Eros 2 Step-up Transformers

[Paul Birkeland]

Incorporated into the Eros 2 are a couple of holes for mounting step-up transformers.  We have used, with great success, the step-up transformers from Sowter.  Just be sure to pick "threaded grommet style E" when ordering so they mount right up in the holes we provide.
Sowter Step-ups
Cinemag transformers with the threaded bushing mount will also fit:
Cinemag Step-ups
Jensen transformers will work, but will require adding some extra holes to the chassis:
Jensen step-ups
Terminals have been left available to provide convenient locations for secondary loading resistors.  Primary loading resistors and loading caps can be installed across each RCA jack.  Instructions for proper installation of step-up transformers will be forthcoming shortly.

 

[denti alligator]

This is very helpful, and it's very tempting for when I upgrade from my Seduction.

My question is: how much does the Sowter affect the overall sound of the Eros? I know it's dependent on the cartridge chosen, but was wondering--especially since there are all kinds of SUTs out there--what effect these Sowters that you've tried have had. Is it a definite improvement, or a matter of taste?

Also, isn't placement key for interference? I'm assuming the holes for mounting are optimal, or would getting an external SUT that can be moved further away be better?

 

[Paul Birkeland]

My question is: how much does the Sowter affect the overall sound of the Eros? I know it's dependent on the cartridge chosen, but was wondering--especially since there are all kinds of SUTs out there--what effect these Sowters that you've tried have had. Is it a definite improvement, or a matter of taste?

The Eros will not work properly with a low output moving coil cartridge unless step-up transformers are used.  We are recommending these transformers because they are well shielded, sound good, and have been available for quite some time (and should continue to be).

Also, isn't placement key for interference? I'm assuming the holes for mounting are optimal, or would getting an external SUT that can be moved further away be better?

Shielding is key.  I had external SUTs and a gen 1 Eros prior to the Eros 2 with Sowter transformers, and I had a very difficult time getting things quiet with my original setup. 

 

[Paul Birkeland]

1.  Pop the resistors out of each RCA jack that go to pin 9 on each EF86 (leave them attached to the socket, just pop out the end sitting in the solder cup of the RCA jack).
2.  Remove the 47K loading resistor on each RCA jack.
3.  Reconnect them at terminals 2 and 17.
4.  Install step-up transformers.
5.  Wire step-up primary wires to each RCA jack.
6.  Wire step-up secondary wires to terminals 1/2 and 16/17.
7.  Install loading resistors as recommended by the SUT manufacturer and/or your cartridge manufacturer.  You can load the primary or the secondary of the SUT relatively easily by either using loading resistors across the RCA jacks (loading the primary), or loading resistors between 1/2 and 16/17 (loading the secondary).

At some point I'll post some photos of my Eros 2 that has this installed.  I had taken some a long time ago but I was unable to locate them.

 

[Paul Birkeland]

Here is a photo showing installation on one side.  Note that my Eros 2 was the first prototype, so the green boards that are in it are different.

You can see that the 220 ohm resistor that would go to pin 9 has been move to the empty terminal next to where the negative lead of the big gold bypass cap sits.  I have added a loading resistor here as well, and the output of the step-up transformer connects here.  The same thing is done on the other side in a mirror image (that's where the empty terminals are, so there's no option).

The primary of the SUT connects across the RCA jack.  In this case, I opted to remove the 47K resistors from the RCA jacks to make installation easier.

The shield wire for the SUT connects to the middle lug of the 5 lug strip in this photo which is chassis earth.

 

[Paul Birkeland]

Here are some pics of ElCraigo's Eros 2 with Sowter 1990s wired as 1:10 step-ups.

 

[denti alligator]

I've always used MM cartridges. What MC cartridges are people using with a SUT in their Eros 2? I'm wondering what would make a significant upgrade from my (very fine) AT MLX150

 

[Paul Birkeland]

The Hana ML has been getting a lot of love.

 

[denti alligator]

Thanks. And I'm assuming the Sowter 9570 would be the SUT to get for that one?

 

[Paul Birkeland]

A 1990 would probably work fine too.  Having the extra taps pulled gives you extra flexibility down the road. 

 

[itsjaw]

Hi

I am thinking about ordering the Eros 2.  I have a HOMC mono cart (Miyajima) and LOMC stereo cart (Koetsu).

Is there a way to add the SUT to the build, but is it possible to add a switch/toggle to go between MM and MC?

I hope so : )

Jason

 

[Paul Birkeland]

It would probably help to know which specific cartridges you have.  It might be possible to simply switch between ratios if the HOMC output level isn't too high.

 

[itsjaw]

Hi Paul

Sure thing:

Miyajima Spirit Mono (HOMC), 5mV, 90ohms internal impedance

Koetsu Rosewood Standard (LOMC), 0.4mV, 6ohms internal impedance

Right now, I use the Miyajima straight into the MM, with the Koetsu I like it loaded at  ~100ohms

Thanks for the help!

 

[Paul Birkeland]

I can't find any data on the Spirit Mono in the high output configuration.  If you bought the normal Spirit Mono and used your Koetsu Rosewood, you'd be fine with a 1:10 SUT for either one, and you could even grab a 1:12 (Jensen makes one, as do others) to get that output up slightly higher.  Otherwise, I would tend to gravitate toward just powering down the Eros and swapping cables rather than trying to add more RCA jacks, a switch, and step-ups all onto that chassis plate.

 

[maarten]

Shielding is key.  I had external SUTs and a gen 1 Eros prior to the Eros 2 with Sowter transformers, and I had a very difficult time getting things quiet with my original setup.

Wouldn't the external SUT be easier to shield? I'm thinking about using an external SUT instead of the Sowter/Jensen/Cinemag to avoid shielding issues.

 

[Paul Birkeland]

Wouldn't the external SUT be easier to shield? I'm thinking about using an external SUT instead of the Sowter/Jensen/Cinemag to avoid shielding issues.

I would suggest considering that we have tested the placement of the Sowter transformers on the Eros 2 to verify appropriate placement and that they don't interact with the power transformer.  You also won't need to deal with another set of interconnects and another drain wire to connect the Eros to the separate box that holds the transformers.

 

[Paul Joppa]

To amplify (sic) PB's points, Jensen warns that for best performance the secondary load must have very low capacitance - a couple feet of coax (100pF) is more than enough to harm the high frequencies. Eros is especially well suited to use transformers, because it uses a pentode input tube with about 4pF input capacitance.

This is different from moving magnet carts, most of which are designed for 100-500pF in parallel with the 47K input resistor. A 3 to 6 foot cable accounts for about half of that, and the typical triode input stage Miller capacitance accounts for the rest.

 

[maarten]

Ok I will go for the Sowter! Will try to find them somewhat cheap (in EU)

 

[maarten]

Just a small question here as my Sowter pair arrives.

In your early prototype picture, you have a 220 Ohm going from pin 9 to the jack. I guess this was changed to 90.9 Ohm later? (You also have an extra heatshrink wrapping on the Right side (in the manual it's only on Left) btw.)

That resistor is a 90.9 Ohm and goes to terminal 2/17 right? There's no need to change it to a 220 Ohm one?

And then, the 47.5k resistors  that used to go from ground to jack, just go to 1-2 (and 16-17).

Thanks for clarifying

 

[Paul Birkeland]

In your early prototype picture, you have a 220 Ohm going from pin 9 to the jack. I guess this was changed to 90.9 Ohm later? (You also have an extra heatshrink wrapping on the Right side (in the manual it's only on Left) btw.)
[/quote]
The pictures I posted are of a prototype Eros 2 that was built before we wrote the manual.