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Another Electro Voice Interface D/Sentry VI thread.

Ok, so if someone has a "D" eq box and wanted the schematic drawn from it.... to whom do you send it?

Also, if you send it to "X" (electrical engineer I presume??), would they be able to translate the schematic into PEQ's so that someone could use an active and bypass the EQ all together?
 
The difference between an interface A eq and D eq is the value of 4 resistors. If you discard the 10khz control.
But the interface A as i measured in the -3dB setting (10kHz) has an exceptional performance for such a simple design. I designed a few high end pre-amps (the best known is the Classe omega pre III) but used quite extensive discrete amplifier toplogies. Very neutral very precise. But here you talk a different leage of musical harmonic liveliness that is new to me. I could easily reverse engineer it but it will take me few hours. i would not advice on a DSP based eq as it will destroy what the ev eq adds.
I am enjoying a different form of music reproduction that is maybe less HIFi but more music.
Intragued by what EV performed in the late 70s I will continue to explore this speaker and make it living room acceptable. The eq will be part of it.
 
All you need to do is take high quality pics of the top and bottom of the circuit board and I think we can figure it out. It should be very similar to the schematics we have posted already.

We may not even need pictures of the bottom, honestly.

When it comes to deciphering the eq curves from the circuit, an electrical engineer should be able to calculate them, especially if he has worked with audio circuits before. I wish I knew how to do that stuff. But I've read the theory behind the eq, so what I said before is very likely the correct curve (a 6db boost with Q=2 at the specified freq, which is supposed to be the FS of the box (which is 1/3 lower than the FS of the speaker)).
 
As the Dr. mentioned above there are quite a few who run an active EQ bypassing
the crossovers found in the EV Sentry III and likely D,s also.

This of course negates the need for the EV EQ box assuming the said active has the flexibility of matching the correct slopes etc.
 
Indeed, an active crossover can be of used but will not work with a standard setting and will require carefull tuning.
The low-pass filter to the woofer is a modified 3rd order, and the 2nd order feeding the vmr is highly compensated to cope with the strange response of that unit. The real clever part of this filter is the fact that with minumum components they achieved crossover filtering and compensation. Look at the graphs of the ST350's in my previous posts. With only a 1.5uF cap and a0.42mH inductor they achieved impressive response and highpass filtering (and the raw response of the 350 is anything but flat)
This all can be achieved by a DSP based crossover, but will be complex in an analog design.
 
Hello forum,
I have investigated the interface A equalizer i have tested on the differences with the schematic that is available online. This design is slightly more advanced and uses one extra transistor (6 per chanel) than the schematic that is part of the Interface A service manual.
The extra tansistor is a current source in the output stage. But there is more to it. In the old design the eq has a 3dB gain at 10k in all modes that is attenuated in two steps. So the 0 dB position is achieved by raising at the input stage and then attenuating at the output stage.
This design activates the 3dB 10k boost in position 1, has a perfect flat response in position 2 and attenuates 3dB in position 3. A much nicer approach.

I might redesign this unit by a new self contained PCB. That is a copy of this 6transistor unit. Use metal film resistors throughout, nicer caps and a jumper selectable LF boost at 29, 31, 33, 35 and 37Hz to tune the unit to the environment. Two of these units in one enclosure could be used in a balanced topology.
I woul probably not use the 10kHz boost and attenuation circuit but leave it for the sake of original design.

Ordering a series of circuit boards would make sense and can be offered here.
 
Peter
There seems to be a need/market for certain EV EQ,s especially if fine tuned some what.
 
Hi Forum,

I would be very interested in a picture of the PCB of an Interface D equalizer. I need to be able to read the resistor color codes.

This schematic can be tweaked. One resistor sets the peak frequency of the +6dB enhancement, the other seems to influence the LF cutoff frequency or Q of the curve.
Building a unit that gives jumper settings of both parameters can be interesting.

The funny part is that the Interface A EQ I have has a Q different to the 5 transistor design.

Does somebody have a good quality picture of an Interface D circuit-board?
 
Peter

In regards to the D EQ design and EV,s response data, is it correct that in

use it applies the full 6 db boost at the base line 38/40 Hz { port

blocked} enabling the 28 Hz figure?
 
