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Rauland-Borg TAC125 into 4 ohm Cab?
Jay Stephen:
I have an old but working Rauland-Borg ("Webster") SS amp that I'd like to use as a subwoofer amp driving a 2x15 4 ohm cab. The amp has 70V and 25V output options. I believe the correct formula to arrive at output impedance is Output Voltage squared divided by nameplate output watts = speaker ohms.
So in my case, 25 squared divided by 125 = 5 ohms.
My cabinet is 4 ohms and I know I could open it up and put the 2- 15's in series (16 ohms) but should I "cheat" and leave the cab at 4 ohms? Or, is there another workaround other than to go the series route?
Thanks.
Keith Broughton:
--- Quote from: JayZ on March 04, 2018, 07:10:37 AM ---I have an old but working Rauland-Borg ("Webster") SS amp that I'd like to use as a subwoofer amp driving a 2x15 4 ohm cab. The amp has 70V and 25V output options. I believe the correct formula to arrive at output impedance is Output Voltage squared divided by nameplate output watts = speaker ohms.
So in my case, 25 squared divided by 125 = 5 ohms.
My cabinet is 4 ohms and I know I could open it up and put the 2- 15's in series (16 ohms) but should I "cheat" and leave the cab at 4 ohms? Or, is there another workaround other than to go the series route?
Thanks.
--- End quote ---
I'm sure you will get some helpful advice once you use your real name as per forum rules.
Jay Stephen:
Re-posted. Apparently someone doesn't like me using the nickname I have had for many years. "I have an old but working Rauland-Borg ("Webster") SS amp that I'd like to use as a subwoofer amp driving a 2x15 4 ohm cab. The amp has 70V and 25V output options. I believe the correct formula to arrive at output impedance is Output Voltage squared divided by nameplate output watts = speaker ohms.
So in my case, 25 squared divided by 125 = 5 ohms.
My cabinet is 4 ohms and I know I could open it up and put the 2- 15's in series (16 ohms) but should I "cheat" and leave the cab at 4 ohms? Or, is there another workaround other than to go the series route?
Thanks."
Keith Broughton:
--- Quote from: Jay Stephen on March 04, 2018, 10:57:59 AM ---Re-posted. Apparently someone doesn't like me using the nickname I have had for many years. "I have an old but working Rauland-Borg ("Webster") SS amp that I'd like to use as a subwoofer amp driving a 2x15 4 ohm cab. The amp has 70V and 25V output options. I believe the correct formula to arrive at output impedance is Output Voltage squared divided by nameplate output watts = speaker ohms.
So in my case, 25 squared divided by 125 = 5 ohms.
My cabinet is 4 ohms and I know I could open it up and put the 2- 15's in series (16 ohms) but should I "cheat" and leave the cab at 4 ohms? Or, is there another workaround other than to go the series route?
Thanks."
--- End quote ---
A couple of points...
What is the actual power rating of the amp?
If there is a 70 and 25 volt output, there is probably a transformer on the output and that could be bypassed for a 4 ohm load.
Most of the 70 volt amps I have seen are relatively low powered and may not be suitable for sub applications.
Jay Stephen:
Thanks. The power output appears to be 125 watts RMS. I used it on a cabinet with 2x12 16ohms and you are correct, it is pretty low power but it was sufficient for my purpose. Unfortunately I haven't been able to locate a schematic but I'd be interested in knowing how to bypass the output transformer and use it on the 4 ohm cabinet.
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