Parts List for Upgrading Polk Model/Monitor 7A's
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I am looking to upgrade my 1978 Polk Model 7A's. I bought them used ~ 2 years ago. I have searched the forum and found some info, but I am in search of;
1. A concise parts list for cap's and resistors
2. I am looking for the best brands available, not necessarily the most expensive but if that is what it takes, that's okay.
3. Anything else I might need to freshen up my Polk 7A's.
Here is what I have for parts so far.
Capacitors
12 µF Capacitor (Tweeter circuit): Typically a 100VDC (or higher) film/mylar capacitor. Both Sonic Craft and Clarity Cap has them that are 200V and 250V respectively. Is that voltage okay?
34 µF Capacitor (Mid-woofer shunt circuit): Typically a 50VAC non-polar electrolytic. Sonicap has this; Gen I Sonicap 34 uF 200VDC - is this voltage okay?
Resistors
4.7 Ohm Resistor: Usually a 5-watt or 10-watt cement wirewound resistor from the factory.
Sonicap has 4.7 Ohm Mills MRA-5 or the 4.3 Ohm Mills MRA-12. Which one is better?
I also have a pair of Polk Model 5's (1982, original owner) and they sound a little cleaner in the mids and highs than the 7A's which is what sent me on this journey. Thanks so much for your help!
1. A concise parts list for cap's and resistors
2. I am looking for the best brands available, not necessarily the most expensive but if that is what it takes, that's okay.
3. Anything else I might need to freshen up my Polk 7A's.
Here is what I have for parts so far.
Capacitors
12 µF Capacitor (Tweeter circuit): Typically a 100VDC (or higher) film/mylar capacitor. Both Sonic Craft and Clarity Cap has them that are 200V and 250V respectively. Is that voltage okay?
34 µF Capacitor (Mid-woofer shunt circuit): Typically a 50VAC non-polar electrolytic. Sonicap has this; Gen I Sonicap 34 uF 200VDC - is this voltage okay?
Resistors
4.7 Ohm Resistor: Usually a 5-watt or 10-watt cement wirewound resistor from the factory.
Sonicap has 4.7 Ohm Mills MRA-5 or the 4.3 Ohm Mills MRA-12. Which one is better?
I also have a pair of Polk Model 5's (1982, original owner) and they sound a little cleaner in the mids and highs than the 7A's which is what sent me on this journey. Thanks so much for your help!
Best Answers
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Tried and true method is always going to be to remove your crossovers and read the values off of them. You should do this because I'm not sure if you have 4.7 Ohm or 4.5 Ohm series tweeter resistor. My later 1979 fairly early 7B have 4.5 Ohm. As far as I know, all 7's have the 2.7 Ohm tweeter shunt resistor (parallel to tweeter).
You want to go with, as a minimum, wirewound, non-inductive, higher power rating (like 10W or 12W). I did Vishay-Mills 12W. If you wanted to splurge there are more expensive film type or other types.
Lots of people have saved money on the caps by going with Clarity Cap CSA, but you will have to choose 33uF since they don't have 34uf. I went with Sonicap 34uf. Again you can go higher end than these but selections are somewhat limited, for the MW cap especially. You won't find 50V or 100V. Everything you consider will be 200V or more. Higher voltage has disadvantage of being larger in size, especially with these film caps.
George / NJ
Polk 7B main speakers, std. mods+ (1979, orig owner)
Martin Logan Dynamo sub w/6ft 14awg Power Cord
Onkyo A-8017 integrated
Logitech Squeezebox Touch Streamer w/EDO applet
iFi nano iDSD DAC
iPurifier3
iDefender w/ iPower PS
Custom Steve Wilson 1m UPOCC Interconnect
iFi Mercury 0.5m OFHC continuous cast copper USB cable
Custom Ribbon Speaker Cables, 5ft long, 4N Copper, 14awg, ultra low inductance
Custom Vibration Isolation Speaker Stands and Sub Platform -
As long as the voltage rating is equal to or higher than the original you're good.
Do not change the ohm value of a resistor, but in this case it's ok to go with a higher wattage rating.
Here's some reading for you. His observations are pretty much spot on.
https://www.humblehomemadehifi.com/Cap.htmlPolitical Correctness'.........defined
"A doctrine fostered by a delusional, illogical minority and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a t-u-r-d by the clean end."
President of Club Polk