The info that I have uses a 6dB boost at 31Hz with half the port closed. The tuning frequency with port closed is also around 30Hz. I calculated the port frequrncy with WinISD pro and that showed a tuning of the D enclosure (closed half port) of 27Hz. I need to measure that next time.
But indeed the D spec of 28Hz is achieved in the above scenario.
 
I received pictures of the original Interface C/D EQ (thanks David Wojnarowski) and could verify the resistors for the interface D filter.

Who would be interested in a generic Interface Equalizer?

I am going to design and build a couple of PCB's fully functional EQ.
A single PCB with a stereo input, stereo output, a single power LED. Internal Jumpers for the 10kHz 3dB boost, a jumper that attenuates 10kHz by 3dB and 10 Jumpers per channel to configure for 29, 31 (interface D), 33, 35 and 38 Hz.
Selectable 230V or 115V AC mains and fully tested.
The schematic will be equivalent to the original with slightly better caps and all metal film resistors.

So what you need to do is get an enclosure, drill 4 RCA connectors, a mains inlet and if you like a front panel LED.

For my own setup I will put two stereo PCB's in one enclosure. One connected to the LF amp and one connected to the MF/HF amp.
One input driving both equalizers.

The price of the board will depend on the amount of PCB's but will be very reasonable + shipping (maybe a batch shipment to the US)

see attached schematic of the original Interface A EQ as I bought on Ebay with improved (flat) frequency response, and on the second page the new design.
 

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Peter,

It's all greek to me (the schematic) and, I also have an EQ...

My question is, are you (or anyone) able to take the eq settings and convert them to PEQ's so someone could use an active?
 
Coytee said:
Peter,

It's all greek to me (the schematic) and, I also have an EQ...

My question is, are you (or anyone) able to take the eq settings and convert them to PEQ's so someone could use an active?
Click to expand...

Like I said in a previous post, the current filter passive filter has quite some compensation embedded in the design. If they were of the shelf standard 2nd or 3rd order filters it would be easy.
The Interface D filter has component values combined to achieve the response wanted as the bare drivers are not that linear.

If you go for active cross-over you bypass these components (by using the different tube plug in the bottom). This means that you power the drivers without compensation other than what the active filter provides you with.
It might work fine, but I am pretty confident that the character changes.

Bi-amping however will give you the original passive filter compensation but with the advantage of supplying an easier load to the amp.
 
Peter, have you measured the input impedance of each of the drivers as loaded in the system? This would be a start toward developing a model for the system. It would be excellent if your measurement system could output .frd and .zma files for the drivers in system.
 
Pete B said:
Peter, have you measured the input impedance of each of the drivers as loaded in the system? This would be a start toward developing a model for the system. It would be excellent if your measurement system could output .frd and .zma files for the drivers in system.
Click to expand...

I have ordered the DATS measurement system and will share the results with you guys.
 
So, I had a pair of EV S1503 cabinets without woofers lying around my project bone yard. After spotting this thread and seeing the interest in the Interface D and combining that with my love of my Sentry lll's, I decided to use the VMR and st350 (maybe t350?) from the boxes and add a woofer. I had four stout empty boxes (1.65 cu. ft. each) and a project was born. I know there will need to be some tweaking. Maybe not, they sound incredible, to me, as I've been involved in studio audio for ages. I used the crossover network from the S1503 (600Hz and 4kHz) and made it external for dis-assembly and flexibility. The tweak, I think, will be wiring the crossover for a 4ohm woofer, the CV. No slop in this bass. The mids were a little "shouty" but an L pad at 12 o'clock (-3db) brought them into balance. These sound GREAT! All program material blends SO well. Fire away with suggestions to refine them further. Sadly, I have no test equipment.
 

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  • Denny's Interface D.jpg
    Denny's Interface D.jpg
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All I can say is get 35 plus watts of tube amplification on them and you will be very impressed!!Ive been thru the gambit of quality SS amps over the yrs with the d's and tube amps made them excel,especially mono tube amps.El 34 tube dynaco's are a special combo
 
Awesome, Turnitdown! I have some S1503 that I cleaned up and used with an old 6V6 console amp. They sound incredible. I'm sure your setup kicks ass!
 
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