Juntunen Guitars Posted July 9, 2010 Report Share Posted July 9, 2010 I have been thinking about designing a preamp to work for the amp I am building. I have designed some diagrams but nothing like a preamp and am not aware of the cost or what all I would need. I do know that it will be solid state because tubes and transformers are expensive and I can't afford those. So does anyone know exatly what all is needed for one besides the obvious treble, bass, volume, etc. knobs and a power supply? I plan on this being built as a rack mount preamp and I will be adding a power supply for my amp that I already have designed for this. The amp is a 2x12 cab with a 250 watt sony Xplod car audio power amp powering it. As of now I will be running my pedal board (basically an RP355 multieffects proccessor and Digitech whammy) into the RCA inputs on the amp. The speakers are bridged to get 250 watts into the two 8 ohm carvin speakers. I want to have a seperate preamp/power supplt thing that I can put the effects into though but need some help on it. Quote Link to comment Share on other sites More sharing options...
Ripthorn Posted July 9, 2010 Report Share Posted July 9, 2010 Most distortion stompboxes are simply a preamp in a little box. If you cruise through some stompbox forums or look at runoffgroove.com, you will find several designs you can use as-is. Also, tubes are not much more expensive than other stuff. Yes, you need transformers and tubes, but if you do it right, you can get a great sounding amp cheap. I did a five stage tube preamp into a push pull tube power amp for really cheap. Of course, it is a low power amp, as I don't gig, but it works great for what I do. A tube preamp might run you upwards of $50, but you could do it cheaper if you used submini tubes. The short and long is that most any stompbox design will work. You can even do two completely separate circuits to have two independent channels for your preamp. It all depends on what you want and the kind of electronics experience you have. no need to reinvent the wheel, just dress it up the way you want. Quote Link to comment Share on other sites More sharing options...
borge Posted July 10, 2010 Report Share Posted July 10, 2010 The RP355 is a preamp. try the mixer/amp switch on mixer. Quote Link to comment Share on other sites More sharing options...
Tim37 Posted July 10, 2010 Report Share Posted July 10, 2010 so your gonna use a hifi car audio amp for your guitar rig any way those rca imputs are designed to take around half a watt of power max after that there gonna start distorting and not in the good overdriven tube guitar amp sorta way its gonna sound like you just turned the volume all the way up in your car and the speakers are rattling kinda way. Quote Link to comment Share on other sites More sharing options...
Juntunen Guitars Posted July 10, 2010 Author Report Share Posted July 10, 2010 (edited) any way those rca imputs are designed to take around half a watt of power max after that there gonna start distorting and not in the good overdriven tube guitar amp sorta way its gonna sound like you just turned the volume all the way up in your car and the speakers are rattling kinda way. I thought about that at first and then thought how does that work if a cd deck is putting 17 watts into the RCA inputs and it does not do that. I did have a few original questions about using the amp for this, what speakers to use, that sort of stuff and I asked one of the guitar players in my band who is a computer designer/programer and he gave me a bunch of into on how to make it sound right and stuff so I am good there. I just thought if I built a preamp I could get more tonal possibilities out of it plus I am the type of guy who likes to wprk on things and do things myself so I think of building a preamp as a challenge I want to do just to try and if it works hey I have a new preamp. Ripthorn that's a good idea I didn't think about stompbox preamps. I will check that out. Edited July 10, 2010 by Juntunen Guitars Quote Link to comment Share on other sites More sharing options...
Tim37 Posted July 10, 2010 Report Share Posted July 10, 2010 your cd deck doesnt put 17 watts to the rca imputs the rca imputs on my kenwood put out .4 watts (that was there new standared a few years ago) my old pioneer put out .7 watts on the rca's. your amp my have high and low imputs if it has high imputs thats where you wire the normal speaker outs of your cd player into the amp. its been a few years since i played with car audio much but i think most of the amps where getting away from high level imputs just too much noise. Quote Link to comment Share on other sites More sharing options...
borge Posted July 10, 2010 Report Share Posted July 10, 2010 RCA's are for signals: low voltage, low current, under no circumstances should 17 watts be going through RCA's, a CD head unit sends high power to the speakers, not the RCA's what 'tonal possibilities' are you looking for? like tim said, boosting the input isn't a good idea, so that leaves EQ and distortion....which your RP should cover... Your RP355, like most multi effect units, is designed to be plugged straight into a mixing desk (hence the switch i mentioned...) self powered speaker ect, hell, I've plugged mine into home hi fi & car stereos, no additional preamp required of course.. thats why they have guitar speaker cabinet simulations: to give guitar speaker frequency response when plugged into full range speakers.... you have a stereo amp and stereo multieffects, it seems a waste to go mono... Why not unbridge your amp and wire your cab for stereo. true stereo effects are a sound to behold. Quote Link to comment Share on other sites More sharing options...
BJPUC Posted July 10, 2010 Report Share Posted July 10, 2010 i had a car amp that you could either use rca's or the speaker outs of your existing radio. of course this was 15+ years ago. so wouldn't that send out more wattage than the rca's? i can't remember the amp brand, but it was prolly 5 years old when i got it. just curious, none of my amps since then have been that way. just food for thought. mmmmm food. Quote Link to comment Share on other sites More sharing options...
Tim37 Posted July 10, 2010 Report Share Posted July 10, 2010 Back in the ninties it was pretty common to have both high and low inputs but the trend has been to not do the high level inputs. Infact I was looking at a amp a while back that uses digital inputs this cuts out a lot of noise. Quote Link to comment Share on other sites More sharing options...
Juntunen Guitars Posted July 11, 2010 Author Report Share Posted July 11, 2010 I must have read the specs sheet wrong, I was tired when I did I know the RP would work like I said before I have had conversations with the computer programmer I know. I was originally going to get a Digitech GSP1011 but got the RP 355 since it was cheaper. They have the same memory chip in them (can't remember the name of it) and I mainly wanted to get one so I could use it with this amp. I don't like to spend a lot of money and didn't feel like spending over $300 for a amp I can use for gigs so I figured I would use an old amp I have around. Stereo effects are something I have never messed with but I will definatly try it out. Quote Link to comment Share on other sites More sharing options...
Tim37 Posted July 11, 2010 Report Share Posted July 11, 2010 may i ask how you plan on powering this amp? Quote Link to comment Share on other sites More sharing options...
ansil Posted July 12, 2010 Report Share Posted July 12, 2010 i did something along these lines a decade or better ago and it worked fine but i was using a custom powersupply and driving four lower wattage all mosfet amps from my rig each one was setup to be like a powered twelve inch cabinet. so we made a glorified stakable unit like from the late eighties it worked well but i found it was easier and sounded better to just get a one space rack unit from carvin. thousand watts 150 bucks or so. Quote Link to comment Share on other sites More sharing options...
Juntunen Guitars Posted July 12, 2010 Author Report Share Posted July 12, 2010 Tim37 - I have a 120V to 12V converter for this. But it can be done with a small battery charger too. A guy I know rigged a home stereo with a car power amp and used a battery charger to power it. ansil - I know it would be easier to get a carvin power amp but their cheapest one is $279 and the whole point of this project for me was to save money Quote Link to comment Share on other sites More sharing options...
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