Further Improvements to the SDA SRS-Custom PCB and SDA Inductor

[DarqueKnight]

Introduction

This report discusses the crossover modification procedure for installing a custom printed circuit board and custom 16 mH SDA inductor into my SDA SRS loudspeakers. A similar modification was previously performed on my SDA SRS 1.2TL loudspeakers (Link: Custom Printed Circuit Board for SDA SRS 1.2TL).

Before and After Pictures


Figure 1. Some SRS crossover wires were soldered directly to the board.


Figure 2. A big pile of SRS crossover goodness...but a mess.


Figure 3. New SDA SRS crossover assembly: main board, support board and crossover cover plate.


Figure 4. Left to right: 130uf capacitor board, main board, 16 mH Northcreek inductor, stock 2.75 mH inductors.


Figure 5. The soup can sized 130 uF Solen capacitors were mounted on a separate circuit board tucked in the corner.


Figure 6. Large inductor mountings. There is a cabinet brace just below the crossover opening that is 4" wide at the front and 1-3/4" wide
at the sides. It provided a good place to mount the 2.75 mH and 16 mH inductors. The inductors were mounted with aluminum nuts and
bolts.


Figure 7. Back during the Jurassic, when my SDA SRS's were manufactured, Polk had not started to use the nice wiring harnesses that
were used with later SDA speakers. The original connections were of the soldered and metal tab/quick disconnect type. I replaced all of
those with plug-in wiring harnesses.

Burn In Procedure for 16 mH SDA Inductor

The upgrade SDA inductors for the SDA SRS 1.2TL's had 100 hours of music played through them prior to burn in on the Audiodharma Cable Cooker. With the 1.2TL inductors, overcooking (blurred transients, small loss of overall detail and clarity, diminished sound stage height, diminished bass slam, loss of micro growl details in bass) was audibly evident after 58 hours of cooking.

The SDA SRS's upgrade inductors had 10 hours of music played through them prior to burn in with the Cable Cooker. With the upgrade inductors for the SDA SRS, I stopped hearing and measuring improvements at the 150 hour mark, but did not hear evidence of overcooking. I processed the inductors for another 93 hours in increments of 24, 24, 24, 12 and 9 hours. Even after an additional 93 hours of Cooker processing, for a total of 243 hours, I did not hear evidence of overcooking. I wondered about this and sent an email inquiry to Northcreek Audio asking if the wire and insulation of these inductors was different from the first set. I have not yet received a response (although I did receive the inductors for my CRS+ upgrade today ).

Another curious thing was that this pair of inductor's post burn in oscilloscope curves never reached the degree of smoothness that the first set did.


Figure 8. Cable Cooker (left) and inductor outputs at 0 hours.


Figure 9. Cable Cooker (left) and inductor outputs at 150 hours.


Figure 10. Inductor output at 150 hours (left) and 243 hours.


Figure 11. Cable Cooker (left) and inductor output pulse rising edge at 150 hours.


Figure 12. Cable Cooker (left) and inductor output pulse falling edge at 150 hours.


Figure 13. Inductor output pulse rising edge at 0 (left) and 150 hours.


Figure 14. Inductor output pulse falling edge at 0 (left) and 150 hours.

Listening Evaluation and Discussion of Results


Figure 15. The inductor upgrade facilitated a sonically heavier and more detailed front stage in my home theater system.

My SDA SRS's are used primarily as the front stage speakers in my 5.1 home theater system and secondarily as two channel speakers for background music when entertaining.

I was curious about whether the new board made an audible difference. I thought about doing listening evaluations between the stock and custom circuit boards. However, Gimpod mentioned that he heard improvements with his new boards over those provided by the upgrade Sonicraft Sonicap capacitors and Mills MRA-12 resistors. I have no reason to doubt this as it is reasonable that a better quality board with heavier circuit traces would provide better noise performance.

The upgrade SDA inductors provided Such Good Sound improvement over the stock inductors that I was reluctant to take them out for further intensive burn in processing. Prior to burn in, the upgrade inductors provided more weight at the sides of the front stage for both music and movies. After burn in, I heard even more image weight and more sonic detail.

