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How good really are the phono stages in the Scott integrateds?

B

brendans

New Member
Has anyone compared external phono pre’s to the internal phono stage in the 222/299/etc? There is tons of mentions that they have great phono stage but I can’t really find anything comparing them to a modern external stage. I’m having a hard time judging if they are great compared to other vintage amps or great period.

I currently have an iphono2...would the internal stage with a SUT do a ~$500-$1000 LOMC justice or would I be better off with the external phono?
 
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They'll have to have been fully restored including the power supply to get near what they were designed for. The challenge with tube phono preamps is that the noise floor will typically be higher than with a well-designed solid state phono preamp.

There are a lot of folks who will swear they sound better in some way but they'll have figured out how to hear past the noise floor.

Cheers,

David
 
Modern RIAA preamps often boast equalization accuracy into small fractions of a dB, whereas the vintage stuff used components no better than 5% tolerance and often exceeds 1dB error at some points in the spectrum. Understand that tiny frequency response deviations are commonly mistaken for positive or negative audio performance signatures, and you have your answer.
 
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When using any of my magnetic cartridges, cranking-it with the needle off the record does reveal a very small bit of hum and hiss. Oddly, with the Micro Acoustics ceramic cartridge, I can pin the volume knob and there is absolute silence.
The passive components that set the RIAA curve in my Scott, as well as Fishers, Eicos, Dynacos, and most other vintage integrated amps are those crummy little PEC modules They do not age well. Yet, my Scott's phono stage sounds spectacular. Ears always trump actual specs, even though the above poster is absolutely correct.
 
The phono stage of my 299A sounds pretty good and is very quiet. I think it also depends a lot on the quality of the 12AX7 tubes you use, too. I think the phono stage on my 299A sounds a little better than the one on my 340A receiver....possibly because it predates PECs and it has discrete components.

The other aspect about the Scott phono stages is the control flexibility- the ability to blend channels and use slightly different rolloff settings.
 
I have and use only Telefunken 12AX7. The only other brand of pre-amp tube that I like is, would anyone here believe, Lafayette, made in Japan. Also, as far as hiss from carbon resistors, it is those very same resistors that flavor the sound the way we like it, so they stay. My biggest issue with the amp is that most of the 6U8A phase splitter tubes stink and I needed to do lots of tube rolling to weed out what sounds best.
 
I've had many Scotts up over the years and still have a pile of them. They pass LP sound, some quite nicely. I've never rebuilt that section of the amp though as it is hard to get at and if it worked I left it alone. I'd be very interested to hear from someone that has rebuilt it and how they liked it afterwards. I suspect the improvement is dramatic.
 
I have a 355 tuner/pre, so not an integrated, but I think it's roughly the same front-end as the 299 series, different from the 130 and 121 pre's. Somebody had gone through and re-capped and replaced out of spec resistors in mine before I got it, nothing boutique but decent. It's definitely a vintage tube phono section sound, a bit hissy and likely a little lumpy in freq response - but it's very good. I don't tube roll much, but here it mattered; vintage Mullard long plate 12AX7s sound best, but the short plates aren't very far behind, could be within sample selection tolerance. Tele's in the pre-amp section.

Bought it in the late '90's. Somebody harvested the original Tele's, and it came with paper-sticker labeled unbranded Chinese 12AX7's - I don't think I've ever heard a worse tube!
 
I rebuilt the phono stage on my 233 , which I believe is similar to most scott phono stages. Replacing the ceramic caps with polystyrene and the coupling caps with vitamin q (oil) made a good improvement. Lastly I rebuilt the phono PEC with discrete parts with matched components. This made a really good improvement. It is a little tricky to get at the circuit. I found that removing the screws that hold the front on let’s you tilt it forward to gain better access.
 
The PECs internal circuitry is clearly marked on the amp's [299D] schematic. This does not make me any less reluctant to do the work. I recall that the same board also has the NARTB eq circuitry. Guess that I will add it to my bucket list. Perhaps it is time to start collecting the necessary parts.
 
I blueprinted one of these phono preamp circuits while repairing my LK72 I can send you a photo of the schematic and BOM if you want to build one to try out
 
Yes. Thank You. This will be wonderful. Should be the same PEC # 222ER for the 72, 72B, 299C and 299D, I hope.
What does the abbreviation 'BOM' stand for?
 
