RSIIb Outboard Crossover Update

[Maxamillion]

OK, I've finally lost my mind - not really, but I've kicked the equalizer upgrade up a notch.

In addition to the PRP metal film resistors, I've ordered nude TX2575 bulk metal foil resistors from Texas Components for the input (2.2 Kohm) and output (220 ohm) positions, 0.1% tolerance. These are supposed to be the ultimate low noise resistors available, and the cost wasn't too bad ($9.40 each, I need 4 of them).

I also ordered Cree Silicon Carbide Schottky diodes (1 amp, 600V) to replace the little silicon diodes in the rectifier and several other positions. These have really come down in price lately, and are only $0.93 each at Digikey. No reverse recovery spike at all in these babies...they should reduce switching noise to near zero.

Once I fit all these new parts, I'll get on with the opamp comparison.

 

[phaedrus]

Jeez Louise, you're going to have the most modded RS-IIB out there. Be fascinating to see how you like it when it comes together. Only problem (for us spectators) is, since you're changing so much all at once, we won't be able to tell which of the mods had the biggest impact and which were nominal. Fun to follow your exploits, anyway.

David

 

[Arkay]

Just re-read and "caught up" on this thread. Great stuff, Maxamillion! :thmbsp: Can hardly wait to hear the report on the final sound. You'll probably have the best-sounding RS IIBs out there!

Thanks for taking the time to share what you are doing! You are giving me the itch to see what more I can do to upgrade my RS IIs with better-quality crossover components (I used normal Solens to replace the caps, and otherwise kept a lot of the original driver wiring, original inductors, etc..., so I am sure there is ample room for further upgrading), but there are too many projects ahead of them, for me to dig into them now (two TT plinths to build now that I've retrieved my scroll saw, and a couple amps to recap, are next on the list...). But it's great to follow along with your project and enjoy the process vicariously.

 

[Maxamillion]

Jeez Louise, you're going to have the most modded RS-IIB out there. Be fascinating to see how you like it when it comes together. Only problem (for us spectators) is, since you're changing so much all at once, we won't be able to tell which of the mods had the biggest impact and which were nominal. Fun to follow your exploits, anyway.

David

David,

I thought about doing it piece by piece with testing in-between but the timing was right to just do it all at once - mainly because I'm waiting on the new diaphragms from Graz to tie it all together, and due to my misadventures with a certain doctor :thumbsdn:, I am two diaphragms short of a full set (my wife says that about me all the time!).

What I can do though is rebuild one speaker with the old diaphragms, and one with the new ones, so that we can at least separate the effect of the crossover/cabinet bracing/equalizer upgrades from that of the diaphragms. And I am reporting on the equalizer updates in a step by step fashion, albeit on different speakers from the RSIIbs.

 

[Maxamillion]

I've almost completed the equalizer resistor swap project, but there were two 1/4 watt 100K resistors I didn't see before (hiding under other components), so I will need to wait for those to come in before I can be completely done - arrggh!

I have replaced all the carbon films with 1/2 watt PRP 1% metal films, except for two 1/2 watt 360K Shinkoh tantalums (there was no PRP available in those values) and Texas Components 0.1% naked Z-film metal films on the input and output circuits (2.2K and 220ohms, respectively). I have also replaced the input and output wiring with 18 gauge solid core silver wire with teflon insulation.

Here are a few in-process shots - the TX naked film resistors are close-up in the second picture.

P.S.: Just a little tip if you try this. Three of the resistors were in very tight confines (under the pots, etc.), and it was very difficult to get the 1/2 watt PRP's in there, so I simply flipped the board over and soldered them in underneath. There is plenty of room under there, and since the board has double sided traces, there should be no difference in performance.

 

[Maxamillion]

The equalizer is complete, and back in the system. All resistors have been replaced (except for the two soldered across the low bass pot - too hard to get to). I put the output TX2575 220ohm resistors right on the output RCA connectors (picture 1) because that shortened the signal path by one board trace and one solder joint. I also replaced the four rectifier diodes with 1A 600V Cree Silicon Carbide Schottky diodes (picture 2). The pinkish-red wires in picture 3 are DH Labs 18 gauge solid-core silver with teflon insulation.

Once I hooked it all up and verified proper operation, I rolled the three opamps: the stock LF353N, the OPA2134 and the OPA2107. It was not even close - the OPA2107 smoked the other two by a large margin. Bigger and more defined bass and mid-bass, and less of everything else, including glare in the highs.

Overall, the highs are more pronounced than before, but not offensively. All the shimmer of a cymbal gets through, and I can always adjust the EMITs down a bit if it starts to wear on me. The sound is much more transparent in the treble region than before.

 

[phaedrus]

Looking good, Maxamillion! Now, is there any chance you can give us an idea of what made the bigger difference - swapping the resistors, or the opamps? I don't think I'm up for going the whole rebuild like you did (great job, BTW), but swapping the opamps may be something I'd be up for.

