To make a long story short, I picked up this power amp kit for $10 to meet a minimum order requirement .  I wanted to see if I could get any opinions on the quality of the design. It's sold as a 30W amp and takes a single +50V power supply. The kit included a couple of heat sinks for the output transistors but I may upgrade to something larger. Here's a link to the instructions with a schematic. Note: The component values are not shown in the schematic (I guess they want you to buy the kit, since they are listed in the printed version of the document included with the kit).

Here's the document:
http://www.mr2-power.com/FK656E-1.pdf

I can supply specific component values if it would be helpful.

I have a couple of specific questions:
1) Am I giving up anything by using a circuit with a single positive power supply rather than the typical bipolar supplies you see on amps like this?

2) Can someone explain how the power supply design they show in the drawing can result in 50V DC? They say to use a 31-0-31 center tapped transformer... Wouldn't that result in closer to 80V DC after it's rectified?
Edit: Nevermind... I think I understand.. Since they used the center tap as the ground reference the two ends of the secondary are tied together in parallel resulting in a +31V AC voltage potential before being rectified... that would result in somewhere around 45V DC after rectification... In theory I could probably get away with a 35-0-35 transformer.


I plan to build the amp regardless (it was only $10 after all) but I would like to know what I'm in for as far as sound quality and robustness of the design.


Thanks in advance,
-Matt

This may seem like a dumb question, but here goes... Is there any obvious difference (with regard to the quality/tone of the audio) between an inverted and non-inverted opamp gain stage?

I understand the technical differences such as the fact that non-inverted stages can't have a gain of less than unity and the fact that the output of an inverted opamp stage is out of phase with the input. But other than these technical differences, why would you choose one configuration over another? To me, it seems that setting a high input impedance on a non-inverted stage is easier since the impedance is set by the pull-down resistor rather than the series resistor before the inverted input.

Any thoughts?
-Matt

after playing around with the LM386 I decied to search for some of the discontinued chips in the same series. At my local electronics surplus store I picked up two each of : LM380 (2.5W), LM383(7W) and LM388 (1.5W).
Does anyone have any experience with these chips for use in guitar amps?  Any sample schematics?

-Matt

This may sound odd... but is there a noticable difference in the sound quality of the amp if you mount the 22K feedback resistor in the thru-holes or directly on to the pins of the LM3886? I know early revisions of the board did not have holes for the resistor, but the rev B does... Any thoughts?
-Matt

In anticipation of my LM3886 kit arriving I took a trip down to my local electronics surplus store (amazing place) to see what they have for heat sinks... I picked up a couple medium sized sinks  for $1.75 each. Think they will be large enough? They seem to be on the small side of what I have seen posted here. How about if I mount the chip to larger piece of copper plate and then mount two (or more?) of these heat sinks to the other side? Here are the dimensions:

4 1/2" L
2 3/8" W
7/8" Thick

16 fins.

Your thoughts?

Ok, I'm still trying to find a good preamp circuit for my power amp (maybe amps, depends how this first one goes!). I've built  a small 25W stereo power amp that runs on a single +12V DC supply. So, that pretty much eliminates any bipolar designs (this time). I built a Professor Tweed ROG pedal for a friend and tried it in front of my power amp but found it MUCH too quiet. At anything less than say 70% the volume was way too low. Even at 100% the power amp was not pushing any decent output. I have verified the power amp is good with a mp3 player and hi-fi speakers so I know that's not the issue.

so, I'm at a loss now...
1) is it reasonable to contstuct a preamp running off +12V DC with sufficient gain to "properly" drive my power amp? I would like the most clean headroom as possible as clipping tripath chips is generally not advised. Of course, all volume and tone controls will be passive.

2) How about using a LM386 as the preamp stage? I've read some posts indicating success with a ruby circuit as a preamp. I'm concerned that the low output impedance of the 386 won't be a good match for the power amp though.

here is the datasheet for the power amp chip I'm using. http://www.datasheetcatalog.org/datasheet/Tripath/mXyzxwww.pdf

I would really appreciate any suggestions or advice you guys could give as I'm a bit in the dark here and don't want to waste a lot of time and money building circuits that won't work for my purposes.

FYI, I do have all the parts to build this: http://www.beavisaudio.com/Projects/ValveCaster/MatsuminValveCaster.gif which I will try at 12V, but I don't have high hopes, so I'm looking for back-up plans.

-Matt

I'm building an amp head based on a 25W stereo Tripath kit (The AMP6-Basic from 41Hz). I'm trying to figure out which is the best way to split the input into the two channels. If I wire the inputs with a stereo jack then any stereo effects plugged in to the amp will output on discrete channels. Any mono plug jacked in will be split between the two channels evenly. My current plan is to build two preamps (one per channel) and simply tie one to each input of the stereo input jack.

Here's the question.. will I be providing sufficient input impedance to "load" the pickups?

The preamp inputs have a 4n7F input cap and a 1M input impedance. Should I raise the input cap to 1.5M so when "splitting" the input of a mono plug the guitar pickups "see" 750K? If a real stereo plug is inserted (either from a stereo effect like a chorus pedal or from a stereo guitar) then each channel will see 1.5M... Does this seem reasonable? Or should I just build the circuits as-is and see what happens?

Here's a link to the preamp stage I plan to use (times 2) http://www.diystompboxes.com/smfforum/index.php?topic=63479.0 I will be running it at 12V since I already use that to drive the power amp.

Any advice is much appreciated!
-Matt

I am brand new to the forum and have been trying to soak up as much info here as I can but I'm still in need of a bit of "spoon feeding" . So, please forgive my obvious "noobness".

I have built and tested an "AMP6 Basic" kit from 41Hz.com ( http://www.41hz.com/main.aspx?pageID=118 ).

So you don't have to read the website, here are the vitals:

• 25W x 2 output
• based on Tripath TA2020 chip
• powered by 12V DC "brick"

So, I want to turn this guy in to a little practice/small gig amp for a friend. I'm either going to have a single guitar input that just gets duplicated on both channels (one preamp) or a guitar preamp on one channel and a mic preamp on the other.

I am having serious problems deciding what to do about the preamp stage. Can I simply use one of the many pedals adapted from old tube amps? (like the kits found here: http://olcircuits.com/olckits.html).
Or, am I forced to build something custom? My goal is to cram the preamp and power amp into a smallish enclosure and run cables to satellite speakers.  My initial plan was to build a simple JFET preamp circuit found here: http://www.till.com/articles/GuitarPreamp/index.html but I'm not sure if that has sufficient gain, and it lacks a tone stack.

I would like something that can run off the same 12V power supply I already have for the power amp. 

Any suggestions? I can build a kit with the best of them, but get very frustrated with perfboard and trying to source obscure parts so I would be more than willing to pay a bit extra for a ready to assemble kit.

Thanks for your patience and any advice you can give.
-Matt Armstrong