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Author Topic: Here's a sneak peak at our new phono preamp  (Read 17807 times)

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Offline Doc B.

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Here's a sneak peak at our new phono preamp
« on: October 07, 2010, 06:27:45 AM »
Come see it at RMAF 2010, in the Magico/Audio Salon/Marutani Consulting room. The preamp was commissioned for a mastering quality high res digital archiving system and features adjustable EQ allow for both RIAA and pre-RIAA vintage LPs.
« Last Edit: October 07, 2010, 06:29:38 AM by Doc B. »
Dan "Doc B." Schmalle
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Bottlehead Corp.

Offline Grainger49

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Re: Here's a sneak peak at our new phono preamp
« Reply #1 on: October 07, 2010, 06:35:19 AM »
That's beautiful!  Who made the front plate?

You got to love any preamp with knobs on the front and knobs on the top!

Can you give me the definition of rollover and turnover?  I have heard them but don't know exactly what they are.  I do know what the RIAA record/playback curves look like.

« Last Edit: December 14, 2013, 04:33:40 AM by Grainger49 »

Offline Doc B.

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Re: Here's a sneak peak at our new phono preamp
« Reply #2 on: October 07, 2010, 08:56:06 AM »
PB did the awesome cabinet design, and PJ did the awesome circuit design. I made any awesome decisions that needed to be made.
Dan "Doc B." Schmalle
President For Life
Bottlehead Corp.

Offline Doc B.

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Re: Here's a sneak peak at our new phono preamp
« Reply #3 on: October 07, 2010, 12:19:14 PM »
Turnover is where the bass boost starts, Rollover is where the treble cut starts.
Dan "Doc B." Schmalle
President For Life
Bottlehead Corp.

Offline Grainger49

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Re: Here's a sneak peak at our new phono preamp
« Reply #4 on: October 07, 2010, 12:23:39 PM »
Thanks!  That makes perfect sense to me.

Offline Wardsweb

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Re: Here's a sneak peak at our new phono preamp
« Reply #5 on: October 07, 2010, 02:30:13 PM »
Wow ! (http://wardsweb.org/misc/drools.gif)

Offline Paul Joppa

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Re: Here's a sneak peak at our new phono preamp
« Reply #6 on: October 07, 2010, 02:47:10 PM »
Turnover is where the bass boost starts, Rollover is where the treble cut starts.
... and shelf is where the bass boost ends.

Shelf: 50/63/80/100/125Hz

Turnover 400/500/630/800/1000Hz

Rollover 40/50/63/75/100 microseconds

Yeah, it's weird that the rollover is spec'd in microseconds and the rest in Hz. Rollover and shelf are often specified by dB relative to 1000Hz, at 10kHz and "very low" frequencies respectively. A lot of historical (non-)standards!
Paul Joppa

Offline Grainger49

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Re: Here's a sneak peak at our new phono preamp
« Reply #7 on: October 15, 2010, 05:42:30 AM »
Isn't there a point that the high frequency roll off can be shelved?  Some say it is necessary, some say it doesn't make any audible difference.  (We only know him as The Stig! A reference to Top Gear)
« Last Edit: October 29, 2010, 09:04:31 AM by Grainger49 »

Offline Paul Joppa

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Re: Here's a sneak peak at our new phono preamp
« Reply #8 on: October 15, 2010, 09:33:55 AM »
Isn't there a point that the high frequency roll off can be shelved?  ...
Yes, a number of people argue that the treble should be shelved around 50kHz because the cutting head was probably shelved there even though that's not in the standard. I've always figured that the mastering engineer should have adjusted equalization so the record sounds right when played back with standard gear.

The cutting head is hardly the only component in the mastering/reproduction chain that might have an imperfect response in the octaves above 20kHz.  :^)  Cartridges and tweeters for example will have much larger deviations. I figure, if one feels the need to compensate for these effects, you really need an equalizer of some sort.

If anyone really feels the need to add a shelf at 50kHz, it's a simple matter of adding a small resistor (267 ohms in Seduction, 316 ohms in Eros) in series with the smaller capacitor in the RIAA network.
Paul Joppa

Offline ironbut

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Re: Here's a sneak peak at our new phono preamp
« Reply #9 on: October 29, 2010, 07:54:35 AM »
Hey Grainger,

Here's a couple of pdf.s you can download regarding historical lp eq (some really interesting stuff about cutting).

www.novotone.be/_site/projets/Projet06/Doc01.pdf

This is from a seminar I attended regarding Columbia records eq.

www.arsc-audio.org/conference/audio2008/extra/galo.pdf

steve koto

Offline Doc B.

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Re: Here's a sneak peak at our new phono preamp
« Reply #10 on: October 29, 2010, 08:26:39 AM »
In conjunction with this preamp I did a fairly extensive chart of recommended EQ settings for various pre 1955 LPs based upon label, era and in some cases catalog number. I compiled it from several different web sources and attempted to filter out the discrepancies. There are about 300 entries IIRC. This will be available to those who purchase the preamp.
Dan "Doc B." Schmalle
President For Life
Bottlehead Corp.

Offline Grainger49

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Re: Here's a sneak peak at our new phono preamp
« Reply #11 on: October 29, 2010, 09:02:05 AM »
ironbut,

Thanks, I downloaded both and will be reading them soon.

To PJ.  I don't hear up in those frequencies (above 50k Hz), and I suppose since you were around aircraft neither do you.  Heavy industry can take a toll.

Offline Gibby

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Re: Here's a sneak peak at our new phono preamp
« Reply #12 on: November 07, 2010, 09:43:52 AM »
This looks so great.  How will the circuit differ from the Eros?

Offline dangerbird

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Re: Here's a sneak peak at our new phono preamp
« Reply #13 on: November 07, 2010, 03:10:34 PM »
very nice indeed

Offline Doc B.

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Re: Here's a sneak peak at our new phono preamp
« Reply #14 on: November 07, 2010, 03:38:02 PM »
This looks so great.  How will the circuit differ from the Eros?

Thanks for the kind words. The circuit uses the same front end tubes, EF86s direct coupled to a 6DJ8/7308, but it uses a 12BH7 to make an additional gain stage that allows for about 12 dB more gain and transformer balanced and single ended output (500 ohms output impedance). It has dual power transformers, and a 6BX7 for the shunt regulator. It also has adjustable equalization and gain trim and uses premium resistors and capacitors.
Dan "Doc B." Schmalle
President For Life
Bottlehead Corp.