SVP-CL voltage selection

Eoin · #1 09-07-2010, 02:13 PM

Hi guys,

Anyone with an Ampeg SVP-CL preamp know how to change the mains voltage? Assuming it can be done.

There are three wires on the primary of the PT which are plugged into sort of blank spots on the board with the fuse etc. And they're indicated on the schematic (as being there but going nowhere). Unfortunately neither the internals nor the schematic indicate what any of the extra wires are. I'm presuming this is the taps for the different primary voltages... but not so presumptuous that I want to start playing with them without checking if someone already knows.

Eoin

Eoin · #2 09-08-2010, 10:18 AM

Bump?

BassmanPaul · #3 09-08-2010, 10:40 AM

I assume this is a US version that you imported? I can't find the schematic on line so can you post it?

Paul

Eoin · #4 09-08-2010, 12:58 PM

It is, yes, though the unit itself has no reference to being a US 115v etc. around the IEC socket at all.

Jerrold Tiers · #5 09-08-2010, 07:54 PM

The extra wires are taps for other voltages. Should be 100 , 120, and 240 (nominal), IIRC.

Any decent tech can swap the thing to the commonly needed mains volts. I forget the details on that one, but measuring the volts on the taps with power applied will easily tell any tech what tap is which.

Eoin · #6 09-09-2010, 06:56 AM

Yeah, I guess I'm basically just trying to avoid having to test it manually. I'm never completely comfortable working on a live unit, no matter how many times I do it.

There are four wires altogether, and the power requirements in the manual show 100/120 and 220/240 so I'm thinking maybe there are taps for 100, 120, 220, and 240?

The frame of the PT is a bit bent out of shape, distressingly. It allows the core to wobble slightly.

BassmanPaul · #7 09-09-2010, 11:31 AM

As Jerrold has arrived I'll bow out and leave the answers to him.

Paul

okcrum · #8 09-09-2010, 11:34 AM

Jerrold can verify this, but with four wires and two windings on the power transformer primary, they are wired in parallel for 120V and in series for 240V. Actual layout varies of course.

EDIT: Ah nm, I just looked at the service data, and this is a 100/120/230/240V primary setup. Your tech can request the service data from Loud; there's a chart showing what gets wired to what for any desired input voltage.

Eoin · #9 09-09-2010, 12:40 PM

Are they colour-coded or by sequence?

Presently I have, from left to right, on the primary:

White - Blue - Black - Grey - Brown

Which currently join to the PCB, as per the schematic on:

J17 - J18 - J16 - J20 - J18

okcrum · #10 09-09-2010, 01:08 PM

Quote:

Originally Posted by Eoin

Are they colour-coded or by sequence?

Presently I have, from left to right, on the primary:

White - Blue - Black - Grey - Brown

Which currently join to the PCB, as per the schematic on:

J17 - J18 - J16 - J20 - J18

Seriously, email Loud and get the chart. There are enough different wiring combinations that the risk of a) me explaining it wrongly or b) you interpreting me wrongly is greater than you just looking at the chart. Loud will get you the data fast; just email or call them.

EDIT: Or, as Jerrold suggested, you can check the taps with a meter to see which are which.

Eoin · #11 09-09-2010, 01:26 PM

I have, but I'm impatient.

I got the schematic from them in the first place, but they haven't been responsive about anything else yet.

okcrum · #12 09-09-2010, 03:31 PM

Quote:

Originally Posted by Eoin

I have, but I'm impatient.

I got the schematic from them in the first place, but they haven't been responsive about anything else yet.

It should have come with the schematic package IIRC.

Eoin · #13 09-09-2010, 04:17 PM

That PDF is all they sent.

Jerrold Tiers · #14 09-09-2010, 08:09 PM

The transformer specs were not always in with the other schematic stuff..... I have a LOT of data, but not everything. much more of stuff I designed all or part of, less on others, nothing on some. And I have a good memory, but again more for things I worked more closely on.

Some transformers were made with a single winding and multiple taps. A low power like that might be done that way, especially with the style of transformer in the SVP-CL.

Looking at the schematic, it seems obviously to be exactly that. Different taps, and one winding, because there is no place for two windings to be connected in series. No two of the J18, J19, J20 are connected.

So all that must be done is to identify the 100, 230 and 240 V windings. you are in the US, so you already know the 120V, right? It should be on J16 now. Probably the black wire.

The common, or neutral, should be on J17, and you plug whichever tap you want onto J16.

Eoin · #15 09-09-2010, 11:19 PM

Okay, cool. That was what I figured from looking at it. It seems quite similar to the voltage selector arrangement in a Marshall 1959 iirc. If the position of tap wires on the transformer follows a logical sequential order then I'm probably looking at swapping the black wire at J16 for the grey one. I guess I'll have to disconnect that convenient little clip thingy for the secondary and pull out the multimeter tomorrow to be sure. Thanks for all the help so far, guys. If anyone has any extra info in the meantime, please share. Still no further response from themselves.

Eoin · #16 09-12-2010, 01:56 PM

That worked fine.

With a 230-115V step-down transformer, I measured 275VAC on the main secondary coil and 14VAC on the heater winding.

After I switched the black wire for the grey wire and plugged straight into the mains, I got 287VAC and 15VAC. I measured 280-290ish VDC on the plate of V4, and 12VDC on the heater filaments.

Thanks for the assistance, guys.

Quote:

Originally Posted by okcrum

Seriously, email Loud and get the chart. There are enough different wiring combinations that the risk of a) me explaining it wrongly or b) you interpreting me wrongly is greater than you just looking at the chart. Loud will get you the data fast; just email or call them.

There are only four combinations, and the same single wire is changeable in each case, so I'm a bit curious now as to what on earth is on that chart.

Loud wouldn't respond to my request for the service data, or my previous request for info on how to change the voltage. They responded almost immediately to my request for the schematic, with a disclaimer and seeking the serial number; and when I sent them the number, they responded almost immediately again with the schematic. It seems they're just ignoring the other questions.

BassmanPaul · #17 09-12-2010, 02:21 PM

I'm glad you were able to suss the thing out. Now you know how to check the next time!

Paul

Eoin · #18 09-13-2010, 09:16 AM

Yeah. They're in sequential order from left to right, so it should be fairly straight-forward if I ever need to change the voltage again. It's unfortunate that the values of the taps aren't printed on the transformer itself, it would have saved some time and effort.

I just have to change the fuse to the correct (250ma time-delayed) value for 220/240V now. Fortunately, they printed that info onto the PCB.