MC SUT from Haufe transformers

[vencel]

Hello,

I would like to ask something since I am not an expert. I hope someone will be able to help me.
I am putting together my SUT based on Haufe transformers. I know the following:

red and green: primary winding
blue and white: secondary winding

(the red and the green wires are in phase)

black: transformer core
black/yellow: transformer housing

The black and black/yellow wires should both be connected to ground (at the preamplifier).

What I don't know is that where should I put the 12Kohm resistor to align the impedance of the Denon DL-103R?
I've read that the secondary winding (blue and white wires) should be loaded with the 12Kohm resistor but I don't know what does this loading mean in practicality?
Where should I connect one end of the resistor and where the other end?
Another question if I should connect the negative of each RCA connector to 1 common point?

Could you please help me with this?

I would really appreciate any help or a photo of a similar desing.

Thanks and regards,
László

[NRG]

Does this help?

http://www.kandkaudio.com/mccartsetup.html

Place the loading R in parallel with the secondary winding. Your 12K will reflect 120R to the cart with a 1:10 step-up: 12000 / (10 x 10)

A 1:20 would reflect 30R....so find the ratio and wire in parallel...but also check if you already have some form of loading IE: if the SUT is to front a MM stage then you need to account for the 47K that its likely to have as standard.

Edit: a 15K on the secondary in parallel with a MM 47K load will reflect 113R to the cart with a 1:10 SUT

[Barry]

Hello,

I would like to ask something since I am not an expert. I hope someone will be able to help me.
I am putting together my SUT based on Haufe transformers. I know the following:

red and green: primary winding
blue and white: secondary winding

(the red and the green wires are in phase)

black: transformer core
black/yellow: transformer housing

The black and black/yellow wires should both be connected to ground (at the preamplifier).

What I don't know is that where should I put the 12Kohm resistor to align the impedance of the Denon DL-103R?
I've read that the secondary winding (blue and white wires) should be loaded with the 12Kohm resistor but I don't know what does this loading mean in practicality?
Where should I connect one end of the resistor and where the other end?
Another question if I should connect the negative of each RCA connector to 1 common point?

Could you please help me with this?

I would really appreciate any help or a photo of a similar desing.

Thanks and regards,
László

Hello László,

Didn't we discuss this some time ago via PMs? To answer you questions

(a) connect the 12K resistor across the secondary winding (blue and white wires). The most convenient place to do this is at the phono socket.

(b) It doesn't matter if the ground of the RCA connectors are connected together at a common point (so-called star earthing), or even if they are connected together at all, but the case, housing, transformer cores and screens must be earthed by connection to your preamp (along with the earth lead from your turntable.

Trust this is of some help

[PS The red and blue leads are in phase, and not as you describe.]

Regards

[vencel]

Hello Barry,

I hope you are fine.
You are right, we discussed it but I was not shure what does it mean in practicality to load the secondary.
I am a bit dumb to electronics...
Anyway thank you very much for you and Neal as well for the help.

THANKS and REGARDS!
László



Hello László,

Didn't we discuss this some time ago via PMs? To answer you questions

(a) connect the 12K resistor across the secondary winding (blue and white wires). The most convenient place to do this is at the phono socket.

(b) It doesn't matter if the ground of the RCA connectors are connected together at a common point (so-called star earthing), or even if they are connected together at all, but the case, housing, transformer cores and screens must be earthed by connection to your preamp (along with the earth lead from your turntable.

Trust this is of some help

[PS The red and blue leads are in phase, and not as you describe.]

Regards

[vencel]

One more question:

what does it depend on if I should connect the RCAs to star earthing or not?

Thanks!

[Barry]

László,

This is how to wire each Haufe T-7883 transformer:

(1) connect the red wire to the centre conductor of the RCA input socket
(2) connect the green wire to the outer conductor of the RCA input socket
(3) connect the blue wire to the centre conductor of the RCA output socket
(4) connect the white wire to the outer conductor of the RCA output socket

(5) connect the 12K resistor across the blue and white wires, at the output socket

(6) connect the black and yellow/black wires together and to the metalwork of the case you use to house the transformers. The best way to do this is to drill a hole in the case and use a small nut and bolt to secure a solder tag.

It does not matter if you connect any of the outer conductors of the RCA sockets together, but if you wish you can do so in one of two ways:
either

(a) remove the insulating washers when fitting the RCA phono sockets to the metal case

or

(b) connect a separate wire to the outer conductor of each socket, and then connect all four wires to the point at which the black and yellow/black wires of the two transformers are attached to the metal case. This arrangement is known as 'star earthing'.

If you choose to earth the RCA phono connectors, you do not need to separately earth the metal case. If you don't earth the phono sockets, then you will have to earth the metal case, by connecting it to the earth terminal on the back of your preamp.

Regarding the use of the 12K loading resistor - it is used to make the impedance, as seen by the cartridge, close to 100 Ohm. Your preamp's phono stage will have an impedance of 47K and this impedance is across the transformer secondary winding. The impedance as seen at the transformer primary will be 47K divided by the square of the turns ratio. Since the Haufe T-8773 transformer has a 10:1 ratio (that is the transformer boost the cartridge output voltage by a factor of 10), the impedance seen at the input will be 470 Ohm.

