Windsor Mods

Geez, can't believe it's been almost a whole year since I posted here. I haven't had much disposable income to spend on projects, but I do have a bunch of stuff I've done but not uploaded here.

These are the mods I've done to my Windsor as best I can recall, going from memory and a couple scratch pages. It's not complete yet, but I thought I'd share these.

The idea was to have a Matamp-style amp with the ability to footswitch into something not unlike a JCM800... or at least that level of gain. The whole 'boost' circuit needs more voicing and tweaking, but it works as is. There's too much different between the two amps, of course, so I stayed mostly towards the Matamp side. The 'boost' takes in and out a third gain stage DC coupled to a cathode follower (e.g. the second preamp tube.) I really like the way that cathode follower crunches, but I didn't want to lose the headroom in non-boost mode. It would be easier probably to make a Windsor go between JCM800 high and low gain (sort of) by simply using the relays to take the second gain stage in and out.

Where was I... Yeah, I just marked up the original Peavey schematic because it would take way too long to start from scratch. There are probably errors or inaccuracies in here too, so maybe don't blindly copy it. I used a bunch of shielded wire and also hacked up the amp's PCBs pretty extensively to do this. Probably a better idea to just use the second preamp tube for an effects loop, or just do a JCM800 clone instead.

Anyway, 3 pages of PDF:

PP Amps - Windsor Mods

Peavey Cab Refurb

So! I've been neglecting my blog for the past few months. I've been busy though. I imagine I'd keep this more current if the posting process weren't such an immense pain.

Anyway, I picked up this old Peavey combo cabinet (used to be a Stereo Chorus) on the cheap, and it'd already been mostly converted to a combo. The tolex had already been stripped and a new back panel added. Really about all I've done to this is sand it, stain it blue, and slap a few coats of shellac on it.

Shellac is probably a terrible finish for a speaker cabinet, but this cab is already beat to hell so I'm not really worried about it getting scratched/dented. Plus I had the shellac already, as well as the blue stain.

I mean, I didn't even make the grille, though I would like to do more work on it. Still have to add a jack plate. I guess this is kind of a silly post, but I just wanted to document that I did it.

Peavey Windsor mods

What a fun little toy.
Okay, picked this guy up cheap and I'm going to somewhat follow through on my "Matange" plans, except I'm dropping the Orange part in favor of a Matamp/JCM800 blend. Hey, its got a third preamp tube, why not?
So far all I've done cosmetically is move the back grille to the front. Not sure I'll do much more; maybe cut a new back grille out of expanded metal.
The preamp is currently fairly awful. Way too much gain, too little decoupling, lousy tone stack. I'm probably going to turn that cold clipper preamp stage into a cathode follower and the tone stack into a James with mid shift. I'll probably use the worthless "texture" control for the FAC. Then I'll use the "boost" relay to switch the second gain stage in and out.
For now I've started in on the power amp mods: 100k for the EL34 grid leaks, suppressors tied to cathodes, grid stoppers up to 47k, and 1k8 screen stoppers (didn't have any 1k5). Very noticeable improvement already!
Incidentally, Peavey seems to have paid the extra nickel for halfway-decent circuit board material. Id rather remove every component in this amp twice than remove one resistor on a Marshall made in the past decade.

Adventures in PL Premium

So, I have the bulk of the gluing done. I have a bead around all the inside edges, and I've glued in all the primary braces. There are four front-to-back, two side-to-side, and two top-to-back. The top panel is going to be partially braced by the shelf port assembly.
Hopefully this amount of bracing will be sufficient to prevent resonating panels. We'll find out after the glue cures, and I wouldn't be surprised to find I need a couple more on the bottom, top, and shelf panels.
PL Premium is the go-to adhesive for speaker cabinets, as it expands while it cures to form air tight seals. It is fairly nasty stuff though; the tube says it's okay for indoor use, but the offgassing is fairly odorous so I can't imagine it being used in anything besides original construction. All the braces are screwed also, so as long add it does a reasonable job, this thing'll be rock solid.

