NUMARK TC 4100 MIXER

Repair Kit

A couple of years ago I opened a listing to offer up a few extra Numark TC4100 Stereo Tape Deck Tone Generator/Mixers I had on hand.  In that listing I identify a pervasive reliability issue with this particular vintage item (individual input channels going dead) and offer the mixers along with the parts that will be needed (either now or later) for repair. That listing comes and goes as my inventory of spare TC4100’s goes up and down.

If you own a TC4100 you either now have, or will have, the problem that listing describes.  I promise!  

As a byproduct of that listing I've received several requests to buy just the repair parts.  These parts are difficult to track down and it's easy to buy the wrong part.  You don’t know what you don’t know until you get a potential substitute part in hand and actually try to install it.  For example, who would have thought that some manufacturer would provide different threads in the mounting holes!!!)?  Or who would have thought that some manufacturer would shorten the stem for attaching the knobs such that the knobs won't install?

Nonetheless, through some trial and error I've found parts that are suitable substitutes for the originals.  The parts contained in this kit are both electronically and physically suitable for use in replacing the originals. 

Buyers don't need to inform me that these replacement pots are not as tall as the originals.  I'm aware of that and these pots work fine.  HOWEVER, don't plan on replacing just the one pot that you have failing!  Because of the height difference the original pots will not co-mingle with these replacements.

Also, I'm aware that the pins on the back of these pots don't perfectly line up with the mounting holes on the circuit boards.  I address this in the installation tips I include with this repair lit.

If you own a TC4100 and you have one of the very few that isn't failing yet, you might want to consider purchasing this repair kit anyway.  I've had to switch suppliers twice as one and then another quit handling the particular pots that are required here.  My current supplier has been unable to fulfill an order I placed several months ago and I’m not sure where that will wind up.  Three months or so from now I expect my current supply to be exhausted.  What I can sell you today I may NOT be able to sell you later.  Word to the wise.  

An avid user of the TC4100 can become very reliant on its unique features to keep an audio system fully functional.  The cost of this kit is pretty cheap insurance to protect you from the failure your machine will eventually exhibit.  To my knowledge there is no "other mixer" that can do what this mixer can do"!

You might want to go read the verbiage in my original listing for a little background if you're interested in this repair kit.  (I’ve included most of that verbiage towards the end of this listing.)  This "Repair Kit" listing will make more sense if you do that.

So, what I'm offering in this listing is replacement parts for the 6 potentiometers required for a complete repopulation of the pots on the mixer.   I'm also including a pair of new meter lamps which you may not need today, but once the mixer case is opened up and you're looking eye to eye at these lamps replacements might be installed as a preemptive strike . 

If you have adequate technical skills (that is, you can use a screwdriver, needle nose pliers, and are proficient with a soldering iron) this is a repair that you can finish on the kitchen table in an evening.  If you don’t know which end of a soldering iron to grab you may want to farm out this project to a more technical friend. 

Stated shipping is for US destinations.  Non US destinations will be shipped through the eBay Global Shipping Center at additional cost to the buyer.

So that's 6 pots and 2 lamps in this repair kit.  I’ll also include a few tips I’ve learned along the way, but don’t expect that to be step by step installation instructions.   

I’ll also include the four page installation guide that originally came with this mixer.

Thanks for looking!

NUMARK TC4100 MIXER

Tone Calibrator

If you need to switch audio inputs and outputs for up to four tape decks, VCR's, CD/DVD players or recorders, your PC sound card, or any other two channel audio player or recorder, you should have this device on your short list.  You'll find here very convenient features that simply don't exist in other switching units.  Go look at the DBX-200X, DBX-400, Vanco TDS-3, SONY SB-300, the AKAI DS-5 or most any other tape deck switching unit out there for comparison.  See if ANY of them include ANY of the following features of the NUMARK TC4100:

·        Two VU meters

·        Internal tone generator

·        Signal level adjustment for the individual decks

·        Complete input and output switching for each tape deck

·        Rear panel inputs& outputs for up to four stereo tape decks

The Numark is the only unit noted here that offers ANY of these significant features, and the Numark offers ALL of them! 

The Numark TC4100 does have a couple of issues:   

·        One is, there aren’t very many of them out there and most potential users don’t even know that this item exists.  I just did a quick eBay search and found over 20 DBX-200’s and just two Numark TC4100 listings...both of them mine.

·        The TC4100 hasn’t been manufactured for over 30 years.  AND it wasn’t particularly well marketed when it was available new.  I could be wrong but to my knowledge DAK was the only retailer selling this mixer (as the “Tape Deck Octopus”) back in the early ‘80’s.

·        People aren’t aware of the unique and significant features of this item.  See above!  So they purchase a lesser item not realizing the advantages they passed up.    