David

 

[Maxamillion]

The resistors and rectifier diodes made a difference in the highs - cleaner and clearer than before. When I then swapped in the opamps, the 2107 gave me the best bass - fuller and more detailed than the other two. Will it have the same effect without the resistor changes? Probably.

You may be able to do an abbreviated version of my rebuild by swapping the opamps and changing the input (2K2) and output (220R) resistors to TX2575.

 

[goat67]

Wow
Great job. Could you put together a parts list? Where did you get the parts from? I really believe the equalizer is a weak point and think I will do some of these mods.

 

[Maxamillion]

Yeah, I thought it was the weak point too, so I did the mods. I actually contacted Marchand Electric about making me a custom equalizer unit - he quoted me a price of $2000 for a solid-state unit and $4000 for a tube unit, so I decided to do the upgrades myself!

I can put together a parts list, but I believe there were various versions of the equalizer made over time. I know that the schematic on Infinity Classics.de is different from mine (and also incomplete as well). There are different resistor and capacitor values and also the Mosfets are different (schematic says VN40AF, mine has VN40AD). I would not rely on a parts list to make the purchases of the components for that reason.

The resistors are a bit of a pain since the codes are not consistent (some have 3 bands, some 4 or 5, and the colors vary as well). I measured them all in circuit, but found that I needed to disconnect one end for a few of them since the fact that they were in a circuit changed their value.

I'll work on pulling a list together anyway - just be careful to check that your unit matches mine.

 

[goat67]

Thanks
Also let us know where you got the parts. That will be a real time saver.
I recapped mine with the exception of the big silver ones I used Muse did not have the big ones on hand, so I will be going back in.....
As far a revisions go I would not use your list verbatim but as a starting point, more interested in the type of components.
Thanks again Jerry

 

[Maxamillion]

OK, Here's a list of the stock parts replaced, along with what I replaced them with and the source:

Resistors (all 1/4W carbon film unless noted, some had 5 bands and a bluish color so they may have been metal film - hard to tell):
(2) 22R
(1) 47R 1/2W
(2) 220R 1/2W
(4) 470R
(4) 2K2
(2) 5K1 carbon comp
(2) 10K
(2) 15K
(2) 39K
(2) 47K
(8) 100K
(2) 110K (update: replaced these with generic 1% metal film resistors from Antique Electronic Supply, they had the 110K value)
(2) 360K
(2) 10M carbon comp

All were replaced with 1/2W PRP metal film resistors from Parts Connexion except the 360K (replaced with 1/2W Shinkoh tantalums from Parts Connexion), the 39K (replaced with 1/4W PRP metal film as PCX didn't have 1/2W), and the 220R and two of the 2K2 (replaced with 0.6W Texas Components TX2575, from Texas Components).

Diodes:

(4) silicon rectifier diodes, replaced with (4) 1A 600V Cree SiC diodes from Digikey

Capacitors:

(2) 5000uF, 50V electrolytics, replaced with 4700uF Panasonic TSHA from Digikey, bypassed with 4.7uF Solen PP from my spares box
(2) 1000uF, 16V electrolytics, replaced with 1000uF Panasonic FM from Digikey, bypassed with 1.0uF Solen PP from my spares box
(2) 220uF, 50V Xicon electrolytics, replaced with 220uF Nichicon Muse KZ from Digikey
(2) 3.3uF PP bypass caps, replaced with 3.3uF Mundorf Supreme from Parts Connexion
(2) .033 PS bypass caps, removed and replaced with 0.01uF Audiocap Theta Film and Foil caps from Parts Express, soldered across the Mundorf Supreme leads

Opamps:

(2) LF353N opamps replaced with Burr-Brown OPA2107AP from Digikey

Wiring:

Input and output wires replaced with DH labs 18ga solid silver wire from Parts Connexion.

Solder:

WBT 4% silver solder from Parts Express

I think that covers it all.

EDIT: This list is now obsolete - see additional changes below

 

[Maxamillion]

One more Equalizer Update

After playing the newly refurbished equalizer for a while, I noticed that the left channel was a bit weaker than the right in low bass. After doing some troubleshooting to make sure I hadn't screwed something up when I did the mods, I isolated the problem to the low bass pot; at the midpoint setting, one side had about 40% more resistance than the other. I tried Deoxiting it, to no avail. I needed a new pot. Both the low bass and contour pots in my unit are 1 Megohm dual pots.

So, I searched the web for a 1 Megohm dual pot of about the same dimensions (24mm diameter pot, 1/4" shaft) and found one at Antique Electronics Supply (AES) - it took a while, there aren't many out there. The pot was made by Neohm, an Italian company. They also had the 1% metal film 110K resistors I couldn't find anywhere else. So last night I replaced the pot and the two resistors. I had to do some adapting of the new pot since it had solder lugs instead of board mount pins - I ended up cutting off most of the solder lugs and soldering some 18 gauge solid core wire onto the stubs to make my own pins. I also had to cut down the shaft length from 2" to make it equal to the other pot (a Dremel with a cutting wheel worked well). I then soldered it all up and did some listening.

