Source UEA 78 RPM Preamp

[Panamafred]

Hey! So I have now come into possession of this interesting 78 RPM preamp. I have a small collection but thought this was worth purchasing. Unfortunately the RIAA preamp produces only hum but the other settings work very well. My 1950's Jazz records sound fantastic on both A & B settings.... but I'd like to know more about this unit and what the labels on these settings mean.

US Col. Late? -- Columbia records-- the later ones presumably?
Vic. Late? --
US Early? --

I recognize your input on this issue would probably be a "best guess" but I'll take a best guess since there is no owners manual and little info on the internet.

Thanks! I'm loving this little unit, would just like to know a little more about it.



From July 1977 Hi Fidelity

 

[tubeactive]

Way Cool ! Source Engineering was here and gone quickly. I own a semi-working, full function preamp, including noise suppression, dynamic range expansion and multiple switchable phono disc equalization.
Working in sound studios back then, Source Engineering would be an elusive, obscure score of a Transcription Phono Preamplifier. When transcribing mono discs, say 78s, 45s and early 33 1/3 LPs and EPs from the pre-RIAA era, your Source phono stage or my full function Source Specialist preamp could come in handily.

Thanks for the treat, 40 years later ! I have never even heard of your UEA. If you look at the switch functions on your unit, a selector switch setting is used in conjunction with the upper Treble Adjust knob to "dial-in" the "proper" phono disc playback curve for early discs. Versatility, in a small package...I would love to reverse engineer that unit !

The few Selector settings indicate limited Phono Turnover ability for each position. In simpler terms, disc equalization uses a Turnover, where the playback curve begins to slope upwards for the bass boost, while that Treble adjust knob provides the Rolloff desired for the usual treble de-emphasis. In your unit, you can digress from the "standard" treble rolloff to suit the disc you would be recording or listening with. So much for simpler terms....

Good sounding Phono EQ with additional noise reduction and dynamic range expansion, can literally blow your ears/brain away with just how good mono discs can playback....

Enjoy and please pm if you have any thoughts of trading or selling the UEA...But, for now, why doesn't the Stereo RIAA function ? If it's a hum problem, we can help...

 

[tubeactive]

TRCP is EQ for 30s and 40s Transcription discs, like those 16 inch discs for radio stations. Vic Late means Victor late. Using the Treble Adjust, you can dial in your favorite sounding rolloff.

I see some microseconds (uSec) numbers on the Trbl Adj knob. Is it a variable knob plus a switch ? The 75 position indicates the RIAA treble rolloff. For Columbia Late, 100 usec is needed, closer to the Max setting. Did u build a power supply for the UEA ? Nice, very useful device...

Hum-wise, stereo headshell and interconnect wiring and grounding should only need some trials, at low volume (!), to find the lowest noise floor. Sometimes, your tt ground needs tweaking.
With many classic tables, motor/plinth ground and tonearm/headshell ground may need to be separately wired to the phono stage, for lowest noise/hum. I have seen/heard older tables which sounded better without the separate ground wire, as well. Perseverance will pay off. You can get lucky with a loose/dirty connection too....

 

[Panamafred]

If it's a hum problem, we can help...

I'm thinking this isn't a run of the mill hum... The turntable has a Shure M44 hooked up and doesn't hum on any other setting. It worked fine through the previous RIAA preamp. Kind of a bummer but I bought it for 78's so I'm glad that works. I appreciate your insight that this would've been a desirable piece of gear back in the day. It's funny because the metal cover isn't even secured to the chassis-- seems kind of flimsy!

Thanks for the help in deciphering the setting labels. The treble adjust is not a switch... Which setting do you think I should leave it on if I am listening to 1950's 78's? The likes of Asch, Savoy, Black & White, and Blue Note. I feel like a can't tell a huge difference between the "A" and "B" setting but would like to know I've got it on the "proper" setting. I would love to see a user manual for this but there is complete dearth of information about this unit. (Which is part of the reason I want to condense this information here)

I bought this with the intention of creating a 28 volt power supply:
https://audiokarma.org/forums/index...-with-a-power-supply-for-this-pre-amp.913019/

But was helped out by an AK'er who had an extra Noise Suppressor floating around.



Reverse engineering this would be insane.... have a look at the guts!


Anyways, thanks for your helpful response!

 

[tubeactive]

Hi....That's a crowded chassis ! Look at the quality polystyrene caps, though. That would be a tough deciphering exercise, but worth the effort. It looks like it has been "tweaked" and some caps were either added or replaced. If it sounds good....Keep on keepin' on....Enjoy this historical unit !