·        There is one shortcoming with this model that I'll thoroughly address below.  I’ve owned literally dozens of this specific model and I currently have 5 of them in use in various stereo and Quad audio systems, and a few more on hand for sale.  Odds are very good that I have more experience with, and more knowledge about, this mixer, by a wide margin, than anyone else trying to sell one.   

A little history first.  In 1972 I had three stereo tape decks and one stereo receiver that had just one tape monitor circuit.  I needed the ability to edit and copy audio tapes from any of my tape decks to any other, and the ability to record and play back through my receiver using any of the three tape decks I had.  I designed and built a tape switching unit using 16 RCA jacks, four switches from Radio Shack as I recall, a heater can from a main frame computer and a mess of wires.  It wasn’t pretty (and still isn’t, see photo) nor an engineering masterpiece.  But it did the job for over a decade.

Then, in 1984, I bought my first Numark TC4100.  At the time The TC4100 did everything I need admirably, with inputs and outputs to spare.  And considering the built in VU meters and tone generator, it added much more function, value, and convenience than any of the simple minded tape switching units that were available at the time.  That is still the case today!

After many years my TC-4100 lost one of the channels on one of the inputs.  And then a channel on another input quit.  And then another.  After enough of that I bought a second TC 4100 right here on eBay that "works perfectly".  But guess what??  It exhibited the same sort of failure...losing one or both channels from one or more in the four inputs, rendering that input(s) unusable!

So I bought another...and another.  And most ALL of them had the very same problem to varying degrees.  For a while I was able to salvage parts from one of them to repair another.  But keep in mind here that I was replacing an old worn out part with another old, almost worn out part. 

Over time my needs changed and the number of TC4100's I had in play grew.  I now have two of them in use in my vintage Quad system, another one in use in the Quad system in my office, and another two in use in the test bed in my shop where I repair Teac tape decks.  And then several more on hand!  (See photos.) 

What I learned is that the level controls (most of them are dual pots (potentiometers) behind the sliders on the face plate) used in this machine have a finite life.  In my opinion, based on many years of hands on experience with many of these TC4100’s, I'm confident that eventually all of the TC4100's out there are going to fail.  I have yet to see a TC4100 that didn’t eventually exhibit this failure.

I went in search of replacement parts so I could repair a few of these units for my own use.  And also I wanted to offer up the TC4100, unrepaired but with the needed repair parts to adventurous users.  Locating a suitable substitute part for these problematic potentiometers was not an easy task to say the least.  Finding a part with dual pots of the correct resistance is easy (is that a logarithmic or a linear pot?).  But there are many physical characteristics to consider beyond simple length and width.  And overlooking any one of them will get you a part that you can't use!  This is the voice of experience speaking.

I’ve now replaced the pots in the five mixers I have in use, and have sold over a dozen for others to repair.   Eventually I exhausted my supply of pots, discovered that my supplier could no longer provide the parts I needed, and had to close the two listings until I could find another supplier.  It took some months but I’ve now found a new supplier and I’m back in business!  The parts cost quite a bit more than they did and I needed to raise prices a little to cover at least part of the additional expense.  But it’s still a bargain considering the features this unit offers compared to what else is out there.  Even if the buyer needs to pay a tech to replace the parts this item is still a "price performer" in terms of the features and functions provided!  

The only problem I've ever seen in 30+ years of use with this model is the pots, and an occasional burned out meter lamp.  The unit you get may work fine upon arrival, in which case the buyer will have successfully stolen the device from me.  But regardless it will eventually need the parts I'll include.  Anyone selling a similar item and claiming that it works perfectly either has the one in a million that actually does work perfectly, or more likely just doesn't know how to thoroughly test it.  I’ve certainly bought my share of “works perfectly’ TC4100's that IMMEDIATELY failed as described above upon arrival and initial testing. 

If you buy one that “works perfectly’ and find that to not be the case when it arrives, keep in mind that I offer the repair parts separately.  

I'll include a copy of a four page installation document that came with my original unit. (Please remind me that I said this!)  Interestingly, this document specifically warns against using "SPRAY CLEANER FOR ANY SLIDE CONTROL".   This is precisely what someone would try given the failure I've seen over and over.  I’ll also include a few tips I’ve learned along the way, but don’t expect this to be installation instructions.  If you can use a screwdriver, needle nose pliers, and a soldering iron, this is a repair that you can finish on the kitchen table in an evening.  If you don’t know which end of a soldering iron to grab you may want to farm out this project.

Please take a look at my feedback: 100% positive with hundreds of items sold.  I can maybe provide advice and council when you get around to switching out the pots.

Thanks for looking!