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September 28, 2020, 02:54:24 AM

Author Topic: Eros 2 Step-up Transformers  (Read 2800 times)

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Offline Paul Birkeland

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Eros 2 Step-up Transformers
« on: September 28, 2018, 06:13:58 AM »
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.
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline denti alligator

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Re: Eros 2 Step-up Transformers
« Reply #1 on: October 21, 2018, 06:21:38 AM »
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?
« Last Edit: October 21, 2018, 06:23:49 AM by denti alligator »
- Sam

Rega P3-24 (w/AT 150MLX) w/Groovetracer upgrades / C4S Seduction / FLAC -->J.River -->DSD256 -->Gustard X20 / Stereomour II / Klipsch Forte II w/Crites upgrades / C4S S.E.X. 2.0 +Nickel MQ Iron / Speedball Crack / Sennheiser HD600 w/Cardas cable

Wish list: Eros / Crackatwo / Tode

Offline Paul Birkeland

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Re: Eros 2 Step-up Transformers
« Reply #2 on: October 21, 2018, 06:49:13 AM »
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 "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline Paul Birkeland

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Re: Eros 2 Step-up Transformers
« Reply #3 on: April 13, 2020, 01:54:00 PM »
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 "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline Paul Birkeland

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Re: Eros 2 Step-up Transformers
« Reply #4 on: April 27, 2020, 09:41:32 AM »
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 "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline Paul Birkeland

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Re: Eros 2 Step-up Transformers
« Reply #5 on: April 30, 2020, 12:45:49 PM »
Here are some pics of ElCraigo's Eros 2 with Sowter 1990s wired as 1:10 step-ups.
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man