Phono stage: DIY, outboard or preamp-bundled?

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Phono stage: DIY, outboard or preamp-bundled?

Postby XLR_silver » Wed Aug 20, 2003 9:19 am

do DIYers in this forum (or in general) build their own (tube) outboard phono stage? if not, why? what are the issues involved?

thanks!


mods,

please feel free to move this topic if you feel that it shouldn't be here.
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Postby m_shoe_maker » Wed Aug 20, 2003 2:16 pm

Its harder to build a phono stage than a line stage because:

1. One has to create an exact RIAA curve, and not a simple gain stage
2. A poorly designed / built phono stage can easily exhibit noise. :evil:

Tama ba mga DIY boys :?: :roll:
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Postby arnoldc » Wed Aug 20, 2003 3:15 pm

tama! kaya hanggang ngayon ay di pa ako nakakagawa at nag ti-tiyaga pa din sa X-LP :cry:
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alternatives?

Postby XLR_silver » Wed Aug 20, 2003 5:59 pm

ako rin, can't afford branded preamps that have a built-in tube phono stage. so my choice is between phono stages of vintage preamps (or integrated amps) and affordable solid-state outboard phono stage like arnold's X-LP (magand rin namang tumunog di ba?). the former usually doesn't have an MC option, pero maganda din tumunog sa MM. so, wala na ba talagang alternatives?
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Postby arnoldc » Wed Aug 20, 2003 6:12 pm

hindi naman masama yung X-LP, tama ka maganda rin, may MC pa!
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Postby setup1 » Wed Aug 20, 2003 10:05 pm

Hi Guys!

Just a few tips from my experience. If you need MC ability, try a good step-up transformer. Even a mic input transformer can be rigged for MC use. As long as it has a high quality winding bandwidth isn't usually a problem because it is "passive", there's no DC current flowing through. Another advantage of an MC transformer is lower noise compared to an active MC stage. Back in the late 80s, I used to see Audio-Technica, Denon AU320, Fidelity Research and etc. MC transformers cheap at Lito Gelano's because they were out of vogue.

Phono preamps are difficult to build mainly because of potential ground loops and keeping the overall circuit free of hum and noise. I remember my first attempt to build the RCA circuit prototype [1-chassis], it took me a couple of days to wire and a couple of weeks to sleuth the hum/noise. I got rid of the ground loops but hum was still pervasive, so I outboarded the PS and that solved the problem. Since the RIAA EQ is "passive" [which to my ears sound best whether 2 stage or 3 stage with split hi and low freq. EQs for each stage like the Arthur Loesch or jc's Siren]. A tube phono circuit with RIAA EQ in the feedback loop [ala PAS or 7C] is generally less fussy with hum and noise.

For the power supply, I personally don't like tight regulation using SS devices in the B+ line, preferring tube rectification, high inductance chokes, moderate capacitance and DC filaments. If you need active regulation, use tubes or passive using OD3s not zener diodes. But that's just my taste.

BTW, what is an X-LP? I've been out of the loop.....

Regards,

Joseph
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Postby arnoldc » Thu Aug 21, 2003 12:07 am

hi joseph, X-LP is Musical Fidelity's solid state phono stage, now superceded by X-LPS.
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Postby m_shoe_maker » Thu Aug 21, 2003 9:31 am

I have purchased and tried several set-ups: :P

1. pre-amp with built phono stage MM and MM/MC (tube and SS)
2. line stage (tube and SS) + MM/MC phono stage (SS)
3. line stage (tube and SS) + MM phono stage (SS) + pre pre-amp (SS)

I must say, I am most satisfied with my current set-up which consists of the following old stuff :P :

Passive pre-amp w/ MM phono stage (tube) + step-up device :P

Why :?: You know me, I'm not the type to say subjective bla-bla-bla to other people. hehehehehe :twisted:

The stuff:

Precision Fidelity C7A - Passive "Pre-Amp" with tube MM Phono Stage
Denon AU320 Step-Up Transformer

Technically, the C7A is a tube phono stage with variable pots to be used for the volume control. It has no active line stage. So you may say its a phono stage and not a pre-amp. :? But it has inputs for AUX/ TUNER (2 line inputs). So its a pre-amp. :? :? If you use this pre-amp just for a digital front-end, you will just end up using it as a passive devise. :(

During the 80s, some audiophiles hooked this "pre-amp" or "phono stage with variable pots" or whatever you want to call it, :? in their pre-amps with active line stages. In effect, these audiophiles have taken a different route. They have made the C7A a dedicated phono stage. Sort of an upgrade to their existing pre-amps with built-in phono stages (during the 80s most pre-amps still included a phono stage). Soon, some of these audiophiles tried removing their pre-amps and left the C7A to stand alone. Some preferred this approached, while some preferred to have an additional active line stage.

