Mosfet clean

[stutter]

Are there any clean amps about here i could build? i know theres the ruby but im looking for around 25/30watts output.It could also just be a preamp,whichever there is.

Cheers

[stutter]

just another quick question,what kind of voltages would i need to get 30 watts out? Cheers

[stutter]

could i build the ruby and substitute the chip for something that will handle 30 watts??...if thats even possible 

[Ben N]

Hold on there. Ruby is a very low power practice amp, ideally suited to bing overdriven. At its heart is a 386 power amp chip. So what s it that you mean by Mosfet? Or by "preamp"?

If you are looking for a higher power solid state amp, there are chipamp designs around, I think at General Guitar Gadgets, among other places.

Also, do a search here for "chipamp".

Ben

[stutter]

Cheers for the info.Just one more question does the LM3886 chip *need* to run into 8ohms or could it also be run at 16?

[petemoore]

  TDA...chip amps, and there's a 'gainclone' amp people like building..
 The chip amps seem like a good starting point, I'm trying to increase mosfet output on mosfet amp I have...
 er..get a new mosfet amp happening for guitar use, using...mosfets mostly, and of course a power supply.
 RG helped me through the PS Voltage finding formula ... Pkv =^[2*I*P]...check that thread and the accuracy of my memory...second time I've typed that in as many days...the thread is a great read, and I've copied it to 'addition to FAQ' for easier search.
 Building fuzz boxes has certain things in common with chip type [transistor or other] amp building, but there is alot of 'semi-charted' territory...most of the designs I've found are striving for perfect waveform amplification...while this is desirable for playback reproduction..or other applications where distortion is undesirable, I'm not certain whether/how much of that is necessary or desirable for guitar amp applications.
 A big difference I'm finding [or not finding] is the availibility of schematics and design info for SS guitar amps.
 Here are some questions and topics I'm seeking answers and information for, still in progress...working on it:
 What is a good' wattage to expect from a simple Mosfet transistor @8ohms.
 What is the next best step toward doubling the power output..
 Push Pull...understanding this and the preamp/phase splitter...and amp better than I do.
 Do I want any distortion in the output amp?..I *think I'm getting distortion from the source follower..it's kind of 'cool, but seems always to be there when level setting is higher, also seems to work with the other distortions...so...it's kind of a 'distorter' amp?
 For a 'mosfender' type sound, clean spanks...I would think most of the 'distortion' would be wanted from heard mostly from the speaker or pre-processing.
 Source driver to speaker...seems to work well, that's what I've tried so far, that and a 9v pre into a 18v pre to get the swing voltage up...it's a really nice 'Mosfet Distorter' amp, I get good kicks w/simple distorter, stereo echo driving the 2 amps into 2x8'' ers, 1.5' speaker separation, 'domeback' rear speaker enclosures, 1 styrofoam bucket, 1 paper mache', bucket resonates good, could be dampened but I like it, the mache' is very damping.
 These amps are designed to be run on 15vdc.
 I'll try running some equations...check my math..
 Vpk = ^(2*8*P*), ...8 ohms and X amount of power.  
 When mosfets share a heat sink, is there a connection, if so, what attention does it require? [I'm using heat sink pads I found, this seems to insulate, depending on the installation, ie heat sink/bolt/mosfet plate.
 For reference:
 - the power supply voltage is nearly always bipolar, and each polarity is close to the peak voltage it can put out. The only difference in peak output voltage and supply voltage is the saturation voltage across the output devices, and that tends to be a couple of volts for bipolar, up to 5V for MOSFET.
- knowing the output power and impedance tells you the power supply voltage. If it puts out 100W into 8 ohms, that's really "100W of a single sine wave with no distortion" so the peak value of voltage is the value that gives 100W into 8 ohms. Since P = (Vpk^2)/2R, we can solve for Vpk as Vpk = SQRT(2*R*P). So 100W into 8 ohms is Vpk = SQRT(2*8*100) = SQRT(1600) = 40V pk. This would require a +/-40V power supply at minimum, and probably more like +/-44V. So the transformer winding would need to provide the AC that rectifies to 88V, or 88/1.414 = 62.5Vct.  
  Vpk = ^(2*8*30)
 2x8=16
 16x30=480
 ^480 = Vpk
 ...21.9 x 21.9 = 479.61...well use '^22 = 484'
 See other thread 'voltage peak to peak'...
 So 22v peak voltage, -/+22v to get Vpp, plus what the transistor wants.. then do the other math or figure +/-23v should get you in the ballpark, I don't know how 'curvy' the math is here, shooting from the hip and comparing to RG's addition of 4v [from 40v to 44v] equates at least approximately to 22v and 23v to get 30w.
 Going over the needed voltage...how bad is it?...if it's a small overshoot, it can easily enough be adjusted for using Zener to drop it down a little...but I would guess it would simply increase headroom if it isn't damaging the transistor...this can all be dug out of the data sheets, using the math...I'm just warming up to the idea..
 Zen Amps [Nelson Pass], show many possible designs of amps, Hi fi oriented as far as I can tell, I typed 'Mosfet Amp' and Mosfet output amp...lots of other stuff...'phase inverter, transistor phase inverter' differential output amp...I'll scour through again..I haven't seen a whole lot about 'guitar amp' designs...perhaps there's a reason it isn't very popular so far, I think part of that is it's alot to go through...when used Mosfet Technology is abundant enough.
 I would like to take a look and try understanding what a popular commercial mosfet amp has going on under the hood, I'm sure something with more fixed values, fewer features could be made to perform quite well...perhaps lifting mostly the driver and output sections, then working the preamp with alternate circuits @lower voltages, like CMOS, Mosfet, Jfet, OA...tube.
 Made big enough to be relatively clean for a 'regular' amp sound I think.
 For distorting a distorter, mosfet driver-amp-speaker actually works quite will IME, I wouldn't mind just having 'that' [it would have to sound bigger to be useful on stage] as the 'distortion' amp...[in addition to my 'tubey' amp which distorts, but mildly...hit the Mosdistort switch, and a whole new source of distortion, all tuned up and ready to distort right on cue, comes into play, alot like distorting my tube amp does now, but I think a separate amp kicked in would sound novel, pique interest to a greater degree.  
 I had a couple Mosfet Tech amps, Fender M-80 [was that Mosfet?] and a Marshall Mos combo, these amps are Bdazz, not something I'd want to get used to using at all times, but...whew...can be a fierce weapon...but, I think, like my Fuzzboxes, the Mosdistorter type amps would theoretically be more useful if tweeked..not the amp so much [I want something that just works good driving the 1 or 2 speakers, probably 12''] then push them in various ways to discover where the actual usable sounds I want are 'hiding'.
 It seems that tubes have time on their side, mucho tube info, amp types, availability of schemata, many of the avenues have had a fine toothed comb go over them at least a few times, a long, well documented history surrounds them...Mosfets OTOH, are recent in comparison, have even more recently seen improvements in component performance and availability...'transistor amp' caught some bad raps early on [it's hard to re-make a bad first impression], this lives on...nope, they 'can't sound exactly like tubes under all conditions, like tubes do'...maybe this is the good 'old news', ...let the new mosfet follies begin !    
 

