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Non ADA Gear => Rack Gear => Topic started by: scsibear on May 20, 2016, 05:35:49 PM

Title: Changing a 115v tranny to a 240v one
Post by: scsibear on May 20, 2016, 05:35:49 PM
Hey guys looking for some advice on this one..

I recently got a 19" rack unit from the US that runs on 115v, i live in Scotland so i'd like to change the tranny to a 240v one, my intention would be to also add an IEC socket on the back of the unit so i can plug it straight into my Furman power/strip board M10eX.

The tranny itself has only some info stamped on the top which is this 500 115 - 259 then below that it says EIA 606 - - 336.
I know from the EIA number that it was made by Woodward-Schumacher and the 336 is to do, with the year and weekly run i.e 3 (1983) 36 is week 36.

The 115 is the voltage not a clue what the - 259 is tho, and i am assuming the 500 is milliamps ?? yes/no ?

The primary on the tranny has 3 wires 2 black one going to an internal fuse and a green for chassis ground, the secondary side has 2 red wires and a yellow going to the board, that then runs to the full rectifier bridge with the 4 diodes.

I was thinking i'd need a 240v - 15v step down but not really sure what other specs i might need to look for...
I include a snapshot of the schematic for your perusal.

Any ideas folks ??

Regards
scsi

Title: Re: Changing a 115v tranny to a 240v one
Post by: rnolan on May 21, 2016, 02:26:47 AM
Hopefully MJMP can work out from the schematic how much power (VA) you'd need in a step down transformer ?  What sort of unit is it ? If it's a preamp or FX unit it wont need as much current as a poweramp so a 250VA step down transformer will be fine. On mine it says 115 AC 250 VA (volt amps) which also worked fine with a B200s poweramp.  We sourced an appropriate 240v toroidal transformer later and fitted it (B200s has room for a toroidal, not all cases do).  Bigger (higher output poweramps need a bigger stepdown transformer). Replacing the transformer is the best option though. otherwise you are now lugging 2 transformers around  :(
Title: Re: Changing a 115v tranny to a 240v one
Post by: MarshallJMP on May 21, 2016, 06:07:44 AM
Is this for a furmann PQ-3?(according to the schematic).
Title: Re: Changing a 115v tranny to a 240v one
Post by: scsibear on May 22, 2016, 12:34:53 PM
Yes this is for the PQ3, I just need to make sure I get the secondary side the correct voltage even at 15v it may be too high, as the rectification and the smoothing will increase the voltage to the peak AC level and the regulation appears to be the two current limiting resistors and the zener diodes. If the transformer is too high those resistors and zeners will end up dissapating the extra power as heat, and i don't want that.

I think the best thing to do would be (as i do not have a 110V shaver socket in this house) is to buy a 240v - 110v step down adapter from ebay (it's a proper one made to run US voltages(mains 110v) from UK sources (mains 240v) and probe the two red wires from the secondary to see what the overall voltage is. That way if say it's 18v then i know i'd need a 9-0-9.

Have you any idea what the 500 115 -259 stamp on the transformer might be ?, specifically the 500 - is that 500mA ?
Regards
Ray
Title: Re: Changing a 115v tranny to a 240v one
Post by: MarshallJMP on May 22, 2016, 01:15:14 PM
I don't think it's 500mA,it's just an EQ.Can you wait until tomorrow?I'll pop mine open en see what i have put in there.I rebuilded mine years ago to 220V.
Title: Re: Changing a 115v tranny to a 240v one
Post by: scsibear on May 22, 2016, 02:21:45 PM
Sure Marshall no worries thanks a bunch  :D
Title: Re: Changing a 115v tranny to a 240v one
Post by: MarshallJMP on May 23, 2016, 09:36:30 AM
So just checked and it seems it draws around 45mA on the +15V rail and 41mA on the -15V rail.(see pic)

I also modified mine so it doesn't use zener diodes but I added a small pcb with a 7815 and 7915 regulator.(see pic)

I used a toroidal transformer with these specs, 2 x 15V/0.167mA

Hope this helps a bit.

BTW do you have the schematic of a PQ-3?
Title: Re: Changing a 115v tranny to a 240v one
Post by: scsibear on May 23, 2016, 02:44:33 PM
Hey Thanks for the info and the pics, I had a brief look online for a transformer but i couldn't find one with so low mA's they all seem to be like 20mA and above, and i know absolutely nothing about toroidials at all, but at least i know for sure it's deffi 15v out, could you recommend which mA rating i should stay below ( I mean a safe range for direct replacement)

Also inside your unit looks totally different from mine, I can see most of the last Two EQ sections in you pic and there is no PCB there at all, in mine there's a board about 2 inches thick running the full length of the unit (see pic).

