What makes the chorus and vibrato effects stereo? (other than the obvious, that they have two channels!) Are the left and right channels out of phase when using the chorus effect? If so, how many degrees out of phase? Do both channels change pitch in unison when using the vibrato effect or does the effect use the two channels in a different way somehow? I understand the way the effects are implemented might vary greatly between the different versions of the amp.
-Matt

good luck finding a Mod 5 I managed to find one at some obscure reseller about 4 years ago but I think they were discontinued. It's not a great speaker, but I have mine in a tiny open-backed cabinet. It would probably do better in a sealed cab to help the bottom end a bit.

In my opinion "boutique" SS amps need to fall into one of four categories to have any chance of being successful.

1) Super small/efficient: Give someone a battery powered amp that can put out a CLEAN 20W of power or so in a TINY package and you can appeal to a small market of buskers or people who want an amp integrated into a pedal board or something. This is likely only going to be useful for people who already achieve their tone entirely from pedals. To satisfy this there are already commercial products out there as well as some DIY projects (take a look at the community amp project over on diystompboxes, http://www.diystompboxes.com/smfforum/index.php?topic=89687.0 )

2) Lightweight, high powered amps. This is one area that seems to be neglected in the commercial space. Through careful selection of lightweight (neo?) speakers and a lightweight carbon fiber or fiberglass cabinet it should be possible to produce a high powered amp that is also very light weight. This is a combination that is simply not possible with tubes due to the iron required. I have plans to build such an amp in the future for a friend who doesn't like dragging his 80+ lb fender blackface twin around to gigs.

3) Modular designs. Again, something that isn't super popular in the commercial space, but if you can produce an amplifier that allows the customer to tailor the sound by swapping in different preamp modules, effects modules, or even power amp sections, then you could have a winner. Lets say a musician switches back and forth between electric and acoustic frequently during his/her act. They could in theory have a two channel amp where the channels are swappable. So maybe they would have a preamp voiced for bluesy electric guitar and another channel voiced for acoustic with more extensive EQ controls.. or whatever) Basically being able to swap module to mix and match your channels as you see fit.

4) You create something amazing. This is always the "gotcha" Every so often someone creates an amp that just has amazing tone and an affordable price. If you can pull this off with limited production runs you could easily have a boutique hit on your hands, but this is becoming more and more difficult as modeling amps become better and better and provide more control. It's getting easier now to buy a modeling amp/fx board that will allow you to dial in your own sound any way you like... that's tough to compete against with a boutique system.

Quote from: dan6896 on January 06, 2011, 02:39:13 AM
yeah, that kit looks great  but i live in new zealand and they cant ship here, i think. I looked around the local electronics stores and they have quite a few kits with matching power supply's. ill probably get one of them.

Qkits is just a US/Canada retailer. The kit itself is made by a company called FutureKit based out of Thailand. They have a distributor in NZ: http://www.surplustronics.co.nz/shop/
I don't see the kit listed on the site but you could contact them to ask if they import it. The future kit part number is FK607.
You could also contact the australian distributor http://www.kitstop.com.au to see if they stock the kit (assuming surplustronics doesn't carry it or costs more)

Good luck with your project!
-Matt

You really can't go wrong with this kit: http://store.qkits.com/moreinfo.cfm/FK607
Uses only a single 12-14V supply rail, comes with a heat sink and is super easy to build... oh and it only costs $10 I used one as the power amp in my Hurricane build seen here. http://www.ssguitar.com/index.php?topic=1237.msg7705#msg7705 Even with that little 6" speaker it was nice and loud.

-Matt

The simple approach:
1) Buy and build LM3886 chipamp kit and power supply into a metal box of some kind
2) Plug in your pedal board
3) Rawk

The slightly more complex approach:
1) Build LM3886 kit
2) Build a simple clean preamp with modest gain and tone controls (a ROG tonemender might be a good choice here. http://www.runoffgroove.com/tonemender.html )
3) Procure or build a suitable chassis and cabinet (head or combo, you didn't really mention which you were after, head is easier)
4) Plug in your pedal board
5) Rawk

The beauty of most modern SS amp chips is that they are dead clean. They're meant for HiFi use. This means that you can rely on your effects pedals to give you any kind of sound you want and the power amp simply makes it louder. All the tone shaping comes from your pedals and the fact that you're running the power amp through guitar speakers which have the right frequency response to produce a good guitar tone. The idea behind the more complex approach is to provide some additional gain in case your pedals don't have enough output to drive your power amp to max output. It also provides some more flexible tone controls as the tone knobs provided on most pedals are pretty crude.

-Matt

Since I know he was active on this forum as well I figured I would post a link to a discussion on the diystompboxes forum about RDV (Ricky Don Vance) . It seems he died back in February. Here's a link to the discussion on the other board: http://www.diystompboxes.com/smfforum/index.php?topic=86797.0

And here's a link to the announcement: http://www.tributes.com/condolences/view_memories/87822622?p=10&start_index=1

-Matt

I was browsing around sparkfun earlier today and came across an interesting stereo chip-amp kit. It seems like it might be good for a small amp (2 x 38W at 4ohm load with a single 18V supply) The fact that it only needs a single power rail might make it interesting for a battery powered amp. The inputs are opamp buffered and it includes everything from the basic components/pcb to a pair of volume trimpots, heat sink, standby switch and clipping indicator LED. If I didn't have so many projects already in limbo I might be tempted to pick one up to play with since it's only $30.

http://www.sparkfun.com/commerce/product_info.php?products_id=9612

Schematic: http://www.sparkfun.com/datasheets/Kits/STA540%20Audio%20Amp%20v11.pdf
Datasheet for STA540: http://www.sparkfun.com/datasheets/Components/General/STA540.pdf

If anyone tries this out be sure to post the results!