Your Denon cartridge likes to see an impedance of ~ 100 Ohm, so the effective impedance presented to the secondary winding needs to be lower than 47K. The 12K resistor is in parallel with the 47K, the parallel combination looks like 9.56K, so with a 10:1 turns ratio the input impedance will look like 95.59 Ohm.

When both the primary and secondary winding resistances are taken into account, the actual impedance seen by the cartridge is 120.1 Ohm.

Regards

[vencel]

Hello Barry,

THANKS A LOT!!!!
That's a very detailed and good description which can be totally understood by such people as myself :-)

I hope now I can finish it soon and post some photos here.

Best regards,
László



László,

This is how to wire each Haufe T-7883 transformer:

(1) connect the red wire to the centre conductor of the RCA input socket
(2) connect the green wire to the outer conductor of the RCA input socket
(3) connect the blue wire to the centre conductor of the RCA output socket
(4) connect the white wire to the outer conductor of the RCA output socket
....
Regards

[Barry]

You're welcome László - glad to be of help.

Looking forward to seeing the photos! :)

Regards

[vencel]

I finished my SUT so I would like to share some photos about it. Please disregard its quality, I am not a professional in drilling and painting.
Even though it might look like the common ground is isolated from the chassis in reality it is NOT.
Before installing its bottom I will fill the box with sand.

Please let me know your opinion (if I did everything correctly).

Thanks and regards,
László

https://dl.dropbox.com/u/22181492/MC/P1050664.JPG
https://dl.dropbox.com/u/22181492/MC/P1050665.JPG
https://dl.dropbox.com/u/22181492/MC/P1050666.JPG
https://dl.dropbox.com/u/22181492/MC/P1050667.JPG

[Barry]

I finished my SUT so I would like to share some photos about it. Please disregard its quality, I am not a professional in drilling and painting.
Even though it might look like the common ground is isolated from the chassis in reality it is NOT.
Before installing its bottom I will fill the box with sand.

Please let me know your opinion (if I did everything correctly).

Thanks and regards,
László

https://dl.dropbox.com/u/22181492/MC/P1050664.JPG
https://dl.dropbox.com/u/22181492/MC/P1050665.JPG
https://dl.dropbox.com/u/22181492/MC/P1050666.JPG
https://dl.dropbox.com/u/22181492/MC/P1050667.JPG

Hi László,

I hope you don't mind, but I turned your 'url's into 'img's, so everyone can see the fruits of your labours.

The RCA phonos are isolated, that is, the outer conductors are not connected. But that should not cause any difficulty, as you have 'earthed' the case with an earth terminal, to which you can connect the tone-arm earth and turntable earth, and thence to the preamp earth terminal.

Nice work László. A neat and professional construction. But why fill the case with sand?

Regards

[vencel]

Why fill with sand?
Just to add some weight so more rigid RCA cables will not lift the SUT up :-)

[Barry]

Why fill with sand?
Just to add some weight so more rigid RCA cables will not lift the SUT up :-)

Haha! Know what you mean - but I never did like stiff and rigid cables. I make my own, and usually choose small diameter/flexible cables.

Regards

[vencel]

Haha! Know what you mean - but I never did like stiff and rigid cables. I make my own, and usually choose small diameter/flexible cables.

Regards

I also prefer flexible cables and I am making my own cables but I also have some more stiff ones.
Do you have a favorite DIY cable design?
Would you share its recipe?

[Moko]

Wow very impressed with your build (& Barry's brillant instructions....exactly the sort of thing that non-electricians can follow easily)

So most importantly how does it sound with your Denon DL103?

I'm seriously tempted to build one myself.

[sq225917]

How cute are they..?

[vencel]

I am really sorry but I had several issues to solve so I could not listen to this SUT yet.
My tube preamp had and still has a slight hum and I am working on fixing it, my EMT-929 tonearm needs to be aligned as I bought a new armboard for my TD-124 and I am hunting for a good and inexpensive armlift. During the summer I did not have much time for these projects but as soon as I will set everything right I will share my impressions.

[anubisgrau]

i've had a pair of these but unfortunately i've never really figured if they are good ones for denon 103 or not. early impressions were okay but then they were installed in a DIY RIAA i've never completely got along with and i sold them all. that said, the new owner really loves it and i have another SUTs for denon 103, whenever its time comes again. now i'm in a benz micro camp...

[Canetoad]

If you choose to earth the RCA phono connectors, you do not need to separately earth the metal case. If you don't earth the phono sockets, then you will have to earth the metal case, by connecting it to the earth terminal on the back of your preamp.

Hi Barry, Does this mean that I don't have to run an earth to the preamp if I earth the RCA sockets in the SUT?

[Barry]

Hi Barry, Does this mean that I don't have to run an earth to the preamp if I earth the RCA sockets in the SUT?

Yes - if you run a separate earth to the preamp as well as earthing the RCA sockets (that is, connecting all of them to the metal case), you will create an 'earth loop', which may cause hum problems.

So:

[1] RCA sockets all connected to the metal case - do not use a separate earth

[2] RCA sockets not connected to the metal case - you must earth the case with a separate lead connected to the preamp earth.

[Canetoad]

Thanks Barry, much appreciated! :)