I was concerned about some loss of integration with the dual LSi 9 speakers used as center channel speakers. After the inductor upgrade, there was tighter integration between the LSi 9 centers and SDA SRS fronts and between the SDA SRS fronts and LSi 15 surround speakers. This most likely would not have been the case had I not performed crossover modifications on the LSi 9's (discussed here) and LSi 15's (discussed here).

I thought the inductor upgrade might make the SRS's too bass heavy, since bass heaviness due to cabinet resonance is a known issue with this speaker. Some people actually prefer the tipped up bass presentation of the SRS over the more accurate bass of the SRS 1.2 and SRS 1.2TL. The inductor upgrade resulted in bass refinement to the point that it sounded like I had less bass. I didn't actually have less bass, I just had a much cleaner bass signal which translated to less cabinet resonance (and apparently less bass). On the other hand, as with the 1.2TL's, I realized more bass tactile sensation after the inductor upgrade.

The direct current resistance (DCR) of the modified SRS's decreased from 4.7 ohms each to 4.4 ohms each with the new 16 mH SDA inductor.

The SRS crossover upgrade, driver and passive radiator rings, Mortite and Dynamat Xtreme all contributed to a cleaner, more detailed bass signal, with a commensurate reduction in cabinet resonance.

After the SRS inductor upgrade, a frequent visitor to my home remarked:

"I don't like this. Now they sound just like the speakers (SDA SRS1.2TL's) in your living room."

Of course, the inductor upgrade did not make the SRS's sound "just like" the 1.2TL's, but they sounded closer to them in the bass region.

Costs

There are much lower cost alternatives to the circuit boards and inductors that I used. You don't even need to use a printed wiring board. A thin wood board with point-to-point wiring works very well. Even if you do not do a full crossover modification, I highly recommend replacing the 16 mH SDA inductor if your amplifier is comfortable with the lower impedance. All circuit boards were manufactured by ExpressPCB.

1. Pair of main PCB's,............................................ ...$268.18
2. Pair of support PCB's,...........................................$ 132.37
3. Pair of 16 mH, 14 AWG North Creek inductors..........$241.95
4. Pair of PCB's for 130 uF capacitors..........................$112.35
4. Mounting hardware for PCB's and inductors..............$ 75.29

Total............................................. ........................$830.14 (A modest amount in the culture of modifications for big SDA's. )

Further Study


Figure 16. All the parts are in for my second SDA CRS+ crossover modification.

References

Link: Improvements to the SDA SRS.

Link: Custom Printed Circuit Board for SDA SRS 1.2TL

Link: LSi 9 Crossover Modification Project

Link: LSi 15 Crossover Modification Project

Link: Audiodharma Cable Cooker Review

[joeparaski]

Wow, nice write-up. Now I gotta ask....how much $$$ do you have invested in these speakers with all the modifications you made? ANd if someone came up to you and said he wanted to buy them, what would you sell them for IF you were to sell them.

Joe

[DarqueKnight]

Now I gotta ask....how much $$$ do you have invested in these speakers with all the modifications you made?

Purchase price (used)............................................ .$1400
Mills resistors, Solen capacitors...............................$ 267
RD0194 tweeters.......................................... ........$ 384
Grille cloth............................................. ..............$ 12
Driver rings, tweeter brackets.................................$ 125
SDA inductors, custom PCB's..................................$ 830

Total investment........................................ ..........$3018*

Solid Wall of Sound for Home Theater Front Stage........PRICELESS

*I should probably add another 5-10 bucks for Mortite and Dynamat Xtreme

If someone came up to you and said he wanted to buy them, what would you sell them for IF you were to sell them.

I'd have to go to the far reaches of my imagination to come up with a price. I'll put that on my "deep ponderings" list of things to think about when I am on the treadmill at the gym.

[gimpod]

DK, Now you've got me thinking about Inductors. Crap!

