Report_Polk 1B refurbish

75.166.173.131

Posted on September 1, 2021 at 09:41:45

walkstoslow
Audiophile

Posts: 277
Joined: November 18, 2012

hello inmates,
per suggestions,
finally finished refurbishing of 35 year old speakers.
Things discovered:
MDF does not age well, while removing drivers I noticed that the Mdf was
nothing but dust as the screws came out.
Thus I drilled the holes out and inserted t-nuts in each mounting hole,
32 per side.
I used the original Polk x-over design.
I Built 3 cross-over sections, isolated from each other, mounted everything on foam pads,on the back of the cabinet, easy to modify if I want.
The hi-pass cross over section had different value resistors,3, 2.5 ohm on one side and 3, 7.5 ohm on the other.
The low pass section was identical and per schematic.
I changed from 34uf electrolytic to 34uf polypropylene caps in the stereo mid- woofers, and lastly I changed the 9.6uf air coils to Erse steel core with half the resistance, on the mid woofers SDA side.
New internal wire, 28awg to tweeters, 14 awg to mid woofers.
I added a brace at the mid point between the tweeters, rear to front baffle.
The speakers are suppose to be mirror images of each other, the polyfill
on one side did not match the other.
Everything is burning in, speakers sound a bit cleaner, imaging seems better, time will tell.
This was a lot of work.
A labor of love....nearly 3 weeks...could not afford to pay someone for this work!

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RE: Report_Polk 1B refurbish

SoundMann

13:20:15 11/28/21

RE: Report_Polk 1B refurbish

sbrook

09:59:46 09/01/21

Pic 4

walkstoslow

13:15:37 09/01/21

...

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RE: Report_Polk 1B refurbish

SoundMann

13:20:15 11/28/21

RE: Report_Polk 1B refurbish

sbrook

09:59:46 09/01/21

Pic 4

walkstoslow

13:15:37 09/01/21

Pic 2

walkstoslow

13:01:53 09/01/21

Pic 1

walkstoslow

12:59:44 09/01/21

RE: Report_Polk 1B refurbish

walkstoslow

10:17:47 09/01/21

RE: Report_Polk 1B refurbish

Coner

11:44:24 09/02/21

which model do you prefer?

walkstoslow

13:06:03 09/02/21

RE: which model do you prefer?

Coner

20:04:30 09/02/21

RE: which model do you prefer?

Schurkey

14:14:10 09/27/21

RE: which model do you prefer?

Schurkey

09:32:18 09/28/21

RE: Report_Polk 1B refurbish

walkstoslow

12:48:23 09/02/21

RE: Report_Polk 1B refurbish

Coner

12:58:21 09/02/21

RE: Report_Polk 1B refurbish

walkstoslow

13:08:31 09/02/21

RE: Report_Polk 1B refurbish

Coner

13:28:06 09/02/21

sit back, take a break and have a beer

Story

09:48:45 09/01/21

RE: sit back, take a break and have a beer

walkstoslow

09:53:10 09/01/21

sit back, take a break and have a beer, posted on September 1, 2021 at 09:48:45
Story Audiophile Posts: 10459 Location: NJ Joined: December 11, 2000	that sounds like a lot of work, now break them in.

RE: sit back, take a break and have a beer, posted on September 1, 2021 at 09:53:10
walkstoslow Audiophile Posts: 277 Joined: November 18, 2012	yes sir, I missed my music something terrible while doing this.... listening to a selection of CTI cd's now.

RE: Report_Polk 1B refurbish, posted on September 1, 2021 at 09:59:46

sbrook
Audiophile

Posts: 232
Location: Florida
Joined: November 3, 2004

Good to hear that they are still viable. A little disappointing to learn of the internal inconsistencies in the build of what was a flagship product from the heyday of Polk as a serious speaker company punching above its weight class. Buddy of mine still has my dad's old SDA Compacts (with factory stands) from the 80's and they are still fine for his needs. The Monitor 10B was my first "real" set of speakers. Still kind of miss them.

Would love to see some pics of your 1B's...