Despite it having a passive line stage, I personally don't have problems in terms of gain. When I am using my MM cart, I bypass my Denon transformer and hook my turntable directly to the C7A. If I use my MC, I hook up my transformer in between the C7A and the turntable.

With MMs, my volume pot is normally set within 10 o'clock to 2 o'clock

With low-output MCs (with transformer), my volume pot is normally at 11 o'clock to 3 o'clock. With high-output MCs (with transformer), my volume pot is normally at 10 o'clock to 1 o'clock.

BTW, I using 86db or 87 db speakers.
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Postby setup1 » Thu Aug 21, 2003 11:50 am

Hi m_shoe_maker!

*Precision Fidelity C7A - Passive "Pre-Amp" with tube MM Phono Stage
Denon AU320 Step-Up Transformer

I agree, the C7A is a well designed preamp with a fine sounding phono stage and unity gain for line stage. If memory serves me right, PF was founded by the same people who started Paragon which used a cascoded circuit [hi-gain] for the phono, just like Kondo's M7 and M10.

PF C7As seem relatviely easy to find there, was there a dealer for these during its heyday?

Regards,

Joseph
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Postby m_shoe_maker » Thu Aug 21, 2003 2:48 pm

Hi Joseph,

You are right, the guy who designed the PF C7A is the same guy who did the famous Paragon Model 10 pre-amp during the 70s. He is Bruce Moore. He was also the guy who placed Audible Illusions in the map, by designing the famous "Modulus" pre-amp during the mid 80s.

During the C7A's heyday, which was early 80s, I believe most audiophiles imported their units from the US. During those days, there were very few hi-end distributors around. :( During that time, most of my 2nd hand units were all 110 volts. It was only during the mid 90s when the Philippines had an influx of distributors bringing in hi-end stuff. :P

As to my C7A, I found it in Lito Gelano's place just gathering dust. Knowing its pedigree, I got it for a P9,000 or something. It was 110 volts. With a provision to be converted to 220 volts, I had this task done by Master Rene Rivo. :P At the same time, I had some filter caps changed. :P
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Postby setup1 » Thu Aug 21, 2003 11:41 pm

Hi m_shoe_maker,

*As to my C7A, I found it in Lito Gelano's place just gathering dust. Knowing its pedigree, I got it for a P9,000 or something.

Might have been the same unit I borrowed when I was choosing between C7A and the Paragon E-1. I took the E-1 because of the external PS.

*the guy who designed the PF C7A is the same guy who did the famous Paragon Model 10 pre-amp during the 70s. He is Bruce Moore. He was also the guy who placed Audible Illusions in the map, by designing the famous "Modulus" pre-amp during the mid 80s.

Didn't he eventually move on to MFA? If so, then the MFA Luminiscence was his final masterpiece. This was a mighty fine preamp design using 6SL7/6SN7 octals....HP had a good preview for this unit in TAS but never followed up..... It was also during this time that TAS featured articles on "Golden Oldies" by Walt Bender and Steven Stone, then the articles just disappeared...perhaps high end manufacturers threatened to pull out ads? I never renewed my subscription and took the classic tube amp/DIY route.

It's very interesting to study the "development" of tube design and their designers. In Moore's case he started with a cascoded phono circuit using 12AX7 variants in Paragon and PF, then he used 6DJ8s [cascaded?] for Audible Illusions, then finally "octals" [isn't that a retro move for an 80s design? maybe that was part of the reason for its failure in the market, no one knew what octals were back then] in the MFA Luminiscence. Moore probably got his inspiration from Grommes, a late 50s design. This is the earliest use of a cascoded circuit for phono preamp I've seen. Never saw an actual unit just the schematic. The AN/UK and Japan M7 and M10 preamps use the same basic circuit except for passive RIAA EQ.

In essence nothing is new under the sun with tube technology. Now that DIY has been re-discovered, a lot of high-end manufacturers' "secret innovations" have been 'uncovered' as marketing hype.....

Keep your soldering irons heated!

Joseph
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Postby Hyperion » Sat Aug 23, 2003 5:36 pm

Passive pre-amp w/ MM phono stage (tube) + step-up device


Looks like the way to go for me too. Maybe even minus the step up since I intend to use high output MM anyway. :D
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Postby m_shoe_maker » Sat Aug 23, 2003 11:58 pm

setup1 wrote:Didn't he eventually move on to MFA? If so, then the MFA Luminiscence was his final masterpiece. This was a mighty fine preamp design using 6SL7/6SN7 octals....HP had a good preview for this unit in TAS but never followed up..... It was also during this time that TAS featured articles on "Golden Oldies" by Walt Bender and Steven Stone, then the articles just disappeared...perhaps high end manufacturers threatened to pull out ads? I never renewed my subscription and took the classic tube amp/DIY route.


Yup, :P you're right again. Bruce Moore was the designer of the MFA Luminiscence back in the early 80s (after the Audible Illusions Modulus pre-amp). :P
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