SP1200, 1700, or 2500 Crossover Diagrams

Culpeper

Active Member
Attached are a schematic and an image of back and front of the circuit board. Interesting how the woofer is not filtered but runs from the "W +" to one end of Caps 1 and 3. The opposite end of these two caps are negative. The particular board is from an SP1700 but the 1200 and 2500 are the same circuit board with the same 700/6500 cutoffs. The only difference is Cap 3. The 1700 uses 3.3uF and the 2500 uses 4.7uF, etc.

I also can't figure out how the switches work. L2 and L3 appear to be resistors? C N S stands for Clear, Natural, and Soft switch settings

This thing is telling me the sluggish old OEM woofer can be changed and won't effect the crossover frequency range.
 

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Thanks for the link. I attached another image as a result. In the center are a couple of tapped inductors.
 

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Those switches have me baffled. I can see where two of the connections = 16 ohms with a DMM, which corresponds with the white resister but I can't figure out what the switch is doing to change the tweeters or squawkers to clear, natural, or soft. Is Clear turning the volume up 3db and the Soft turning it down 3db? I don't think they are changing the crossover frequency. I can't find anything on these types of switches. They appear to be exclusively Sansui, no pun intended.
 
I've measured the inductor and two transformers

351 = .348mH

202T1 = Clear 1.99mH, Natural 1.053mH, and Soft .342mH

301T1 = Clear .298mH, Natural .132mH, and Soft .039mH
 
Original factory setup. No filter on the woofer. Basically, a 2nd order bandpass (700/6500) on the midrange and a high pass (6500) on the tweeters. The original woofer acts as its own inductor and has a low frequency range. Thus, the muddy bass and superb highs on some of these vintage loudspeakers. Some of these crossovers come with 3.3 or 4.7uF caps. The difference is minimal. This is the typical Sansui ferrite core crossovers they bragged about back in the day.


"Transformer Type 12 dB Crossover Network

Here's the Sansui's exclusive knowhow of the transformer. The transformer type network is designed to let each of woofer, midranges and tweeters function in its most suitable frequency range, assuring clear sound even at the crossover points." [only there is nothing on the woofers]

"Specially Designed Level Control

The Sansui's exclusive transformer-type crossover network changed the level control from the conventional volume-type attenuator to the latest tap-type control whose operation does not influence the damping characteristics at all. This level control has three positions to adjust clear, natural and soft. The "natural" position is for the average rooms; "clear" for the rooms where the highs are swallowed up and the lows are exaggerated and "soft" for rooms where the lows are swallowed up and the highs are exaggerated." [explains nothing. Natural is the advertised 700/6500 crossover for the bandpass and 6500 for the high pass. Clear lowers the respective crossover points and Soft raises them. Soft has the most noticeable effect. The 16 ohm resistor only works on Clear.]
 

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Replaced original sticky woofers with same weight 8ohm woofers (Pioneer A30IR50-51F) and added a filter. Original crossover is the same. Basically just added a 1st order 2mH inductor on the woofer. Port boxes are tuned at about 60Hz. Before the end of Hotel California's steady bass riff sounded like one continuous note. Now, it sounds proper and can make out the bass as meant to. Bass is no longer not vibrating the room but is still very much there.
 

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FR graph. Original system (green) and the new woofer (black).
 

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Woofer with and without RC circuit.
 

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The original Sansui woofer may have used a 4 layer voice coil and possibly a heavy cone assembly to provide a natural HF roll-off. All I can see is cost cutting measures in place. The tapped inductors simply allow for the levels to be changed and I would think the 16 ohm resistors are fitted , partially to flatten the impedance and to prevent a brief open cct. event from happening when a switch is operated. Obviously this is not a speaker that was intended to be used with high powered amplifiers or made to suit serious listeners. Those Japanese fretwork speakers of the 60,s and 70,s were made for people who went for looks and features at an attractive price . Unfortunately it gave them a poor reputation that took many years to overcome.
 
