Difference between 1986 and 1988 1C studios?

dpowell

I picked up a pair of SDA 1C studios off of craigslist today. $175. 1 SL2000 needs replacing. Cosmetically they are a 7/10 with a few dings and scratches. Perfect for a casual listening garage rig. Great vintage polk sound without lots invested. The seller threw in a Yamaha receiver for $25.

Now for the SDA advice. I am very curious about a few things:

I pulled one of the MW6510's and it had a date stamp of July 1988. The driver said for use in CRS and SDA II but also had a stamp of SDA 1C.

The XO appeared to be the same as the XO in my 1986 1C's. The interconnect is the pin/blade type.

One thing that is different on the back plate which contains the binding posts is that there appears to be a second set of inputs with the red/black colors opposite of the primary binding posts. When I look inside, I see that wires are connected to those inputs. What are those for?

Are there any other differences between the model years and would I see any benefit from moving the newer mid drivers from the garage cabinets to my primary listening cabinets?

I've done an initial 30 minutes of listening and can tell immediately why the SL2000 to RDO194 tweeter is a recommended upgrade. I forgot what the SL2000's sounded like. I need to replace one for now. Is there any reason I can't relace it with a RDO194 and leave the rest SL2000's and just replace them as they go bad? If it were a primary listening rig, I wouldn't consider it.

Thanks in advance.

Tony M

Congrats first on a great deal on a great set of speakers!

Well the other three SL-2000's will drown out the one RD-0194 but you'll keep the curcuit flowing nicely.

The extra binding posts? maybe for bi-amping..

F1nut

1C's never came with two sets of binding posts.

phocion

I had my 1989 1C's open over the weekend to toss in some new x-overs (Thanks again Gimpod!), here is a pic from the passive in unmolested form:

Sounds like someone may have upgraded the pin/blade connection with new binding posts, which does have wires that run directly to the inputs.

george daniel

pics would help

dpowell

george daniel wrote: »

pics would help

Good point. I'll get some pics posted tonight after I finish helping my mother in law move back into town. :eek:

A couple of clarifications:

The pin/blade connector is original and not replaced.

There is only one set of regular binding posts and they are original.

Nothing appears to be modified.

dpowell

Snapped a quick pic before I had to leave. Note the smaller red and black inputs directly to the left and right of the pin/blade connector.

Toolfan66

I would pull the passive and see if they are hooked up when you get back that is..

gimpod

I can tell you right now that's not stock. Looks like someone slapped in a pair of Banana Jacks something like these Banana Jacks. This could have been an attempt to bi-wire these 1C's. I would look inside at the crossovers to see if they've been modified.

dpowell

On my phone at the moment. Pretty sure they are connected and it didn't look like a 'custom' job but I will pull the passive when I get home and take some pics.

gdb

There is a karma for some SL2000s going on,you might want to jump into it.

DarqueKnight

dpowell wrote: »

Note the smaller red and black inputs directly to the left and right of the pin/blade connector.

gimpod wrote: »

This could have been an attempt to bi-wire these 1C's. I would look inside at the crossovers to see if they've been modified.

I have run across 1C's that were modified to "split" the crossover into high and low frequency sections. In most cases, the traces connecting the HF and LF sections were cut. In other cases, either the HF or LF components were relocated to a separate board with point-to-point wiring.

dpowell

One mystery solved; another created......

I pulled the passives this morning and took a few pictures. Some of you SDA gurus who have more face time with the insides of these than I do may have seen this right away but it took a minute of being distracted by tracing wires back to the XO to finally lock in on the answer to the question as to why there is a second set of binding posts but the answer is simple. They are replacements for the pin/blade IC connection.

They appear to be done professionally. The soldering is excellent.

I grabbed a 20' length of spare 12guage M!@#$ter cable and some banana plugs and am back in business.

I may have an answer as to why this was done. When I went to plug in my extra pin/blade IC cable, I noticed that I could not insert it into the right SDA speaker. This led me to discover a piece of the pin from the original SDA IC cable stuck in the socket. I was able to remove the pin quite easily but my guess is that someone had them professionally modified instead of ordering a replacement IC.

I will try and contact the seller and ask but when I bought them, she said they were her mom's and hadn't been used for quite some time.

The sticker on the XO confirms they are 1C's.

Toolfan66

Nice!!! You only need to use the binding post that connects to the blue wire. you could build a Dread Naught AI-1 SDA Cable then you would want to use both bindding post then you could use a non common ground amp without strapping the negitives (if the manufacture allows you to strap them)

DarqueKnight

dpowell wrote: »

...the answer to the question as to why there is a second set of binding posts but the answer is simple. They are replacements for the pin/blade IC connection.

...my guess is that someone had them professionally modified instead of ordering a replacement IC.

Pin/blace IC's have been unavailable from Polk for a long time and they rarely show up on the used market. Whoever was responsible for the modification obviously didn't think the broken pin could easily be removed and they didn't know that only the pin connection carried a signal and that a replacement IC could have easily been made with ordinary RCA connectors.

The next mystery is why did someone harshly jerk the IC out of the socket at an angle such that the pin snapped off? One way this could have happened is if someone had stood behind the speaker and grabbed the IC cable and jerked upward. The flat blade bent upward as it came out of the socket and the hollow pin snapped off.

dpowell

DarqueKnight wrote: »

The next mystery is why did someone harshly jerk the IC out of the socket at an angle such that the pin snapped off?

Good question. There are no signs of trauma to the binding post plate. Nothing appears loose. One other possibility is that some sort of damage occured to the pin/blad cable while unplugged (i.e. stepped on etc.) that made it weak and the rest of the job was finished when reconnecting the cable. I may never know but I am going to ask the seller if she can ask her mom (assuming she is still alive).

DarqueKnight wrote: »

Whoever was responsible for the modification obviously didn't think the broken pin could easily be removed....

The funny thing is that it took me all of 45 seconds to remove the pin with a small flat head screwdriver. Of course that wouldn't matter much if they couldn't replace the cable and didn't know the blade connection portion was not a requirement.