Looking to Pull the Trigger, but...

BNAL · 2332

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Offline BNAL

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on: July 31, 2016, 09:39:03 AM
I have been looking to pull the trigger on a new phono pre and with the current deal on the Eros  i'm extremely tempted. The only thing holding me back is I'm running a passive volume control switch with a 10K ebay DACT attenuator. The Eros product page states that at least a 15k input impedance is required.

Does this mean that I should change the attenuator to 15k or higher. The manufacturer of the amp recommends with a passive pre that you should not use a attenuator. The other option could be using a buffer.

Any recommendations would be greatly appreciated.

Brad Nalitt
Iron Upgraded S.E.X. Amp 2.0
Foreplay III
Quickie w/PJCCS
Eros Phono
Blumenstein Orca Speakers, Baby Benthic Subs
S.E.X.y Speakers W/FT17H Horn Tweeters
Thorens TD 125 MkII W/ Shure M97xE JICO SAS Stylus


Offline johnsonad

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Reply #1 on: July 31, 2016, 12:20:03 PM
I can't help you Brad but I wanted you to know I bought one too with this sale😊

Aaron Johnson


Offline galyons

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Reply #2 on: July 31, 2016, 12:53:10 PM
The manufacturer of the amp recommends with a passive pre that you should not use a attenuator. The other option could be using a buffer.

All a passive pre is is connectors, wire and an attenuator. So, this comment is, to me, confusing.   

The Eros is spec'd for a 0.47uF output cap. Mine shipped with a 1.0uF cap.  The issue is the low frequency fall off.  Calculating Fo at 0.47uF, the Eros output with a 15k next stage input impedance gives you 22.6Hz. That is a bit high.  If you build with the 1.0uf, Fo would be 10.6Hz.  Still high. Where Fo is the crossover frequency, this is the 3dB down point, the signal will be essentially flat at 10 times Fo.

At more typical, at least for tube gear, input impedances, say 50K or 100K, you would have  Fo's of  6.8Hz and 3.4Hz, respectively with a 0.47uF output cap.   PJ may have other reasons for the 15K minimum input impedance, as well.  Check with your amp's manufacturer to see if there are any issues with a passive having 50K or 100K input.

All of that being said, I would jump on the Eros sale.  When built out, it is a marvelous piece of kit. Mine has bested some very well regarded pricey commercial units!

Cheers,
Geary
 

VPI TNT IV/JMW 3D 12+Benz LP-S>  Eros + Auralic Aries + ANK Dac 4.1 >Eros TH+ Otari MX5050 IIIB2 > BeePre >Paramount 300B 7N7 > EV Sentry IV-A

Thorens TD124/Ortofon RMG-212/SPU >Seduction > Smash^Up> Paramour 45 MQ >K12's


Offline BNAL

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Reply #3 on: July 31, 2016, 02:28:38 PM
Geary,

Thanks that makes sense. Now I see why I would need to add a buffer to proved the >15K input and lower output impedance the amp needs.

Arron,

You did recommend the Eros, and I will take your advice and pull the trigger.

I will take the savings and put is towards a buffer.

Thanks,
Brad

Brad Nalitt
Iron Upgraded S.E.X. Amp 2.0
Foreplay III
Quickie w/PJCCS
Eros Phono
Blumenstein Orca Speakers, Baby Benthic Subs
S.E.X.y Speakers W/FT17H Horn Tweeters
Thorens TD 125 MkII W/ Shure M97xE JICO SAS Stylus


Offline tsingle999

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Reply #4 on: July 31, 2016, 02:48:38 PM
For another idea you could run the eros into a quickie.
I use a reduction into the quickie and run a separate preamp for other sources.
Quickie is great!

SGS iTransporter with Qobuz & Roon to Optical Rendu to BH DAC (Battery) / Wavelegth Cosecant to BeePre to 300b(ehemoths) to Jagers.
Bottlehead Stat headphone amp with Wavelength Brick DAC


Offline johnsonad

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Reply #5 on: July 31, 2016, 02:50:44 PM
Thinking back on it, I've used the Tube Phono (same output impedance I believe via RCA) with a MQ Ingot which has a 10k input and honestly I didn't notice the difference.  This time I used the $150 in savings to upgrade resistors and capacitors in the signal chain. This is my third Eros/Tube Phono variant and should be the last 😊

Aaron Johnson


Offline BNAL

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Reply #6 on: July 31, 2016, 02:58:38 PM
I pulled the trigger. I just could not pass on the deal.

Brad Nalitt
Iron Upgraded S.E.X. Amp 2.0
Foreplay III
Quickie w/PJCCS
Eros Phono
Blumenstein Orca Speakers, Baby Benthic Subs
S.E.X.y Speakers W/FT17H Horn Tweeters
Thorens TD 125 MkII W/ Shure M97xE JICO SAS Stylus


Offline johnsonad

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Reply #7 on: July 31, 2016, 03:05:10 PM
I hope that you enjoy it as much as I have! This will be the second Eros in my current system (one for tape).

Aaron Johnson


Offline Paul Birkeland

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Reply #8 on: August 26, 2016, 08:10:03 AM
The issue is the low frequency fall off. 

There is indeed this issue, but also the issue that whatever you have connected to the output of the Eros will load down the 6922 output stage.   We have found that the performance of this stage seems to hold up reasonably well down to a 15K load, but going lower risks higher distortion operation. 

On your 10K control, you can add a pair of 5K resistors between the output of the selector switch and the input of the 10K attenuator to bump the impedance up a little bit.

Adding a Quickie will also completely remedy the issue. 

Just out of curiosity, what's the input impedance of your amplifier?

-PB

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline BNAL

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Reply #9 on: August 28, 2016, 02:29:20 PM
Just out of curiosity, what's the input impedance of your amplifier?

I believe it is 25k.

I going to build a buffer and use a 100k eBay DACT attenuator..

Brad Nalitt
Iron Upgraded S.E.X. Amp 2.0
Foreplay III
Quickie w/PJCCS
Eros Phono
Blumenstein Orca Speakers, Baby Benthic Subs
S.E.X.y Speakers W/FT17H Horn Tweeters
Thorens TD 125 MkII W/ Shure M97xE JICO SAS Stylus


Offline xcortes

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Reply #10 on: August 28, 2016, 06:16:26 PM
I use a tube repro (three of them actually) from the unbalanced output which is a circuit identical to the eros iirc. My preamp is a pair of Magnequest silver 10k:10k inputs (Mexico series, of course) feeding a 10k pot and the sound is superb.

Xavier Cortes


Offline BNAL

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Reply #11 on: August 29, 2016, 05:21:48 AM
I use a tube repro (three of them actually) from the unbalanced output which is a circuit identical to the eros iirc. My preamp is a pair of Magnequest silver 10k:10k inputs (Mexico series, of course) feeding a 10k pot and the sound is superb.

Xavier,

Aaron said the same thing, so I feel confident that if I just use the passive it will spit good. Thank you for your experience, it helps.

Brad Nalitt
Iron Upgraded S.E.X. Amp 2.0
Foreplay III
Quickie w/PJCCS
Eros Phono
Blumenstein Orca Speakers, Baby Benthic Subs
S.E.X.y Speakers W/FT17H Horn Tweeters
Thorens TD 125 MkII W/ Shure M97xE JICO SAS Stylus


Offline johnsonad

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Reply #12 on: August 29, 2016, 01:11:26 PM
Xavier and I wouldn't steer your wrong and we are using the same speakers. I just added subs to mine. Give it a try 😊

Aaron Johnson