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October 05, 2022, 05:10:15 AM

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#1
Guitar News / Re: Acorn Amplifiers unveils "...
Last post by Puguglybonehead - October 02, 2022, 09:27:37 PM
How did I not notice this sooner? Yeah, I read that interview. Those amps have now jumped a 'decade' in price all over ebay, craigslist, etc. I remember my sweetheart was doing opening sets at a lot of metal shows about 10-12 years ago. A lot of the junior shredders were showing up with low-end Peavey amps like these. They get great sound when they're mic'd.

This reminds me of that Jimmy Page interview many years ago, when he revealed that he did the entire first Zep album with a Tele and a 22-watt Supro amp. Little Supro amps of every description skyrocketed in price afterwards. They do sound great though, as do those little Peavey Decades.

What I want to see is a pedal based on the Heathkit TA-16. Now there's a unique sound.
#2
Amplifier Discussion / Re: Fender 112 Deluxe Plus
Last post by phatt - September 30, 2022, 07:41:38 AM
Glad it helps,, I'm not qualified enough to understand some of the more complex power amp designs but yes once you remove the current protection it makes more sense.
I've designed a few plain and simple power stages and had great success just by installing a PTC on the output. In this case one PTC would replace 18 extra parts and as likely in this case the Protect circuit may well be adding to the problem.
If a poly switch fails the amp stops working and you only need to replace one part.
PTC is a Poly Thermal Capacitor, Often called a poly switch because they switch to high resistance when they reach the set threshold. They do this switch faster than a power transistor can fail, effectively doing the same job as the rather complex current limit in the power amp.
BTW Tassie I buy them at Jaycar if you want to source some. ;)   
Link,,,  https://www.jaycar.com.au/rxe185-ptc-fuses-speaker-protection/p/RN3468?pos=2&queryId=4192c822761e620ef506c2f53a24ce71 

Re my drawing;
I'm still miffed about R69 & R66. ???
I think R66 is added Fback from output but R69 is really weird as they connect to
C37 & C38 which are filter caps for the opamp supply which I would assume would normally go to ground but they are summed at R65 which goes back to main output.
While R66 takes it back to the junction of R62 & C35.
Maybe better minds might like to comment on that subject.
Phil.
#3
Amplifier Discussion / Re: Fender 112 Deluxe Plus
Last post by Tassieviking - September 30, 2022, 04:54:49 AM
Great explanation Phil, helped me understand it better.
Thanks.
Michael
#4
Amplifier Discussion / Re: Fender 112 Deluxe Plus
Last post by FenderDeluxe112Plus - September 29, 2022, 05:07:36 PM
Thanks a lot for this - will start working through this over the next few weeks.
#5
Amplifier Discussion / Re: Fender 112 Deluxe Plus
Last post by phatt - September 29, 2022, 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.
#6
Schematics and Layouts / Re: Randall RF-1003 Footswitch...
Last post by Montywitha-Y - September 28, 2022, 12:11:50 PM
Thanks Joecool85!!!
#7
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/
#8
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.
#9
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
#10
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!