Post by Ben N »

dorukakkus wrote: 13 Feb 2022, 19:34 I play at home mostly but I play in a Band. So maybe 30watts
If you're used to tube amps, a 30 watt (RMS) chip amp may be disappointing in a band context, because unlike a tube amp, you don't ever want that chip amp to saturate. So your peaks have to stay within the amp's headroom, whereas with the tubes, you may just be hitting the amp's sweet spot when the power tubes start saturating. So, point is, you should probably double the wattage number of whatever you consider a suitable power level with tubes, all other things being equal. Also, while a tube amp may not sound great at reduced power, a chip amp should be fine, since all the tone generating is happening upstream. So a more powerful than necessary amp ought to be ok--just turn it down, and change gain & eq in the preamp accordingly.

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Post by dorukakkus »

Sorry for my late response. I think I am going to use the bigger brother of the TDA2030, TDA2050. The reason I decided to go with this one is the IC being an AB class IC. And slightly more power (around 25 watts). I dont't think i will be able to build a tube power amp with my current budget. Altough I have made 2 of the preamp part of the circuit. Who knows in the feature I will build one. I will keep the post updated.

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Post by ppluis0 »

dorukakkus wrote: 21 Feb 2022, 17:19 I think I am going to use the bigger brother of the TDA2030, TDA2050.
Hi dorukakkus,

Try to download the schematic from this link: https://elektrotanya.com/marshall_vs30. ... nload.html

In this particular amplifier a small amount of speaker current is positively feedback to a input of the TDA2050 to decrease the damping factor of the power amp section. This is done with an 0.1 Ohm 2 Watt resistor labelled R49 that can be seen in the page 2 of that document.

This way the speaker has less control from the amp resembly the undamped character of a tube amp.

Cheers,
Jose

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Post by dorukakkus »

Thank you for the tip! So if I understand correctly according to my schematic+the resistor https://prnt.sc/8SwNazbsVo5M this is the right way to do it. Correct me if I am wrong

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Post by ppluis0 »

Hi dorukakkus,

Unfortunately your diagram is wrong due the low ohms resistor short the inverting input to ground.

Try to redrawn the aforementioned Marshall output stage deleting things like headphones or line out jacks to see clearly the feedback paths.

There is a interesting link regarding speaker current feedback: https://sound-au.com/articles/guitar-amps.htm

Cheers,
Jose

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Post by bajaman »

Oh Oh - a member tried to build this pedal and had some problems with the tone control not functioning correctly - after checking I discovered mistakes in my schematic - my sincere apologies - here is the correct tone control stack schematic
Once again my apologies
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bajaman
amended tone stack.GIF
amended tone stack.GIF (8.18 KiB) Viewed 1200 times
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Post by dorukakkus »

So a little update. Could not find a vero board anywhere. So i thought my 17 year old self, I can design a pcb and print it out and jam on the amp pretty easily. I was horribly wrong. It does work but very poorly. Very low volume even when it is connected to a power amp. And it has a white noise issue. Finally the tone stack does nothing. I dont think there is a problem with the schematic so it is obviously this pcb. I think there is a misconnection somewhere but my knowledge is not enough to find it. If someone have time for this troubleshooting project it could help anyone trying to build it. Thanks in advance.
hiwatt dr103 v2.pdf
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Post by uncleboko »

dorukakkus wrote: 13 Feb 2022, 19:34 I play at home mostly but I play in a Band. So maybe 30watts
Don't forget that 30watts will not sound twice as loud as 15 watts, so for more headroom go for 60watts. Oh and loudspeaker efficiency also comes into the equation. I can remember a big argument with the other guys in my band back in the 60s, who insisted I "need" a 50 watt amp because my 20 watt was not loud enough - I discussed this with a relative who repaired electrical gear, and he managed to get me a couple of celestion 12" speakers which gave me more volume at 20watts than a Vox AC30!!

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Post by dorukakkus »

uncleboko wrote: 19 Feb 2023, 15:20
dorukakkus wrote: 13 Feb 2022, 19:34 I play at home mostly but I play in a Band. So maybe 30watts
Don't forget that 30watts will not sound twice as loud as 15 watts, so for more headroom go for 60watts. Oh and loudspeaker efficiency also comes into the equation. I can remember a big argument with the other guys in my band back in the 60s, who insisted I "need" a 50 watt amp because my 20 watt was not loud enough - I discussed this with a relative who repaired electrical gear, and he managed to get me a couple of celestion 12" speakers which gave me more volume at 20watts than a Vox AC30!!
That was my thought too. While troubleshooting i seperated the preamp and the power amp sections. Then soldered an output jack the the circuit. So basically I made it a pedal without the enclosure. Plugged it into a normal amp that i have.(vox vx2 modelling amplifier) When disconnected the volume of the amp is loud. But when it is engaged volume decreasses massively and the problems i have listed starts to occur.


Last bumped by dorukakkus on 20 Feb 2023, 21:16.

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