Comparing battery-powered phono pre-amps, from RS ($$) to ASR ($$$$) ... and beyond!

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#42
Here's a couple more photos so that you can absolutely verify that your preamp is a match for the photo above.

First, here's the view of the etch side of the module shown above. Be sure to locate the "DS 101" mark - this gets referenced in some of the hot-rod modding discussions:

RS 42-2111 etch side (macro).JPG

Also, here's a view of the bottom of the case, showing the tag & the date code:

Techcessories ID tag & date code.JPG

FWIW I've looked, and have yet to locate a definitive date code decoder ring for this item.
Oh yeah, other than the "Techcessories" name this sticker is identical to my other unit, including the catalog number, which self-identifies as
"Radio Shack (R)". (RS date code = "9A5")

Happy hacking!
 
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#43
Hmmm, I just took another look at your pre-amp, and I noticed that your case is different (forcing you to desolder to disassemble, whereas mine has notches in the case allowing me to just remove 6 screws & slide it out?)

I also noticed in your photo that your module has the identifying mark of (I think) "406 3V16" ? Q: Your phono amp otherwise looks identical -- is yours also model #42-2111?

Aussie module ID '406 3V16'.jpg
 
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#45
Over here on the other side of the planet I'm trying to build confidence that the schematic we're referencing really matches the phono preamp I've got. Good news - by angling the module just so, I was able to capture some of the markings on the components themselves.

In particular, the transistor on the right is marked "C1740" which is a *match*!

RS 42-2111 component markings readable (best).JPG

So, when you pull one of your phono preamps apart it will be interesting to see if you have the same components I do, but they are just mounted on a new PCB? (Note: The soldering on your module looks a lot less 'globby' than the one I just took apart?)

No matter what, we'll either end up working on the exact same circuit...or you may uncover a revised (better) circuit that I can compare & contrast my unit to. Either way, we'll both exit this project with more knowledge (& possibly better vinyl sound?) than when we started...

Good stuff!

3D
 
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#46
Thank you Sir, what are the quality of the capacitors like?
Well, when the item being upgraded is new, the capacitor upgrade conversation seems to be bounded by cost, size, and suitability for either the signal path or bypassing the power feed to the active components. And if you can't afford spreading the capacitor caviar everywhere, then you put the best stuff in the signal path, and the more affordable stuff for bypassing duties...

As for the physical size vs. electrical capacitance trade off, that is also a consideration. For example, if it was imperative to you that the original Rat Shack case be retained, then some of the oversize 'primo' stuff simply won't fit. But if you were to put the module into a cigar box or coffee can (tip of the hat to Bob Carver :0) ...then all kinds of capacitor exotica can now added to the potential upgrade list.

****

But we have to figure out just how OLD our phono preamps are? Yours might be new, but I'm thinking that my date codes harken from '95 & '96? If this is true, then no doubt the caps have dried up, and even if I have no choice but to renew with electrolytics, then I have to do *something*.

But at the very least I *can* tell you that there's a dude on eBay who's recapping these phono preamps & then selling them for ~$100. And sure enough, his photo is showing evidence of capacitor changes:

eBay auction RS 42-2111 component side .jpg

Wish I had a more concrete recommendation, but I haven't had time to do the proper research on this opportunity. I *do* know from reading around that some of the talent in this forum possess well-reasoned opinions on capacitor upgrades...and of course, the smaller the voltages you are working with the bigger the difference that the 'quality' of the capacitor will make, especially in the signal path. (And looking at the schematic you can see that they are there in this design.)

That's all I got for the moment. Hopefully some other Tone Warriors reading this will jump in & share their hard-won experience with us.

Cheers --

3D
 
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#50
Modded board on the left, your board on the right?
Correct! Left board is currently on offer on eBay, seller's name is 'a1tiptop111'.**

1) Right board is a NOS (New Old Stock, never used) classic 42-2111 battery powered outboard phono amp (with RIAA equalization) to allow a standard turntable equipped with a conventional MM (Moving Magnet) cartridge to be connected to the AUX or TAPE input connections on a standard (typically low-cost) preamp that had no phono imputs. (Or did have a phono section, but now it's noisy/buzzy/broken -- for example, vintage Marantz receivers are known to have their phono stages go noisy & require component replacement. (!)

In English, this was a low-cost product that provided the ability to connect a MM cartridge-equipped turntable to a cheap preamp that had no phono input section. Or, it was used as a band-aid/workaround for folks with busted phono stages who didn't want to spend money repairing them. Of course, those who equate $$$ = quality, then obviously these affordable phono preamps couldn't possibly sound good... :0)

****

2) Once Moving Coil cartridges turned out not to be a fad, the high end preamps of the day would usually have both MM & MC inputs, and this was considered a selling feature. NOTE: The vast majority of consumer gear never added MC phono imputs to their preamps.