"He was screaming 'I HATE YOU, I HATE YOU, I HATE YOU!!' as he slid further down the rabbit hole" :tongue:

[hearingimpared]

Beautiful!

[DarqueKnight]

DK, Now you've got me thinking about Inductors. Crap!

"He was screaming 'I HATE YOU, I HATE YOU, I HATE YOU!!' as he slid further down the rabbit hole" :tongue:

Awwwwwwwwww...don't hate the player, hate the game.

Speaking of players, Janne just informed me that he will be ditching his newly installed Northcreek 14 AWG, 1.3 ohm DCR, 16 mH inductors for Solen 10 AWG, 0.56 ohm DCR, 16 mH inductors.

Link: Solen S1016.0 Inductor

Such good game.

[hearingimpared]

Awwwwwwwwww...don't hate the player, hate the game.

Speaking of players, Janne just informed me that he will be ditching his newly installed Northcreek 14 AWG, 1.3 ohm DCR, 16 mH inductors for Solen 10 AWG, 0.56 ohm DCR, 16 mH inductors.

Link: Solen S1016.0 Inductor

Such good game.

LOL! Ray! Didn't you mean hate the sin, love the sinner!?!

[DarqueKnight]

A sweet pair of speakers gets sweeter...and more liquid.

I just completed the installation of a custom PCB and SDA inductor in one of my SDA CRS+ (1989 version) pairs.


Figure 1. Stock PCB and SDA inductor at left. The new board is 32% larger.


Figure 2. Before: Stock PCB and SDA inductor.


Figure 3. After: Custom PCB and inductor assembly.


Figure 4. Top view of populated new CRS+ PCB.

The yellow thing in figure 4 is a 40 uF AudioCap PPMF shunt capacitor for the dimensional driver. Sonicraft does not make a 40 uF capacitor. I would have had to parallel two 20 uF Sonicaps, or stack them one on top of the other, or place one 20 uF cap on top of the board and one on the bottom, or make the board bigger to accommodate the additional capacitor.


Figure 5. It was a challenge fitting a larger board in that tight corner, but I made it work.


Figure 6. Setting up for listening evaluations.

The newly upgraded pair is one in a set of identical twin CRS+ pairs. This affords me the uncommon opportunity to hear the effects of the upgrades against an unmodded identical reference.

More later....

[DarqueKnight]

LOL! Ray! Didn't you mean hate the sin, love the sinner!?!

It's the same principle. Although, I get the impression that some people look upon our hobby as a sinful indulgence.

[dcoil]

Another great review DK! And your pics always help clarify exactly what you're doing. I'm getting a good 'speaker education' reading through these posts. Hey, I now even know what DCR is

I am anxious to hear what the Solen 0.56ohm inductor does to the bass. How much will the total speaker DCR change? I guess not substantially (couple of points?) in regards to the load on the amp.

[dcoil]

DK, I'm in the process of modding the XO'r. I see that the two stock 2.75mH inductors are held to the faceplate aluminum 'L' brackets with a what appears to be a ferrous bolt (it's at least magnetic). When you relocated them to the shelf below the XO, you attached them with an aluminum bolt. Will this make any difference in the audio characterstics?

[DarqueKnight]

No.

The nominal 2.75 mH inductors measured 1.8 mH without the steel bolt and 2 mH with the bolt.

The nominal 16 mH inductors measured 15.6 mH without the steel bolt and 16.5 mH with the bolt.

[DarqueKnight]

I changed the capacitors in one of my CRS+ pairs from AudioCaps to Sonicaps and the improvement in clarity was fantastic! I was able to do a direct comparison between a pair of CRS+'s with the Sonicaps and an identical pair with AudioCaps.

AudioCaps are better than Solens and Sonicaps are better than AudioCaps, so Sonicaps are much better than Solens and I decided to ditch the SRS's Solens (except for the very large value 130 uF and 91 uF caps).

