Yes, I picked up a surplus heat sink at my local salvage yard. It's aluminum and measures 9" long by 4" tall by 2" thick with 10 fins running along the 9" length. Hopefully it will be sufficient, if not, I will add some fans to it or just buy a bigger one

Thanks guys. I'm going to go with the 200VA and see how it works. This amp will be so loud that I doubt it will ever be pushed to full volume (but it's nice to know it can!).

I'm going with a transformer from http://www.antekinc.com/  the AN-2222 to be exact. Unfortunately once you get above 100VA they only provide increments of 100VA so my next option would be the AN-3222 which is 300VA. It weighs 7.3lbs (3.3 kg) vs 5.8lbs (2.6 kg) for the 200VA model. Antek claims the transformers are good for 20% more than the rated output power so that will hopefully be fine. The price difference isn't too much of a concern though with the 200VA model costing $29 and the 300VA costing $36 (both will cost $10 to ship in the US). I'm trying to keep the weight of my amp down as much as possible though. A pair of 10 or 12" speakers, the tranny and the large heat sink I have will quickly add up to a fairly heavy amp! I doubt I can afford to drop the cash for Neo magnet speakers so keeping the transformer weight down will help

-Matt

I've done a search and have seen some conflicting reports on what size transformer is required for one or two LM3886 chipamps. I'm hoping to get a clear answer
I want to run a pair of LM3886 chipamps in a stereo configuration. They will each be driving 8ohm loads and the secondary windings of the transformer are 22V each. So, the Transformer is 200VA with two 22V secondaries.. Is this sufficient? The two power amps will share a power supply board (all are from chipamp.com).

I've seen some posts that claim 160VA is enough to power two LM3886 amps while others have said that a single LM3886 should have a transformer between 160-200 VA.. what's the real story??

thanks in advance for clearing this up.

-Matt

I have a couple of these PCBs at home that I haven't built yet. My latest goal is to build something super clean and loud (think Roland JC-120). I'm probably going to pick up a second LM3886 kit and build a stereo 2x12 combo amp using this preamp.

So, my question is, do you have any sound clips of this preamp running through an LM3886? From your description it seems to produce a great clean tone.

-Matt

I ran across a cheap power transformer on Ted Weber's site today and thought I would share. This would be helpful for anyone looking to build a hybrid amp with a tube preamp and a SS power amp. The price is great too at only $12!

https://taweber.powweb.com/store/magnetic.htm Do a search for "flea power" on that page and you'll find it.
Here's a direct link to the spec sheet:
https://taweber.powweb.com/store/lopo_pt.jpg

275V CT @ 50mA secondaries and 6.3V @ 1A heater secondaries. Should be enough to run 2-3 preamp tubes from the 12xx7 family.
They even have a nice cheap OT for low wattage amps right below it. Perfect for the type of hybrid solution I'm after where the "preamp" section is really just a low wattage tube amp complete with preamp/power amp and OT running into a dummy load and tapped for further amplification by a high powered SS amp.

Enjoy!
-Matt

One additional option is to buy the version of the LM3886 that has electrical insulation on the "tab". That will eliminate the need to electrically insulate the connection between the chip and the heat sink. If the tab on your chip is black you have the insulated version and can get away with simply using good heat sink compound for thermal transfer. If your tab is silver in color then you have the non-insulated version and will need to take one of the precautions outlined by the previous post.
-Matt

if you like the combination of both circuits I would just ditch the tone control on the tweed since it's so limited compared with the tone mender.

What kind of speaker/cab are you using? In most SS amps the preamp provides all the "tone shaping" and the power amp is as linear (and clean) as possible. However, the frequency response of a guitar speaker in a proper cabinet contributes greatly to the "guitar amp tone" you're after. If you're using HiFi speakers you simply won't get the same sound.

Have you tried piggy-backing both your pedals together? Run the tweed into the tone mender and see how that sounds. I've found that the prof. tweed sometimes doesn't have enough gain to drive a Hi-Fi power amp to full volume. The input impedance of that amp is 30k (per channel). With the professor tweed your output impedance is at least 20K at max volume. That means your signal voltage is nearly cut in half even at max volume on the pedal. I would try a simple buffer on the output of the professor tweed to make sure you're getting good voltage transfer between stages.  A simple source follower configuration with a spare MPF-102 fet should do the trick.

You could try something like this:


I haven't built it yet but simulations I've run in spice look promising. The tone control doesn't have the characteristic FMV "notch" but rather is dead-flat at the middle position and gives a very wide range of adjustment and substantial boost/cut to the high or low end when adjusted accordingly.
Modify the circuit to run from a +/- 15V supply if you want the cleanest possible option. As it's drawn now there's DC across the gain cap so it may be scratchy.

You can check your local yellow pages for speaker repair shops. They usually have some speakers lying around either from customers who never paid for the job or just used stuff they pick up over the years and refurbish. Some shops deal more with PA speakers than guitar speakers but they can be used in a pinch and are likely far better than consumer grade speakers.

small Jensen MOD speakers can be very cheap. They are not terribly efficient but they will do the trick. The 8" can be had for around $20 from major retailers like MusiciansFriend.com. You can always try hitting up local pawn shops and buying junker amps to strip for parts. They can be useful for transofmers, knobs, chassis, cabinets and speakers. It's very likely you can pick up an entire amp for less than the cost of a single new speaker.

you can always take your chances on non-instrument speakers but you'll likely spend more money on junk that you can't use than you will save by not going with a purpose built speaker. Also take a look at Ted Webber speakers. His ceramic signature series speakers are very well regarded and the smaller ones are quite reasonably priced, more than the jensens but they are better speakers too. The ceramic 8" Webber speaker is $24.. pretty good! They will handle the output of your TDA2030 quite well.

Since you're building this from scratch you could probably save yourself some components and solder work if you use a TL074 opamp and use one of the two spare opamps to replace the output buffer. Since this is a bipolar supply already it would be very easy to do.

Yeah... I noticed that soon after I posted. The circuit I ended up simulating is attached along with the frequency response curves for "full" bass (90%), full treble and the mid position. The response seems a bit "extreme" with a great deal of boost (12-16dB) at the extremes but no gain at the mid setting. I adjusted some of the RC filter values to get the mid scoop around 1kHz... I'll probably have to play with the filters some more to get a response curve I like.

I wasn't able to find a POT in the LTSpice library... As you can see I'm just using two resistors and adjusting the values to simulate adjusting the pot wiper.. Is there an easier way to do this? Maybe even have the simulation adjust it for me?

Thanks! I'll give it a try. So, any thoughts on the proposed circuit?

I think I found a fatal flaw... I was wrong, there is a DC path to ground so adjusting the tone pot will affect the overall gain since the blend pot combined with the 22K resistor to ground will act as a voltage divider... hmm.. bummer. I'll still try simulating the circuit though.

Profit?? What's that? I thought all of this was just somewhere for me to sink my unused money

I'm wondering if anyone has had any success building an active version of the BMP tone control. I've read the section in Teemuk's book about active tone controls but I'm still not confident that what I have will work (I have not yet breadboarded it). I've attached a rough schematic of my idea. Do you guys think this will work? There's a DC path from the output back to the inverting input, so the bias offset can make its way back. Adjusting the tone pot shouldn't affect the overall gain of the opamp since there's no DC path to ground in the feedback loop.

Finally... Can anyone point me to a tutorial for simulating these circuits in LT Spice? I know how to produce a simple simulation to measure the gain and clipping characteristics but I'm not sure how to simulate the frequency response curve.