Upgraded 1.2TL xovers new way & circuit error found

RichCanDo

Thank you Mark for bringing this to the attention of the Polk company. Nice to know they care about a product out of production for so long.

Answer #1 provides the TL tweeters "hook up" in Negative polarity. I was under the impression the crossover circuit caused a change (reversal) to the phasing. Therefore I would understand "hook up" to mean (+) from tweeter connects to (-) marked on the board. (Because the board markings are reversed) If the xover circuit caused a phase reversal, the tweeters are actually connected in the proper phase.

The above reply from Polk does let those upgrading from 1.2 to TL know they have to rearrange the pins on their tweeter wiring harness to obtain proper tweeter phasing.

#2. Makes sense. If I remember correctly, although mylar and most film capacitors provide better specs in several areas for audio use, they provide some detrimental specs, one is a higher DF.

"As to the jumper question – we wrestled with tweaking this section and may actually have had an option in the board that we chose not to use in the end. Matt seems to remember something like that as well."

I know nothing about xover circuits. I am wondering why the resistor bypasses the 12uf cap. My tweeter (isolated) sounded better to me with the 750 mica cap and the resistor out of the circuit. (No jumper) Sound is warm without jumper, harsh with jumper. I assume it is the resistor causing the harshness. Maybe this is why Polk tried to tweak this part of the xover circuit. (Isolated the tweeter may sound better without the jumper, but the jumper is required for the tweeter to "blend" properly with the other speakers.)

Above explains why a few of us do not have jumpers. I would expect the "tweaking" would have been something done during early production of the 1.2 TL's. Yet also I would expect tweeks to be done in the lab. I would think if Polk decided against any tweeks, units sold would have the jumper installed. I guess they had decided to go with the tweak (remove jumper), yet it was a awhile later before they decided against the tweak and reinstalled the jumper.

Thanks again,
Rich

dorokusai

Polk Audio has always supported the vintage era loudspeakers and as far as I know, will continue to do so.

I did it moreso to ensure you weren't passing out misinformation. I'm sure that some loudspeakers went out the door with a problem or so, **** happens. I don't try to re-invent the wheel when I upgrade vintage gear and have also run across an anomaly or two in my travels....and 40 or so SDA's that I've owned.

If it sounds better after the changes, good for you, enjoy. I'll post whatever additional information they email me when I receive it.

thejck

Bring back this thread from the dead..I came across this when trying to troubleshoot a crossover issue.. Did we ever reach a consensus as to which way is better?

Is having the 22.5 resistor parallel with the 12uf cap for T3 a good thing or a bad thing. According to the circuit diagram from the model speaker thats the way it should be.
But then I read the possibility that polk excluded this intentionally to improve the sound. If the resistor does not need to be in parallel with the cap would removing it from the board serve the same purpose?

was this discussion continued elsewhere?

RichCanDo

I preferred the sound without the jumper, but left it installed. It seems most have the jumper so I assume that it is as it should be. Leaving the jumper out may effect the circuit in other ways. - At the moment the speakers are in storage. - Maybe others have tried with and without the jumper and will comment.