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PRF members' tech journal

All your geeky questions about electronics, microphones, tape machines, etc.

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Re: PRF members' tech journal

Postby endofanera on Fri Jul 21, 2017 4:30 pm

weezy wrote:Pretty much finished the Peavey 215 cab.

This looks fantastic. Salut!
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Re: PRF members' tech journal

Postby weezy on Sat Jul 22, 2017 4:04 pm

thanks, it looks ok for what it is.

Image
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Re: PRF members' tech journal

Postby Stinky Pete on Sun Aug 06, 2017 5:50 pm

So for the last 6 weeks my Deluxe Memory Boy has been out of action. Dry signal, but the delay side was dead. I tried everything, I rebiased it, swapped and jumpered various BBD stages and I checked the pots and connections and various test points - all seemed fine.

A friend of mine loaned me his Memory Toy for a couple of shows and I had a horror attack when at last practice it had the exact same issue. I decided my PSU must be killing Memory Boy's and took it out, ordered a new supply over the weekend.

Before I boxed them both I plugged the Memory Toy into the new supply - WORKED FINE! Holy shit, I thought, and plugged in my Memory Boy. BOOM! Whined like crazy, so I just rebiased the BBD's and it's back again. I guess the DC-DC converter for the BBD stages wasn't getting enough voltage.

Always check your power supply, kids.
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Re: PRF members' tech journal

Postby Nate Dort on Thu Aug 17, 2017 7:22 am

Image

Took a chance on an old Brüel & Kjær 4007 microphone advertised as "low output." The capsule assembly was secured with loctite, so I didn't try to remove it until I went through the electronics. I couldn't find a schematic anywhere, so I traced it out:

Image

I replaced nearly every component in the thing with no improvement, so I went for the capsule. A little bit of heat, a small piece of leather to protect the surface, and some channel-locks were able to unscrew it. The foil layer was dented and creased and probably touching the backplate in some areas. Definitely nothing I can fix myself. I've got an inquiry into DPA, which took over the B&K mic division years ago. I suspect it will cost more than it's worth and I'll probably just sell this thing to cut my losses.
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Re: PRF members' tech journal

Postby Nate Dort on Fri Aug 18, 2017 11:58 am

Nate Dort wrote:Image
Image

I grabbed a Rocktron Velocity 300 power amplifier from ebay for $100, sold as "Channel 2 not working." It's a 150 W x 150 W stereo power amplifier in a 1U rack case, or you can run it 300 W bridged mono into 8 ohms. Looking at the photos in the listing, they had it switched to "bridged" mode, which disables the channel 2 outputs and routes all the power to channel 1. I had a hunch that they didn't know how to use the thing and assumed it was broken since there was no signal on channel 2. Well, it showed up yesterday and I was right. This things works perfectly and looks nearly new, except for a minor cosmetic dent in the back near the AC inlet. I'm guessing this was an unsold B-stock item or something, because it's in the original box with all documentation.

I'm going to use this thing with the Ampeg SVT-IIP that I just fixed and put them in a small 2U rack case. Curious to see how it compares to the GK 800RB.


Image

Snagged a nearly-new Rocktron Mainline a couple weeks ago, also sold as "Channel 2 not working." It's basically the same as the Velocity, but with a switchable line/instrument level input. Output stage is exactly the same (same PCB). This time there was actually something wrong with this one. Channel two looked like it was dropping half of the output waveform, so I immediately suspected the main output stage. One of the Sanken SAP15 output transistors was bad.

Subsequent research tells me that the SAP series are notorious for blowing the integrated emitter resistor on the die, which is why they were discontinued. The fix is to use the Sanken STD03 series, which are the same darlington pair, but they omit the emitter resistor. Same pinout, just in a slightly smaller package. I just had to put a 0.22 ohm 5W resistor between the emitter and the output. I went ahead and did all four transistors across both channels while I was in there.

This fixed the output, but I think I figured out why one SAP15 blew in the first place. The fan didn't seem to be coming on at all, so it probably overheated. There’s a thermistor in series with the fan that triggers the fan to come on at 65 C. The 24 V rail (which runs the fan) completely failed while I was testing the new transistors. That rail also runs all the signal routing relays, so I also lost output completely. The LM7824 regulator was getting really hot. I powered the rail from an external supply and it wasn’t drawing excessive current, even with the fan running. New 7824 fixed it. Everything is working well now.

The Mainline seems to be voiced slightly different from the Velocity, just based on looking at frequency sweeps on the AudioPrecision. The knob positions don't directly translate between the two units, so it's not flat with everything at 12 o'clock like the Velocity. More like 9 o'clock on the Resonance and 3 o'clock on the Presence control.
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Re: PRF members' tech journal

Postby Nate Dort on Sat Sep 09, 2017 1:27 pm

Nate Dort wrote:Whoops, I bought a Hiwatt Custom 20 project today. Gonna need to fix it and build a cabinet for it now.

Image

Image


This thing arrived yesterday, packed about as well as I've ever seen anything packed before.

The original PT smelled like burning, so I popped off the bell covers and sure enough, all the tape was melted around the core.

I'm 99% sure the PO wired the new Mercury Magnetics PT incorrectly, which is why it blew up again. The MM transformer has a 260-0-260 (center-tapped) winding for the B+ voltage. He should have used just the 260 and 0 connections to get ~360 VAC after the full-bridge rectifier. Instead, it looks like he used both 260 connections into the bridge and floated the CT (if the two scraps of red wire going into the bridge are any indication), producing 732 VAC after rectification. That blew up the first filter cap. That's when he gave up, I imagine.

