Replacement Toroidal Transformer

[adamg]

I would appreciate recommendations for / where to buy a replacement transformer for my Unison Research Unico P integrated amplifier.

 

It currently uses a 250VA unit

 

Edited May 26, 2013 by adamg

[Telecine]

What is the problem A? Buzzing? Humming?

[Cafad]

How goes that amp Adam?  (apart from the transformer, how does it work with the KEFs is what I mean)

[adamg]

You guessed it...the amp was sitting around for sometime before I bought it second hand about 4-6 months ago.

 

It developed a hum a month or so ago which has started creeping up above acceptable levels at times. i.e. you can here it in the room from a few metres away. Its only barely audible in the speaker if you put your ear to the speaker at 0 volume.

 

Unison Research said to expect some noise due to the size of transformer but I think its above normal levels now.

 

I've tried dampening top and bottom with little effect.

 

I intend to get it serviced and replace the transformer.

[Telecine]

Sounds like a replacement might be your only option if you have already tried to dampen it. Zaphod might be able to suggest something if you send him a PM.

[rocky500]

I thought when a transformer hums, it comes from the unit itself and not from the speakers.

Could it be a earthing problem?

[adamg]

The hum is from the transformer itself.

 

The faint hum in the speakers may be microphonics of the preamp tube?

 

No reason the think the hum is an earthing issue. If anything it started when I accidently turned the amp off / on very quickly but that probably me just being paranoid.

[Zaphod Beeblebrox]

The hum is from the transformer itself.

 

The faint hum in the speakers may be microphonics of the preamp tube?

 

No reason the think the hum is an earthing issue. If anything it started when I accidently turned the amp off / on very quickly but that probably me just being paranoid.

 

Toroidal transformers have a number of advantages over EI transformers. Unfortunately, they also possess a number of drawbacks. One of those drawbacks is associated with small amounts of DC impressed on the mains supply. It is possible that there is no fault with your transformer and that it is reacting poorly to small amounts of DC. You can determine this, by obtaining a 240 - 240 isolation transformer and using that to connect your amp to the mains with. If the noise disappears, then you have your answer. If it does not, then it is likely the transformer is faulty.

[adamg]

Thanks ZB. Any recommendations ?

 

Could only really find this locally http://www.tortech.com.au/product/-iso-300es/

[Zaphod Beeblebrox]

Thanks ZB. Any recommendations ?

 

Could only really find this locally http://www.tortech.com.au/product/-iso-300es/

 

That should be fine, however you should see if you can borrow one, rather than buying one. It could be that the transformer is faulty.

[adamg]

That's the plan....

[VanArn]

It appears that the Unico amplifier has appeared in different formats.It would be of benefit if the  correct valve  for this version is a 12AX7/ECC83 as appears in the manufacturers specs and in some of the reviews.Also if the amplifier is fitted with the optional phono pre-amp. board;then the transformer may require re-positioning or a shield fitted to minimise induced hum from the batched lead-out wires.Also check that the mains is set for 240 V a.c. on the internal selector board.Other causes of hum can be caused by ground loops, close proximity to other electronic equipment (especially switched  mode power supplies) and leakage via faulty insulating materials.

[adamg]

Hello VanArn

 

This is a relatively new problem.

 

The stock tube for my particular model is a 12AU7/ECC82. The current tube is a NOS ECC82/6189/12AU7WA however I have also tried a NOS replacement of the Philips ECC82. Both were sourced from a reputable supplier (Watfords). The problem existing before swapping the tubes.

 

The amp does have the optional phono stage.

 

Looking for an Isolation Transformer as per ZBs recommendation I started this thread which has some more info and suggestions of DC in the circuit potentially from outside of my home. Can't think of anything else changing.

 

Regarding the 'other sources of hum' would these result in hum from the transformer itself or at the speaker.

 

Testing the amp in another set-up sounds like a simple first step. Otherwise it looks like its a matter for a technician to look at.

 

Thanks everyone for your input.

Edited June 2, 2013 by adamg

[Zaphod Beeblebrox]

Looking for an insulation Transformer as per ZBs recommendation

 

I don't wish to sound pedantic, but it is important you know the correct term for what you want.

 

It is an ISOLATION transformer.

[adamg]

I don't wish to sound pedantic, but it is important you know the correct term for what you want.

 

It is an ISOLATION transformer.

 

Yes slipped up there.

 

I haven't been able to try an isolation device yet but have tried the amp two different mains circuits at another place. No noise on one and a little but nothing like at home on the other.

 

From this I'm assuming the hum is in deed caused by DC in the mains at home. Turned everything off yesterday and hum was still there.

 

Brought the amp into work to check out another circuit and what-da-ya-know - hummin' like the best of 'em.

 

Has anyone any experience with a DC blocker / mains filter as discussed here

 

Isotek and Mains Cables Are Us make a mains cable with a blocker. David at MCRU can supply a blocker with IEC inlet then captive lead out for $500.

 

The thread above pointed out this bit of circuitry ready for fitting in a box. Not sure if its compatible for use with a integrated / power amp or Aust conditions?

Edited June 2, 2013 by adamg

[Zaphod Beeblebrox]

Yes slipped up there.

 

Whats your thoughts on a mains cable with a DC Blocker ?

 

I presume the DC blocker is a capacitor? Do you have a cite? It could be worth a try.

[adamg]

I must have been editing as you were replying.

[Zaphod Beeblebrox]

I must have been editing as you were replying.

