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August 08, 2022, 05:56:26 PM

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#11
Amplifier Discussion / Re: Fender 112 Deluxe Plus
Last post by FenderDeluxe112Plus - July 23, 2022, 03:29:19 PM
I am reading 30.00vac at r82. Does this   suggest the rectifiers are faulty? You cannot view this attachment.
#12
Amplifier Discussion / 12w Marshall
Last post by Tassieviking - July 22, 2022, 01:39:40 PM
I started to looking into building a 12 watt Marshall by mixing all the 12watt Preamp circuits I found, and also mixing the 12 watt and a 30 watt amp circuit in Marshall amps so I could make any one of the 12 watt amps with 12 to 30 watts output on the same PCB. You just had to pick the right components to make the version you wanted.
Some 12 watt amps had a Bias pot and some did not. Mk1 preamp has diode clipping and the later ones dont, etc.

I got derailed when my dad got sick, traveled from Tassie to northern NSW (Australia) and spent 4 weeks with him. Had to go back to Tassie for medical reasons and be with my family for a week, then back as dad passed away as soon as I left, stayed 5 weeks then back home for Doctor visit and now I am going back up to pack what I want to keep and sell the rest, sell houses, cars,  etc.
I am going to sort all my stuff nice and neat when I get a chance because its hell trying to go through your parents stuff when they are both gone and everything is all over the place.

Anyway, this is as far as I got on a 12 watt amp before the wheels fell off.
I was going to post the KiCad files  of the PCB when I finished and still might when or if I get back to it. I put a jumper on the board if reverb is not wanted, and a place for effects to be inserted which can be bridged if not wanted.
I made the PCB so TO3 transistors had to be wired in or TO247 can be used on PCB.


#13
Amplifier Discussion / Re: Adafruit PAM8302 Amplifer
Last post by phatt - July 22, 2022, 08:26:27 AM
Quote from: Loudthud on July 18, 2022, 04:04:16 AMThis effect is not what I would call "Diode hash". It's not any fault with the diodes. The circuit is doing exactly what the math says it will do. To get rid of the "1+" effect, use the inverting form of feedback. See attached. The one disadvantage is the low input impedance, so you really need an input buffer like the TS pedal.
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Hi , thanks for that, yes I worked out years back that using inverting circuits tends to produce a better result, but was never quite sure why, so ta that makes sense.
I think I got slewed with the term crossover and Expansion at zero crossing. I'm Still not totally clear on that point and also, if I remove the diodes in the sim then the jagged edge on peaks is gone. Of course it just square waves but the flat top peaks show no hash. A bit hard to compare because it hits the rails so early.
It's certainly and interesting subject.
#14
Amplifier Discussion / Re: Adafruit PAM8302 Amplifer
Last post by phatt - July 22, 2022, 08:23:09 AM
Hey it's not too bad but likely to struggle if you want distortion.

Hey you have a BBoard,,Maybe test some of the Marshall circuits that *TassieViking* mentioned on first page?
FWIW,
     In My 30 plus years of building guitar circuits I can say that if you just want to strum a few clean chords then bandwidth and tone shaping will not be much of an issue but if you want OD/Distortion, crunch, big fat sweet singing leed guitar tones then you will spend years building land fill if you don't research the bandwidth issues of Distortion,, an Why do I know this,,Well I have draws full of land fill circuits that went nowhere. In all those years I've only had a few success circuits that actually worked well. It's a long journey but I'm glad I persevered in spite of all my failures as those fails taught me stuff that I may never have known otherwise.
Phil.
#15
Amplifier Discussion / Re: Fender 112 Deluxe Plus
Last post by phatt - July 22, 2022, 07:37:31 AM
Yes, maybe check them.
Phil
#16
Amplifier Discussion / Re: Adafruit PAM8302 Amplifer
Last post by Carriage - July 22, 2022, 03:58:42 AM
Here are some samples. The first file is the yamaha thr on its own for reference (usb out). The difference between the other two is the feedback resistor in the first stage. The second gain stage isnt included yet. The tonestack pots are somewhere vaguely pleasing. Guitar is a strat bridge pickup

I think I'm reasonably happy with it at lower gain but at higher gain there's this fizzy distortion on top. I think that may be the op amp distorting (based on some Spice sims) so I'm thinking about putting a unity buffer in front of some other clipping diodes in the front as a boosted/hotter signal is going to make it worse. Not sure yet though. Maybe some filtering would be better but I think I'm struggling with no headroom and then the OP07 isn't rail to rail to make things worse.

It's also unclear how much the Yamaha is helping. Still waiting for the 8302 board.

Yamaha
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200k
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500k
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#17
Amplifier Discussion / Re: Fender 112 Deluxe Plus
Last post by FenderDeluxe112Plus - July 20, 2022, 10:24:31 AM
Just ran the preamp out into another amp. The buzz is there but it is quieter now and does not sound like the previous 100hz hum.
With the main filter caps replaced, could the next suspects be diodes breaking down under load in the power supply?
#18
Amplifier Discussion / Re: Adafruit PAM8302 Amplifer
Last post by Carriage - July 20, 2022, 06:50:39 AM
So I added the tonemender tonestack to the breadboard and with the gain down in the first stage it sounds like advertised.

With the gain up I still wasn't so happy with it. At very specific gains it sounded okay but past that it sounded kind of like the clean with a fuzz/noise behind it. I don't know if the analysis is leading me to think that but it's not particularly pleasing.

I put the clipping diodes after the tonestack to not much difference. I then removed the ones in the first stage and it's  heaps better to my ear.

There's still a few things I want to fiddle with plus I realised the op amps I've bought aren't designed for single sided supply, though they're working. I'll try and get some sound samples too when I get some time
 
#19
Amplifier Discussion / Re: Fender 112 Deluxe Plus
Last post by FenderDeluxe112Plus - July 20, 2022, 04:57:05 AM
Checked the ac on speaker 3.59vac
It drops to 1.32 wiith a jumper from cr3 anode to ground.
#20
Amplifier Discussion / Re: Fender 112 Deluxe Plus
Last post by FenderDeluxe112Plus - July 20, 2022, 04:36:02 AM
I also checked for broken pads/cracked solder and all checked out ok.

Thanks,
Andy