RE: Report_Polk 1B refurbish, posted on September 1, 2021 at 10:17:47

walkstoslow
Audiophile

Posts: 277
Joined: November 18, 2012

Yes, I was very surprised, about the cross over values, I understand that
too much business is bad business. Polk was definitely busy.
I am thinking that "Polk" suffered from Supply chain problems too.
I would whole heartedly let your friend know what I found, I inherited these speakers from my 91 year old mother in-law 4 years ago.
I also thought they sounded nice, wish I would have taken a look inside then.
Much better sounding now....

Pic 1, posted on September 1, 2021 at 12:59:44
walkstoslow Audiophile Posts: 277 Joined: November 18, 2012	Can't seem to post all at once

Pic 2, posted on September 1, 2021 at 13:01:53
walkstoslow Audiophile Posts: 277 Joined: November 18, 2012	another one

Pic 4, posted on September 1, 2021 at 13:15:37
walkstoslow Audiophile Posts: 277 Joined: November 18, 2012	last one

RE: Report_Polk 1B refurbish, posted on September 2, 2021 at 11:44:24
Coner Audiophile Posts: 3703 Location: S.W. Washington state, USA Joined: November 17, 2001	I have that same model here, as well as the smaller one with three 6" drivers, not 4.

RE: Report_Polk 1B refurbish, posted on September 2, 2021 at 12:48:23

walkstoslow
Audiophile

Posts: 277
Joined: November 18, 2012

I messed up,
initially used 14awg on the tweeters, the wire is so stiff the terminal on the the tweeter disconnected from the tweeter coil I think.
This happened on 2 of the 4 tweeters.
I was able to buy two good tweeters on e bay.
I should get them tomorrow.
The other two tweeters I connected with 28 awg, they seem to be working fine, the original cable was 16awg I think.
I have soldered coil leads to tweeter terminals in my early years when my eyes were better.
I have not figured out how to get the tweeters apart yet, some strange, "X" driver or something, have you any experience with this problem?
Suggestions would be helpful...
I think the use of t nuts made a huge difference in the sound of these speakers, very "solid", my speakers were actually 2 rights instead of right and left, I fixed that.
Stage seems better right to left...listening last night with only one tweeter per side, I was definitely hearing more detail..
thanks for listening..

RE: Report_Polk 1B refurbish, posted on September 2, 2021 at 12:58:21
Coner Audiophile Posts: 3703 Location: S.W. Washington state, USA Joined: November 17, 2001	I would not bother with a tweeter repair...if it is just a terminal wire, then okay, but the later version Peerless cloth dome is said to be an upgrade.

which model do you prefer?, posted on September 2, 2021 at 13:06:03
walkstoslow Audiophile Posts: 277 Joined: November 18, 2012	which model do you like better? I am an old "fullrange" kind of guy,less parts more efficient the better. this multi driver speakers are a different animal,,, I have a 1938 GE AM/Short wave floor standing radio with a fullrange 18" speaker, i feed the 6v6 amp with a mono input from a cd player, magical sound..open back maybe 2" off the wall...

RE: Report_Polk 1B refurbish, posted on September 2, 2021 at 13:08:31
walkstoslow Audiophile Posts: 277 Joined: November 18, 2012	thanks for the advice...

RE: Report_Polk 1B refurbish, posted on September 2, 2021 at 13:28:06
Coner Audiophile Posts: 3703 Location: S.W. Washington state, USA Joined: November 17, 2001	If there's a Polk forum at their site, it would have all kinds of tweeter upgrade info. Could be there's just a knockoff model avail.

RE: which model do you prefer?, posted on September 2, 2021 at 20:04:30
Coner Audiophile Posts: 3703 Location: S.W. Washington state, USA Joined: November 17, 2001	Well I'm just re-selling them, I don't have any preference, really. They don't do deep bass at all, they must have been optimistic on the spec sheet.

