The "Forum Amp" design thread

[jkokura]

Brilliant.

Pete, you're one of my favorite people. If you ever record that, I want a copy.

Jacob

[brett]

Go Pete.
Hi
RE: What would you suggest instead of a regulator for dropping 19.5v down to 14 or 16v?

A simpler (equally power-wasting approach) is to use a couple of 1N4004s.  They take minimal space, provide polarity protection, handle an amp (or two) and drop 0.7V each.

Note, however, that very very few devices blow at 20V if they are rated at 18V (ie they take something like the 0.001 percentile voltage for failure and add a couple of volts).  An EEs might know about "padding" and "stacking" the ratings? e.g. LM386s are run way overvoltage

I notice that printer power supplies are often 32V and a couple of amps (around 50W).  Ideal for supplying a discrete amp.  It might run a pair of 12AU7s if you wanted a valve amp (a la Firefly).
cheers 

[tominator]

 In the days of my youth I was shown what it's like to have an amp !
 Then I reached that age where I too got to feel a volume ramp.
 No matter how I tried all my notes just came out sounding damp.
 Good Amps Bad Amps..you know I've had my share, with all the HV's they kept inside I was just too shy to dare...
 Still 16 I got an amp with a sound as sweet as could be...
 It only took a couple days...my speakers blow on me.
 I swore I'd find the driver..would last me 'till the end.
 Then I found some other places for money I could spend...ohwaoughh !
 Chorus.

[Taylor]

Just a quick update: I decided to go in 2 directions with this.

One will be a super simple, tiny amp. It has a clean high impedance input buffer, volume knob, power regulation, and power amp. No EQ, no clipping, just clean amplification. It fits in a 1590A. 20 watts, and the nice chipamp features like automatic protection if the speaker terminals short, etc. So, a clean 20 watt amp that fits in a 1590a. Of course, you could build it in something bigger and add your favorite preamp. But even without an added preamp, you can plug your guitar straight into this guy.

Prototype PCBs have been ordered for this.

The second will be the one with 3-band EQ and a clipping/comppresion section. Still ironing out the details on that design. I wasn't too pleased with any of the common 3-band tone stacks, due to the inability to boost mids. I'm working on a gyrator-based mid section, with Baxandall bass and treble.

[deadastronaut]

yeah that sounds cool,  20 watts is plenty for my needs, i like the idea of the eq section too. nice one taylor.

look forward to this one..rob.

[phector2004]

20W in a 1590A? Count me in! 

Will it be a snug fit with input/output jacks?
Any need to make a hole for the heatsink?

[Taylor]

Well, to me anything is a snug fit in a 1590a  I'm 6'1" with Sideshow-Bob-sized feet. The PCB is 1.1" x 1.7".

I don't think a heat sink will be necessary - the regulator and chipamp will need to be screwed to the enclosure, which according to my tests so far provides adequate heat-sinking.

[kin0]

I wanna build an 20watt amp too (power by 12-14valt). I have a preamp but I am not sure which power amp to build. It is my first amp but I built couple of stomp boxes before. So which project do you recommend (A cheap kit is fine too)?

[Taylor]

Uh, well obviously I think you should build my amp rather than somebody else's. 

If you're looking for an unbiased opinion you'd get better responses by starting a new thread.

[zambo]

i think he means preamp with eq or just power amp...i think? anyway...I want the power amp badly! Whats the power supply like? Do I have to build it seperate or can I use a walwart type deal?

[Taylor]

Ah, well comparing my 2 amps, one is just clean power with a volume knob. If you want any tone-shaping, distortion or sound enhancement of any kind, you'll need to add your own preamp to it, or build the full amp, which acts more like a guitar amp, where you can shape the tone and add overdrive.

Power supply: it will operate from a laptop power supply, in the range of 12-20volts. I will have details accompanying the build instructions on what power supply to use. But you don't have to build the power supply and there are no high voltages to deal with.

[Ice-9]

Hi Taylor, I logged on tonight to especially re read this thread, to find the thread has been updated is inspiring. I just received 5 x TDA2050 in the post today so will need to do a little messing around but in general your project will be going along similar lines to what i'm doing, although i want to build my amp into a cab/ combo style. I am also hoping to add onboard digital fx based around my own FV-1 module. I also have went for gyrator based tone section but on treble mid bass and presence. I might also addheadphone and speaker simulator outs. Mind i do get carried away with what i want.

Anyway  I just wanted to say i'm following this thread with great interest and I am looking forward to the next update.

[zambo]

this sounds sweet! Will this power amp be able to handle a bass as well ( assuming the proper preamp is used)?

[Taylor]

Yep, I'm a bass player more than a guitarist, and I really like it, even without any EQ. Nice low end. It is 20 watts, of course, which isn't enough for a bassist playing live in most cases, but I do think 20 watts is louder than most people think. It's only half as loud as 200 watts. There is a weird watt obsession in the musical world, of which I used to be quite guilty. As a casual musician, I used to use a 1600 watt power amp because I thought I needed that much power. 

[zambo]

LOL!!! I am actualy building a 5 watt Trainwreck style amp so I can actualy use the volume knob on 7 at a gig! Yeah I think 20 is good. I want to put a line out for live use anyway. I wil probably use a tube pre but tuned for guitar or tuned for bass accordingly.. I just want some good power amp choices and GOOD solid state power amps are hard to find. So how do I get a board, b.o.m. and parts?

[Taylor]

I have to get the prototype boards (probably about a week and a half) then get the full run made (about 2 weeks more). So boards and documentation should be available in about a month.

[zambo]

sweet! I will be keeping an eye on this thread. Cant wait

[bassmannate]

I'm really excited about this! I've been catching up on this and I was a little disappointed when you were talking about adding an integrated preamp. I'm really glad that you're making it possible to take that out! Someone else may have thought of it already, but what might be neat is to put it in a larger rack mounted enclosure with SEVERAL pre amps and a rotary switch much like a Line6 POD works to select different amp models. The possibilities are quite literally endless with a nice clean power amp! Can't wait! Count me in after I build my valvecaster and Ruby!

[bassmannate]

Since I work at Best Buy, I really like the idea of using a laptop power supply since I can get new ones for fairly cheap. Probably not as cheap as eBay though.

[JKowalski]

Since I work at Best Buy, I really like the idea of using a laptop power supply since I can get new ones for fairly cheap. Probably not as cheap as eBay though.

I get all my laptop power supplies for $1.99-$4.99 at my local thrift stores (Goodwill and Savers).

Never found a bad one, and there's always a wide selection - even up to 150 watts!