Quote from: teemuk on March 22, 2008, 01:30:48 PM
For anything else... Well, the problem is - I likely could recommend some stuff but the information you give is quite scarce. You just state that it should be about 10 - 20 watts and pristine clean (not an easy equation by the way). That's not a very informative description. Do you only need a power amp or do you need a preamp as well? What about features? Tone controls (if yes, what kind), loops, limiters, feedback suppression etc? Overrall simplicity? Can you work from a schematic or do you need PCB layouts as well? Give us something to work on...

Thanks for the response.
I was thinking of a fairly simple amp involving preamp, poweramp and passive tone controls. I don't think I need any loops or limiters and hadn't even thought of feedback supression. Overall something fairly simple. I can read schematics, and studies engineering 20 years ago, but am just a hobbiest. Yes, I can work from a schematic (at least the less complicated ones) and prefer that for simple point to point wiring.

The .5 and 1 watt amps I have built don't have enough power. On the other hand years ago I bought a big old 100 watt Fender (thinking I needed that to emulate some people's sound) and that was WAY too loud. I was thinking that sincle wattage is logarithmic something in the middle (~10 watts) might be suitable. I just want to avoid the fender situation where you are trying to find a nice volume level somewhere between 0 and 1!

Teemuk, you mentioned the LM3886. Are there any good fairly simple schematics out there for a preamp, poweramp, tone control amp using this chip?

Thanks,

Craig

Hi,
I have built a few Rubys, Noisy Crickets etc. Next I want to make something a bit more powerful - perhaps around 10 ~20 watts. But I would use it strictly for amplifying an archtop guitar for solo jazz so I am looking for sparkling clean sounds without distortion. (I figure this is opposite to most people.) Can anyone recommend either an amp schematics or a good IC chip for this kind of purpose?

Craig

Hi,
I'm no expert in this area by any means, but I have lived in Japan for most of the past decade (and used electronics things I bought over from Canada @ 120v). My understanding is that in general you are almost always OK underpowering anything. If you go the other way - plugging in a 100v appliance to 120v mains - you could be in for some trouble. It is like having a variac and turning the juice down a little bit. Your hair dryier or toaster isn't going to mind one bit (althought you may notice the hair dryier running slightly slower). It shouldn't make a bit of difference for an amp either (as far as I can tell). Think about an amplified device that runs on batteries. As they get emptied the voltage drops, but the device will keep operating normally (until the battery dies). By the way, I know nothing at all about the insides of Fender amps so can't address that other question.

If you are REALLY concerned you can always by a transformer. I bought 4 or 5 of them when I moved back to Canada for a while a few years ago. In that case I was taking some very expensive stereo and other electronic equipment made for 100 v and plugging it into 120 v which would make them run 'hot' and burn out components (so I was told).

One last factor to consider is the fact you you never really get EXACTLY 100 or 120 volts. That is the average, but it fluxuates up and down by some amount (that I don't know). So electronic devices are made to operate on one very narrow voltage setting anyway.

Hopefully someone more knowledgeable will get back to you. By the way, where are you? I am in Osaka. If you are in the Kansai area there are 'duty free' shops in Nipponbashi (or in Akihabara in Tokyo) that have 120-100v transformers.

Craig

Quote from: joecool85 on December 30, 2007, 08:08:43 AM
It looks good to me, I'd say you might have a bad solder.  Go through and resolder all your joints and it may work better.

Thanks for the re-assurance. I will check out the joints and resolder. (I probably also should have replaced the tip by now.)

Craig

Quote from: tonyharker on December 30, 2007, 06:21:24 AM
It looks like you have missed the link between pin 1 of the Volume control and earth!

Tony

Ah yes, I did miss that on the drawing. I had initially NOT wired pin 1 to ground, but did add a connection from pin 1 to ground after, but there is still a slight hum. (Major hum before.)

