The "Forum Amp" design thread

[Taylor]

None taken. It's the simple truth that you can't please everybody, so my job when putting these projects together is to balance out the various opinions and come to a single conclusion. That necessarily means that it can't be perfect for everybody. For example, I'm including a preamp, with switchable clipping, and a 3-band EQ. For you, I guess this is not enough. But for others, it's too much! Whaddaya gonna do?

[Brymus]

Thats cool,I thought the preamp was to be whatever pedals we use.
So I like that your are adding the preamp and TMB,that is a big plus.

And yes ,I am bummed no channel switching 
That would have made it worth my time to build and learn from.
For me I have enough amps that rely on pedals for channel switching.
I dont have a DIY amp that does it on it's own.

But like you said,what are ya gonna do...

Glad I could express my opinoin with out offending you. 

[rotylee]

how about a charge controller to connect rechargeable battery's to alternative energy sources, cigarette lighter or wall as an option or with it in mind.?

guess it could be done separate.
http://www.solorb.com/elect/solarcirc/lvd1/index.html
AA Battery Solar Charger
http://www.solorb.com/elect/solarcirc/aacharge/index.html

[rotylee]

stumbled upon this site about building a portable video device it has info and pcbs of amp and preamp projects :
http://translate.google.com/translate?hl=en&sl=es&u=http://www.construyasuvideorockola.com/&ei=nWWRTIbTIYK78gbOy5igBg&sa=X&oi=translate&ct=result&resnum=1&ved=0CBUQ7gEwAA&prev=/search%3Fq%3Dwww.construyasuvideorockola.com%26hl%3Den%26client%3Dfirefox-a%26hs%3D862%26rls%3Dorg.mozilla:en-US:official%26prmd%3Div
PDF:
http://www.construyasuvideorockola.com/downloads/tda2050.pdf

plug and play DLNA?
network playback?
http://wiki.xbmc.org/index.php?title=UPnP_Sharing
http://free-electrons.com/pub/video/2008/elce/elce2008-scholz-coherence.ogv

usb stick playback?
http://dspdap.sourceforge.net/building.html
http://www.frankvh.com/mp3-player.html

[Top Top]

I just want to chime in and say Taylor I think you are doing a fair job with coming up with these decisions and I look forward to building one. The general idea fits very well with my personal interest in building amps. Kudos on not including mains power in the project as my last two experiences with electrocution weren't that cool 

I personally probably won't build the diode clipping section in to mine, but it will be easy enough to omit, so no real issue there. I think you are doing a good job of leaving it open and flexible enough to be useful to a lot of builders.

[Brymus]

Yeah I think its a good project.
I misunderstood,in that I thought it was just a power amp that you had to plug your pedals into as preamps.
I just didnt see the appeal of that.
But a simple complete guitar amp with a TMB tonestack sounds like it should appeal to alot of people.

[Taylor]

I just want to chime in and say Taylor I think you are doing a fair job with coming up with these decisions and I look forward to building one. The general idea fits very well with my personal interest in building amps. Kudos on not including mains power in the project as my last two experiences with electrocution weren't that cool  

I personally probably won't build the diode clipping section in to mine, but it will be easy enough to omit, so no real issue there. I think you are doing a good job of leaving it open and flexible enough to be useful to a lot of builders.

Thanks for the encouragement.   Listening to your album right now, actually. I'll really be looking forward to seeing your build, as I think you have a cool aesthetic going. Where are you in the country, BTW? Just curious if there's any chance I could see a show.

I think it's a solid feature set I've decided on, which provides a nice little niche. As I said, it can't be all things to everybody but I think it's good, and I know I'll build several of them, to have around for different purposes.

So now the difficulty turns to the implementation, making sure things don't overheat/melt/explode/kill your speakers, etc. I see some serious datasheet studying in my future.

[Top Top]

Thanks for the encouragement.   Listening to your album right now, actually. I'll really be looking forward to seeing your build, as I think you have a cool aesthetic going. Where are you in the country, BTW? Just curious if there's any chance I could see a show.

I think it's a solid feature set I've decided on, which provides a nice little niche. As I said, it can't be all things to everybody but I think it's good, and I know I'll build several of them, to have around for different purposes.

So now the difficulty turns to the implementation, making sure things don't overheat/melt/explode/kill your speakers, etc. I see some serious datasheet studying in my future.

I'm in California... though I'd like to make it pretty much everywhere again one of these days...

I have looked at datasheets for a fair number of the amp chips and dissected several power amps that use them (mostly in general car audio or home stereo type applications). Generally they seem to be designed to be implemented pretty simply, like just a handful of caps and resistors. The most important thing seems to be that big finny chunk of aluminum attached to the chip  

[therecordingart]

Come on...the Randall RG100ES preamp section with a lower wattage power amp.

