It's been awhile since my last post. I've been very "productive" last week so the preamp "test rig" is almost finished (more about that next time). Meanwhile, I managed to record two audio clips (as promised  ) for you to hear the sound of assembled power amp.

DigiTech RP300 modeling guitar processor was used as a preamp (no effects and simulations - only equalizer (bass, middle, treble) and reverb added). The pedal itself doesn't have high enough output to drive the amp properly    so "the punch" is less than it should be with adequate preamp.

The setup used was :

Fender Stratocaster (neck and middle pickup individually) - RP300 - Power amp with built in speaker - Mic - Behringer mixer with tone controls flat - PC

http://sharebee.com/4c02458c - Neck position pickup (clean)
http://sharebee.com/6ba66253 - Middle position pickup (clean)

Didn't record overdriven tones because I wanted to hear harmonic content of the amp itself. All comments are welcome.

QuoteIf you don't mind me asking, what is your background?  Are you an engineer or something?

Yes, I have a master's degree in electrical engineering. My current employment doesn't include anything "audio-based". I'm dealing with SCADA (Supervisory Control And Data Acquisition) systems implemented in electrical substations. Briefly - Substations are equipped with microprocessor relays (for protection and control) and an RTU (Remote Terminal Unit) which processes all of the necessary signals and enables remote supervision from the supervision center. My department's job is to administer and maintain the whole SCADA system - both software and hardware.
I've been playing a guitar for over 20 years and soon after I became a music addict, "the analog audio electronics virus" infected me too. Haven't been cured since.    :duh You can see the consequences clearly.
Didn't post anything for days, sorry. I have a very busy schedule. Last week ... :grr. I'll try to upload sound clips and further information concerning the amp building process as soon as possible.

The output stage is powered, finally. The first impression is that the amp is very quiet. You can hear a low level hum only if you put your ear up against the speaker. DC operating points are within +/- 5% of calculated and simulated values 0:). Quiescent current is very stable (bias servo is doing its job correctly).

The test equipment used :



With 1Veff/1kHz input signal, the amp produces 11.37 Veff output into 8 ohms dummy load or 16Watts RMS (A little more than I aimed for).



Temperatures (heatsink and transistors) after one hour of working on the verge of clipping could be seen in the pictures below :



Temperatures (heatsink and transistors) after one hour of severe clipping could be seen in the pictures below :



Output waveforms :



Although the amp uses mixed mode feedback, output waveforms were recorded with a classic voltage feedback. The reasons are ... Shall we say, more obvious stability test results. I didn't upload a picture of 10kHz square output wave also, because the input signal was fed throughout bandpass filter at the amp's input (low pass : -3dB @ 45kHz). After all, this is a guitar amp not a Hi-Fi one.

P.S. : Sound clips will be uploaded soon.

First, I'd like to thank you all for the kind words - very encouraging. In the meantime I managed to finish the chassis (1mm thick pressed steel, black coated). The partially populated chassis could be seen in the pictures below :

Top, rear & front :

   

From left to right - Input jack, Drive, Volume, Normal volume, Treble, Bass, Middle shift switch (tone voicing), Reverb, Footswitch jack (with panel switch for Normal/Overdrive mode), LED indicator and power switch. There are also a fuse holder, speaker and line out jacks on the rear panel. Still have to "win another hard battle" - the preamp. As for now, I'm satisfied with the reverb circuit, tone stack and the normal/overdrive switching section.

QuoteInfo on the cabinet?  Did you build it or buy it.  Looks real nice!

Cabinet was built by a very good frend of mine (he did almost all of the woodwork) and me. It is constructed of 18mm thick birch plywood with finger-jointed sides.

QuoteMust have taken plenty of time to plan that all out so that everything fits so perfectly.

You are very, very much right about that.

Next time - Powering the "semi-amp", measuring and output waveforms ...

Something I have been working on for the last two months - A 15W combo amp with 8" Jensen speaker and footswitchable boost and reverb.

Amp cabinet :

 

Output stage, Power Supply & Transformer, Mains PCB, Speaker & Line Out PCB :

     

I shall keep you informed of progress.

It's 4049 based overdrive - All 6 inverters used, two separate switchable sections. I wanted to make them foot-switchable but, as you can see, there is a lack of space inside the chassis.

It was originally Ross amplifier (Fame series - model Reverb 25). The sound was horrible so I modded the output stage, reverb and tone stack using the original PCB. Input gain stage, overdrive and channel switching modules were added as my own creations.



Sound sample - From clean to high gain

http://www.sendspace.com/file/it9e4o