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PostPosted: 28 Aug 2015, 09:31 
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See previous posts for the original "Mimic" which is Bruce Heron's (Oddwatt) OPAMP based MM phono preamp. What makes this a Special Edition (SE)? From the images above you will see Solen (French) caps which are on the output replacing cheaper NP electrolytics and from the rear high quality gold plated RCAs now replace the lighter versions. Once more WBT silver based solder has been used and silver plated fine copper wire for hook-up. This is consistent with the "Bourbon" build matching hook-up wire and solder employed. A battery test point is provided at the front.

The enclosure is the same as before and now matches perfectly the Boozhound Labs based MC preamp. As usual the enclosure is bitumanised heavy Al lined. I matched the exterior look of both phono preamps to make them appear as a matched pair. On first listen the sound is OK. But more listening notes to follow.

My blog entry; http://retro-thermionic.blogspot.com.au/2015/08/mimic-se-mm-phono-preamp.html
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Projects: "Sanctum" - 12AU7 and 6AS7 direct coupled headphone amp | "retro-Oatley 6J6" - 6J6 push-pull headphone amp with OPTs | "Mimic Carbon" - carbon resistors and PIO caps. MM phono preamp
Website: retro-thermionic


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PostPosted: 28 Aug 2015, 17:13 
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Hi Mark, The preamp is amazing even me with the performance level. I used 5uF WIMA MKS on the last one. Just great sound. The 63 volt WIMAs are smallish and work well on pcbs.

If anyone builds one for AC mains use.....or inclusion in another piece of gear like a line stage then I found that using a LM7809 in front of the Meanwell DC to DC (to + and - 12V) converter made it even quieter. The residual noise with shorted inputs is below what I can measure.

Good listening
Bruce

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PostPosted: 28 Aug 2015, 18:12 
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gofar99 wrote:
Hi Mark, The preamp is amazing even me with the performance level. I used 5uF WIMA MKS on the last one. Just great sound. The 63 volt WIMAs are smallish and work well on pcbs.

If anyone builds one for AC mains use.....or inclusion in another piece of gear like a line stage then I found that using a LM7809 in front of the Meanwell DC to DC (to + and - 12V) converter made it even quieter. The residual noise with shorted inputs is below what I can measure

Bruce, yes it continues to amaze and thanks for the tip. Do you sell the preamp as a kit?

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Projects: "Sanctum" - 12AU7 and 6AS7 direct coupled headphone amp | "retro-Oatley 6J6" - 6J6 push-pull headphone amp with OPTs | "Mimic Carbon" - carbon resistors and PIO caps. MM phono preamp
Website: retro-thermionic


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PostPosted: 28 Aug 2015, 20:07 
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Another great cap is the Panasonic ECWF 8-)

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PostPosted: 28 Aug 2015, 23:36 
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G'day all, yes it's a fine phono stage design. One of my favourites. On my versions I haven't used anything remotely 'boutique' component wise, but basically just good quality passive components, and all powered by an existing DIY plus and minus 15 volt power supply (ESP P05B power supply).

The only other changes to the circuit I've used are the additions of 47 ohm resistors to the output for buffering purposes, as at least in theory op amps don't like driving a heavy capacitance load directly, although the OPA2134 certainly can....it is a very well designed dual op amp with excellent performance. Regards, Felix.


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PostPosted: 29 Aug 2015, 00:11 
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Agree, a great chip.

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Projects: "Sanctum" - 12AU7 and 6AS7 direct coupled headphone amp | "retro-Oatley 6J6" - 6J6 push-pull headphone amp with OPTs | "Mimic Carbon" - carbon resistors and PIO caps. MM phono preamp
Website: retro-thermionic


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PostPosted: 29 Aug 2015, 09:11 
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Hi, Unfortunately we don't have this as a kit yet....a good chance it will become one as the design is scheduled to be the standard phono stage in an integrated (tube based) preamp with remote control which is next in the que. A stand alone version would be a no brainer. It would however from a cost standpoint fall in a bad range. There is much competition.

I alos added later a 47R in the preamps when used for possibly heavy loads. Since everything I feed one into has a Z in of around 100K this is really not required. BTW I use the same IC for a headphone amp. With a 47R and 220uF (non-polar) cap. It easily feeds my 64 ohm phones. The OPA2134 is really an excellent all around audio IC.

Good listening
Bruce

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PostPosted: 29 Aug 2015, 09:21 
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Thanks Bruce. Take a look at the Boozhound Labs MC. Schematic. Nice and simple. The kit I have our performs everything else I have heard.

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Projects: "Sanctum" - 12AU7 and 6AS7 direct coupled headphone amp | "retro-Oatley 6J6" - 6J6 push-pull headphone amp with OPTs | "Mimic Carbon" - carbon resistors and PIO caps. MM phono preamp
Website: retro-thermionic


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PostPosted: 03 Sep 2015, 08:13 
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Because the chip has a differential PS you really don't need output caps. But this means that the device it drives should have no DC on the input. I have a rule with my gear. No input caps but all have output caps or transformers.

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Projects: "Sanctum" - 12AU7 and 6AS7 direct coupled headphone amp | "retro-Oatley 6J6" - 6J6 push-pull headphone amp with OPTs | "Mimic Carbon" - carbon resistors and PIO caps. MM phono preamp
Website: retro-thermionic


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PostPosted: 03 Sep 2015, 13:40 
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There's noting wrong with a good bipolar cap, like a film cap or if needed, a Nichicon MUSE ES series on the out for that "Just in case", especially with a pre ;)

I've had quite a few amps in for repair where the pre went haywire, dumped DC into the power amp. The one on my bench now is a Bryston amp and one pair of $6K Focal's went *BOOM!* from DC through a pre :eek: :bawling:

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* Ratings are for transistors - tubes have guidelines*
Home: GeeK ZonE
Work: Classic Valve Design


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