MUCH better! The new pot sections are within 1% of each other in resistance at the midpoint (I think I got lucky as I doubt these pots are made to that tolerance), and the bass was much more consistent from the left and right speakers. Having them at the same level also provided improvements in imaging and tightness of the bass.

So FYI; those who do these upgrades may want to check the pots while you are in there.

 

[cdfac]

Max, did you get the OPA2107AP or APG4? i don't even know if it makes a difference. based on your results i'm going to swap those in for the LF353N's in my RS1b XO.

 

[Maxamillion]

They are the AP.

 

[Maxamillion]

Still waiting for the Graz diaphragms for my RSIIbs to be complete. So, I upgraded my Supratek preamp output coupling caps to Duelund CAST. They are very expensive but man do they sound great! The tonal balance is just about perfect! Well worth the money IMHO.

Anyway, once the CAST were in, I hooked the RSIIb equalizer back up to see how it sounded through the Snell speakers I'm using as substitutes for my Infinitys, and I noticed that the modded equalizer seemed to add a bit of brightness or glare to the upper frequencies, versus listening to the CAST-modded preamp without the equalizer in-line. In an effort to alleviate this I soldered 0.01uF Audicap Theta film and foil caps across the Mundorf Supreme caps, and voila! The brightness was greatly reduced, and the overall sound was much smoother at the top end. I will update the parts list to include the Audiocap Thetas, I think they are a very worthwhile tweak.

 

[Maxamillion]

An equalizer revelation!

Sometimes you don't notice the most obvious things.

I was mentioning my equalizer upgrades to someone on the DIYAudio forum, and they wondered why the output coupling caps were so large. Lo and behold, I calculated what the -3dB point should be, and I could easily get by with just a 10uF cap instead, and still have a corner frequency <2Hz!! This means I can get rid of the electrolytics completely! I have no idea why Infinity would put those large electrolytics in there, but they did!

So I got my nerve up, grabbed a pair of wire snips, and snipped the 220uF electrolytics right out the circuit, leaving only the 3.3uF Mundorf Supreme and the .01uF bypass. I plugged it in and WOW, there was the clarity and transparency I had been searching for - the improvement was HUGE. The bass was a bit on the weak side, but that's because I need to bump the total uF up to ~10. I ordered additional Mundorf caps to get it up to 10, and will report back after I put them in. Just thought I'd share.

 

[Maxamillion]

So, I received the additional caps and bumped up the output to 10.43uF by adding a 6.8uF Mundorf Supreme and a 0.33uF Mundorf Silver/Oil to the 3.3uF Mundorf Supreme already in there. I removed the 0.01uF Audiocap Theta from each channel. This is about as much cap as I can fit in that box! See picture attached.

For the first 2 hours or so of use after this change, I thought that I may have made a mistake, as the bass was thin and the treble was too bright, but that began to change at ~3 hours and by 5 hours the balance was nearly perfect. I could actually hear it changing as I was listening - very weird. The sound now is very full and incredibly transparent; I don't think I can take this unit too much farther in terms of improvements.

In summary, the removal of the electrolytics in the signal path is a MUST DO for anyone upgrading one of these.

 

[Maxamillion]

So, still waiting for Graz, so I did some more to the equalizer. I replaced the PRP gate stopper resistors on the on the MOSFETS (470R) with TX2575s, to great effect. Big increase in clarity, those things are amazing, but pricey. I may go back in again and put a few more in, they are so clear. I did notice that I had to tweak the contour pot a little higher after that as the TX2575s tend to make the sound a little hotter on top.

Also, I noticed that the two little green caps on the input to the bass level pot were mylar (polyester), which I greatly dislike. Mine were 0.033uF in value (the schematic said .029uF), which just happens to be the exact value of the polystyrene bypass caps I removed from the output of the equalizer way back when. So I replaced the mylars with the PS film and foil caps from the output, and it seems to have given me a bit more fullness in the bass and a little bit better clarity up into the mids. Not bad for a freebee. The PS are axial, so I had to solder a little lead extension on one end, but no big deal. I'll probably end up replacing the other 4 mylar caps (all 0.39uF) in the equalizer as well eventually, with PP.

 

[Maxamillion]

I have one word for you - OPA827.

I swapped the OPA2107 opamps for OPA827s on Browndog adapters just to see how this vaunted new SiGe opamp from TI would sound in the equalizer. The adapters are needed since the 827s are single opamps and are surface mount only, so each adapter holds two SMD 827s, with pins to fit into the standard DIP-8 socket.

These things are amazing! Clarity, impact, tone are all far superior to the other opamps I've tried, from low bass up to the treble. Highly recommended if you feel like opamp rolling. These are definitely staying in my equalizer. They have them premounted for sale at the link below, or you can save a lot of money and solder the opamps to the adapters yourself.

http://cimarrontechnology.com/pre-mountedcomponents.aspx