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Messages - jfetter

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Amplifier Discussion / Current boosted LM3886, TDA2050 etc..
« on: December 19, 2007, 12:23:59 PM »
Does this look like it would work? The feedback position looks problematic.

Amplifier Discussion / Re: anyone ever build any small class D projects?
« on: October 18, 2007, 08:44:05 AM »
How did it turn out?

Amplifier Discussion / Re: Ramsey class D
« on: July 13, 2007, 02:49:38 PM »
the IC is "presoldered", you have to install the caps and resistors- not too hard.

I have used this eval board/kit to drive a "red fang". Veryy loud.

I have not used this new one:....bridged 50w -> 3ohm

My new project is using a jfet (fetzer) preamp and a dsPic33f dsp for a one chip instrument amp. It is in the software & parts procurement stage. I'm using an Analog Devices 100ksample A2D with a "ucd" dsp "in-the-loop" design. its fun anyway.

Schematics and Layouts / Re: 60W Power amplifier
« on: July 06, 2007, 10:49:15 AM »
 you might try my method, build the amp using conventional methods ie feedback, spice model etc but then use a output "isolator". The best ss amps i have ever heard were always capacitor output coupled, then add to that a series air core high resistance inductor. You end up with a bandpass output that is somewhat isolated from the load. use a hefty zobel. use a simple first order model for the inductor, 8ohm load .3 mH cutoff at 5khz(or less!), let the speaker gen harmonics. clipping sounds great again.

its all counterintuitive but try it. if you have an existing amp add the network and enjoy.
I'm designing a high power class d amp and will use this concept again. Keeping the jfet preamp. Air core toroidals are much better but not too available..

Amplifier Discussion / Re: help with issue in my amp
« on: June 27, 2007, 09:56:49 AM »
Buzz is generally broadband noise. If you run on battery only and unplug from AC is it still present?

Is the amp "Class D' ?

Amplifier Discussion / Re: Pentawatt layout TDA2030A and TDA2050 etc
« on: June 19, 2007, 10:48:27 PM »
I had some pine boards in the garage , so here is the pinebox head, no more vibration.

All ctls at 12:00 on this example of Lenny lead in, no effects ie reverb or anything. I still think I may run the gain down somewhat. The clean to dirty threshold may be too low. not sure yet.

I'll post the schematic eventually but for now just keep the zine here until perfect.

Found the "vibration". I swept with the function generator and found two points; one at about 100hz and another at 210hz.

The strong 100hz was the front panel! The weaker 210hz was entire chassis box. So I have to rethink the packaging.
The output filter is for sure the way to go on SS amps. We all agreed the unit sounded like a 5E3 Deluxe.

Having Fun with it.

Two short examples...
Amp is on max volume , center tone and center gain.

1st is on a strat using front pickup.
2nd is on Les Paul with bridge pickup.

The cab has a bad resonance at C# , you can hear it on the low registers( some people like that though) . Have to do some cab work and possibly reduce gain. Mic at aprox 6" in front with a stien e609.

Amplifier Discussion / Re: final assy
« on: May 13, 2007, 08:50:43 PM »
Here is the final assy, switched to the 'Governor' for grins. The LED gives a brite starr appearance. I used a Geezer cab and mounted as shown with the right angle brackets. The chassis is mounted 0.25" from top of cab to allow air movement. The preamp board(is super quit) has a copper sheet shield but otherwise the chassis is open.

The soud is Fetzer like with very nice asymetrical clipping. Output filter is  -6db at 4000hz and does not allow hard clipping. the tone can scream.

Preamps and Effects / Boss/Fender FD-1 and FBM-1
« on: May 09, 2007, 11:41:16 AM »
I'm impressed with these pedals from the tone demos at

Don't own one yet. Has anyone disassembled? Please show pics.


Amplifier Discussion / Re: Pentawatt layout TDA2030A and TDA2050 etc
« on: April 29, 2007, 09:11:09 PM »
Finally got the head put together. I changed my mind on the clipping diode, took it out. The 6db filter on power amp output serves that purpose just fine and isolates the FB loop from load. So it becomes a partial current source open loop.

Also pictures of my lab bench. Probably looks like everyone elses. Working on the cab/head setup now. BTY the tone ckt is an active muff. The effect pedal is for input ckt saturation testing.

Amplifier Discussion / Re: Pentawatt layout TDA2030A and TDA2050 etc
« on: April 16, 2007, 07:51:58 PM »
Its a .lib file that is used by Orcad Layout (pcb layout program). If you don't have access to Orcad try eagle

I have not checked but it may actually have the pentawatt pkg in library. The free version is ok for two sided small boards, exactly what ss preamps and poweramps use.

Then send the gerber cad files to online.  They are the cheapest fastest no hassle.

The front panel is a free cad program from , very easy to use and attached is my example. No setup charges and you can buy one , two or production quantities.

unzip the and open the .fpd file with frontpanelexpress program.

Amplifier Discussion / Re: Pentawatt layout TDA2030A and TDA2050 etc
« on: April 12, 2007, 11:19:39 PM »
Here is the new panel and chassis mock-up.

I picked too large router bit for small text engraving. Also forgot to pick grained finish. It still looks OK. The panel light is a radiio shack neon indicator lens and holder. I removed the neon assy and replaced with a 5,000 mcd 10mm red led. Its just a prototype so I'm trying out new.

Double drilling the panel/chassis is unnecessary by using the open end of the Bud CU-622A.

Amplifier Discussion / Re: Pentawatt layout TDA2030A and TDA2050 etc
« on: March 20, 2007, 03:01:47 PM »
Seems like you have to be logged in to see them. The circuit sounda sweet, now doing a front panel with "Front Panel Designer". I did put one soft diode to pre clip prior to supply running out, so no PS ripple present even at high levels.

I've ordered a Weber 6X9 8ohm to experiment with a 'local' speaker in the head. The test speaker to date has been a Red Fang.

The idea is a compact head that can be used for recording or practice. It will look like a head but is really a combo.

Then add a reverb in next design.

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