7c monitors upgrades

jrosa

I have 7c monitors that I purchased in 1986. I was thinking to upgrade the crossover. Is there schematics for these anywhere? What should I upgrade caps, resistors? Which tweeters do these have?

Thanks

F1nut

Just pull the board, values are printed on the caps and resistors. Same for the tweeter.

bigaltx24

7Cs will have SL2000 tweets.

westmassguy

The schematics for the 7C are at the top of this section: http://forum.polkaudio.com/discussion/38755/polk-audio-speaker-wiring-schematics-more-all-models-except-sda#latest
The New Replacement Tweeter for the SL2000, is the RDO-194-1.
You can also further upgrade the crossovers to accept the RDO-198-1 Tweeter, which is even better than the 194.

littlewoodboats

westmassguy wrote: »

The schematics for the 7C are at the top of this section: http://forum.polkaudio.com/discussion/38755/polk-audio-speaker-wiring-schematics-more-all-models-except-sda#latest
The New Replacement Tweeter for the SL2000, is the RDO-194-1.
You can also further upgrade the crossovers to accept the RDO-198-1 Tweeter, which is even better than the 194.

Could you direct us to the process for the RD0198-1upgrades please? I also have a set I would like to do.

westmassguy

littlewoodboats wrote: »

westmassguy wrote: »

The schematics for the 7C are at the top of this section: http://forum.polkaudio.com/discussion/38755/polk-audio-speaker-wiring-schematics-more-all-models-except-sda#latest
The New Replacement Tweeter for the SL2000, is the RDO-194-1.
You can also further upgrade the crossovers to accept the RDO-198-1 Tweeter, which is even better than the 194.

Could you direct us to the process for the RD0198-1upgrades please? I also have a set I would like to do.

Use the Monitor 5B SL3000 schematic found in the same section

littlewoodboats

Thanks. Is there a preference for replacing the polyswitch? I think I remember a few SDA discussions talking about everything from a plain jumper to a .5 ohm resistor. Is there a consensus of opinion of how best to proceed?

westmassguy

All resistors should be changed to Mills, MRA-12s, or Mundorf Mox. The Poly Switch gets a .5 ohm resistor. You'll also need to change the Hi-Pass Inductor, .27mh @ .5 ohms. You'll not find one readily available.

Jimbo18

My 7C's have the SL2500 tweeter, so it's not definite that his has the SL2000. I bought mine off a Polkie who said they were the stock tweeters. And I think the replacement for that is the RDO-198.

A photo would confirm his tweeter model.

westmassguy

A photo of his actual crossover would be better.

Jimbo18 wrote: »

My 7C's have the SL2500 tweeter, so it's not definite that his has the SL2000. I bought mine off a Polkie who said they were the stock tweeters. And I think the replacement for that is the RDO-198.

A photo would confirm his tweeter model.

A photo of his actual crossover would be better. People sometimes swap tweeters without knowing what they're doing
Your 7s, if originally equipped with 2500s are referred to as Series 2

littlewoodboats

Mine have the SL2000 with crossovers matching the 1st revision M7 drawing shown at the top of this section. I was hoping there might be an easy way to convert them to the Series II configuration. I have a set of 5jr+ series II redone with the RD0198-1's and crossovers refreshed using Dayton caps and mills resistor. The sound is fantastic and they work well as the fronts in my media room. They are supposed to be in my office so I need something new for the media room. Monitor 7's seemed like a good choice as I have always been a fan of the monitor line and the larger side will make them better for music.

The inductors are where I get lost. Both the SL2000 and the SL2500 drawings show a .22mH inductor in the tweeter section. Are they the same DCR? My .22 mH inductors measure .550 ohms. If they are the same then the rest of the parts in that side of the circuit should not present any problems. My M7 crossovers are shown with a 1.55mH inductor (I do not know DCR) in the bass side where the Series II M7 shows a 1.75mH. The Jantzen catalog shows a few 1.75mH inductors but I have no idea if any of them would be correct.

I can solder and follow a schematic but picking coils is a job best left to the pros

westmassguy

You have two possibly three choices:
Upgrade the caps and resistors, and drop in some RDO-194s.
Upgrade the crossover per the 5B SL3000 Mod, which requires a .27mh inductor @ .5 ohms, and an additional 5.8uf shunt cap.
Upgrade and change the value and quantity of the the Caps in the Hi-Pass, and change the large spool inductor per the Rev2 drawing.
I've upgraded many Monitor 7s and 5 to use the RDO-198.
In each case, I found it much easier to replace the small, Hi-Pass shunt inductor with the proper .27mh inductor.
You can special order .27mh @ .49 ohm inductors from Parts Express Part # 000-1640 , and wait 8-10 weeks.
If you have an accurate LCR Meter, you can buy a stock 20 gauge .3mh Inductor, unwind it to .27, and pad it with a .15 or similar value Mills Resistor.
That's what I do.