Vintage Mark-style PCB and chassis kit

[Jay Omega]

Want to gauge interest on a PCB set and chassis kit for a Markish amp. I've designed a chassis and it's off to a metal shop for quote, an overview and some features I'm planning to include:

• Boards setup to accommodate a IIC+ circuit with some extras offered further down the Mark lineage and some other things I've wanted to try
• 17" wide steel chassis with welded seams
• Aluminum front and rear faceplates
• Chassis would fit in authentic Boogie head shell, combo, or rackmount enclosure
• Amp construction similar to vintage Mark IIs with four power tubes, reverb, and graphic EQ
• Would include a high level builders guide, BOM along with suggested vendors, and schematic. This would not be tailored towards beginner builders
• Front panel overview
  • Input and external foot switch jack holes, circuit board compatible with authentic Boogie rhythm / lead mode switch
  • Typical Volume I thru Lead Master 3/8" potentiometer holes, front panel labeled with typical pull functions
    • Add a pull function label to the Middle control for Mark IV Mid-Gain / Harmonics function
  • Switch holes for Rhythm / Lead mode and Graphic EQ In / Out / Auto
  • Five band graphic slider cutouts
  • Power and standby switch holes
  • Pilot light hole
• Rear panel overview
  • Convenience receptacle, fuse holder, and IEC inlet cutouts
  • Jack holes for slave out, 16/8/4(x2) ohm loads, effects loop send / return, and the following remote switchable functions:
    • Two or four output tube operation (simul-class / class A or 60/100W)
    • EQ in/out, reverb on/off, rhythm/lead mode
  • Pot holes for reverb, presence, slave out level
  • Holes for two toggle switches
    • One dedicated for two / four output tube operation
    • One "voicing" switch. Could be used for things like
      • Pentode / triode
      • Mark IV pushed presence function AKA extreme mode
      • Switching feedback network from C+ to Mk IV
• Bottom overview
  • Similar to Mark II layout with five preamp tubes, reverb jack between V2 and V3, and four power tubes
  • Jack holes for underside functions that can be plugged if you don't use them: preamp / power amp junction, reverb / eq switch jack, reverb send, and one extra for users choice
  • Output transformer mounting holes would fit a variety of commonly available transformers

I don't know pricing yet. Also may go with powder coated aluminum chassis with direct silkscreen as opposed to steel chassis with faceplates. I'm looking at a run of ten complete board sets and chassis to start. Anything you don't like or want to see on there?

P.S. - I decided against a switchable C+ / C++ for this project. The amp could be built to C++ specs if desired, but I would not supply a schematic

 

[JD]

Following

 

[quad48uF]

Count me in! Amazing work!

 

[Jay Omega]

Below is a 3D rendering of the draft design without the faceplate. I've been in discussions with the company that makes Dr Z's chassis as they are not far from me, but they have been slower to respond than I'd like. May look to engage some other metal shops if I don't hear back within the next week or so

 

[electric mayhem]

Nice job. I'm likely going to have to wait for another run but I really would like to do this. Here are some thoughts I had.

As for the head shell a consideration is the bolt holes- IIB or III? Iirc it was changed at IIC+ but maybe IIC. Personally I'd love a long chassis but I'm probably a minority.

Are you finding push/pull pots available for the typical values?

I know you were using the IIB and I don't remember if you built more than the preamp board, so do you have boards for PS, EQ circuit, EQ control, and DR output? Much of that could be hand wired or turret if not but the EQ control board of some type would be needed. I wouldn't care if it had EQ but I figure most people would.

Since the CTS sliders with tabs are no longer made, do you have a plan for holding the EQ board to the chassis?

No switch for 1/2 power or Class A if someone finds a donor simul tranny? Full power full time works for me so this is just asking.

I like the C14 jack opposed to a power cord.

 

[Jay Omega]

Nice job. I'm likely going to have to wait for another run but I really would like to do this. Here are some thoughts I had.

As for the head shell a consideration is the bolt holes- IIB or III? Iirc it was changed at IIC+ but maybe IIC. Personally I'd love a long chassis but I'm probably a minority.

Are you finding push/pull pots available for the typical values?

I know you were using the IIB and I don't remember if you built more than the preamp board, so do you have boards for PS, EQ circuit, EQ control, and DR output? Much of that could be hand wired or turret if not but the EQ control board of some type would be needed. I wouldn't care if it had EQ but I figure most people would.

Since the CTS sliders with tabs are no longer made, do you have a plan for holding the EQ board to the chassis?