"BOM" means Bill of Materials.

I restored the 0.022uf coupling caps in my phono circuit on my LK-48 about 14 years ago with SonicCaps and the phono stage sounds quiet and dynamic. I'm using Telefunken 12AX7s in my stage. The next thing I want to do is remove the PEC for the RIAA circuit and replace the rest of the tone capacitors behind the faceplate.

For me, it's hard to say if the phono stage is completely quiet, but I don't have any humming or hissing even when turned up loud.

It sounds wonderful to me in my system. Very pleasing and dynamic with the Tele's.
 
Years ago, I owned an LK-72B. Replaced all the coupling caps with WWII-vintage Vitamin Q. Sounded sort of 'dark'. With this amp, I will need to choose more wisely.
I don't want to put a whammy on this 299D, but it runs cooler than the LK-72B ever did, and is like a block of ice when compared to the Fisher X-202-B.

Telefunkens up front. Raytheon phase splitters. GE NOS 7591, and one Mullard 5AR4. And NOS GE #47 pilot bulbs. No chinese light bulbs here.
About the 5AR4. I discovered a long time ago that one must never, ever, ever shut power to the amp, and then fire it up without first giving it a short rest. This is how one blows a perfectly-wonderful rectifier tube. Mullard 5AR4 are not cheap. They will last a very long time with this simple precaution.
 
Thanks for all the info. As I presumed, sounds like if I have a decent external phono stage available it’s not necessarily worth choosing a Scott (vs Eico, Sherwood, etc) for the phono stage.
 
All evening I have been listening to my 222C with a Grace F-9 and it is quiet, open, and precise. The phono stages on my 2275, Yamaha C-85, and MAC 1500 are very nice, but the Scott tops them all. Oh, and the Grace cart helps too. Listening to Frank Sinatra's Only The Lonely was downright startling at times. Too real?
 
Aren't most tube phono sections more or less the same; a 12AX7 with the RIAA parts between the sections? Most I've seen call for a 7025, the spiral filament version of the 12AX7.
 
jaymanaa said:
Aren't most tube phono sections more or less the same; a 12AX7 with the RIAA parts between the sections? Most I've seen call for a 7025, the spiral filament version of the 12AX7.
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There's a surprising amount of variation in vintage phono preamp designs. Most are either passively equalized, as you describe, or actively equalized via feedback to the first cathode, but you will see hybrids of those two as well as pentode front-ends and freaky stuff using wild cartridge loading schemes for equalization. Many later dual-triode designs use positive feedback via cathode coupling to goose up open-loop gain, which seems counter-intuitive when you consider the overall negative feedback, but it really does improve LF equalization accuracy.
 
BinaryMike said:
There's a surprising amount of variation in vintage phono preamp designs. Most are either passively equalized, as you describe, or actively equalized via feedback to the first cathode, but you will see hybrids of those two as well as pentode front-ends and freaky stuff using wild cartridge loading schemes for equalization. Many later dual-triode designs use positive feedback via cathode coupling to goose up open-loop gain, which seems counter-intuitive when you consider the overall negative feedback, but it really does improve LF equalization accuracy.
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Interesting, what are your thoughts on the RCA tube manual stage? It's the only stage I've used that always seems to bring compliments?
 
jaymanaa said:
Interesting, what are your thoughts on the RCA tube manual stage? It's the only stage I've used that always seems to bring compliments?
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I study these things, but I don't have enough experience constructing them to offer reliable guidance. One of the authorities, Doug Self, insists that passively equalized preamps can never approach the dynamic range of feedback equalized designs. But Doug resides in the SS world, while tube preamps might inherently have acceptable dynamic range due to (usually) much greater supply voltages. One of my unfinished projects is a discrete transistor passively equalized RIAA preamp that operates directly off the high voltage rail in a Dynaco SCA-35. I thought it would make a superior phono preamp section for that chassis by eliminating the heater supply, among other things, but I've turned into a demonic serial begetter of weird power amps and never got back to the SCA-35 project. The breadboard works pretty well...
 
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