Here is the quintessential USA disc playback chart, acknowledged as reference grade...

https://midimagic.sgc-hosting.com/mixlabls.htm

As you will notice, your disc choices above indicate the AES playback curve for most of those labels. AES EQ uses a 400Hz Turnover with Rolloff of 63.6 uS (2500 Hz). This means the treble cut is -12 db at 10KHz from the O db reference, (centered at 1Khz). While 400Hz is +3 db, 2500Hz is -3 db from the 0 db portion of the playback curve. These plus or minus 3db "transition" points are technically known as asymptotes within the playback curve.

RIAA phono EQ uses a 500Hz Turnover with a Rolloff at 2122Hz (75 uSec.). RIAA bass resonance or peak is at 50 Hz. 2122 Hz is -3db from the playback curve's flat portion and 500Hz is +3 db. RIAA EQ specs the high freq slope at -13.7 db at 10KHz. Note your Treble Adjust marking at 75, which would be for most post 1954 discs. There are exceptions, so it is lovely that you can dial-in your preferred treble rolloff setting with your Source Engineering UEA preamp.

Because the RIAA and Columbia LP Turnover is 500 Hz, the "extra" 100 Hz above the AES 400Hz Turnover is just a bit more prominent than it would be if one of your Turnover (lower knob) settings was actually intended for the AES playback curve. More importantly, the difference in the 10KHz Rolloff slopes must be understood. If the two curves, AES vs. RIAA, were superimposed, the Rolloff slopes differ between 1.7 db and 2 db depending on a specific treble frequency. This is not as small a difference as anyone might believe. If you played the known AES discs with RIAA playback EQ, the sound will be better than acceptable, but that AES playback curve will allow treble upper harmonics to really shine. Horns, piano and drum "action" like cymbals will indeed sound more lifelike if the disc was "encoded" with the AES recording curve and we played that disc "decoding" using a precision engineered AES payback curve vs. the usual precision engineered RIAA phono playback curve.

In the late 1930s, phono EQ really began to develop, industry-wide, but there really were no set standards as to which recording and playback curves the studios and radio stations would use. Home (consumer) radio-phono sets usually only had a tone control, at best, at that time. After WWII, home HiFi began setting up quickly. By 1947, magnetic cartridges were in favor, thanks to companies like Clarkstan and GE offering their Variable Reluctance phono playback wares to the public. The Audio Engineering Society was formed, with professionals overseeing and having Audio Engineering (became Audio) magazine as their platform. In 1948, Columbia intros the Lp, with a 500Hz turnover, 100Hz bass resonance peak and treble Rolloff of 100 uS (or -3db at 1592 Hz, -16db at 10KHz). In 1949, RCA intros the 45 rpm discs, with yet another unique phono EQ. In 1950, the AES made a bold attempt and issued their AES playback curve to the industry, an "averaged" playback curve which they hoped would become thee standard. Their very noble intention was to convince the studios (as well as radio stations and equipment manufacturers) that their producers can record their discs with whatever recording curve and production qualities they deemed proper, but, they should make sure their discs sound "right" using the AES playback curve. In this way, more discs and equipment would get sold to the pros and consumers. Their admirable ploy worked for a while.

In 1952, RCA devises their "New Orthophonic" playback curve. Soon after, the AES recommends this curve become the new standard phono EQ playback curve, as does the RIAA, the Record Industry Association of America. With big record companies like Columbia and RCA selling the most discs, it is no surprise that RCA's New Orthophonic recording/playback curve became the RIAA phono EQ curve....

Recording curves are the inverse of our playback curves, pressed into the discs. While proper EQ was eventually standardized, having phono preamps with switchable or variable phono EQ is the way to go when playing earlier mono discs. I wrote a longer essay, which you might want to scan or read, when you have some more reading time, which includes phono EQ history and analysis, implementation in one of my fave preamps and some very cool links to many more disc playback charts. If you simply google search Phono EQ Design, it should come up as the fourth of fifth entry. Entitled "Phono EQ: Design, Retrofit and Disc Playback Charts," I hope all disc collectors will enjoy this. I separated the rather wordy thesis into three threads, in sync with the title, if you choose to scan portions as needed.

https://www.lencoheaven.net/forum/index.php?topic=25066.0

Honestly, I like to "share the knowledge to share the wealth" of enjoyment in playing and spinning discs. After all, this hobby/obsession is really about listening to the records....ENJOY !