Bottlehead Forum
Bottlehead Finished Products => Legacy Products => Tube Phono => Topic started by: Doc B. 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.
-
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.
-
PB did the awesome cabinet design, and PJ did the awesome circuit design. I made any awesome decisions that needed to be made.
-
Turnover is where the bass boost starts, Rollover is where the treble cut starts.
-
Thanks! That makes perfect sense to me.
-
Wow ! (https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fwardsweb.org%2Fmisc%2Fdrools.gif&hash=a72fd0676f078c71e0585ff897503eb3b468feae)
-
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!
-
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)
-
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.
-
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
-
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.
-
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.
-
This looks so great. How will the circuit differ from the Eros?
-
very nice indeed
-
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.
-
This looks so great. How will the circuit differ from the Eros?
This was a custom one-off, specifically made to have the flexible equalization. To do that and keep the controls from interacting, the equalization was separated into two parts, which eliminated the option of an unbalanced output from the second stage, so the only output is the balanced line driver third stage. (In our original Repro tape head preamp, from which this preamp was derived, both outputs were available. The first two stages of the Repro are similar to the Eros.)
The other difference is the Eros has a servo bias, which allows a wider range of EF86 tubes to work. We are still looking at other bias methods, so it's not clear what will be in this preamp when it is finalized.
These high-end products also use many expensive high-quality parts, which drives the price up a lot.
-
Any chance of a less sneaky peak? I keep looking in hoping for some more pictures...
Paul
-
I'll try to get another pic up today when I get in to the office.
-
That would be great - unfortunately I've had to retire my Seduction as it has to few inputs ;^) I did initially try an upstream switch-box (Manley Skipjack) but here were just to many problems with three cartridges, two step-ups...oodles of hum, cables routing and so on - is the sneaky phonostage a single input?
(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi142.photobucket.com%2Falbums%2Fr81%2F4will8%2FASC2.jpg&hash=2f09d56d51f0a43e2a17270b30d9a46460428d49)
Paul
-
The phono preamp can be customized to some extent. If you order an RIAA only version there is more room to make changes to the layout. PB does the case design and builds them, and I will ask him if he could fit in more inputs.
There are a couple of pics here, about the third post down:
https://www.head-fi.org/forum/thread/515603/seattle-meet-10-2-10-impressions/30 (https://www.head-fi.org/forum/thread/515603/seattle-meet-10-2-10-impressions/30)
-
Wow, the sneak peak picture left me quite unprepared for its true size, when you add something for perspective :^0
Paul
-
Yeah we thought it looked pretty enormous - until we set it next to a Pacific Microsonics Model 2 DAC and a Spectral preamp. Folks are so used to our relatively small and lightweight kits that the size and heft of the Tube Phono has kinda thrown them for a loop when we have taken it to shows. It's not so big that it won't fit on an equipment rack shelf like any other gear, but you're not going to sneak it onto the same shelf with a turntable.
-
but you're not going to sneak it onto the same shelf with a turntable.
Oh I don't know - My turntable shelf is over 6 foot long, it used to have three turntables on it before I consolidated them into one turntable with three arms - so plenty of room ;^)
Paul