I saw that on the instructions, and they didnt mention a series resistor. I'd look at putting one with the LED.

QuoteAnd went from a Dr Z tone control to a Marshall TMB in the last version.

Is this the Marshall TMB?

http://i419.photobucket.com/albums/pp276/Bry928/SolidState%20Amps/12Watt-TDA1519B%20build/386PreAmp_2.jpg

 I think the best choice will be the one that has the most tone shaping. The Noisy Cricket Mk II looks like the leader with a grit switch, gain, volume and tone. Smokey's got gain and a tone switch, Ruby's and Little Gem have volume and gain pots. I have had my eye on the Tonemender as well, so naturally I searched for it in this forum and found an improvement, the PhAbbTone box, by the username phatt. Might have to breadboard a few.

Thank for the tips re preamps. If I can do overdrive easily and keep it cheap, no reason not too.

I have wired the amp to a 4Ah 12v SLA battery, it arrived charged from new, I havent used it long enough to comment on how long it will power it for. I hooked a Onda mp3/4 player and it sounded terrible. Distorted and not loud at all, nowhere near the volume needed for an amp that will do some outdoor work. I then tried a laptop as a source and what an improvement, the amp sounds pretty good, actually really good. With the mods the guys are doing in the link in my early posts, this would be one sweet hifi amp. Tone controls are not great, but they can be improved. It has run for maybe 5 hours at low volume at work here and the battery has dropped maybe 0.2V, to around 12.6. No heat that I can feel anywhere in the amp, the laptop power supply is warm. So a very positive first impression, I think this amp will be up to the task.

Next step it to hook a mike up to it. I have also found a delay pedal so I may get some idea what the reverb will sound like. What is the difference between delay and reverb anyhow?

Stay tuned, and please post comments.

Edit: I'm answering my own questions. Does it get any sadder than talking to yourself on an internet forum? Anyhow, http://www.harmony-central.com/Effects/effects-explained.html

Very interesting, thanks for that. So it may be a matter of starting a speaker collection and swapping them around untill the best sound is found.

I have been thinking a lot about the sound I want out of the amp, but I only have what I have heard on YouTube and downloaded mp3's to go off. I purchased a few of Adams lessons, I have downloaded a lot of the YouTube ones of Adams and Jon Gindick, and I have instructional material with cd's, my favourite being Brendon Power's "Play Irish Music on the Blues Harp". From these examples, I prefer the "clean" sound of the harps. When Adam demonstrates a technique, then plays it through an amp, it sounds harsh and grating. I am certain the little mike he may be using when recording the lessons is not doing the sound justice and it sound a million times better in real life, but I still like the sound of a undistorted harmonica. I think the amp should have the ability for a bit of overdrive, but I dont know if it is going to be as important in this amp as it would be in a amp designed for electric guitar. I kindoff pictured this amp would be used with acoustic guitar more that electric, maybe some electric bass (only because I already play bass, not sure how it will handle low frequencies).

Anyone care to comment on the need for distortion, and how much, for harp?

I now have the amp, it is a small circuitboard and wont take up much room at all. Next step is to decide what size and how many speakers. I need 2, one for each channel, and I'm thinking 8" drivers, but this is only based on "I seem to recall reading that a few well known harp players prefer 8's". Their size and weight fits the design criteria, as long as they sound good. I think Adam Gussow talks about his combo's, one tube, one SS, both with 8's in his 2nd youtube lesson, but I may be wrong. I think the best design I have seen is on Bill Fitzmaurice's site with the fairly new XF Guitar Cabs.
Link here:

http://billfitzmaurice.net/XFCabs.html

The smallest is 2x10", I asked on the forum regarding the possibility of scaling it down for 8's. Bill replied "You can, though it will take quite a bit of graphics design skill to do so." My graphic design skills are high school geometry, but if its just a matter of getting the 4 angles correct on the speaker surround parts I think I could eventually figure it out, and scaling down the rest of the box will be easier, good enough for prototype purposes. All this should be ok as long as Im not missing some very crucial points, like the lengths of the inside dimensions cant be the same as the 1/4 wavelength of the 8th harmonic, or the change in box volume will mean the formally crystal clear highs will now sound like mud.

