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Messages - ponchojuan

Amplifier Discussion / Re: First Act Amps
October 23, 2009, 10:23:47 AM
I'll keep trying...
Amplifier Discussion / Re: First Act Amps
October 23, 2009, 10:21:20 AM
well let's try this approach.
Amplifier Discussion / First Act Amps
October 23, 2009, 10:19:56 AM
Well I finally got into Boston and headed over to First Act on Boylston.  Its a pretty funky place.  Unfortunately I dind't have a camera.  They have a lot of guitars, some designed by them and made in China.  Cheap $150-$500.  Other made in Somerville by hand going $1000-$3000.  Very differet custom designs but all looked relatively well made.

The Amps that previously discussed on this board are there.  And they work as advertised.  Pretty amazing for under $80. 

They also have a bunch of custom special stuff kicking around.  One custom amplifier was a boutique made JTM45 clone.  All handwired.  Very well done.  They only want $800.  With Green Celestions. If your ino town you have to go there.

The play-budget is tight right now, but I sprung for a new toy.  This ipod dock that has a guitar input with volume, tone, and crunch, control.  It actually mixes the signal pretty well, and the 40W amp pumps enough bark.  Not a bad deal.  Sure beats paying Bose a few hundred dollars.  Here is a pic.
[<table style="width:auto;"><tr><td><a href=""><img src="" /></a></td></tr><tr><td style="font-family:arial,sans-serif; font-size:11px; text-align:right">From <a href="">Drop Box</a></td></tr></table>Poncho
Based on his comment about power dissipation under continuous signal, and rail swing, I would SWAG that this is a Class G/H amp design, likely an IC with some cap muscle.

But the enclosure does look pretty sweet...some of the new small drivers  can take some very large intermittent power.

Teemu's comment is quite accurate.  Proper V-I limiter specs should not effect the amp signal significantly  if done correctly.  Trying to overdive transistors like they are tubes gets quite ugly.  They are not the same and don't respond  the same as they are driven out of design range.   I can't tell you how many bad amp designs in the early 1970s tried this a failed badly.  This being said, you can design circuits that mimick the distortion characteristic of tube amplifiers (clipping, compression, power sag, etc...) designs from the 1980s started this and it still continues, but cheap DSP has made this sort of old school.

Why not go the other way>  use solid state to better manage the characteristics of tube circuits?  Probably not very cost effective for commercail application but sure a fun possibility for a cool one off amp with lots of effects control.
Amplifier Discussion / Re: Heatsinks for your poweramp
September 16, 2009, 12:35:36 PM
The first one could be interesting if you chimney-effect the enclosure and heatsink.  The current holes are way to skimpy.
Amplifier Discussion / Re: Class D Amp Recommendations?
September 08, 2009, 01:30:01 PM
A number of guys on the DIYaudio site have been playing around with this amp board to get familiar with class d amplifiers.  They can be tricky to do from scratch.  Take a look.  Seems pretty good bang for the buck.

Steve has the same MFG/model toroidal at 100VA for 17.95.  Possibly another option.  2 for $36.

Sorry to be hard on you guys, but as hackers I know you can take it. :)

After reading through much more of the site, I understand better where many of you are coming from.

Ive' been an EE for over 25 years designing HPC as well as analog sensor systems including some AA designs over the years..  We EEs often get too theoretical, and less pragmatic about construction.  I apologize for my comment;  there is a lot of practical knowledge here learned by many hard knocks.

My concerns we're due to comments like designing a power supply before the amplifier.  As an engineer this sounds silly.  Pragmatically,  ICs are a cheap date so use what PS stuff is on the shelf.  I now get it.

Randy, sorry for the spelling slip if your reading;  God Bless.


Amplifier Discussion / Marshall MG Series
August 26, 2009, 09:34:26 AM
It appears the MG series of Marshall amps is using the TDA7293.  The IC appears to be used in both the MG50DFX as well as the MG100DFX.  Here are the schematics.  I have the 100W and like the sound and projection.  Seems pretty rugged and does not put out that much heat.

I will have the 100W apart this weekend and will snap some pics to share.

I started this thread to to create a central point for understanding what the major vendors are using for their power amp section in their product lines.  I think there is a lot to be learned from their designs as well as track records for reliability and performance.

Many vendors are now using power IC audio amps with good results.  If you have information to share based on your own newer amps or experience under the hood, please share.  Please keep conjecture, hypothication, and SWAG to yourself. "Just the facts Mam".

Damn this is a horrible thread.  So much misinformation and pundit opinion.  I encourage everyone to read an amplifier design book like G Randy Stones, or any of the other good design and theory books out there,  before proclaimating expertise.  Let's not create threads of misinformation.

I disagree.  I have this amp and like it a lot.  It was cheap; I paid $185 for mine.  It can be really LOAD, but has a lot of control and switching.  BE sure not to leave the amp sitting with cords plugged in.  The switch MOSFETS are sensitivity to high voltage static.  Play one at Guitar Center.  The proof is in the riff.

Wow I'm !n Boston.  I'll swing into the First Act store next week and check things out.