[petemoore]

  Check the data sheet, but, running at 2x the ohmage will increase longevity, decrease heat dissipation and output volume.
  Not that a perfectly acceptable performance and heat dissipation can't be had at 8 ohms.
  Volume controls, bass controls etc., how hard you strum, all influence these factors, ie, it might sound loud enough @16ohms, about the same as 8ohms, but with the volume control turned up, it won't turn to '11' though, unless you stencil 11's on the front panel.

[alextheian-alex]

Cheers for the info.Just one more question does the LM3886 chip *need* to run into 8ohms or could it also be run at 16?

There is a spredsheet for the 'overture' series chips that will let you plop in the values and see what comes ouy... NO, you don't have to run it at 8 ohms, and you can use the sheet to maximize the output at whatever impedance you like.

[dschwartz]

this is a great forum about solidstate guitar amps:

http://www.ssguitar.com/

all you need to know is there..
I strongly recommend TDA2050 chip..they sound very good for guitar (small marshalls valvestate uses them) and very easy to build, using the datasheet application (the datasheet includes PCB and layout!)

[petemoore]

 I haven't checked out the above link, Rod Elliot at http://sound.westhost.com/project36.htm
  ESP has some great amp info ! Page around in there..cool stuff !
  That project is just one I was reading about, nice and simple, he seems to like BJT's, perhaps some of the topology would lend itself to mosfet technology.
  Shooting for 10w-12w using mosfets might be a good start, but I'll be reading more soon.
  Right now I'm going to look at the above link, the title looks on subject.

'
 

[stutter]

Hmm lots of good info but i still need some to find out something.The projects At GGG ask for a bipolar power supply.This amp will be inside a tube amp as a seperate clean channel.Could i just run it of one of my tube pins that is at about 29v? instead of using a bipolar power supply.

[petemoore]

 BTW..
  Where's a good source of these chips, I'm not seeing any Mouser or SB chips of the TDAxxxx or the lm3886 types?
  And dern if I can't tell yet if I got the order in at National Semiconductor..daft Email 'dumped' it instead of putting it in my inbox from junkmail..