Quote from: teemuk on May 11, 2010, 12:01:16 PM
Alternatively, you have yourself a stereo setup. ;-)

That's the way I plan to go with my dual LM3886 setup. Of course there's nothing wrong with a 100W+ single speaker amp, but the reality is that most amps in that power range have a pair of 10 or 12" speakers. There's nothing to stop you from having a mono preamp split into both channels. Then you can still claim the 100-120W power output and include a stereo effects loop for next to no effort. Just makes for a much more flexible build overall. Keep in mind the Roland JC-120 was also "just" a 2x60W stereo amp with mono inputs, some built in stereo effects and an external stereo effects loop.
-Matt

one thing to keep in mind is that the LM386 won't break up as nicely at high voltages unless it's driving a low impedance load like a speaker. If you run the output directly into the input stage of a power amp (which is usually on the order of 10-50K ohms rather than the typical 4-16 ohm speaker impedances) you should lower the supply voltage to ensure you get good breakup if that's what you're after. The datasheet provides plots of the maximum output voltage swing vs. supply voltage for various loads. Unless you're driving a speaker you want to look at the plot for infinite load. To mimic the kind of clipping (maximum output swing) you would get when driving an 8ohm load with a 12V supply you will need to lower the supply voltage to about 7.5V. Of course, you could also add an 8ohm resistor to ground on the output to simulate the load as well. I did not try that with my setup though.

For maximum efficiency (battery life) you should look into a "class D" amp. The tripath kits from www.41hz.com are quite good. If you've never soldered SMT components before you should go for one of the through-hole kits. The AMP6-Basic is pretty good and gives 2x25W from a single 12V supply.
-Matt

Another good option to reduce the voltage coming out of your tube preamp is to run it through a tube power amp and output transformer All joking aside, I believe that is the best way to achieve true "tube tone" with SS cost/weight per watt. While the transformers used in tube amps are where a great deal of the cost goes, the cost of those transformers is directly related to how powerful you want the tube amp to be. If you're bulding a tube amp with 5W or less of output then you can get away with much cheaper transformers. You can pick up nice 5W SE output transformers for less than $30. The output transformer also does a great job of getting the output voltage down to a more manageable range. Think about it, 5W of power across an 8ohm load is only ~6.3V RMS . Much easier and safer to attenuate down to the 1V RMS range than say 60V RMS. Now if you use the 4ohm tap on the transformer then you will only have to contend with half the voltage, so ~3.15V RMS. Now at that voltage range you should be able to just add a 10-20K volume pot in front of the power amp and be done with it. That will give you tons of clean headroom (run the tube amp at a low volume to get a clean sound and crank up the SS power amp volume to make it loud) while still being able to achieve low volume overdriven sounds (crank the tube amp volume and lower the SS power amp volume). Of course, the trade-off is that you could in theory crank both volumes and still clip your SS amp, but that's the price you pay for lots of clean headroom AND the ability to push into overdriven sounds. To solve this you can use something like a VGA (Variable Gain Amplifier) stage on the input of the SS amp to guarantee that you will never exceed its maximum input voltage, or you can add some simple diode clipping right before the amp. It's not going to sound like tube amp clipping, but it will surely sound better than clipping the SS amp and also afford you some protection.
-Matt

Quote from: slim_blues_boy on October 12, 2009, 01:44:50 PM
@armstrom
I'm thinking the same, build a power amp and use my pedal as the preamp.
I'm planning to use my multi effect AX100G.
as for the kit, it also seems interesting. unfortunately I live in the far east and shipping cost would be expensive.
so I think I'm just gonna look schematic for power amp for now.

Many of these kit companies are based out of Asia and have local distributors there.  Here's a list of distributors for the FutureKit kits (TDA2030, and others) http://www.futurekit.com/distributor.php

As for the velleman kits, they're a European company but seem to have distributors all over the world too. Find your closest one here: http://www.velleman.eu/ot/en/dealer/search/

I ran across this peak limiter circuit and was trying to understand how to control the max output voltage. The author gives guidelines on adjusting the attack and decay times but not the limit voltage.

http://sound.westhost.com/project67.htm  (circuit in figure 2)

My ability to understand what is going on in this circuit is severely limited so I was hoping someone here could shed some light on how the limit voltage is set. Does it have anything to do with the forward conduction voltage of the diodes? I would like to be able to change the max output voltage to something closer to 1V RMS rather than the 1.65V RMS that it currently has. Of course, I could always take the easy way out and put a voltage divider on the output to get the max voltage down where I want it to be, but that seems like a bit of a hack
-Matt

The first thing to keep in mind is that you will have to greatly attenuate the tube preamp. Depending on how many gain stages you use and what kind of other losses are introduced (tone stacks, for example) you will end up with very high signal voltages coming out of your preamp stage. Most SS power amps are set up to handle 1V RMS or less input signal and will clip horribly at any signal above this level. As for the suitability of the LM3886 I think you're on the right track. These chips are known for being very linear and transparent. They're very low noise when built with a good circuit layout.
-Matt