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August 20, 2019, 11:45:46 AM

Author Topic: Eros Mod questions  (Read 367 times)

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Offline Robin H

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Eros Mod questions
« on: April 04, 2019, 09:27:46 PM »
I have been running a heavily modified Seduction since 2002. Love it. The mods are serious surgeries with off-board power supply and additional output section. The mods added a lot to the sound which I liked.
I’m planning to move on to the Eros 2 and will do similar mods by using the exiting parts from my Seduction as possible.

Here are my Seduction mods and a few questions:
1.   Mundorf silver/gold caps in the RIAA circuit.  Is the Eros use the same RIAA cap value so I can use my Seduction caps?
2.   The off-board power supply is: 260-0-260 tranny, 6x4 rectifier, balanced chock input loaded, followed by CLCL, followed by OD3 regulator. The original tranny stays in but supplies 6DJ8 heaters only.  What is the min voltage input supply required to the Eros HT regulator? Will the 6x4 and chock power supply benefit Eros?  BYW, any idea what is better from the Eros HT regulator sounds compare to OD3?
3.   I added a 5687 tube output section to the Seduction. It is kind of combine a preamp into the phono amp. It is then able to drive a passive preamp and longer cables. So I can retire my Foreplay which had an off-board tranny, chocks and OD3 power supply.  The original Seduction output coupling caps were removed and the 6DJ8 directly couple to a 5687 tube (grid at around 70V). The 5687’s plate is loaded with a 5K:600 transformer.  Is the 6DJ8 section in the Eros similar to the Seduction so I can use the 5687 output section as well?
Thanks

Offline Paul Birkeland

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Re: Eros Mod questions
« Reply #1 on: April 05, 2019, 05:10:54 AM »
1.   Mundorf silver/gold caps in the RIAA circuit.  Is the Eros use the same RIAA cap value so I can use my Seduction caps?
The RIAA caps in the Eros are not the same values, but they are not particularly hard values to find.

2.   The off-board power supply is: 260-0-260 tranny, 6x4 rectifier, balanced chock input loaded, followed by CLCL, followed by OD3 regulator. The original tranny stays in but supplies 6DJ8 heaters only.  What is the min voltage input supply required to the Eros HT regulator? Will the 6x4 and chock power supply benefit Eros?  BYW, any idea what is better from the Eros HT regulator sounds compare to OD3?
While getting the 0D3 shunt reg would be a huge upgrade to the Seduction circuit, the power supply in the Eros will be a massive improvement over a cold cathode regulator tube. (We know this from our experiences with Foreplay III and Smash which both used an 0D3 in the stock circuit, with the upgrade containing the power supply that's in the Eros)

3.   I added a 5687 tube output section to the Seduction. It is kind of combine a preamp into the phono amp. It is then able to drive a passive preamp and longer cables. So I can retire my Foreplay which had an off-board tranny, chocks and OD3 power supply.  The original Seduction output coupling caps were removed and the 6DJ8 directly couple to a 5687 tube (grid at around 70V). The 5687’s plate is loaded with a 5K:600 transformer.  Is the 6DJ8 section in the Eros similar to the Seduction so I can use the 5687 output section as well?
The power transformer in the Eros will not support the heater current nor the extra regulated B+ current to add another dual triode. 

It sounds like perhaps the original PT, 0D3 power supply, and a 5687 with its interstage transformers could be made into a linestage booster to sit next to the Eros 2. 
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline Robin H

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Re: Eros Mod questions
« Reply #2 on: April 06, 2019, 01:19:07 AM »
Thanks PB.
That would be the plan B to make the 5687 stage a separated preamp or a booster like you suggested.
The only reason I'd like to put the 5687 stage into the phono stage is to eliminate the output cap. And that would be the only benefit from all the hassles.
Anyway, I definitely will build the Eros stock and then have some fun with mods...

Thanks,
Robin

Offline Paul Birkeland

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Re: Eros Mod questions
« Reply #3 on: April 06, 2019, 06:08:52 AM »
Yeah, if you wanted to directly couple a 5687 onto the last stage of the Eros, you're looking at needing a 400V power supply, which you'll need to regulate, then you'll need to recalculate the dissipation of many of the parts to be sure that this extra voltage doesn't cause destruction.  All the R2 resistors would need to be adjusted, and you would need to have a new power transformer custom wound.  The transformer will be much larger, and you're adding another tube, so now we need a new chassis plate that's larger and a bigger base... the snowball will continue rolling and ground the deeper you go! 

On the positive side, you will eliminate one coupling cap by going from Seduction to Eros, so adding one in between Eros and your booster preamp will be a wash in that regard. 
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline Robin H

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Re: Eros Mod questions
« Reply #4 on: April 06, 2019, 07:57:23 AM »
Thanks PB.
I just ordered the Eros 2 and downloaded the manual.
The schematic answered many of my questions.

I added the 5687 to Seduction was because a new, beefier, off-board regulated power supply really improved the Seduction big time.
And it just happened that with the new power supply also gave me a bonus that I could easily add a direct coupled 5687 stage onto it.  Everything just matched perfectly and worked great. So, it was the way to go.

On the other hand, the Eros 2 has very sophisticated regulated power supply and really doesn't need any help.
Also, it operates at higher voltage which means adding a direct coupled stage is not practical and efficient.

While reading the schematic and forum, I have decided keep it stock, no big surgery, just some mods:
Mundorf coupling caps
Add chokes (I have a few on hand)
Old stock EF86 and LED bias
I believe I shall be very happy with it and spend my time on the 5687 line booster/preamp.

Thanks again,

Robin

In case some one is interested, my vinyl set up is: Garrard 301, FR 64 (re-wired with Cardas), Decca Super Gold.
I have run this setup for 32 years and in the past 16 years it was happily singing with the Seduction.

Offline Paul Birkeland

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Re: Eros Mod questions
« Reply #5 on: April 06, 2019, 01:37:17 PM »
I would recommend leaving the chokes out.  While the chokes will knock down the power supply noise, this is meaningless once you have the hybrid shunt regulator.  What could be meaningful is the magnetic field thrown off by the choke if you should happen to put step-up transformers in your Eros down the road. 
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline Robin H

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Re: Eros Mod questions
« Reply #6 on: April 07, 2019, 04:52:41 AM »
That make sense.  It is very sensitive at such a low signal level.
Would shaded choke help?

Thanks,
Robin

Offline Paul Birkeland

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Re: Eros Mod questions
« Reply #7 on: April 07, 2019, 05:18:26 AM »
It might, or it might not.  My suggestion is that the benefits of a choke in the Eros power supply are negligible while there may be some risk of problems arising when you add a step-up transformer.
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline Robin H

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Re: Eros Mod questions
« Reply #8 on: April 07, 2019, 05:45:47 PM »
Thanks. It's good to know.
I shall spend the time and hassles on other more effective mods.

Best,