Peavey cab bracing

Busy day! I got 2 of the 3 dimensions braced, and got the cutout for the jack cup done.
The braces are going to be screwed and glued. I cut little Xs in the tolex before I drilled pilot holes, and I'm going to counter-sink the screws a bit so I cab glue the tolex back over the screw head. It won't be seamless, but it'll look better than screw heads sticking out.
Still trying to figure out how I want to mount the shelf port, and I cut the back panel 1/16" too tall, so I'll shave that down.
Gluing day is going to be a real treat; I've got to place the braces in a certain order or they block each other from fitting, and some of them are so tight they have to be hammered into place. Fortunately there's some working time with PL premium.
Can't wait to hear this thing!

Peavey cab update

I got the big panels taken out of the divider (why did they use OSB for the baffle and back but ply for the divider?!) and "Swiss cheesed" the material I couldn't rout out.
I don't think I'll drill holes through the other braces unless I get really bored. To be clear, this does have a purpose: not only am I removing weight from the cab, but I'm also increasing the volume of air available inside the cabinet. The front-to-back internal dimension is actually only 9 5/16", so without any bracing or the speaker I only have a maximum of 2.9 cu. ft. to work with. Cutting big holes is obviously great, but cutting 3/8" jokes in 3/4" square braces? Probably not so much.
Also, not going to lie, six year old me was really happy doing this.
I have most of the braces cut already, so the next step is screwing and gluing them in place. Not really looking forward to trying to tune the shelf port. It's so big that the length calculations are fairly insensitive to minor variations, so hopefully it won't be too bad.

Peavey Bass Cab Conversion

This is a Peavey tnt Combo, a bass combo amp that put out 50W. The amp part is long gone, but I got the cab for a whopping $15. It has separate chambers for the amp and the "ported" speaker enclosure.

The existing speaker enclosure part is only about 1.8 cu. ft. thanks in part to the shallow construction (10" internally, front-to-back) but also to the section reserved for the amp (4" of height!). The overall maximum internal volume is roughly 3 cu. ft., which is a great starting point. I'm going to brace the hell out of this cab and use the existing front slot for a shelf port. I'm assuming/hoping for roughly 2.5 cu. ft. after installing the speaker, all the bracing, the volume taken up by the port.

The baffle is actually OSB (chipboard) so it might make sense to just replace it, but I'm going to try to avoid that for now. It's dadoed into place, but actually rattling so hopefully a bead of adhesive and possibly some cleats will fix that.

I've been having fun in WinISD trying to find a decent (and cheap) driver for this box. I've finally settled on the Dayton Audio PA380-8, which is (thermally) rated to 500W. I'm going to tune the cab to 50 Hz, which looks life an optimal point for balancing low-end extension and excursion. I'll add the plots from WinISD when I get a chance.

50 Hz is on the high end of bass guitar cab tuning, but a lot of commercial cabs are actually tuned about here. While a low E string is around 40Hz (and the B below that roughly 30Hz), not much of that fundamental is picked up by, well, the pickups. By far, the more important frequency to worry about is the second harmonic (first octave), which will be 80 (or 60) Hz. If you'd like to see evidence of this, search the TalkBass forums for "waterfall plots", which show frequency spectrum content over time in a lovely 3D format.

Anyway, even with the cab tuned to 50 Hz, the driver I've chosen hits -3dB around 50Hz, so even the low B should be quite loud. As much as I wish I were making a subwoofer, I'm not, so I don't need to worry about covering that range.

Plus my other bass cab is tuned to 45 Hz. That one's a real treat, an Eden Nemesis 212 that I fitted with MCM drivers. That cab requires a great deal of bracing as it can shake roughly 100 pounds of other amps and cabs to the floor. Not that I've let it, but objects that size and mass being turned into that old electronic vibrating football game, well, that's just a massive waste of energy.

But back to this Peavey: I've got to seal the back where the amp used to be, cut out the internal "top" that separated the amp from the cab, brace the living daylights out of it, verify the tuning, and then line the inside.

Total cost so far:
Cab- $15
Baltic birch- $35
Driver- $75
Jackplate- $5

Still need to buy: adhesive, lining, screws, paint, etc.