[Hupla]

Apologies if this has been said I haven't read the whole thread and in a hurry, but I think maybe it would be a good idea to include instructions on how to mod you PCB or add all the other things people are asking for, like channel switching and such. Or even if you make a basic platform for people to mod on to. We could have a forum with suggestions and instructions covering everyone's needs.

[Taylor]

Apologies if this has been said I haven't read the whole thread and in a hurry, but I think maybe it would be a good idea to include instructions on how to mod you PCB or add all the other things people are asking for, like channel switching and such. Or even if you make a basic platform for people to mod on to. We could have a forum with suggestions and instructions covering everyone's needs.

Yep, if you've seen my other PCB projects, you can see that I always include extensive information on modifying them in the PDF document that accompanies the PCB. So I will definitely cover as much as I can, although this is a bit more open-ended than building a stompbox, so there' no way I can do it all in one document. Having a separate forum for it is an interesting idea - if it really takes off I will talk to Aron about that.

[phector2004]

Hey Taylor,

I fired up my wall-wart powered chip amp, cranked the volume up from 'bedroom' to 'basement', and noticed something strange... it hums whenever I touch anything in the signal pathway, whether it's jacks, plugs, cables, or even the guitar itself (strings, bridge, pickups, tuners, etc). I remember seeing a safety video somewhere where the same thing happened with a store bought amp when people cut off the grounding prong from their power cords... think it was posted on this forum, don't remember what exactly was causing it to hum.

I have a gut feeling my amp buzzing may be related to my 2-prong power supply (although it seems weird to me that it should even matter, cause normally the ground prong shouldn't be doing anything  )

Do you think something similar could affect the Forum Amp?
Does anybody know if there's anything concerning this to consider that may not have been implemented in my amp?

[DaveM]

Well when you touch anything in the signal path, you're basically a big antenna for hum.  Even a grounded amp would do that.

[Top Top]

I think what's turning me off of the laptop supply is the unknown. I know the look and what amp transformers do. I have no idea what a Laptop supply looks like let alone where to get one or what it's like to use. After all, it's made to power a laptop, not a guitar amp. Wouldn't be better to use stuff that's made for guitars?

That's just my thought process. Maybe I need to get out of my box.

Jacob

A laptop supply is just like a wallwart, but with higher amperage output, generally. They are also a dime a dozen.

It's my guess that these two reasons are why Taylor has chosen that type of power supply.

Edit: I thought the above comment was made at the end of the thread (recently), but somehow I missed the fact that it was from 10 days ago  

Taylor, by the way, I just bought some TDA2005 chips today. I am going to start with the datasheet schem and see what I can tack on the front to make it more guitar friendly. If I beat you to it and come up with anything useful, I will certainly share what I've got with you.  

For my attempt, I will probably build a really simple preamp myself though, maybe not much more EQ other than switchable input caps. I still don't think your plan is a bad one and I think that like the ruby has made it easier to gear the 386 to guitar players looking for some home jammin' this idea could be a step up from that and make it easy to get into something a little louder without a lot of complication or expense.

[DougH]

I haven't read this whole thread but these guys sell SS power amp kits for less than it would cost me to even think about a design, let alone coming up with a PCB for it. I would go the kit route for the power amp and then have fun coming up with a preamp (or not- just plug pedals into it or etc...).

[defaced]

I have a gut feeling my amp buzzing may be related to my 2-prong power supply (although it seems weird to me that it should even matter, cause normally the ground prong shouldn't be doing anything  Huh)

Actually it is doing something, but not like what you're thinking.  It's grounded to the chassis which is a huge shield for your circuit.  And guess where your guitar string ground ends up after it goes through the cable/preamp/etc - the chassis ground.  Somewhere your circuit needs to be Earthed, for safety and noise reasons. 

[Kitarist]

What about making a simple single ended tube amp? That would be much better and it would probably sound amazing

[Taylor]

What about making a simple single ended tube amp? That would be much better and it would probably sound amazing

That's a fine idea, but totally different from the concept of this. Check out the Firefly if that's what you're looking to build - no point in redesigning that, especially since I'm not a tube guy and would have no idea how to do so.

[Taylor]

I haven't read this whole thread but these guys sell SS power amp kits for less than it would cost me to even think about a design, let alone coming up with a PCB for it. I would go the kit route for the power amp and then have fun coming up with a preamp (or not- just plug pedals into it or etc...).

Yep, somebody posted that a few pages back, and it has definitely given me pause about whether to continue with the project, especially given all of the dissent about what the project should be. I thought it would be cool, but I'm not sure now if enough other people agree to make it worthwhile.

[Hides-His-Eyes]

I think it would be cool!