Here's a sneak peak at our new phono preamp
- Thread starter Doc B
- Start date
Grainger49
New member
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.
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.
Grainger49
New member
Thanks! That makes perfect sense to me.
Paul Joppa
Moderator
... and shelf is where the bass boost ends.Doc B. said:
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!
Grainger49
New member
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)
Paul Joppa
Moderator
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.Grainger49 said:
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
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.
Grainger49
New member
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.
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.
dangerbird
New member
very nice indeed
Gibby said:
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.
Paul Joppa
Moderator
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.)Gibby said:
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.
paulw
Member
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?
Paul
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
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