Craig

Hi,

I built a couple Noisy Crickets earlier this year and really love the sound of these little amps. I ended up giving them away to people and recently built another one for myself. I have done all of them on perfboard with small changes. I am not 100% happy with the latest one. It has some hum that I don't remember the others having. Also the LEDs don't work. I have checked the original schematic and thought that I did everything correctly. Could some of your more experienced people have a look at my layout and see if there is something obvious wrong with it? I made a diagram of the layout in Illustrator - sorry for it being a bit messy.

Thanks,

Craig

Quote from: R.G. on April 11, 2007, 08:52:03 AM
Go to google.com and enter " (part number) datasheet". The (part number) should be the full part number of the FETs; what you were told is the shortened version. Those numbers should have "2S" in front of them, so look for 2SK170, 2SK246, and 2SK30.

Great post. Thanks for the info. When I asked about a J201 the guy had replied "oh we don't have 2SJ201" and I had wondered about that.

QuoteThe 2SK30 is a good choice for buffers in a 9V effects box.

Good, I just bought a couple of those on the shop guy's recommendation.

Quote
Look for Vgsoff or "gate cutoff voltage", Idss, and Yds. Vgsoff is the voltage that when applied to the gate will cut off conduction completely. The J201 is unusual because it has a Vgsoff of only 0.1 to 0.5V, the smallest of any depletion mode JFET I've ever seen. The 2SK30 is 0.5 to 4.0 as I remember, and it's a good choice for self bias in a 9V environment.

I have already downloaded a few datasheets, but couldn't figure out what amongst all of that technical information was important. Again, thanks a lot for helping a newbie.

Tonight I was just looking over the schematics for the Ruby and the Little Gem Mk II (both of which use an FET as an input buffer) and a simple guitar preamp schematic which uses a FET as a preamp. (The latter is at: http://www.till.com/articles/GuitarPreamp/). As far as I now understand it a preamp boosts the signal by about 3 dB. But an input buffer has no effect on increasing the gain, but only increases the voltage (or is that current?). How is it that these three circuits are very similar (but none identical) but only one of them acts as a preamp? Still trying to wrap my head around how FETs are used in general terms.

Quote from: teemuk on April 10, 2007, 01:51:00 PM
Besides, the substitutes recommended by component stores are selected on totally other principles than "tone" and you should be familiar with the parameters a FET in some specific circuit needs to have.

Thanks for all the information. How can I find out about the parameters of any FET? I have seen datasheet information for the J201 somewhere on the internet, but how about other FETs such as the ones recommended by the shop? Or, more importantly, if I do find datasheets for different FETs how to I compare them? What are the important parameters? (Perhaps I just have to spend more time with that theory document you linked to.)

Hi,
I want to make a few low wattage guitar amps. Projects like the Little Gem Mk II and Ruby (http://www.runoffgroove.com/littlegem.html) use an FET in an input buffer. I built one Ruby with a J201 I ordered online which doesn't work - I think it is because I soldered the FET directly and didn't use a socket. (Live and learn.)
They suggest one of:
    MPF102
    J201
    2N5457

The thing is, I have found that I live really close to a large number of electronics parts stores (in Osaka, Japan) so it is easier and cheaper to buy parts locally rather than order from SmallBear et. al. I just asked about buying such an FET at 3 different stores. At one they had tons of FETS, but said they didn't sell any of those three. At another store a helpful guy told me they don't sell those, but suggested one of three others that are the same. They are:
    K170
    K246
    K30

I bought one of each to try out. I am wondering (1) if these ARE substitutes and (2) how one knows what can be substituted. Doing a web search has so far not given me much information. It seems like there are other choices for FETs around here, but I have no idea how they are different.

Also, can anyone explain simply what an "input buffer" is/ does? and what purpose an FET serves here? I have read the wikipedia entry on FETs but don't really get it.

Thanks.

Hi,
I am interested in building the Little Gem (http://www.runoffgroove.com/littlegem.html) amp. It has been about 2 decades since I have picked up a soldering iron and I am afraid that things that may be obvious to others are not to me. I am wondering what value of capacitors are supposed to be used with the little gem. On the schematic it specify the value. It has just "100", "220", "0.047", "0.01". I am sure this is obvious to everyone else, but is this supposed to be uF, pF, nF or what?

Thanks in advance