[DarqueKnight]

The phase and impedance response curves for each modified SDA SRS speaker are shown below. Stereo Review magazine measured the impedance response of the SDA SRS in their November 1985 issue (p. 90):

"The system impedance was between 5 and 6 ohms between 70 and 200 Hz, rising to 13 ohms at 53 Hz and dropping to slightly below 5 ohms at 20 Hz. Above 200 Hz, it rose to 19 ohms at 1,000 Hz, rolled off to 4 ohms at 1,000 Hz, and stayed between 5 and 6 ohms from there out to 20,000 Hz."

[DarqueKnight]

Introduction

The 0.4 mH 22 AWG and 0.7 mH 25 AWG inductors in the high frequency section and the 2.75 mH 18 AWG inductors in the low frequency section of my SDA SRS's were replaced with Jantzen perfect lay inductors. Jantzen only had a direct replacement for the 0.4 mH 22 AWG inductor. The 0.7 mH 25 AWG inductor was replaced with a 0.75 mH 26 AWG inductor that was unwound to 0.7 mH. The 2.75 mH 18 AWG inductor was replaced with a 3 mH 18 AWG inductor that was unwound to 2.78 mH.

The Jantzen inductors were special ordered from Parts Express. Parts numbers and prices are:

0.40 mH 22 AWG, part number 1489, $2.94 each.
0.75 mH 26 AWG, part number 1160, $1.89 each.
3.00 mH 18 AWG, part number 1068, $14.09 each.

The standard delivery time for Jantzen special orders (from Denmark) is eight weeks. This order arrived in two weeks-four days.

Table 1.

Figure 1. Jantzen 0.4 mH, 0.75 mH and 3 mH perfect lay inductors.


Figure 2. Unwinding 0.75 mH inductor to 0.7 mH.


Figure 3. Unwinding 3 mH inductor to 2.78 mH.

Unwinding both 0.75 mH inductors to 0.7 mH required removing 26.5" of wire. Unwinding the 3 mH inductors to 2.75 mH required removing 62.5" of wire for three of them. The fourth inductor required 66.5" of wire removed.

Installation


Figure 4. Custom SRS crossover board with original bobbin wound high frequency inductors.


Figure 5. Custom SRS crossover board with Jantzen perfect lay high frequency inductors.


Figure 6. Original bobbin wound 2.75 mH 18 AWG inductor and comparable Jantzen inductor at right.


Figure 7. Jantzen 2.75 mH low frequency inductors installed aside Northcreek 16 mH SDA inductor.


Figure 8. A layer of Sonic Barrier Black Hole was placed between the crossover circuit board and bracing
board for additional vibration damping.

Impedance Response Measurements

Impedance plots were generated by Dayton Audio's Woofer Tester 3 software.


Figure 9. Left SDA SRS impedance response after Jantzen HF/LF inductor modification.


Figure 10. Left SDA SRS impedance response after Jantzen HF/LF inductor modification.

Table 2.

Figure 11. Retired after 26 years!

Listening Evaluation

The left speaker was done first and compared to the right. There was a hard shift to the left in apparent sound level, along with the harsh, grainy highs and smeared bass experienced with previous mods with these inductors. There was an immediate increase in clarity and, surprisingly, in image weight. With the SDA SRS 1.2TL's, there was an initial decrease in image weight followed by a increase in image weight as the inductors burned in. Balance was restored to the sound stage after the right speaker was done. The next listening session was done after 13 hours of music play, at which time all sonic aberrations were gone.

Summary of Sound Improvements

1. Improved overall clarity and detail, particularly in dense, complex orchestral and choral pieces.
2. More low level detail as evidenced by hearing more as a song is fading out and by turning the volume way down.
3. More bass articulation and micro-growls.
4. More ambient information (echoes and reflections).
5. Apparently louder sound due to lowered noise floor.
6. Increased image weight.
7. There were no changes in image localization or sound stage dimensions.
8. There were no changes in tactile sensation.


Figure 12. SDA SRS's in my home theater system. Such Good Sound!

References

1. Upgrade-High-Frequency-Inductors-For-The-SDA-SRS-1.2TL

2. Curly-Maple-End-Caps-and-Side-Strips-For-The-SDA-SRS