As regards the schematic yes i have, it also has the Stereo Mod included so here it is
Title: Re: Changing a 115v tranny to a 240v one
Post by: MarshallJMP on May 24, 2016, 05:20:11 AM
I think my unit is a lot older and my pcb is different then yours.

Now for the transformer You need at least 50mA a side!!You don't need to stay below it but above it.

So I recommend something that has 2 x 15V 100mA or above.(3.2VA or 5VA)

I'm using this one   http://be.farnell.com/multicomp/mcfm50-15/transformer-toroidal-2-x-15v-5va/dp/9531530

The yellow pcb is not original,that's something I added.
Title: Re: Changing a 115v tranny to a 240v one
Post by: scsibear on May 24, 2016, 05:34:24 AM
Thanks Marshall, I found the exact same one as you used on the UK Farnell site from you link, so i'll go order it now.
Yes i saw the yellow pcb add on what is that doing ?
Title: Re: Changing a 115v tranny to a 240v one
Post by: MarshallJMP on May 24, 2016, 05:44:47 AM
Farnell also has a French devision btw.

Well that pcb is connected to the transformer,I added a full bridge rectifier,2 caps and 2 voltage regulators (7815,7915) so it outs out a steady +-15V to the furmann pcb.And got rid of the 15V zener diodes.
Title: Re: Changing a 115v tranny to a 240v one
Post by: scsibear on May 24, 2016, 05:54:53 AM
Ahh i see nice one, I think i'd have to go on an electronics course to be smart enough to know what i was doing with that kinda thing, I actually quite fancy doing a course, maybe i will look into it.

Ohh BTW i meant to ask, the On/Off switch on your unit, did you have to change that to a higher rating to take the 240V or was the original one still ok ?
Title: Re: Changing a 115v tranny to a 240v one
Post by: MarshallJMP on May 24, 2016, 01:31:07 PM
Mine doesn't even have an on/off switch  :lol: just EQ on/off

It's a standard schematic,same is used in the MP-1,MB-1 etc...

http://www.eleccircuit.com/wp-content/uploads/2007/05/power-supply-regulator-15v-15v-1a-by-ic-7815-7915.2.jpg
Title: Re: Changing a 115v tranny to a 240v one
Post by: scsibear on May 25, 2016, 07:56:14 AM
Yes I see it, it is the same cool tnx  :thumb-up:
Title: Re: Changing a 115v tranny to a 240v one
Post by: MarshallJMP on May 25, 2016, 01:16:10 PM
They even sell these on ebay ready to go

http://www.ebay.com/itm/15V-1A-AC-DC-Regulator-Power-Dual-Supply-input-15-18V-7815-7915-Full-Parts-/301036463175
Title: Re: Changing a 115v tranny to a 240v one
Post by: scsibear on May 25, 2016, 10:30:16 PM
Hmmm, now that's mighty handy !!
Title: Re: Changing a 115v tranny to a 240v one
Post by: MarshallJMP on May 26, 2016, 12:14:59 AM
Yep ideal to put in your pq-3 and to get rid of those zener diodes.
Title: Re: Changing a 115v tranny to a 240v one
Post by: scsibear on May 28, 2016, 06:00:29 AM
Marshall there's one more thing I'd like to ask coz this has got me really confused.

I know from what you've told me before your PQ3 does not have an On/Off switch just the EQ On/Off thing. As you know i'm going to fit an IEC socket inlet with switch and fuse on my unit. Let me try and explain what's confusing me so much !

The IEC Socket says it's 250v 10A fuse, but surely a 10A fuse is massive for this, I have Two other units a compressor and a Graphic EQ which both have the IEC sockets, But the fuses inside those are both slow blows t160mA and the other is a t200mA. Now from what I've been led to believe the Fuse here is to protect the Primary in the tranny from blowing what size of fuse should i be using here ?

I see from the Toroidial you have and the one i ordered the secondary current Nom says 167mA so is that the fuse size i should be getting and putting in there ?

Regards
Ray
Title: Re: Changing a 115v tranny to a 240v one
Post by: MarshallJMP on May 28, 2016, 07:04:34 AM
The power is 5VA on that transformer so the primary max current will be 21.7mA,so best is to use a T100mA fuse if you can get one.
Title: Re: Changing a 115v tranny to a 240v one
Post by: scsibear on May 28, 2016, 07:10:48 AM
Brilliant Marshall many thanks man I appreciate it  :)