No switch for 1/2 power or Class A if someone finds a donor simul tranny? Full power full time works for me so this is just asking.

I like the C14 jack opposed to a power cord.

The mounting holes are for a IIB as that's all I had access to. I assumed the IIC variants were the same, does anyone know if they're different? The only benefit I see in the long chassis is that the presence control is on the front panel. 17" would have more mounting options and would be lower cost

For push pull pots, I've found both 1M and 250k CTS pots. For other values, you just have to buy a CTS pot of whatever value / taper you want and swap out the resistive element with the switched pot. Not ideal, but that's what's on the market today. I would show how I do this in the builder's guide

The chassis is compatible with the PCBs I designed for power supply, power amp, preamp, EQ driver and graphic. There are many ways to design and build an amp, I've used them all over the years, but for this project I chose to stick with PCBs and construction style similar to the vintage Mark IIs.

The graphic board would be mounted to the chassis via mini toggles for EQ In/Out/Auto and Rhythm/Lead mode switch, same as I did in the IIB->IIC+ conversion prototype. The fader board will be compatible with readily available pots, same as the ones I used with the 60W IIC+ build in the shown in the IIB->IIC conversion thread

I did include a hole for two or four power tube operation, which is the Class A / Simul or 60 / 100 switch depending on which four tube model you have. Boogie sells the simul-class output transformer from their factory store, I bought one recently. I'd bet others offer a replacement as well, though I'd always say go with Boogie if you can.

I dislike attached power cords, but I rearranged the rear panel with an IEC jack so it will wire up the same way as a IIC+

Also, I forgot to mention, there is a hole in the bottom to accommodate Boogie's fan.

 

[Matt Henley]

I would be interested.

 

[Nerd]

Sub'd

 

[msi]

I'd be interested but I'd need a bit more information before commiting.

 

[AxH]

I'm interested!

Parts availability to/in Europe is important. FX loop probably a must, but pre-/poweramp junction would work I guess, if levels are right?

Another project you might think of creating something for is, for e.g. a Hammond box of suitable size: A IIc+ preamp with simplifications such as perhaps only one channel (lead), with functions as switches instead of push/pull knobs, and knobs instead of sliders for graphic eq. For use with separate power amp or in FX return.

 

[mrscary]

I'm in for one or two

 

[guitarman59]

How much, or ball park price for the chassis kit? I'm interested.
Ed

 

[Montauk]

Interested! (Europe)

 

[dominique@france]

Nice job. I'm likely going to have to wait for another run but I really would like to do this. Here are some thoughts I had.

As for the head shell a consideration is the bolt holes- IIB or III? Iirc it was changed at IIC+ but maybe IIC. Personally I'd love a long chassis but I'm probably a minority.

Are you finding push/pull pots available for the typical values?

I know you were using the IIB and I don't remember if you built more than the preamp board, so do you have boards for PS, EQ circuit, EQ control, and DR output? Much of that could be hand wired or turret if not but the EQ control board of some type would be needed. I wouldn't care if it had EQ but I figure most people would.

Since the CTS sliders with tabs are no longer made, do you have a plan for holding the EQ board to the chassis?

No switch for 1/2 power or Class A if someone finds a donor simul tranny? Full power full time works for me so this is just asking.

I like the C14 jack opposed to a power cord.

Hey
cool
i'm very interesed about this project.
can you realize a price evalution ?
thx for your answer
dom

 

[Jay Omega]

Hey all,

Still don't know about pricing. I haven't revised the chassis prints based on feedback from the fab shop so don't yet have final numbers. I also need to mod the PCB designs for the fab-house and get a quote.

I haven't had much time as I'd like to spend on this lately, but will be picking up again in the near future. Since I will have to front the money, I'm going to start with a run of ten chassis and PCB sets. If the kits sell I will do another run, if they don't I will probably build them over the years and sell as completed amplifiers.

Also, I'd like to add an option for pre-cut head shell plywood pieces. These would be unfinished, so it'd be up to the use to paint / glue / tolex.

The chassis will also be compatible with the newer mark head cabinets / combos so that it could be used in genuine Boogie housings or any aftermarket.

 

[Nerd]

Im still interested

 

[Vinzenz]

I'm in for 1-2

 

[Less02]

would the preamp pcb fit in the real mkiib chassis? If so, I would be interested for the pcb alone.

 

[JammyDodger]

I would be interested, thanks!

 

[WaxCapacitor]

I’d buy !