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PostPosted: Wed Aug 02, 2017 9:47 pm 
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Location: Victoria, BC, CA
I've wanted to venture down the vintage restored valve road for quite some time. Having grown up with Eico and Bogan amps in the household when I was a kid, I can still recall the huge sound of these amps driving my Dad's University full range drivers in massive, furniture grade boxes. There is a 1959 Paco SA-40 integrated that has been beautifully restored by a very impressive individual that I've come to know in the neighbourhood. I've seen and heard some of his pieces, and they sound very good indeed. But I'm wondering about the phono stages in these old amplifiers. Given that it was all about vinyl, tape and tuner at the time, I'm assuming that the phono stage would be quite good. Or not? The stage that I'm listening to now in my Sugden A25 is very good, but I'm wondering whether I would likely have to buy an outboard phono stage to realize good quality vinyl playback with a vintage tube effort?


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PostPosted: Thu Aug 03, 2017 5:37 am 
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Location: Markham, ON, CA
Vintage integrated amp often has low gain in the phono stage. So I think you can buy an extra phono preamp to make them great.


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PostPosted: Thu Aug 03, 2017 6:31 am 
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Probably a sweet sounding amp, although I imagine the MM phono section would be lacking from that era (impedance, gain and poor shielding would result in noticeable hum).


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PostPosted: Thu Aug 03, 2017 6:36 am 
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That is a superb childhood memory. If I'm a indifference to the last comment about vintage gear having low gain phono stages that's not necessarily true. Because of the era and age old gear will generally have a distinct sound and you are correct the fact that vinyl was King of the Heap as far as sources go in the day (and still is now) most designers built their gear around the premise that they (the end-user) would be using a turntable. As with anything, results will vary. If you're using a modern low output moving coil cartridge and external stage probably will be a necessity. Have fun!


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PostPosted: Thu Aug 03, 2017 9:34 am 
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Location: Stratford, ON, CA
Hi,

The main technical purpose of the phono stage is to invert and normalize the RIAA curve which is applied to the recorded signal when the 'master' for what will become a pressed record is 'cut' on a lathe. Application of the RIAA curve allows for all the recorded information to be represented in the grooves in an analog fashion (microscopic hills and valleys). A secondary purpose of the phono stage is to add gain to the signal coming from the cartridge, which is measured in tiny milli-volts, before handing that signal off to the high level (or tone control) stage where further gain is added in order to finally arrive at a 'line-level' signal that then feeds the amplifier or the amplifier section of an integrated amp.

Three factors will affect that signal in a vintage tube phono stage.

1) The choice of the circuit. Many variations were (and still are) possible and choices in those days were based on parts cost, complexity, and builder preferences.

2) The choice of the tube type. This is tied in part to #1 above, but in that era (1959) there were dozens and dozens of small signal tubes to choose from and only by trial and error did the later builders settle on a few trusted types such as the 12AX7. The final list of trusted types became known for being exceptionally euphonic, for tolerating massive input spikes (like when someone accidentally drops the tone arm) and for low noise and whoosh.

3) The quality of the other non-tube component parts, such as resistors and capacitors, is highly variable. Carbon resistors and small signal capacitors of that day had wide fluctuation in part tolerances and this further declined with age and heat. Hum and noise would enter the circuit as parts values deviated from their original specification and the all-critical RIAA inversion would often become off-specification.

The upshot of all this is that most vintage tube phono stages (if stock and untouched), when they are compared to a contemporary sample may sound quite soft and diffuse with higher levels of hum and noise and some masking of fine details. If they are really way off the RIAA specification, they will place emphasis on some parts of the frequency range over others, such as enhanced mids or bass and often with reduced high frequency content. Your Sugden integrated may also have experienced some drift but the parts quality is high.

Now a lot of audiophiles come to prefer this aural presentation - it is often quite pleasant to listen to and very seductive. I too loved it for many many years. Furthermore, in some cases it can be enhanced by tube upgrading (if a still available tube type was used) or by rebuilding the phono stage boards with better component parts. But sometimes this back-fires as the better parts will seek to return the phono stage to RIAA specification which may or may not have now become the owner's actual preference.

If the phono stage in the vintage integrated amp you are considering is untouched, then its 'technical performance' can be exceeded by many relatively inexpensive outboard phono stages made by Cambridge Audio, Musical Fidelity or even Bellari or ART. For about $100 you can pick up a new or used contemporary outboard phono stage and try it out. Up the food chain a bit you might investigate Graham Slee products and then there are those very dear connoisseur phono stages by companies like EAR and Audio Note and many others. But remember that 'technical performance' is not actually synonymous with listening pleasure for either you or any other audiophile.

If the amp you are considering has been rebuilt and retubed then ask the builder what was done to the phono stage (if anything) and after listening to it for a while if you like the aural result then stick with it. It sounds to me like the rebuilder of the proposed amp was careful and thorough and he may be able to further tweak the original phono stage in a direction you might like.

