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April 04, 2020, 10:38:29 PM

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31
Schematics and Layouts / Peavey Mixer: PV8USB Schematic and Repair
« Last post by paelgin on March 28, 2020, 10:34:43 AM »
Howdy all.  Hope you are all doing well during this shelter-in-place time (Covid-19).

Several years ago (2014), I bought a broken Peavey PV8USB mixer on Ebay hoping to repair it with my amateur skills and tools.   After diagnosing that the NCP3063 boost/buck/inverting converter would not function with the corner blown clean off (reminds me of Dirty Harry), I set about attempting to repair it.  Mouser got my order for several NCP3063s, a Zehner that I thought might be bad, and a couple replacement LM317s. 

I took my soldering iron to the NCP3063 which is surface mount.  I got it off, but also accidentally took one trace up from the board.  So in frustration, the mixer went into a drawer for future consideration.

It is now the future (compared to 2014).  In February, I bought two broken PV6USB mixers off of Ebay to practice on (since I really want the PV8USB).  I spent several weeks watching YouTube videos about soldering SMD (surface mount devices) and discovered a new product that I had never heard about before: "Chipquik" SMD removal solder.  It has a lower melting temperature and stays liquid longer: add flux, then melt onto the leads on both sides of the chip, keep it hot and the chip floats off.  Works AWESOME!

So I worked on the PV6USB (similar problems: I discovered that a common fatal error made by users is to try the power supply for the PV6 non-USB, which is 16VAC, with the PV6USB which uses 15VDC 500ma and that blows the power regulator[side note: seems like a weak design when adding a diode might avoid issues]).  One PV6USB works almost as expected (the USB receives but doesn't send) and one PV6USB works with no USB. 

So here is the schematic from Peavey. I could not find it online (and still cannot), so I had emailed Peavey who then sent it to me. This PDF has been indispensable, but I wish the part numbers were searchable on the layout page as well as the schematic to make locating parts easier. Maybe the PDF has layers that my Adobe Reader cannot see.

More later (have to replace all seven 4565 dual preamp SMD chips connected to the inputs, and more).  Thanks for allowing me to share.

Phil in gorgeous Young Harris, Georgia, USA
32
Preamps and Effects / Re: EVH 5153 preamp with LND150
« Last post by stratitis on March 27, 2020, 02:23:30 PM »
Thanks for your detailed reply.
Still a lot of work to do.  I try to extract a simplified schematic (one channel) as you did, to build a prototype for testing.
33
Guitar News / Way Huge "Chalky Box" pedal - normal OD pedal + chalk board paint
« Last post by joecool85 on March 27, 2020, 09:37:24 AM »
Way Huge has debuted a new pedal with an existing circuit inside.  The Chalky Box is actually a Saucy Box, but with chalkboard paint on it.  Sounds silly, but this is actually pretty neat!  I think I would considering finishing a DIY pedal this way.  Not 100% sure I'd spend $119 on this one from a store, but I rarely buy pedals and if you are one who does, this isn't out of line price-wise with anything else on the market.  Check it out!

https://www.guitarplayer.com/gear/way-huge-debuts-new-chalkboard-paint-covered-chalky-box-pedal
34
Preamps and Effects / Re: EVH 5153 preamp with LND150
« Last post by Katoda on March 26, 2020, 08:27:20 AM »
Do you know if they sound different?
I thought they are nearly the same, maybe I'm wrong.
How did you "adjust" the single stages?

Yep, the 5150 III is made by Fender, not Peavey, the schematics are still widely available via google search. :) It does sound a bit different, a bit more high end bite, but the underlying feel of the 5150 is pretty much the same.

I only built the high gain channel, the cleans on the original 5150 are not that impressive and the other two channels of the 5153 would require a lot more gain stages.

The adjusting was done by comparing the two circuits, LND150 and the original 12ax7 stage. The plate or drain resistor is the same, so is the grid resistor and the coupling capacitor. The diode biasing circuit is exactly the same as proposed in KMGs article, but the bias circuit (with the PNP BJT transistor) is adjustable with a trimmer. What would be the cathode resistor and bypass capacitor in the tube stage are changed slightly by comparing the KMGs Marshall preamp circuit and the original JCM800 schematic. I used what i had, so it was the next closest E24 value. Instead of a 1.8k resistor I put in a 2.2k one and so on. The bypass caps are not really that important here, as the 5150 by itself already cuts bass below 800Hz in the first stage. I think I left them at 1uF.
Also, I put in a 500k gain pot with a resistor to decrease the maximum gain. It has a lot of it.

Most of the circuit in the preamp I recorded is 5153, but I didn't have any room on the perfboard left for a source follower tone stack, so I just made it plate driven, as in the original 5150. That probably cost me some highs, as the impedance is higher, but it wasn't that bad.
35
Preamps and Effects / Re: EVH 5153 preamp with LND150
« Last post by stratitis on March 26, 2020, 08:02:45 AM »
Sorry, still found 5150 III schematics (Fender).  ;)
Which one did you refer to?
Did you build all 3 channels or just one?
36
Preamps and Effects / Re: EVH 5153 preamp with LND150
« Last post by stratitis on March 26, 2020, 07:46:15 AM »
Do you know if they sound different?
I thought they are nearly the same, maybe I'm wrong.
How did you "adjust" the single stages?
37
Preamps and Effects / Re: EVH 5153 preamp with LND150
« Last post by stratitis on March 26, 2020, 07:41:00 AM »
Unfortunately I could not find schematics of the 5150 III (=5153 ?).
All I found is the attached ones:
38
Preamps and Effects / Re: EVH 5153 preamp with LND150
« Last post by Katoda on March 26, 2020, 06:53:57 AM »
That's great, so I could use one of my cheap practice amps as final amp for testing.
To supply about +300V I could use 2 mains transformers back to back (for example: 230VAC -> 30VAC -> 30VAC -> 230VAC -> rectifier -> ~320VDC)
Could you post your schematics, please?
Two back to back transformers will be fine at such low currents, that's also how I got the high voltage to the preamp.
Unfortunately I don't have the schematic, I followed the official tube amp schematic while adjusting it for the LND150 circuit directly on a piece of perforated pcb. I described the changes a couple of posts back. It has been a while since I last tinkered with that preamp, but if you really need the schematic, I can whip something up in KiCAD. It might not be *exactly* the preamp that was demoed, since I don't remember every detail, but it will probably sound closer to the real 5150/5153 (if you want a schematic, do tell which 5150 version are you after).
39
Preamps and Effects / Re: EVH 5153 preamp with LND150
« Last post by stratitis on March 26, 2020, 04:09:10 AM »
I used a TDA2030 power amp, I think I had the tube amp at the band rehersal place.
That's great, so I could use one of my cheap practice amps as final amp for testing.
To supply about +300V I could use 2 mains transformers back to back (for example: 230VAC -> 30VAC -> 30VAC -> 230VAC -> rectifier -> ~320VDC)
Could you post your schematics, please?
40
Hi Katoda,
thanks for your explanation!
May we discuss at your 5150-III thread?
https://www.ssguitar.com/index.php?topic=3931.msg30925#msg30925
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