Agreed, but the cabs are solid, the crossover is printed, original damping material is no joke, and the caps were replaced. You should see the Sansui ones where the crossover is wired up on a plank of compressed cardboard. I have them on a 80W HK amp. The highs are outstanding and back in the day they would demo these by letting the upper range blow out a candle. That info I got from Atkinson at Stereophile who is older than dirt, lol. Nevertheless, there is enough potential with these that some simple replacement decent caps and a modern simple filtered woofer replacement can't resolve to reverse the manufacturer cost saving bug-a-boo. And I'm not sure at that time what was used had any measurable difference based on the playback media at that time. Including amplifiers that complemented them. Klipsch is still toting their classics, people are cloning their design, and these particular Sansui boxes can easily and cheaply brought to that level without spending a couple thousand dollars. All I have in these is the cost of good caps, bargain woofers with a bobbin inductor that cost a few dollars. The RC circuit I'm going to put on the woofers is where I am probably getting too extravagant. But, what the heck. Attached is a typical Klipsch crossover on a wood plank which people clone and/or sell for a couple of hundred dollars.
 

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Also, looks like my woofer is rolling off at about 650Hz based on that 2mH inductor. It crosses over the midrange at about 1000Hz.
 
I've lurked for a long time, and found this thread. Great reading for me, as I'm considering rebuilding on of my 3 pairs of 2500s. Very interested in what you're doing with the crossover, good info. I've been thinking of completely rebuilding the factory crossover and getting rid of the switches and possibly going with Lpads for the mid/high behind the crossover, just to make it easy on me.. I used the Dayton DATS to measure the T/S of the woofer (info at end of post) and tried to measure the inductors, but DATS had a hard time below .5mh. Thanks for posting up your findings. WiniSD, if I'm using it right, puts an ideal box at 11cft! Bad as I hate to do it, I'm thinking of putting the Dayton DC300-8 12" Classic woofer in as a replacement, and your woofer bypass looks ideal with it. I still may rebuild the cabinets and retain the lattice grills.

Would definitely like to see pics of how your new crossover is laid out. I recapped one of the crossovers already just using Mundorf E-caps and will be using just the mid/high combo for my center channel in HT combined with Klipsch KG4s and HSU dual 10" sub.

My audio listening is in a separate room using an HK 3475 and I'm using an 8" bucket sub as a midbass (70-200) and a TC Sounds 12" for lows. I've upgraded the wiring inside the cabinets as well as polyfill and weatherstripping on the back panels. Love my 2500s.

T/S as measured by DATS:

* This data was exported from the Dayton Audio Test System: DATS
*
* Piston Diameter = 241.3 mm
* f(s)= 85.46 Hz
* R(e)= 5.167 Ohms
* Z(max)= 30.14 Ohms
* Q(ms)= 4.842
* Q(es)= 1.002
* Q(ts)= 0.83
* V(as)= 29.35 liters (1.036 cubic feet)
* L(e)= 1.768 mH
* n(0)= 1.744 %
* SPL= 94.52 1W/1m
* M(ms)= 34.71 grams
* C(ms)= 0.1 mm/N
* BL= 9.805
* K(r)= 0.3454
* X(r)= 0.3894
* K(i)= 0.1606
* X(i)= 0.4374
 
Great job. That is good useful information. I'm just using the stock recapped crossovers. I ended up with the 1st order inductor and zobel network between the crossover and the woofer since the crossover just bypasses the woofer anyway.
 
I just got a couple of 1.5mh coils in this week to try them out on the factory woofers. Hopefully I'll get them installed this week.
 
Culpeper, any chance you build these cross overs & sell them ? I have a pair of SP-1700 I was thinking about replacing the caps in, then I saw this thread and I'm really interested in your woofer upgrade and doing the cross overs. Did a search for the woofers you used and of course they are discontinued, any other good options you know of ?

Thanks in Advance

Agreed, but the cabs are solid, the crossover is printed, original damping material is no joke, and the caps were replaced. You should see the Sansui ones where the crossover is wired up on a plank of compressed cardboard. I have them on a 80W HK amp. The highs are outstanding and back in the day they would demo these by letting the upper range blow out a candle. That info I got from Atkinson at Stereophile who is older than dirt, lol. Nevertheless, there is enough potential with these that some simple replacement decent caps and a modern simple filtered woofer replacement can't resolve to reverse the manufacturer cost saving bug-a-boo. And I'm not sure at that time what was used had any measurable difference based on the playback media at that time. Including amplifiers that complemented them. Klipsch is still toting their classics, people are cloning their design, and these particular Sansui boxes can easily and cheaply brought to that level without spending a couple thousand dollars. All I have in these is the cost of good caps, bargain woofers with a bobbin inductor that cost a few dollars. The RC circuit I'm going to put on the woofers is where I am probably getting too extravagant. But, what the heck. Attached is a typical Klipsch crossover on a wood plank which people clone and/or sell for a couple of hundred dollars.
 
