installing VVR2 in rocket

[norburybrook]

Morning all,

Once again my inexperience and lack of knowledge is thwarting me in my amp tinkering!!!

So, I have a Hall VVR2 I want to install in my rocket/wreck to control the power of the whole amp. So therefore I need to be able to control the B+1 voltage.

Now, the example on the Hall instructions show a SS rectified amp with the first power filter cap BEFORE the standby switch so wiring the B+ in and out to the board is very simple and straight forward.

OK, so here's where I'm struggling on my rocket. If you look at the layout you can see that if I installed after the standby switch it would be before the filter cap. So I'm confused how to wire after as the first filter cap has connections from the rectifier, also from the transformer and the choke, so three connections.

How do I wire the B+ in and out then so it's after the first filter cap?

Marcus

[martin manning]

Rewire your amp so that the reservoir cap is before the standby.

[norburybrook]

Rewire your amp so that the reservoir cap is before the standby.

Thanks Martin , I had a feeling you would be the first to answer.


Actually, looking at how to do that, couldn't I just tap the red wire going to the choke?



Marcus

[martin manning]

The new pup is getting me up and moving very early!

So basically I'd connect straight to the filter cap from the rectified and wire the choke and the OT centre tap to the standby switch then?

Exactly.

Would you bother adding extra filter caps to the input to filter out the bit of DC that can cause scratchy volume pot? I've a feeling that unless you're reducing the voltage massively then it won't be an issue. I just want to take the edge off the amp now and again so won't be dialling it back hugely.

Probably true. I'd try it without first and see if you run into any problems.

[norburybrook]

Ha, I got so far then realised where did the return from the standby go? i.e the point i'd tap the B+ in and out top the VVR

Hence my edited post... if it went to the second filter cap wouldn't I be shorting out the choke?


Marcus


p.s. our dog is 10 now so I've forgotten about puppies and early starts..... not conducive to late night gigs!!!

[martin manning]

It'd be like this without the VVR.

[norburybrook]

thanks Martin, But wouldn't it be easier just to tap into the red wire connection to the choke?


also, as space is very tight over there on the front panel/chassis would there be any problems installing it on the back, opposite the input jacks?

it would be a long-ish run the board and back. I know it's high voltage, but the current is low so does that mean interference would be minimal. Should I fly them straight over everything in the shortest route or go round the perimeter of the chassis?

other option is to mount he PCB/Pot on the front panel next to the stand by switch and have the mosfet connect to the board by wires so it can be screwed to the chassis for heat dissipation.


Marcus

[martin manning]

The "B+ out" on the VVR board connects to both the input side of the choke and the OT CT. The "B+ In" comes from the reservoir via the standby switch. So, re my marked up layout you would disconnect the Choke and OT CT wires from the output side of the standby and run them to the B+ Out, and add a new wire from the output side of the standby to the B+ In. The VVR board can go on the back panel, you would only be running a single wire from the standby switch straight across the chassis.

Or maybe you are thinking of putting the VVR over on the input end of the chassis? That would make for some long runs. I would think between the fuse and the speaker jacks would be the best place. You'd have to reroute the filament leads a bit, but that wouldn't be a big deal.

[norburybrook]

The "B+ out" on the VVR board connects to both the input side of the choke and the OT CT. The "B+ In" comes from the reservoir via the standby switch. So, re my marked up layout you would disconnect the Choke and OT CT wires from the output side of the standby and run them to the B+ Out, and add a new wire from the output side of the standby to the B+ In. The VVR board can go on the back panel, you would only be running a single wire from the standby switch straight across the chassis.

thanks Martin,

AH.. the OT CT was the confusion here. As they say a little knowledge can be dangerous

thanks for explaining that. i'll need to add a terminal strip I think so I can physically connect the two thick wires from the OT and choke to the VVR board as it has tiny connections.

I'll let you know how it goes. Need to drill some holes now, time to make some masking tape collector bags for the swarf .

Marcus

[martin manning]

See edit above, though I'm not sure how much space the VVR board takes up or how much room is under it when it's installed.

[norburybrook]

problem is getting the mosfet attached flat to the chassis as it's bolted down so the heat can be transferred.

Only place I can do that with it attached directly to the board is over by the input side, which would mean a long run, but the mosfet would be attached directly to the board and there'd be plenty of space to mount it.

like I said I could mount the VVR board minus the mosfet on the front panel by the stand by switch but I'd have to mound the mosfet somewhere else and then run wires to the board.

which is the better option?

Marcus

[martin manning]

Additional lead length to the FET is not the best idea since they can oscillate. Is the FET soldered to the board yet?

[norburybrook]

No it's not, I've left it in the anti static bag until I know what I'm going to do as they're fairly fragile with static etc...well compared to all other valve amp components


If I mount it at the front then I can mount the FET close but not 'actually' on the board, so the wire runs would be 2 inches maximum I'd say.


Marcus

[martin manning]

You could do that, but I think I'd add a 220 or 470 ohm gate stopper resistor at the FET's gate lead.

[norburybrook]

Thanks to Martin and AmpMike for your help.

In the end I left things as they were regarding the standby switch and split the connections at the first filter cap by adding a turret strip to make an extra connection.

I also managed to squeeze the VV board in next to the standby switch.


Works really well, I'm very pleased with the result. The volume pot on the guitar does indeed get a bit scratchy once you're at about halfway on the VVR knob. I was wondering if I added a larger resistor to raise the lowest voltage level if that would stop the scratchiness or just move the usable range to a different part of the pot sweep.


Anyway, job done and a useful addition to the rocket/Wreck

Marcus



p.s. thanks Bob for suggesting the 0.1uF cap in series with the input to the grid. Works well, not 100% but it's very workable now. Only had a large 600w orange drop available but I presume it won't matter what it is.