Howler - combo amplifier

[Mangas]

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.

[J M Fahey]

Congratulations.
Very nice, very professional.
Please post the preamp, when you have it.
Juan Manuel Fahey.

[Brymus]

Congratulations.
Very nice, very professional.
Please post the preamp, when you have it.
Juan Manuel Fahey.

Yeah what he said.

[iTzALLgoOD]

Info on the cabinet?  Did you build it or buy it.  Looks real nice! :tu:

[teemuk]

Looks good. Solid and professional. Must have taken plenty of time to plan that all out so that everything fits so perfectly.

[joecool85]

You get chip points for that one, looks like a very well built amp.

Any sound clips for us to hear?  What'd you use for preamp/poweramp circuits?

[Mangas]

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.

Info 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.

Must 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 ...

[joecool85]

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.

Info 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.

Must 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 ...

You'll have to enter this one into the next SSGuitar contest.  I look forward to any schematics/circuit ideas you want to share as well as sound clips.

[Mangas]

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.

[joecool85]

Excellent information, very interesting. 

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

[Mangas]

If 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.

[joecool85]

If 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.

Quite impressive background.

Glad to have you aboard, post when you can as it is very enjoyable seeing your projects.   :tu:

[Mangas]

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.

[joecool85]

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.

My computer at work didn't want to be fun and let me play the clips, thanks for posting an update though.

[Mangas]

The Pre amp "test rig" is finished. All necessary modules (gain stages (op amp based and fully discrete), buffers, summers, clippers, ...) are assembled and tested. Everything is ready for the final tweaking (at last).

"The motherboard" :

   

Modules :



Some modules inserted into the board slots :

   

I know some of you think I'm moving too slow, but building a guitar amplifier from scratch (especially a solid state one) is very demanding "activity" and takes a lot of time, effort and patience to be properly done. I'm not trying to emulate anything here like ... "turning a transistor into a tube" (maybe this will happen someday ... during the full moon ... just kiddin'  ). I would be very happy if the final result turns out to be something that plain sounds good.