KennyG, recap your existing SP1700 crossovers. Put a first order 1.5mH inductor for the the Sansui W-110 woofer between the speaker and the SP1700 crossover. The output signal from the amp is fed directly to the woofer. Adding the inductor will create a simple 850 Hz 1st order crossover for the woofer. If you want to replace the woofer that is fine because the originals are rated at 8 ohms so replacement is a matter of the same size. You can use the same size inductor as explained above.
 
KennyG, recap your existing SP1700 crossovers. Put a first order 1.5mH inductor for the the Sansui W-110 woofer between the speaker and the SP1700 crossover. The output signal from the amp is fed directly to the woofer. Adding the inductor will create a simple 850 Hz 1st order crossover for the woofer. If you want to replace the woofer that is fine because the originals are rated at 8 ohms so replacement is a matter of the same size. You can use the same size inductor as explained above.

Any chance you have a list of what I would need to recap mine and do the mod you did on the woofer, capacitor quantity & values need ? I would like to be able to order everything and then break the speakers down for the refresh.
If I decided to go the B&K Cross over route, is the (Type AA) the one you have posted the correct one to use for this app ?
 
For each speaker cabinet 1 each...

https://www.parts-express.com/erse-15mh-18-awg-i-core-inductor-crossover-coil--266-552

https://www.parts-express.com/jantzen-audio-22uf-400v-z-standard-capacitor--027-266

https://www.parts-express.com/jantzen-audio-33uf-400v-z-standard-capacitor--027-270

https://www.parts-express.com/jantzen-audio-10uf-400v-z-standard-capacitor--027-282

Here is an example on replacing them. I actually seal the new caps on top of the old ones with silicone adhesive you can get at the hardware or auto parts store.

https://retrovoltage.com/2011/04/05/refurbishing-vintage-sansui-sp2500-speakers/

The inductor is placed in the cabinet between the crossover and the woofer on the positive side. You may need additional speaker connectors and wire. I glued a piece of 1x2 cheap pine lumber inside the cabinet wall to mount the inductor.

See the diagram below for the inductor on the "low pass" woofer....

http://www.erseaudio.com/CrossoverCalculators/First-Order-2-Way
 
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You are not going to hear an advantage using a Klipsch cloned crossover. I was just using them as example to compare and contrast with the stock Sansui "SP" crossovers. The Kipsch crossovers are for specific Kipsch speaker systems.

Also, you should test each speaker in your cabinets and make sure they are all good before upgrading the crossovers. You never know, you might have a broken tweeter or midrange that will need replacing.
 
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First off THANK YOU, really appreciate the help. But of course I have a couple more questions. lol

The inductor I'll be installing going to the woofer, the positive lead from the cross over, does it matter which lead it connects to on the inductor ?

I've tried finding the Pioneer woofer you used with no luck, Looking thru what parts express has now and I'm considering trying a Visaton brand. Any chance you could glance at the specs on it, see if its comparable to the Pioneer you used ?
https://www.parts-express.com/visaton-w300-8-12-woofer-8-ohm--292-588



You are not going to hear an advantage using a Klipsch cloned crossover. I was just using them as example to compare and contrast with the stock Sansui "SP" crossovers. The Kipsch crossovers are for specific Kipsch speaker systems.

Also, you should test each speaker in your cabinets and make sure they are all good before upgrading the crossovers. You never know, you might have a broken tweeter or midrange that will need replacing.
 
Looks to be a good replacement woofer. Check the OD and ID dimension with your current cutout in the cabinet to be sure. It doesn't matter the connection on the inductor. It is not marked in or out.

Mounting Information for new woofer from website...
  • Overall Outside Diameter12.01"
  • Baffle Cutout Diameter10.98"
  • Depth4.72"
 
Not an expert at this, but this is the woofer I was considering for my 2500s: https://www.parts-express.com/dayton-audio-dc300-8-12-classic-woofer--295-320 Sealed, it's ideal for the 2500 cabinet.

I think what will hurt any replacement is the lower efficiency of choices.

I'm going to add a 1.5mh coil with RC (50uf !! and 7.5ohmR) and stock woofer and see what that does before I consider a replacement. The size of these cabinets is going to limit any of the low end output, but I think this approach will clean it up quite a bit with a recap on the factory crossovers.
 
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