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September 29, 2022, 10:34:25 PM

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#1
Thanks a lot for this - will start working through this over the next few weeks.
#2
Amplifier Discussion / Re: Fender 112 Deluxe Plus
Last post by phatt - Today at 07:48:21 AM
The Blue and Orange traces are the main audio path from U1 output.
Blue side carries positive wave while Orange is Negative wave.
CR5 to CR8 are the bias diodes for the output Tr's.

C39 & C40 are the Bootstrap setup (Google these things to learn more)

R76 is the ground lift to speaker Neg terminal, Current Feedback is then sent through R77 & C35 and returned to pin 2 of U1

The circuit uses both voltage Fback as well as Current Fback.
R65 sets Voltage FB while the combination of R76, R77 & C35 deliver the Current FB and meet at Pin2 of U1.

Remember these amp designs are Current Feedback via R76 so Speaker neg is ground lifted. *So don't ever ground the speaker neg back to chassis Com*. :-X

I've deleted most of the current Protection parts to help you see the circuit in it's basic form,, *Which is just a current Boosted opamp*
Of course without the over current protection the Output Tr's would instantly blow if the speaker wires were shorted out.
(No need to ask how I know that to be true,,  :'(  )

So if all the parts in my Edited drawing check out ok then I'd suspect the protection setup has malfunctioned when the Pwr tr's blew.
So that would be Q8 & Q9 as well as those associated diodes an Caps etc.

Now I may have missed something so don't take this as completely correct.
hope it helps, Phil.You cannot view this attachment.
#3
Schematics and Layouts / Re: Randall RF-1003 Footswitch...
Last post by Montywitha-Y - September 28, 2022, 12:11:50 PM
Thanks Joecool85!!!
#4
Guitar News / Blackstar AMPED 1 - Pedalboard...
Last post by joecool85 - September 28, 2022, 11:42:04 AM
Blackstar has thrown their hat in the ring for best solid state pedalboard power amp with the AMPED 1.  With 3 voicings, 6 "response" settings, 3 band eq, and built in reverb, this isn't a straight-forward power amp, or a modeling amp per-se, but rather somewhere in between.

100 watts of power, 8 ohm and 16 ohm compatible, on-board power reduction feature, and loads of connectivity available for output (speaker, headphones/line out, USB, XLR).  It also features two 9v output jacks to power pedals up to 500ma.

With an MSRP of $499 USD, it isn't exactly cheap, but it isn't boutique pricing either.

https://www.gearnews.com/blackstar-amped-1-100-watt-amp-for-your-pedalboard/
#5
Amplifier Discussion / Re: Fender 112 Deluxe Plus
Last post by phatt - September 28, 2022, 10:08:24 AM
The most likely fail of the power amp was a short circuit or running very low Z speakers at high volume for long periods. Well you could try replacing Q8 & Q9 as they may have blown when the power units failed.
They are just there as over current protection but that setup is not fool proof so now they maybe actually causing the problem. They are not part of the Audio pathway only protection from shorts and over current.
The active audio parts of the power amp are only the opamp front end and the 4 power darlingtons which deliver the grunt to drive the speaker.
Don't hold me to it but I think that the amp might work with Q8&9 removed.
Try at your own risk. :-X  I'm kinda busy at the moment but I'll try to draw up a signal path overlay on the Pwramp section might help you understand the circuit. Phil.
#6
Schematics and Layouts / Re: Randall RF-1003 Footswitch...
Last post by joecool85 - September 27, 2022, 09:10:05 AM
I looked up the manual for this and found it is a two button switch on a TRS 1/4 cable.  This just means it uses a stereo 1/4" cable rather than standard mono guitar cable.  Testing will be the same way, but you will go from the ground at sleeve (ring closest to the wire) to the tip or to the middle ring.

https://www.randallamplifiers.com/wp-content/uploads/sites/9/2019/09/RG1003HMANUAL.pdf
#7
Schematics and Layouts / Re: Randall RF-1003 Footswitch...
Last post by Montywitha-Y - September 27, 2022, 12:46:31 AM
Thank you. I will test that as soon as I can. It is a 3 channel amp, so if there's any further technical info to make things work correctly to switch between the 3, I'd sure appreciate it. Like I said, I am new to these concepts and am looking for greater understanding. Thanks all!
#8
Schematics and Layouts / Re: Randall RF-1003 Footswitch...
Last post by joecool85 - September 26, 2022, 09:14:57 PM
Quote from: Montywitha-Y on September 26, 2022, 04:53:59 PMI'd like to start by thanking you all for having me in your forum! I'm new to both solid state amps and to electronics builds. I am wondering if anyone here has a schematic or wiring diagram (makes noob blood boil just slightly less) for the foot switch that works with the Randall RG1003H amp head. It seems I'm deeply allergic to the idea of paying $100 for this foot switch (when they can even be found). If not, I would humbly ask if an owner of that foot switch could take a good picture of the layout and post it? Anything would help. Thanks, again!

I haven't looked this one up, but most amps just simply short the tip and sleeve of a 1/4" cable for the switch.  To test this, plug in a guitar cable, and then use a wire (or other piece of metal) and short the tip and sleeve - see if it changes the channel on the amp - it probably will.  If so, you'll need to determine if it needs a momentary or standard switch.  If it switches channel when you connect the two leads, then changes back to the original channel when you disconnect, you need a standard switch.  If it stays switched until you touch the leads together again, you need a momentary switch.
#9
Schematics and Layouts / Randall RF-1003 Footswitch for...
Last post by Montywitha-Y - September 26, 2022, 04:53:59 PM
I'd like to start by thanking you all for having me in your forum! I'm new to both solid state amps and to electronics builds. I am wondering if anyone here has a schematic or wiring diagram (makes noob blood boil just slightly less) for the foot switch that works with the Randall RG1003H amp head. It seems I'm deeply allergic to the idea of paying $100 for this foot switch (when they can even be found). If not, I would humbly ask if an owner of that foot switch could take a good picture of the layout and post it? Anything would help. Thanks, again!
#10
Amplifier Discussion / Re: Fender 112 Deluxe Plus
Last post by FenderDeluxe112Plus - September 26, 2022, 03:12:56 PM
Thanks for your help Phil-  I will have another look at the power amp- will pull the heatsink diodes cr6-8, plus cr10/12 and check the electrolytic caps.
If anyone has any ideas about how to track this fault down, I would be glad to hear them. Thanks, Andy