Vintage Mark-style PCB and chassis kit

[Jay Omega]

When I have built the mkiv clone, my second prototype was using relays. You might experience some popping noise when switching chanels, unless you mute the amp like the newer models during the switching.

I hope not but you may be right. I put large series resistors in place that are bypassed by the relays and fly back diodes around the coils so hopefully it’s minimal. I’ve done other switching schemes like that on different amps that weren’t audible

 

[msi]

I hope not but you may be right. I put large series resistors in place that are bypassed by the relays and fly back diodes around the coils so hopefully it’s minimal. I’ve done other switching schemes like that on different amps that weren’t audible

I have vactrols but would go for the relay version. I have a few now, but in 10 years probably not.

 

[candletears7]

How have I only just seen this now?
I’m definitely interested in an export version!

 

[Jay Omega]

The output transformers arrived today and are looking handsome.



Chassis are supposed to ship today, so hopefully I’ll have one of these up and running within the next week or two!

 

[Jay Omega]

So these showed up today



Next steps will be fit testing the chassis mated components and then building the DRG and HRG

 

[Jay Omega]

I believe these chassis are going to work out. Apparently the powder coat is significantly thicker than the shop said it would be, I had to clean it up a fair amount to get everything ready to build.

First step was to mount the bottom chassis mounted items and I installed the EQ board to test the fit.

 

[Jay Omega]

I haven’t had as much time to work as I’d like but here we are







Most of my time has been spent finding parts and figuring out what I need to complete the build so it’s been slow progress. I started wiring the power amp, will hit the rest of the power stuff next and get it ready for the first test. Unfortunately I won’t be able to spend any more time on this until next week

 

[rarebitusa]

Unfortunately I won’t be able to spend any more time on this until next week

Dang...

 

[orionz06]

Just heard of this today, interested for sure!

 

[Jay Omega]

Got the proto fired up last night for the first test, I ran the Triaxis into the underside preamp / power amp junction. All the power amp stuff worked as intended and it sounds glorious.



It’s a bit of a rats nest currently, I will tighten up some of the wiring after everything has been checked out.

Getting close, this project is looking promising

 

[Hoplite22]

Got the proto fired up last night for the first test, I ran the Triaxis into the underside preamp / power amp junction. All the power amp stuff worked as intended and it sounds glorious.

View attachment 4400

It’s a bit of a rats nest currently, I will tighten up some of the wiring after everything has been checked out.

Getting close, this project is looking promising

Looks awesome man !!

 

[Jay Omega]

Looks awesome man !!

Thank you!!

 

[Jay Omega]

I’ve got the preamp board started, time for the bigger components

 

[Jay Omega]

Here is the current progress on the preamp board. Next step will be attaching some of the flying components and wires before install

 

[Hoplite22]

Here is the current progress on the preamp board. Next step will be attaching some of the flying components and wires before install

View attachment 4408

Looking good !

 

[Jay Omega]

Preamp board is prepped and ready for install.

The LDRs tested well so I’m calling it good. I have to make up a few more switched pots and had to order more sacrificial resistive elements, should be arriving later this week.

If all continues to go well I should have a completed amp in the next week or two

 

[rarebitusa]

Quick update - I have been unable to identify any readily available LDRs that have acceptable performance with the stock IIC+ circuit. Due to this challenge, and the dwindling supply of NOS Vactec VTL5C1s and VTL5C4s, I would only suggest my initial preamp board to those that can source Vactecs, or more experienced builders that are able to modify the stock circuit if appropriate to work with alternative LDRs.

For less experienced folks, or those that can't find original Vactecs, I plan to offer a relay-based preamp board as an alternative. While designing, I've added an optional feature that is not available with the LDR boards which is automatic activation of the Bass Pull Shift feature while in the rhythm mode. I never use the Bass Shift in the lead mode but always/ like it on when playing clean. The biggest downside of the relay based board is that the amp will not activate the LED if using an original Boogie Mark II foot switch.

I will be building one of these as well with my test builds before accepting any orders, here is a sneak peek of what it will look like

View attachment 3848

I'm curious so are the "Xvive VACTROL LED OPTOCOUPLER VACTEC VTL5C1" a suitable replacement or not? I've read some posts that say they are ok, others not. Appreciate you weighing in. TIA

 

[Jay Omega]

I'm curious so are the "Xvive VACTROL LED OPTOCOUPLER VACTEC VTL5C1" a suitable replacement or not? I've read some posts that say they are ok, others not. Appreciate you weighing in. TIA

Back when I was scouring / testing, I decided they're not a good fit unfortunately. I was pretty disappointed that they are marketed as a direct replacement, they weren't even close from what I remember. Luckily Banzai music sells the real deal, NOS Vactec VTL5C1, three are needed to complete an amp. Two of the NSL-32SR2 can be used alongside those in the VTL5C4 positions

 

[rarebitusa]

Luckily Banzai music sells the real deal, NOS Vactec VTL5C1

Thanks... reason for me asking was I'm pretty sure I've lost the Treble Shift on my IIC+. Haven't poked around yet to verify for sure, but it seems likely as there's not much else to that circuit control. Also pinged Mesa with no response. So appreciate you chiming in.

 

[Jay Omega]

Thanks... reason for me asking was I'm pretty sure I've lost the Treble Shift on my IIC+. Haven't poked around yet to verify for sure, but it seems likely as there's not much else to that circuit control. Also pinged Mesa with no response. So appreciate you chiming in.

From what I remember, the forward voltage is much higher on the Xvive VTL5C1 so it won’t really turn on when used in parallel with the Vactecs. There is also a 750 pF ceramic cap that could’ve failed, the pot switch, or the associated wiring. If you turn the power on to the amp, leaving the amp in standby, pull the treble shift and put it in lead mode. Read the resistance between the vactrol LDR terminals (the side closer to the big power supply electrolytic cap). If it’s reading 1-2k, your LDR is still OK. You should read approx 10M if you push the treble shift back in