edit: check this out, very interesting. Open back, sealed, or ported?

http://www.webervst.com/sptalk.html

http://www.diyaudio.com/forums/class-d/90500-lepai-t-amp-ta2020.html

There is a huge 50 page thread on these amps in the DIYaudio forums, adding inductors and higher quality and different value components, bypassing the tone controls etc. One guy had a hand drawn schematic which I neglected to save. I don't think these chip amps can be paralleled or bridged, so I'm thinking the best way to set this up is send the same signal to both input channels and connect 2x8" drivers. I have ordered one, hopefully it will be here next week.

I think at the start I will experiment with the gear I have before trying out that reverb PCB from OCT Distribution, though I did email them and they answered and said they will be happy to freight one to me overseas, so that's excellent. Always good when a company replies like that, thanks OCT.

I have a Sure SM58, never tried harmonica through it, (any comments on the suitability of this welcomed), I will run it through a Sansamp Bass Driver to the amp.

I have also found a 12V 4AH SLA battery. I need to find out what voltage this puts out at full charge, because I think some guys had blown the chip from running of a charging car battery at just above 14v.
I also wonder if 4AH will be enough, at full noise drawing 2 amps we get around 2 hours? How will the battery like that kind of power draw?

So many questions!

This looks like a cheap way to get into one of those chip amps:

http://shop.ebay.co.uk/?_from=R40&_trksid=m38&_nkw=Lepai+TA2020+

There are people modding them if you search. I'll have to try to find a circuit diagram.

I don't know if the chip is stereo out, do you mean it applies effects to separate channels then mixes them internally for a mono output?

Re the mike input, I meant there will be different impedance between a guitar and a mike, or is it fairly simple to built a High Z / Low Z switch on the amps input? Maybe it would it be better to have a low Z XLR socket for mikes and separate High Z for the guitar input.

I don't know if I read it wrong but I thought if you have the echo and the reverb level at zero on the pots, you will have a clean signal. But I think you still need to be able to switch between options.

On this link there is schematics for a guitar pedal, http://www.oct-distribution.com/datasheets/SKRM-C8-G01.pdf , they have used a multi op amp chip, there is bypass and what must be volume as well. Also an IC connected to the 8 position switch, I think that IC connects to the EEPROM and not the 3 switches on the main effects chip as the main chip cannot be programmed. So we need another PCB.

I can follow most of the schematic, but what is the opamp with pins 12, 13 and 14 for? Is it just connected up in this way because it is unused?

I have no experience with harp through amps, how essential will eq'ing be? Is it common to cut the highs out for example? And does anyone use distortion?

Edit: http://www.runoffgroove.com/tonemender.html
This site rocks. Hows this for some EQ?

Im pretty keen to have a go at it, but want to get some advice before I start, my DIY projects seem to end up tripling the original estimated budget.

The pre made effects board seem to have the eeprom with pre loaded effects, not the factory ones which is a bonus, one of the factory ones is labeled as "test". The advantage of having two channels on the amp means it may be possible to have some kind of mixer and mix a clean signal with an effects one (I think the correct term for this may be wet and dry signals? Or am I thinking of sandpaper?).

I wonder if there would still be a need for a pre amp, or a simple 3 band eq, or a little distortion, or seperate impedance inputs for mike for the harp, and guitar. Also for efficiant speakers, the Fitzmaurice jack 10 might be worth looking at.
http://www.billfitzmaurice.com/Jack.html

Feel free to post at other forums, the more info the better.

I'm looking at doing the same thing with the 41Hz amp ( http://www.41hz.com/shop/item.asp?catid=42&itemid=43 ) and this little gem:

http://www.spinsemi.com/products.html

http://www.oct-distribution.com/

for a bit on onboard reverb. If anyone has advice I'd appreciate it.