SDA SRS GEN 3 crossover

gregmoyers

I am the original owner of SDA SRS gen 3 and have enjoyed them with many amps over the years and 2 years ago set my Nak PA7 aside for a Thershold S500 which took it to a new level. This got me looking to find out what is available to update these amazing speakers to restore and mod them. In the process I discovered the tweeters I got from Polk 20 years ago to replace the original SL2000’s are actually SL2500! Bad! But they played that way all that time. I have the proper RD0194’s and I can’t wait to get them in. Now all my focus is on all the other mods to the cabinet and crossover. Before I do a complete rebuild on the crossover’s I am eliminating the poly switch and want to replace the 16mH bass inductors. So far the Jantzen C coil 14AWG .16 DCR has come recommended. Does anyone have any other suggestions before I order these? The Threshold can drive anything out there so I’m not concerned there. All advice and guidance is appreciated as I am not an expert here. I’m also wondering where and how to mount these. Thanks!

pitdogg2

There are other 16mH inductors out there, Erse and Solen are two. But I will say that you will need to have a good meter especially with the Erse. My experience is they come close but no cigar. One of mine was WAY over the other was just the under 16mH. In the end my guy got them both the same but if you just put them in as they came there would have been mis-matched speakers. For the money I believe you are better with the C-coil. Parts Express now or did carry them at a good price.

skipshot12

This is gonna be a cool for me to read as you post.

I’m a recent recipient of the gen 3 SDA SRS’. Picked mine up this past June.
Great place here for guidance on your upgrade adventure.

I started my modding about fairly quickly after about of a month of listening to them at bone stock.
I then had the urge to tap into the modern of yore’s minds and, not done yet.

My personal recommend is to start with the easy mechanical upgrades first.
Sealing up your cabinet, Dynamat extreme the MW’s & the passive, some Black Hole 5.
RD0-194-1 oh yea.

This is where I’m at with my upgrades.
Now going into my crossover. I’ve gotten the 120uf caps. Solen was recommended to me here as they’re not as critical as the rest.

I’m hoping you doing this, along with reading your progress, will spark my fire to keep going.

Skip

gregmoyers

I talked to Dave at DHS and he said my Threshold will be fine with the Jantsen C coil.
So far my cups are done with new binding posts and NL4 Speakon sda cable. 0194 in.
I broke one of the polyswitches trying to untwist it after not being happy with too much hi end after twisting the leads to short them. Now waiting for 4 Mills resistors to put .5 ohms in place. I am reluctant to rebuild the board myself given the lack of space on it to accommodate the HUGE new caps. Cant wait to hear the new C coils
To be continued.

skipshot12

^ You found the 194 tweets to be too much with the poly replaced with a jumper?

gregmoyers

Yes.

gregmoyers

Are you gonna do the crossover’s yourself? Are you going to use an expansion board for the caps that won’t fit?

skipshot12

Really want to hear your thoughts, bass, with the larger wire inductor.
From reading club polk sounds like it’s a sweet improvement upgrade.

Am thinking of that inductor upgrade too once done with the caps & resistors.

gregmoyers

I have another problem now.
I have no dimensional array sound in any of the 4 drivers on left channel. Cable good. Drivers good. But no sound from left dimensional array when pan all the way to right. What could cause THAT?
Has to be one of the crossovers?

invalid

Why does the threshold s500 say on the back panel not to common between the left and right outputs? I always thought these were not common ground amps.

pitdogg2

While not an expert by any means it sure looks common to me.


Another while different it also appears the same



Looks a LOT like an Adcom 555 internally as far as the caps and binding posts

invalid

It may very well be, but then there is this on the back panel

skipshot12

Have you taken an ohm reading of your - binding posts?

audioluvr

invalid wrote: »

It may very well be, but then there is this on the back panel

That's a weird way of saying " do not allow the +'s to come in contact with one another or anything else.

Schurkey

pitdogg2 wrote: »

While not an expert by any means it sure looks common to me.

My own guess is that the thing is balanced/bridged; but even if it were not, it'd be easy to hide a couple of resistors in the path between the negative terminals and chassis ground.
10 ohms between each channel's negative binding post and ground (20 ohms between the two channels) made my amp unlistenable with SDA 1Bs until I poked a jumper wire into the two binding posts, which bypasses the resistors as far as the SDA is concerned. Doing that with a bridged/balanced amp will let all the smoke out of it, though.

skipshot12

Someone correct me if I'm wrong but, pretty sure you would want to see less than 1 ohm between the negative posts?

I had reservations with my Phase Linear amps until I did the ohm test. Even though I saw 0.6 ohm between the - speaker posts i was still extremely cautious when I hooked them up....
Caution is always good when not absolutely sure.

pitdogg2

@Schurkey while I can agree on the resistors, looking at pictures of the amp it is single ended. Can an amp be balanced with no balanced/xlr connections?

Schurkey

pitdogg2 wrote: »

@Schurkey while I can agree on the resistors, looking at pictures of the amp it is single ended. Can an amp be balanced with no balanced/xlr connections?

Sure. Aragon built balanced amplifiers that had an internal circuit board that provided the proper regular- and reverse-polarity signals. Most of those amplifiers had the XLR connector and no inverter circuit board, but a few were ordered with an RCA jack and the circuit board.

In addition, there's non-balanced amps like the original Carver M1.0 which was single-ended, but had one channel in reverse polarity, and the the + and - output terminals for that channel were labeled backwards to provide correct polarity to the speaker. They'd fry if you tried to common-ground them via an SDA cable. Having one channel in reverse polarity allows generally-monophonic bass notes to draw power evenly from both halves (+ and -) of the power supply, reducing the size of the power supply needed.

An ohmmeter is the best way to determine if an amplifier is suitable for use with SDA speakers. If there's essentially zero resistance between the negative terminals of the two channels, you should be good-to-go. If there's more than ~1 ohm resistance...more investigation needed.

gregmoyers

[img]https://us.v-cdn.net/5021930/uploads/editor/k1/4v61llvl4ji8 .jpeg[/img]
All doubts put to rest with this.

pitdogg2

Care to share ?

gregmoyers

Oh, sorry been out for a while.
Very very happy to find this Threshold S550E
Hard to find. The last model from Nelson Pass with Threshold before he left for Pass Labs.
One of the heavyweights built in ‘94 along side the big Krells and Levinson. Sounds absolutely awesome. I’m a sucker for these vintage gems.