Quote from: FleshOnGear on September 23, 2023, 05:47:05 PMThe are some big positives for this amp. The cabinet is sturdy. Even stock the clipping circuit is sufficiently tube-like in tone. And, these are relatively cheap on the used market. Just a few tweaks and I got a great, dynamic metal tone.

Rock and roll!

Starting to look good!

This sounds like a great platform, but not something I'm very familiar with.  Care to share any pictures?  We'd love to see it!

Quote from: GeezerB on August 31, 2023, 12:46:52 PMJust bought a loupe... great tip thank you.   I also believe I may have solved my issue! I reflowed all the joints on amp board just in case... and the transistors that were held on by screws I removed and cleaned up the connections.   And cleaned the hell out of the "Mute" switch... could not play too loud last night due to sleeping house but did not hear any popping and sounded good... so I believe my problems were the bad power amp connections combined with the Zener diode in the preamp.   Thanks to the forum... what a feeling.

Glad to hear you got it fixed up!  I always love a happy ending.

Quote from: GeezerB on August 23, 2023, 10:28:32 PMI input a nice clean 1k sine wave, and here is the result from both the preamp out and from the power amp out... both appear to be wonky. 

I guess this tells me at least that the distortion is starting in the preamp section at least?  But it still seems that the power amp should be louder.

I guess I also need to understand the function of Gain and Master...Gain is there for crunch, but doesnt control volume?

First time using this scope, it is really cool to use such a powerful tool for diagnosis, cant wait to use to greater potential and understanding.

Gain is really preamp volume.  The higher you turn up the gain, the more it will saturate into distortion (depending on the amp, this could be setting the gain on 3 or 4, or maybe 5 or 6 before serious distortion kicks in).  The master is the volume control between the preamp and power amp.  This controls the overall volume at the speaker level.

To be clear, turning down the gain will decrease volume as well but it does this in the preamp section and as it is turned down it will decrease volume as well as distortion.

Quote from: Tassieviking on August 04, 2023, 10:34:15 PMAccording to the SUNN BETA service manual:
The Sunn Beta has 1.75v P-P out at the master line output, but each individual channel has only 1.1v P-P at the preamp line output.
Sunn Beta basically has 3 effect loops.
If you made a single channel the output to the power amp is only 1.1v P-P which should be ok, and you don't have to crank the volume pot all the way around.

If anything you might not get enough signal to drive the TPA chip to full power since the Beta figures are peak to peak.

I think it should be OK.  The TPA3116 has gain from 20 to 36db.  I haven't done the math to verify, but I think this should get close.

If you crank up the volume on the clean channel, is there a similar sound?

Quote from: Domin9797 on August 02, 2023, 01:59:54 PMYeah but often shipping costs more than PCB. TPA3116 is good choice too but im not sure if i want PA which cant sound "good" while clipping. I have only 20W speaker so im little bit limited.
I know about his circuits. His MDR will be my distortion channel or at least distortion pedal. Im not sure about 59 Bassman since there arent any sound clips of it. Another idea is his Orange emulator

Personally I don't worry about clipping the power amp.  You can design the preamp in such a way (utilizing diode clipping for instance) that you can't clip the power amp section no matter how hard you drive the front end.

Quote from: Tassieviking on August 02, 2023, 12:16:23 PMIf the crunch is developed in the Power Amp then you are out of luck, unless you have lots of thick blankets.

An L-pad would take care of this as it takes on some of the load at the speaker level.

Is RL the expected load, or does there need to be a resistor there?

Quote from: phatt on July 19, 2023, 07:38:21 AMHi Joe,
        Sadly no as that hard drive died and took with it a lot of stuff. I do have some pcb pictures on CD somewhere but they are the early versions which were hand drawn and the early circuits are different.
It's not a hard circuit to layout as there are not many parts and only one chip.
Someone on another forum posted a perfboard layout of it, just let me know if you go in that direction and I'll post it.
Phil.

I'll keep you posted.  I have a few projects in front of it, so it could be a few months or more.  Thanks!

Quote from: Domin9797 on July 16, 2023, 04:55:18 AMAny schematics for it? Links aren working anymore

Schematic is posted above and works still.  https://www.ssguitar.com/index.php?action=dlattach;attach=3610

Quote from: Diary Of An Axeman on July 18, 2023, 03:20:55 AMI just fixed the the expression pedal for an old 1968-1969, Univibe .
Plugged it started playing it for a couple of weeks and the fuse blew out .
I did the old aluminum foil tick and found the unit still works, then I unplugged it and  took out the foil and put the unit away.
Would any of you techies out there know what kind of fuses that 1968-1969 Univibes used.
Any help would be greatly appreciated .

Looking at a schematic, I would hazard a guess that the power draw is somewhere in the 100ma range.  I would try a 250ma fuse and see what happens.  If it is too small, I wouldn't feel bad trying a 500ma (in case my guess of 100ma running load was off by a few factors).  I can't imagine it would need more than that though.

Curious, what size fuse did it have in it when it blew?

Great sound on that intro, I can see why you want to emulate this.  Honestly though, it shouldn't be too hard.  The Honey amp can sound like this with gain turned up about 1/4 to 1/3 (depending on what pickups are on your guitar).  I feel like this is yet another issue where tone stack in many preamp designs shared online are garbage.  A lot of times, tone stack before the heavy gain stages can fix your drive sound issues.

If you want to play with some stacks and adjust a circuit, check out TSC in the web: https://www.guitarscience.net/tsc/info.htm

I generally like a gentle sweep mid cut centered around 500hz as a good starting place.

Quote from: phatt on July 14, 2023, 05:46:40 AMThe Triumph Overdrive was impressive.
Smart move adding a decent tone control on a dirt pedal.
And designing one where the midrange actually works.
That's why I love my PhAbbtone so much as the mid control is very potent.
Humm, maybe he has been reading the forums and found my circuit.      Phil.

I'm actually planning on building a PhAbbtone at some point.  You don't happen to have a PCB layout available do you?