Title: Re: Changing a 115v tranny to a 240v one
Post by: MarshallJMP on May 28, 2016, 07:22:44 AM
No problem that's what I'm payed for  :lol:
Title: Re: Changing a 115v tranny to a 240v one
Post by: scsibear on May 28, 2016, 08:55:55 AM
LOL  Yup...Hey I knew i had a better schematic set somewhere for the PQ3 I found Em all...here ya go  Enjoy..
Title: Re: Changing a 115v tranny to a 240v one
Post by: MarshallJMP on May 28, 2016, 11:21:39 AM
Thanks,seems my unit is from 1982.Neither schematic seems to fit my unit.
Title: Re: Changing a 115v tranny to a 240v one
Post by: scsibear on May 29, 2016, 08:25:06 AM
How strange, my unit has a date stamp of 83 inside it presuming it's 1983 of course, the wiring across the eq pots look similar to yours in that wiring diagram, but it's totally different on mine at that point as mine are all mounted straight onto the pcb. I know there was a later re-issue I'm presuming that was the Blackface version with a front Input, i know we both seem to have the original Greenface with the red knobs.
Sorry the schematics don't seem to correspond to your unit I'm afraid that's all the schematics i could get on it.
Title: Re: Changing a 115v tranny to a 240v one
Post by: MarshallJMP on May 29, 2016, 06:33:20 PM
I dated mine with the date stamp on the pots.

I also found the green ones (original ones) were made from 76 to 81 and they changed the green to black.
Title: Re: Changing a 115v tranny to a 240v one
Post by: scsibear on June 10, 2016, 04:13:15 PM
Hi Marshall, Ok my Transformer I ordered from Farnell finally arrived today it was out of stock hence it took so long coming. Could you check me on my wiring please?
Primary winding colours (3 wires) Brown 240v, Blue 0v and Grey 115v
Secondary winding colours (4 wires) Red 15v/0.167A, Black 0v, Yellow 15v/0.167A, Orange 0v
I assume i join the Black and Orange wires of the secondary to give me the centre tap ?
However the Primary colours are a little confusing for me, I presume the Brown 240 is the Live (goes to fuse), the Blue is Neutral, so that would leave the Grey 115v as Ground ?  is that correct ?  If not could you please advise
Thanks
Ray
Title: Re: Changing a 115v tranny to a 240v one
Post by: MarshallJMP on June 11, 2016, 03:37:28 AM
Yes black and orange togheter for the center tap

DON'T ground the grey wire unless you want to order an other one  :nono:  ;D
Just put a piece of shrink tube over it (or some tape if you have to),it doesn't have to be connected.
Title: Re: Changing a 115v tranny to a 240v one
Post by: scsibear on June 12, 2016, 12:36:04 PM
Ohh I see so with the primary side it's basically a choice then as in 240v OR 115v the one you want you use(in my case the 240v), the one you don't you just do not attach it and blank it off so it doesn't make contact with anything at all.

Great Marshall many thanks once again
regards Ray
Title: Re: Changing a 115v tranny to a 240v one
Post by: MarshallJMP on June 12, 2016, 02:21:08 PM
yep that's it

No problem, let me know if you need other  info.
Title: Re: Changing a 115v tranny to a 240v one
Post by: scsibear on June 16, 2016, 02:30:20 PM
Hi Marshall I ran into an issue, the fused IEC & switch combo i bought is actually too big for the chassis so I'm just going to get a fused IEC socket instead, there is an SP on-off switch already on the unit anyway and I was wondering if i can use that ? it seems to be a Swann series 40 (2 pins) but it says 12v on it, would i be able to use that switch or do i need to get one rated at 240v. The one in the unit doesn't say anything about Amps, i went to the web site and they sell an SP on-off 16 Amp 250v almost an identical switch but I just don't know what amp/voltage rating i should be using.

Please advise
regards
Ray
Title: Re: Changing a 115v tranny to a 240v one
Post by: MarshallJMP on June 16, 2016, 02:39:21 PM
From what I can tell these switches should be able to handle 250V.How is it hooked up now?

http://www.thermalproducts.com.au/swann-rocker-switches-40-series/

As for current the max was like 25mA so no problem there.
Title: Re: Changing a 115v tranny to a 240v one
Post by: scsibear on June 18, 2016, 10:37:51 AM
At the moment it's hooked up like this:

US style 3 pin moulded plug, colours are Green wire is the earth comes into chassis and gets screwed onto the leg of the trans as chassis ground, then 2 black wires for the live and neutral, one black wire comes into chassis then goes to an internal plastic fuse holder the other end is one of the black primary wires on the US 115v trans.
The other black wire comes into chassis and is attached to one side of the on/off switch, the other side of the on off switch is the second black wire on the primary side of the US 115v trans...that's it. There are only 2 black wires on the Primary side.

BTW that web link you gave is the exact one i was looking at the switch looks exactly like the top one on that page except it has the 12v stamped on it.

I was going to wire mine like this

Title: Re: Changing a 115v tranny to a 240v one
Post by: MarshallJMP on June 18, 2016, 10:41:42 AM
I think you can wire it up like in your pic.