I traced out the small PSU board and got everything hooked up the way I thought it should go. I can't think of a way to wire the PT to the SP4T mains voltage selector switch to make it universal input though. It's a dual-primary PT, not a single primary with a bunch of taps. Not a big deal, but it would have been nice to get it close to stock functionality.

Found some new 22 uF 450 V caps at the local electronics store, so I replaced the missing one and the existing one on the board for good measure. Fired it up and voltages looked good and nothing smoked, so I moved it upstairs and plugged it into a cab. JFC, this thing sounds phenomenal.

My dad has a bunch black walnut and a decent woodworking shop at his house, so I might enlist his help to build an enclosure for this thing. Maybe finish it with some Tru-Oil that I have leftover from another project.

Either that, or a genuine torlex snakesking cabinet.
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Re: PRF members' tech journal

Postby weezy on Sat Sep 09, 2017 9:03 pm

Torlex or GTFO
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Re: PRF members' tech journal

Postby Nate Dort on Sun Sep 10, 2017 6:58 am

weezy wrote:Torlex or GTFO


That's going on the next round of shirts.
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Re: PRF members' tech journal

Postby Rodabod on Sat Sep 16, 2017 9:57 am

Nate Dort wrote:Took a chance on an old Brüel & Kjær 4007 microphone


May be worth emailing Tim Campbell and asking if he wants to have a crack at it.
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Re: PRF members' tech journal

Postby Nate Dort on Sat Sep 16, 2017 10:39 am

Rodabod wrote:
Nate Dort wrote:Took a chance on an old Brüel & Kjær 4007 microphone


May be worth emailing Tim Campbell and asking if he wants to have a crack at it.


DPA ignored my inquiries. Ended up selling it for $75 more than I paid. I'll let the next guy worry about it.
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Re: PRF members' tech journal

Postby Nate Dort on Mon Oct 16, 2017 7:28 am

Nate Dort wrote:My dad has a bunch of black walnut and a decent woodworking shop at his house, so I might enlist his help to build an enclosure for this thing.


Image

Started on this yesterday. My dad didn't have as much black walnut left as I thought, so I grabbed a piece at the local millworks. We roughed in the box and front panel. I still have some routing to do after I get it glued up, but I think it will turn out alright. Still debating on the finish.
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Re: PRF members' tech journal

Postby Nate Dort on Mon Oct 23, 2017 8:59 am

Image

Image

Got all the routing done on the enclosure this weekend. I originally planned to use another piece of walnut for the front panel, but the router snapped off a chunk of it, so I had to scrap it. I found a small piece of figured Myrtle at the woodworking store, so I made it out of that instead. Everything seems to be fitting together well. Just need to sand away some of the burn marks that the router left (myrtle is notorious for that), sand through 220 grit, then start the finishing process. I'm going to start with wet-sanding Danish oil into it to fill the grain, then possibly some satin lacquer to finish.

Need some new screws and finish washers for the chassis, as the ones that came with it have giant pan heads on them. Also need some feet.

I found a sign-maker online to engrave a new Hiwatt logo for me for $16 shipped. Should be here in a few days. Curious to see how it turned out.
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DittoX4 looper problem

Postby scrotescape on Sat Nov 04, 2017 9:58 am

Hiwatt Looks nice and heavy Nate.

On the bench is a dittox4 looper, these things have a microsd card inside that holds the firmware...I have a good card that will boot and the bad card that is not recognized in peadal or as a drive. Anybody know how to format a replacement card?
Dont I need to format and then burn disc image?

These pedals seem flaky crap, as everything does when google reveals prevalence of problems.
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Re: PRF members' tech journal

Postby bassdriver on Mon Nov 06, 2017 6:25 am

Nate Dort wrote:
Image



that looks fantastic!
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Re: PRF members' tech journal

Postby Nate Dort on Mon Nov 06, 2017 7:20 am

That's just the raw wood. Wait until it's finished.

I did a couple of coats of danish oil, wet sanded with 500. Now I'm on coat 4 with satin wipe-on polyurethane. Should have enough coats on by the end of this week.
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Re: PRF members' tech journal

Postby weezy on Thu Nov 09, 2017 1:54 pm

I snagged FM Redline's HH Bass Machine head from his local MGR. Sounds pretty tits, so it's a keeper. Popped it open to see if the light-up logo was a myth and sure enough there's two tiny little receptacles for two tiny bulbs probably made of un-obtainium.

Edit: I measured and think it uses midget bulbs with an E5 base. Ordered a couple online, I guess we'll see.

Image

Image
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Re: PRF members' tech journal

Postby Nate Dort on Fri Nov 17, 2017 7:45 am

DONE!

Image

Image

Image
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Re: PRF members' tech journal

Postby Dr Tony Balls on Fri Nov 17, 2017 9:42 am

NICELY DONE!
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Re: PRF members' tech journal

Postby weezy on Fri Nov 17, 2017 1:44 pm

^ that's classy.

I got proper bulbs for the HH Bass Machine light up logo.

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Re: PRF members' tech journal

Postby endofanera on Tue Nov 21, 2017 9:33 pm

Nate Dort wrote:DONE!

Image

Goddamn, yes. So great.
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