I just pruchased a used D150A and downloaded the service manual from this site, but I'm a little confused. Is it safe to run the D150A at 4ohms per side? I've got four 8 ohm 10" speakers rated at 120watts each, and I'm going to run two of them per side with the D150A in mono mode. If I configue a pair of these speakers in series, they will be 16 ohms and the amp will run them at about 65watts per side. I've also seen a rating of 90watts at 4ohms in the service manual but it doesn't seem to recommend this set up, and I'm not clear if it means 8 ohms per side or 4 ohms per side.

If I configure a pair of 8 ohm speakers in parallel they will be 4 ohms, can I safely run two 4 ohm loads on the outputs of the D150A in mono mode? I'd like to run this configuation if possible in order to gain the additional power from the amp, but I'm not clear that the D150A is rated to run that way.

**1**

# D150A, what cabinets?

Started by oldfclefer, Aug 11 2005 05:00 AM

5 replies to this topic

### #1

Posted 11 August 2005 - 05:00 AM

### #2

Posted 11 August 2005 - 04:17 PM

QUOTE(oldfclefer @ Aug 11 2005, 05:00 AM)

I just pruchased a used D150A and downloaded the service manual from this site, but I'm a little confused. Is it safe to run the D150A at 4ohms per side? I've got four 8 ohm 10" speakers rated at 120watts each, and I'm going to run two of them per side with the D150A in mono mode. If I configue a pair of these speakers in series, they will be 16 ohms and the amp will run them at about 65watts per side. I've also seen a rating of 90watts at 4ohms in the service manual but it doesn't seem to recommend this set up, and I'm not clear if it means 8 ohms per side or 4 ohms per side.

If I configure a pair of 8 ohm speakers in parallel they will be 4 ohms, can I safely run two 4 ohm loads on the outputs of the D150A in mono mode? I'd like to run this configuation if possible in order to gain the additional power from the amp, but I'm not clear that the D150A is rated to run that way.

If I configure a pair of 8 ohm speakers in parallel they will be 4 ohms, can I safely run two 4 ohm loads on the outputs of the D150A in mono mode? I'd like to run this configuation if possible in order to gain the additional power from the amp, but I'm not clear that the D150A is rated to run that way.

Mono mode is Bridge-Mono Mode. Bridge-Mono Mode takes both sides of the amplifier, combines them, and makes a bigger Mono (single channel) amplifier. To do this the speakers would have to be connected to the positive output terminal of channel 1 and the positive output of channel 2. In Bridge-Mono the D150A was rated for an 8 ohm load. A four ohm rating was given in the service manual but was not recommended. Bridge-Mono connection is not an option for four 8 ohm speakers as this would actually be a 2 ohm load.

In two channel mode the D150 was rated for 95 watts per channel into an 8 ohm load and 155 watts per channel into 4 ohms.

You have four 8 ohm speakers (two per side) that would be a 4 ohm load per side. You don’t say if the speakers are rated each at 120 watts Continuous, Program or Peak.

If they were rated at Program Power the amplifier needed should be able to do around 240 watts per side with a 4 ohm load (for 3db of headroom to handle peaks in the signal source) and be in the power range of 192 to 288 watts If they were rated for 120watts Continuous each then the amplifier needed should be able to do around 480 watts per side with a 4 ohm load (for 3db of headroom to handle peaks in the signal source) and be in the power range of 384 to 576 watts.

In both Continuous and Program ratings the D-150 would fall shy of the power requirements. Even with just one of your speakers per side the amplifier would fall short for both Continuous and Program power as the D-150A is rated for only 95 watts/ch at 8 ohms.

### #3

Posted 12 August 2005 - 06:39 AM

Thanks for your prompt reply.

So if I run two of my 8 ohm speakers in series that makes 16 ohms with a 300w RMS rating (150w RMS ea. actually as it turns out), and I run both sets of two at 16 ohms, that means I have an 8 0hm load the D150A and will push about 75watts into each load. Is that correct?

I know that the speakers are rated higher than the amp, but I'm a bassist and I like to know that I've got room to push my rig at 100% if necessary. I'm using the D150A to amplify the high end of the bass spectum in a biamp system and 150 watts will be more than enough.

So if I run two of my 8 ohm speakers in series that makes 16 ohms with a 300w RMS rating (150w RMS ea. actually as it turns out), and I run both sets of two at 16 ohms, that means I have an 8 0hm load the D150A and will push about 75watts into each load. Is that correct?