Cheers,
David Neice

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Last edited by buybye88 on Thu Aug 03, 2017 9:59 am, edited 2 times in total.

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PostPosted: Thu Aug 03, 2017 9:42 am 
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Location: toronto, ON, CA
How old is vintage? There is an Audio Research pre that was all point-to-point wired that I think sounds very nice.


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PostPosted: Thu Aug 03, 2017 10:00 am 
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1959 in this particular case


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PostPosted: Thu Aug 03, 2017 10:28 am 
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The phono stage on vintage tube equipment was mostly designed for MM cartridge that has a minimal output of 2 millivots at 40 dB gain, which is ok for most recordings in that era. However, keep in mind that most of them have a very low signal to noise ratio which means they're very noisy compared to today's tube design. If you can live with that shortcomings then, by all means, go for it.


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PostPosted: Thu Aug 03, 2017 12:43 pm 
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cyrus wrote:
1959 in this particular case


OK, so vintage goes to at least 1959. Does it go into the 70's?


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PostPosted: Thu Aug 03, 2017 4:04 pm 
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I have no idea. To some, yes, to others not. I don't think there is a cut and dry cut off year for vintage, although it's probably safe to say that most audio enthusiasts would consider 1959 as vintage. If you like, you can delete the word vintage from my original posting.


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PostPosted: Thu Aug 03, 2017 4:18 pm 
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Vintage is one of those terms that everyone has a different definition of. For some it means over 1 human generation old (approx 20 to 25 years). For others it means over 50 years old and yet others insist that is is anything over 4 or 5 years old. In electronics terms, it might mean pre-transistor aged or pre-solid state. At my age, it is the age difference when I start calling guys "sonny boy"!!!


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PostPosted: Thu Aug 03, 2017 5:52 pm 
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1950's is perhaps a little too vintage for phono technology. Sometimes vintage phono inputs are pretty damned good. this is mine....

Image


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PostPosted: Thu Aug 03, 2017 6:50 pm 
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Location: Leduc, AB, CA
The brands you mention take me back to my earliest days when my cousin introduced me to "stereo", in the very early 60's. Back then there were 2 main sources - records and radio. AM sections in dedicated tuners were not always present and even in Montreal at that time, FM stations were few and often not in stereo. Tape recorders were highly expensive pro or semi-pro models and difficult to find for audition. As all sources would go through the main line stage of the pre-amp or integrated amp, that part of the picture had to be capable, especially as that was the "easy" part.

The true test of the pre-amp section was the RIAA stage. Much was made in those days about the various equalizations offered for the various records types out there, but by the time stereo had taken over and mono records were no longer produced, designers could be more focused to a specific standard. Before this time, it was common to find recording and recommended playback characteristics printed on the back of record jackets. I was once able to borrow a Leak integrated to compare with my Fisher integrated, and was quite surprised at how similar their sounds were. The phono stage was the showpiece and then cartridge designers also had to produce a more standardized product.

It took many years before tube circuits were ever matched by solid state devices and their designers. Cyrus, your neighbour could provide valuable information in getting the best out of your Sugden unit. I would be very tempted to go that way, especially if you can find a cartridge that hits its sweet spot. You have a rare opportunity to experience the best of a golden age. I would expect a much greater improvement with turntables and arms and spend my money there first, if necessary. Enjoy.


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PostPosted: Thu Aug 03, 2017 7:03 pm 
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Location: Woodstock, ON, CA
Cyrus

I have a vintage Fisher x101-st and Fisher x101-d one from 1958 or 59 and one from 1964-65 and both are quite good once the coupling caps are replaced. The old caps will no doubt be noisy and worn out after almost 60 years!

Mine are upgraded and restored by a professional.

No hum or noise at all. The line stage in both amps is the quietest I have ever heard. My previous pre amp was a Linn Kairn and Linn Klout used on the LP12.


Old phono stages only work with MM and then that was considered low gain.


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PostPosted: Thu Aug 03, 2017 8:46 pm 
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Thanks all for your valuable input and comments. The Paco in question has been completely rebuilt, phono stage included, as in all caps and resistors. The transformers are original, and are Fisher units. The amp is a thing of beauty, and even the chassis looks as close to new as you could get, with it's cosmetic restorative efforts. This guy is really amazing and literally has thousands of tubes, all laid out in specially made tube drawers floor to ceiling, along with perhaps 20-30 beautifully restored tube pieces, some that I've never seen before or knew existed (very early Pioneer tube receivers that look essentially new). The Paco has over 40 hours invested into it's restoration, and the chap is a retired electronics engineer with 45 years of rebuilding and restoring audio equipment. I suppose what it would come down to, is more circuit design for the phono stage in question, as opposed to any consideration regarding old, out of spec components. I suppose I posed the question regarding phono stage quality of the Paco, given that my Sugden A25 on board stage is so good. I'm hoping to not have to go with an outboard if I can, although I will only know upon taking it for a spin of course.


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