EPI M-110 Rebuild

[Guido57]

In the later 1970's one of the speakers I wanted to audition was the EPI 100.  Unfortunately, the salesman at the only place I could find them did not want to hook them up and tried shoveling so much bullshit on me in an effort to get me to buy their house brand I left and never went back.  These came up for free on the local Craig's List, obviously a fixer upper pair.  The previous owner still had the woofer for the mutilated cabinet so I decided to give it a go.  The butyl surrounds on the woofers have definitely stiffened and I decided to replace them with fillet foam surrounds that are still on their way.  A listening test to the complete speaker showed the degradation  from age and their storage in an unheated garage.   As a first step I put on new binding posts and replaced the crossover with the common EPI setup of a 10 uF capacitor parallel to the tweeter while adding a 1.5 ohm resister.  This brought the tweeter back nicely.  I will replace the baffle on the mutilated one and already have a tweeter for it.  Once I've got the basics together I'll decide on the next step.  One thing I don't understand is the capacitor was attached between the rheostat and the negative terminal of the speaker, with the negative terminal of the tweeter connected to the middle terminal of the rheostat, and I was quite surprised they are 25 ohm.

[JKent]

Good luck with this resurrection. Have you tried contacting Huw Powell at Human Speakers? https://www.humanspeakers.com/e/epi110.htm

According to the product description and the schematic, these are 8 ohm speakers and the crossover should not be wired as you describe.

[ra.ra]

On 3/21/2020 at 5:48 AM, Guido57 said:

....replaced the crossover with the common EPI setup of a 10 uF capacitor parallel to the tweeter while adding a 1.5 ohm resister. 

Hi Guido - - - my comments are based on limited experience with the EPI-100, which uses the same drivers and crossover configuration as the 110 model. I want to mention that the cap in this circuit is in series with the tweeter (not parallel), and also ask where you've seen this notion of a 1.5 ohm resistor.

Pic attached shows original EPI-100 crossover, which appears to have wiring connections very much like the one shown in your pic. (Pay no attention to the 8uF cap value rather than the typical 10uF - - this remains a mystery that has not been solved.) I know the wiring does not look exactly like the schematic, but I'm accepting it as accurate since the speakers sound so wonderful. And just like yours, my pot controls are 25-ohm, 5-watt.  

[Guido57]

Oops, my bad.  I meant to say series, not parallel.  The resistor is in there to attenuate the tweeter while I'm evaluating, cleaning and rebuilding; the pot is currently removed for the process.  It's 1.5 ohm because that's what I had on hand.  Everything is on quick connects for now.  The mystery to me is the cap is on the negative side of the tweeter with the pot between the driver and the cap.

[Guido57]

Finished with a new surround on one of the woofers and installed it into the complete cabinet.  The sound is good.  Next step is putting a new baffle in the hacked up cabinet.  When I have a working pair I'll do some more critical listening and compare them the other speakers I have.

Huw's response to questions on the crossover:

"It's normal, the pot is just something they had to have back then for

fashion's sense. All the way up is "flat".

 

The order components are in when they are all in series does not matter."

[ra.ra]

Thx for update on crossover components. I really like having the rotary control in the tweeter circuit, but I think it only showed up in the early issues of their popular speaker models. When you see the x-o replacement that Huw offers for sale, it is nothing more than some decent binding posts, a bit of wiring, and a new (rebranded) cap, all mounted to a small plastic panel. 

[Guido57]

Update:  The tweeters sounded muted when compared to other speakers.  Removed the resistor and still had the problem.  On advice from someone on AK I pushed the sides of the inverted domes lightly and the tweeters came to life.

 https://audiokarma.org/forums/index.php?threads/epi-100m-masonite-tweeters.911400/reply&quote=13713607

I could now hear what gave these speakers their reputation.  One of the pots was giving really high ohm readings, so I hit all the rivets connecting the pots' tabs and now get a uniform 24.2 ohms for the outer tabs on both.  All done with the one usable box.  Cabinet with the mangled baffle is still in process.  

[Guido57]

Rebuild is complete to functioning level.  I went with Hu's method of crossover: new binding posts and polypro cap.  Pictures show'shelf for setting new baffle, baffle in place and completed rebuild.  Short listening session makes me think I'll follow what Pete B did restoring a pair of 100's: putting an L-pad to modulate the tweeter.  I feel the tweeter is much too loud in comparison to the woofer and an L-pad is more appropriate to the quality of the speaker's sound than the original potentiometers.  Vocals are heavenly but low end is weak.   I would think pots were used because they're cheaper than L-pads.  While removing the mutilated baffle I also stripped the vinyl.  Ruts, dent and dings were filled with Durham's Rock Hard Water Putty.  Really smashed edges and corners were rebuilt with QuickSteel epoxy putty.  The cabinet of the mate will get the same treatment eventually.

Actually listening to vocals makes me wonder if Advent would have been better off buying or licensing this tweeter.  Maybe I need to listen to some cymbals first.

[Guido57]

I've been re-reading Pete B's EPI Restoration thread.  He mentions rheostat, my speakers has potentiometers.

"Potentiometers are often used to vary voltage and rheostats are used to vary current."

In my limited understanding current is volts times amps and is measured in watts.  It may take some time before I understand the significance of this.  My question at the moment is would the potentiometer change the resistance, and therefore the crossover point? What goes on in a rheostat circuit is much easier to understand than the voltage divider action of the potentiometer.

[genek]

Rheostat is the generic term for a variable resistor. A potentiometer is a type of rheostat that has been configured to act as a voltage divider. Distinguishing by typical use is a bad idea, because anyone can use them for something atypical simply by the way they are wired into a circuit (by using only two or all three terminals).

 

[Guido57]

My issue/question is referring to understanding a potentiometer as a voltage divider in layman's language.  Maybe I'll just have to buckle down and read a bunch of electronics tutorials.

However I did eventually find an old AK post by Zilch that answered the question for my application.

[Pete B]

That definition is wrong.  A rheostat is usually a high power wire wound device, I've never seen

a strict definition but it is what I've learned over the years and I do think that it has only two

connections.  I've seen EPI 100s with the level control and it is wired like a rheostat just adding

resistance in series with the tweeter, it is wire wound but not very high power.   I also found 25

ohms from the factory.

I used 50W 8 ohm Lpads from PE in my own EPI 100 rebuild, because it is a better way to go

and much higher power.

[Guido57]

Basic restoration is done, with Lpads replacing the pots/rheostats.  Wanted to post the before and after pictures of the mutilated one next to each other.  I find I like the Lpads a little lower than halfway.

I'm very pleased with the sound and find the bass response better than I expected.  I will be listening to these exclusively for a least a week before I do any direct comparisons.  Both cabinets are now stripped to bare MDF, with my final choice of finish depending on how they fare in comparison to some other  speakers.