Transitional 1Cs

JayCee

Hi,

I have what I believe are transitional 1Cs. I purchased them approx 1 year ago and they've never lived up to the SQ everyone raves about. I've replaced the SL-2000s with RDO-194s and the wow factor still alludes me. My components aren't the problem and the drivers are in working order. I own 1.2TLs and 2As which I've swapped out w/no unforeseen SQ problems (to include different rooms). As expected, the TLs are awesome but compared to the 1Cs, the 2As sound much better. So, my conclusion is the XOs are not pulling their weight?

I'm going to upgrade my XOs but have a few questions. With respect to the transitional nature of my speakers...the XO consists of 2 circular boards (dated, 28 Aug 87), rather than the single rectangular board most folks appear to have. From what I've researched, I believe they are close to the 1B schematics but can't exactly match the cap/resistor values to either the 1B or 1Cs. The label on the back of the cabinet says "SDA-1", the cabinet is 1C (oak end caps), the IC is blade/blade and the drivers are 6510/6511. The CP "Transitional SDA Series List" states the cabinet's were 1B but mine is 1C (see pic below).

I have the XO boards out and just disconnected one set from the risers to check the back side for a part number..."E2105-1 LF Board" and "E2103-2 HF Board" are scribed into the circuit (please see attached pics). I used the SDA driver/XO cross-reference list posted on CP and my XOs don't match the 1C (BE1618-B), and the 1B doesn't have a board # listed.

I'm following gim54pod's threads on the 1C circuit boards he created and am very interested. My questions are:

1. What's known about the apparent transitional boards I have?
2. Has anyone worked on them?
3. If I'm able to purchase the boards gim54pod created should I go that route?
4. Values for the inductors on my current boards are not listed how do I verify them?

Any insight or advice you can give me is appreciated.

Thanks,

John

kawizx9r

Don't take this the wrong way but did you properly position your SDA 1C's the way they're supposed to be? 6" to 2' away from the rear walls (which mainly affects the bass response you receive), and a good 2'-4' away from the side walls and 6'+ between each other. No toeing in either!

Btw, the crossovers look just like the one's I had in my SDA 1-C Studio series.

Will add though that upgrading the caps/resistors on your stock X-O will dramatically improve your SQ.

JayCee

kawizx9r wrote: »

Don't take this the wrong way but did you properly position your SDA 1C's the way they're supposed to be? 6" to 2' away from the rear walls (which mainly affects the bass response you receive), and a good 2'-4' away from the side walls and 6'+ between each other. No toeing in either!.

Not taken the wrong way at all...;) I don't post much, but I do sit back and take in what's discussed, try to do my homework and ask for help when needed.

W/the exception of the 2As, the 1Cs and 1.2 TLs are spiked (Mye Sound spikes) plus each time they are moved, they're leveled and measured exactly from the back wall with no toe in. 6" is just right compared to other distances within the range you've mentioned (experimented in the past) and they're 8' apart. No immediate/adjacent side walls w/the way the room is designed.

Definitely missing the mids, not bass...I'd describe it as a lack of dynamic range or a full/rich sound. Driver push test is solid. I was shocked at the difference when swapped w/the 2As, which leads me to believe it's something internal to the signal path.

Thanks for the reply,

John

Toolfan66

I have only seen two different crossovers for the 1C's and yours are nether of the two..

I would like to know if those are correct..

Good luck on the upgrades!!!

helipilotdoug

Have you checked to make sure you don't have some drivers out of phase?
Go to this link:http://www.polkaudio.com/forums/showthread.php?t=55888
Scroll down to the last post, and download the SDA Quick Troubleshooting.pdf
This might help you track down your problem. Hope it helps.

JayCee

TOOLFORLIFEFAN wrote: »

I would like to know if those are correct..

You and me brother...I had the same thought when I started snooping around for answers; perhaps that's why they don't sound right. Another reason why gim54pod's boards would be perfectly timed. Between your aftermarket parts in my TLs and 1Cs (TL XO cover, rings and tweet mounts for both sets) and possibly the new gim54pod designed XO boards, I'll have every CP fabricated mod that I know of.:cool:

Although I'll be bummed if my XOs are not the correct ones, I keep reminding myself, "It's all about the journey".:)

John

JayCee

helipilotdoug wrote: »

Have you checked to make sure you don't have some drivers out of phase?
Go to this link:http://www.polkaudio.com/forums/showthread.php?t=55888
Scroll down to the last post, and download the SDA Quick Troubleshooting.pdf
This might help you track down your problem. Hope it helps.

Thought I did, but now that I looked it over again I realize it was w/my 2As when I first picked them up. I have the 1Cs completely apart, so am going to push on w/the XO upgrade...don't have time to reinstall everything. I may never know if afterward, they work as advertised. Thanks for reminding me of the troubleshooting guide.

John

geoff727

I had a pair of early serial number -1C's. The PCB's looked exactly like what you have there, with one exception. All the parts on mine matched the parts shown on the crossover schematic posted here. It looks like there's a 15 ohm resistor on your high-pass board, whereas the schematic lists a 7.5 ohm value (along with another 7.5 ohm and a 2.7 ohm).

FTGV

From the component values that I can actually see in the pics it looks to me much like the schem for the 1C. I can't see the values on the Mylars I assume they are 12uf and 4.4 uf.It appears the 15 ohm resistor is paralleled with another resistor(possibly also 15ohms) which would make the combined value 7.5 ohms.On the low pass board it appears there is another cap paralled with one of the 20uf's.I assume it is also 20 uf which would give the net value of 40uf just like shown in the schem.

geoff727

FTGV wrote: »

It appears the 15 ohm resistor is paralleled with another resistor(possibly also 15ohms) which would make the combined value 7.5 ohms.

You're right. That 15 ohm is paralleled with another one. I didn't see that other one hanging out down there. Makes perfect sense now.