 

I haven't tried the blocking capacitor route. It should work though. Whatever you do, DON'T spend $500.00 on a solution. That's just crazy. You could buy an isolation transformer for less and gain superior results.

[adamg]

This was Tortechs response when querying them for a solution:

 

I doubt there would be DC in the mains causing hum.
It is usually high voltage or noise in the mains.
If the unit is from overseas rated to maybe 220V or 230V, this could be causing the hum, as it would be over-volted.
Solution would be voltage reducer or possibly a mains filter.

 

Reinhart at rkcables suggested this unit from Tortech which I assume is another isolation transformer:

 

http://www.tortech.com.au/category/audio-transformers/

 

However if the problem is occurring at various locations the most logical seems to be to try another transformer.

 

I'm using Cafads Burson amp on the same circuit and it doesn't seem to have a problem. Got a vintage Hitachi on the same circuit with no issues either?

 

I've also just realised that a mate of mine is an instrument tech and I think he can measure DC on the mains.

[Zaphod Beeblebrox]

This was Tortechs response when querying them for a solution:

 

I doubt there would be DC in the mains causing hum.

It is usually high voltage or noise in the mains.

If the unit is from overseas rated to maybe 220V or 230V, this could be causing the hum, as it would be over-volted.

Solution would be voltage reducer or possibly a mains filter.

 

Well, the guys at Tortech have forgotten more about transformers than I will ever know. They are worth listening to. In fact, if it was a Chinese transformer, I'd back their statement 100%. Chinese transformers can be spectacularly bad quality. You could test for this, by taking your amp to a tech who uses a variable autotransformer (aka: Variacâ„¢) on his/her bench (I use them, as do almost all techs). You can quickly verify if over-Voltage is an issue.

 

Reinhart at rkcables suggested this unit from Tortech which I assume is another isolation transformer:

 

http://www.tortech.com.au/category/audio-transformers/

 

Yes.

 

 

However if the problem is occurring at various locations the most logical seems to be to try another transformer.

 

Yes.

 

I'm using Cafads Burson amp on the same circuit and it doesn't seem to have a problem. Got a vintage Hitachi on the same circuit with no issues either?

 

IF my hypothesis is correct, then products that do not use toroidal power transformers will not experience a problem. Most Australian built products do not exhibit power line problems when used in Australia. They know how to build for local conditions. Unlike everyone else.

 

I've also just realised that a mate of mine is an instrument tech and I think he can measure DC on the mains.

 

That is possible.

[adamg]

So my issue remains unresolved....in short

• Tortech have checked the trannie on the bench and the conclusion was the transformer is not silent but very quiet and appears well designed for 240V (thanks to Kamal at Tortech who was most helpful).
• DC in the mains at home measures about .22 mV which I understand could theoretically cause the transformer to hum.
• Tried one DC blocking circuit inline with the main cable - no change.
• Have improved dampening of chassis - no change
• The Aust distributor is adamant that a new transformer will fix the issue based on the experience of WA Unison Research owners who's transformers are not coping with the 260V in WA - my area runs stable 240V

 

...........Also check that the mains is set for 240 V a.c. on the internal selector board.......

Now I should have had a closer look but the transformer is marked as set to 240V- although you can also see its been re-soldered (below).

 

In my original post you can almost see all colour coding for voltage leads from trannie. They are:

 

0V Black   100V White    110V Yellow    120V Orange

0V Blue    100V Brown    110V Green    120V Violet

 

The selector board was configured as follows:

 

A - Black

B - White

C - Yellow

D - Orange

E - Blue

F - Red

G - Green

H - Violet

 

Currently the selector board has the E-Blue & H-Violet circuit bridged.

 

 

 

The tech guys at Unison Research (Italia) have been very helpful / patient but are a little slow at responding to the million dollar question - what is the correct setting for 240V?

 

Can anyone here offer some advice in the interim?

 

I assume the Orange & Violet should be bridged but that theory would mean its currently set to 120V which doesn't make sense.

 

[midyim]

The connection is set for 240Vac.

Mains input is 1{black} and 8{violet}.
Connection is between 4{orange} and 5{blue}...giving 120V+120Vac.

I have had issues with EI type transformers buzzing due to lack of "iron" as they were designed for 60hz supply...don't know if that relates to toroid types.

[Toma Audio]

Hi Adam,

I have the new Isotek gear at the shop now if you want to try out a few bits and pieces to try to get a solution. At least they claim to block DC.

As an aside the difference they make sound wise is a genuine benefit as well.

[adamg]

The connection is set for 240Vac.

Mains input is 1{black} and 8{violet}.

Connection is between 4{orange} and 5{blue}...giving 120V+120Vac.

I have had issues with EI type transformers buzzing due to lack of "iron" as they were designed for 60hz supply...don't know if that relates to toroid types.

 

 

 

 

The connection is set for 240Vac.

Mains input is 1{black} and 8{violet}.

Connection is between 4{orange} and 5{blue}...giving 120V+120Vac.

I have had issues with EI type transformers buzzing due to lack of "iron" as they were designed for 60hz supply...don't know if that relates to toroid types.

 

Thanks midyim - I see the link now.

 

Hi Adam,

I have the new Isotek gear at the shop now if you want to try out a few bits and pieces to try to get a solution. At least they claim to block DC.

As an aside the difference they make sound wise is a genuine benefit as well.

 

Thanks for the offer Geoff - will be in touch.

[Cafad]

Hey Adam, if you drop in on Geoff see if he is ready to hand over the Onkyo 9070.  If so feel free to run off with it and give it a run for a week or two, see how it drives those KEFs.