3) The third category is a MC phono preamp (outboard) with it's own RIAA equalization network, designed to successfully connect an even lower voltage output MC cartridge to a regular line level preamp input. NOTE: These are almost always targeted at the high end community & priced accordingly.

4) The last category is another kind of a 'band-aid' fix: a MC 'head amp' where a MC cartridge is given just enough boost in order to be connected to a standard (MM) phono input. NOTE: This only supplies gain, with no RIAA equalization onboard. John Curl was a pioneer in this area.

****

If you are relatively new to vinyl and you are confused by all this, it's basically something that evolved over time, and it can be pretty confusing. And for the old guys that grew up with all this, apologies for restating the obvious. :0)

FWIW --

3D

**("2227 auctions, 100% positive feedback" - disclaimer: I've never dealt with this individual at all, just grabbed their auction photo to illustrate the point that these phono preamp boards are routinely modified out in the wild...
 
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derek92994

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#55
That would be handy, after about 15 hours of solid use on a stock unit. the battery went from 9.5v to 9.2v. Im curious as to what the battery life is on a standard duracell alkaline battery.
 
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#58
That would be handy, after about 15 hours of solid use on a stock unit. the battery went from 9.5v to 9.2v. Im curious as to what the battery life is on a standard duracell alkaline battery.
derek92994, once I start using these battery-powered phono preamps I was considering moving to something rechargeable along these lines.

Then again, there seems to be a lot of discussion between the Ni-mh vs the Li-ion camps. The Lithium ion batteries are supposed to last longer...but at the same time (due to the # of internal cells) the Li-based batteries aren't quite a full 9 volts when they are 100% charged? (As compared to the 9.5v that you measured from your battery?)

****

So, depending upon how how much/how little I actually listen to the TT, I'm thinking if it's only occasional usage then I'd stick with the original-style single 9v battery. But if for some unknown reason vinyl really brings the main system alive and the TT ends up in heavy rotation then I wouldn't hesitate to go with a set of (6) x 1.5v D-cell batteries in series to provide many hours of listening per recharge. (And of course, just like with power tools if you configure with 2 sets of 6 batteries and the right charger you end up with a virtual 'non-stop' listening capability.)

I know the above seems complicated, but the near-unanimous reports of a dead-silent phono stage from these battery powered preamps motivates me to figure out the best overall solution to the battery implementation details. Please be sure to let us know how many listening hours you get from your 9v batteries...

Cheers --

3D
 
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J!m

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#59
I got four nice rechargeable D cells from China a while back.

The Sony D5M uses two, and regular cells don’t last too long. These last at least as long; probably longer, and have a mini YSB plug in them with an LED, so no fancy charger needed. Not expensive. eBay of course.

It started with D adapters that take three AA batteries each, since I’m already using those everywhere. But the single D has higher mwH than any three rechargeable AAs combined.

The D5 steps up from 3V to 6V so voltage isn’t an issue.
 
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#60
So, while waiting for other stuff to arrive I decided to bone up on these little RS battery-powered phono preamps. Before I knew it, I had dove down a weekend-long rabbit hole, especially when it came to modifying them for improved performance. (A *lot* of people have thunk/discussed/listened to these back in the day.)

In the interest of science I am going to (try to) document what I dug up, and present it as coherently as I can.

To provide some structure, I am going to split this all up into 3 separate posts:

1) How to get the most out of these phono preamps in stock condition.

2) How to mod these phono preamps -- which parts in which order, & why

3) Using these inexpensive preamps to help improve your understanding of electronics theory. (Reading schematics / SPICE / etc.)

****

When something is nice-sounding, relatively rare, and costs $200 or $2000+, it makes one hesitant to tear it apart & start modifying it.

"Sure, it's supposed to sound better after changing the op-amps, caps, & resistors for the newer/better/quieter parts...but if it *doesn't* sound better (or worse, is broken during the act of installing the upgrade) ...well that would be a *true* waste of a nice piece of equipment!"

And so, we get stuck in the 'Analysis leads to Paralysis' loop yet again...

But for $20 + shipping/tax for the chance to understand/modify/improve a phono stage that created literally dozens of threads across the audiophile web sites with scores of audio enthusiasts arguing the relative merits of this modest box punching way above it's sonic weight? What a great low risk/high reward hot-rodding opportunity! :0)
 
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