I know that the speakers are rated higher than the amp, but I'm a bassist and I like to know that I've got room to push my rig at 100% if necessary. I'm using the D150A to amplify the high end of the bass spectum in a biamp system and 150 watts will be more than enough.

### #4

Posted 12 August 2005 - 10:59 AM

QUOTE(oldfclefer @ Aug 12 2005, 06:39 AM)

Thanks for your prompt reply.

So if I run two of my 8 ohm speakers in series that makes 16 ohms with a 300w RMS rating (150w RMS ea. actually as it turns out), and I run both sets of two at 16 ohms, that means I have an 8 0hm load the D150A and will push about 75watts into each load. Is that correct?

I know that the speakers are rated higher than the amp, but I'm a bassist and I like to know that I've got room to push my rig at 100% if necessary. I'm using the D150A to amplify the high end of the bass spectum in a biamp system and 150 watts will be more than enough.

So if I run two of my 8 ohm speakers in series that makes 16 ohms with a 300w RMS rating (150w RMS ea. actually as it turns out), and I run both sets of two at 16 ohms, that means I have an 8 0hm load the D150A and will push about 75watts into each load. Is that correct?

I know that the speakers are rated higher than the amp, but I'm a bassist and I like to know that I've got room to push my rig at 100% if necessary. I'm using the D150A to amplify the high end of the bass spectum in a biamp system and 150 watts will be more than enough.

If I get what you are saying you are looking at doing a series parallel combination with the speakers to get an 8-ohm load so you can operate the amplifier in Bridge-Mono.

In this Series/Parallel combination two groups of two speakers are combined in series creating two16-ohm subgroups. Connecting these subgroups in parallel produces a total load impedance of 600 watt/8-ohms to the amp.

With an 8 ohm load in Bridge-Mono the D150 A is rated for 315 watts output. That’s about 50v to the total load.

For parallel branches with equal impedance the available power to the speakers will divide out into the two branches equally.

In the series subgroups you would use Ohms Laws for each device in the series subgroup. Each speaker would have about 25 volts across it at full amplifier output. Using the power side of Ohms Law the Power to each device would be equal to the square of the Voltage across the device divided by the device Impedance.

So………… each 16 ohm series subgroup will have available to it about 157 watts and each speaker in that subgroup will get about 78 watts with a D-150A.

In this series parallel combination each device would be getting about the half power it could handle when the D150A is at full output. If you pushed the amplifier you could cause clipping and possibly damage the speakers. It is always better to have more power than to little because of the peaks in program material. Likewise in the case of a guitar the sustained notes can act very close to sine waves requiring more power from the amp to reproduce the note(s) extended period of time.

### #5

Posted 12 August 2005 - 11:17 AM

Thanks D.

That's the info I was after.

That's the info I was after.

### #6

Posted 29 September 2005 - 06:42 AM

QUOTE(oldfclefer @ Aug 11 2005, 06:00 AM)

I just pruchased a used D150A and downloaded the service manual from this site, but I'm a little confused. Is it safe to run the D150A at 4ohms per side? I've got four 8 ohm 10" speakers rated at 120watts each, and I'm going to run two of them per side with the D150A in mono mode. If I configue a pair of these speakers in series, they will be 16 ohms and the amp will run them at about 65watts per side. I've also seen a rating of 90watts at 4ohms in the service manual but it doesn't seem to recommend this set up, and I'm not clear if it means 8 ohms per side or 4 ohms per side.

If I configure a pair of 8 ohm speakers in parallel they will be 4 ohms, can I safely run two 4 ohm loads on the outputs of the D150A in mono mode? I'd like to run this configuation if possible in order to gain the additional power from the amp, but I'm not clear that the D150A is rated to run that way.

If I configure a pair of 8 ohm speakers in parallel they will be 4 ohms, can I safely run two 4 ohm loads on the outputs of the D150A in mono mode? I'd like to run this configuation if possible in order to gain the additional power from the amp, but I'm not clear that the D150A is rated to run that way.

Dude You can load that chicken down to almost a dead short.. If ya put it in the mono mode it will really put out at 4 ohms .I ran both of mine like that for years . KEEP IN MIND THO ,THAT IT WILL GET HOT ,SO PUT A FAN BEHIND IT SO THE THERMAL PROTECTION WONT ACTIVATE . OH YEA THE STEREO MODE WORKS GOOD AT 4 OHMS TOO .

YRs ago ,an Independent testing lab, took a DC300A (A bigger version) of the D150A ) They ran a 60 hertz signal to the inputs ,hooked a washing machine to the outputs ...washed a full load of clothes with it ,and said it never deviated from factory specs .So like... what more does anybody need to know see ya Sloan