RE: which model do you prefer?, posted on September 27, 2021 at 14:14:10

Schurkey
Audiophile

Posts: 121
Location: The Seasonally Frozen Wastelands
Joined: May 14, 2015

1. Something is wrong if you're not getting deep bass out of a Polk SDA 1B.

Common problems are air leaks in the cabinet, screwed-up, ancient caps in the crossover, or the polyfill having dropped-down in the cabinet over time. Lift the polyfill back up where it belongs--not hanging down into the area behind the bassive radiator. And make sure they're wired correctly, not out-of phase with each other.

2. Polk does have a forum; you're looking for the "Vintage Speakers" section.
https://forum.polkaudio.com/categories/vintage-speakers

3. The original tweeter from the 1B and similar-age Polk speakers is the SL2000. The SL2000 has been replaced by the RD-0194-1, it's a drop-in, no-modification upgrade which does not have the resonance at 11--12K. Polk is sort-of still selling the '194s; I ordered two from Polk Customer Service last week. Supposedly, I got the "last two" in stock. Later that day, another guy posted that he'd contacted Polk CS, and HE'd gotten the "last two". They've been selling the Last Two to various people for months. I do NOT understand, and I still have a week to go before "mine" should arrive--so I'm a little nervous.

4. The mid-woofer magnets are attached to the speaker frame with glue. Over time, the glue bond has a history of failure. Guys are using epoxy or construction adhesive blorted around the outside of the magnet where it contacts the pole piece and the speaker basket, to prevent magnet shift. Easy to apply BEFORE the glue actually fails. Once the original glue fails, the magnet and voice coil shifts, locking-up the driver. They can be cleaned, re-aligned and re-glued using anaerobic thread locking compound (Loctite 271 or similar) or other thin-bodied adhesive, but it's a pain in the tuckus.

I did some of the modifications to my 1Bs perhaps ten years ago--fresh film caps instead of electrolytics, replaced the upper tweeters with the updated ones, added the ERSE steel-core inductors for the SDA circuit, lifted the polyfill, and made sure the cabinets were reasonably air-tight (there's always some leakage out the voice-coils and dust-caps of the mid-woofers).

Those speakers are real sweethearts with the singular problem that they cannot be used with non-common-ground amplifiers. My amplifier had 20 ohms resistance between the negative terminals of the two channels, (Partial Non-Common Ground) and that 20 ohms made them sound unlistenable. I poked a jumper wire with banana ends into the negative terminals of the two channels, and instant bliss. The jumper wire CANNOT be used with "balanced" or "bridged" amplifiers, you'll blow 'em up.

RE: which model do you prefer?, posted on September 28, 2021 at 09:32:18

Schurkey
Audiophile

Posts: 121
Location: The Seasonally Frozen Wastelands
Joined: May 14, 2015

Stuff I forgot, and just remembered.

You should have a 2-ohm resistor, and two 2.7-ohm resistors per high-frequency crossover (one per cabinet.)

In actual listening, I prefer to replace the 2-ohm resistor with a lower value. 1.8 ohm works well. This will boost the level of the tweeters, makes the speakers a bit brighter. May not be a benefit in all situations, in all rooms, and for all ears. But brighter is a definite benefit for me.

The 2.7 ohm resistors value is fine as-is.

There's many brands of "audiophile" resistors, but "Mills" are a good value and fine performance. They fit the original circuit boards better than the big, ceramic-block resistors, for those who don't build their own circuit boards.

I think someone was messing with your crossovers before you got to them.

The silver-dipped mica 750 pF capacitors can be eliminated when better (modern film) caps are used in place of the original Mylar and electrolytics.

Most guys remove the "Safetyguard" tweeter protection device. Every time they trip...they degrade. Some add a low-value (1/2 ohm or less) resistor in it's place. I used jumper wire.

https://us.v-cdn.net/5021930/uploads/attachments/1/8/5/1/1/31011.pdf

RE: Report_Polk 1B refurbish, posted on November 28, 2021 at 13:20:15
SoundMann Audiophile Posts: 588 Joined: October 21, 2015	I have a set of 2B's that I have modified in various ways. New caps, resistors and tweeters primarily. I don't like the official replacement tweeter which rings, and therefore are fatiguing. I replaced them with 2500's out of the last monitor series.

Speaker Asylum

Report_Polk 1B refurbish

75.166.173.131