NAD - HXDA 30 1x12 Combo in Paisley

[dmatthews]

My Boogie has a single 8 ohm output and 2 x 4 ohm outputs. The 4s are wired in series yielding 8 ohms. But I’ve run 2 x 8 ohm cabs thru it for years with no problems. That amp loves 16 ohm loads. The Super Dallas (based on the Anniversary’s power stage...same PT) has discrete 4, 8, and 16 ohm outputs with external cab jacks for all but 16 ohm. Those are in series...a pair of 8s yield 16 and a pair of 4s yield 8 ohm. If unsure, ask PRS.

Sounds similar to the HXDA, no?

 

[shinksma]

My Boogie has a single 8 ohm output and 2 x 4 ohm outputs. The 4s are wired in series yielding 8 ohms. But I’ve run 2 x 8 ohm cabs thru it for years with no problems. That amp loves 16 ohm loads. The Super Dallas (based on the Anniversary’s power stage...same PT) has discrete 4, 8, and 16 ohm outputs with external cab jacks for all but 16 ohm. Those are in series...a pair of 8s yield 16 and a pair of 4s yield 8 ohm. If unsure, ask PRS.

Sounds similar to the HXDA, no?

Yep, sounds similar. I'll fire off a quick email to PRS, see what they say. And when I get a chance (probably weeks from now!) I'm also going to take a multimeter to those jacks and see what is directly connected to what.

 

[shinksma]

But, while I review what was in the 25th Anniv manual, it states this bit:

This scenario could most commonly be the use of an 8 ohm extension speaker along with the internal speaker—connect each to the 4 ohm jacks since their combination produces a 4 ohm load.

Now that mention of the "internal speaker" is a little weird, because I don't recall seeing the 25th Anniv amps come in a combo form which is where you'd have an internal speaker.

But, it sounds to me like PRS changed the design of their pairs of output jacks to be in parallel, vs series for the Super Dallas, assuming Boogie's statement is accurate. But I will note that the Super Dallas amp manual says (total quote first):

Speaker Jacks: Get into the habit of checking these first. The jacks include a connection for 4, 8 and 16 ohm loads. There is an extension (EXT) included in parallel with the “speaker out” jack. Use the extension speaker jack for adding a like speaker load, being careful to calculate the total impedance for the two loads. For example, two 16 ohm loads would total 8 ohms and two 8 ohm loads would total 4 ohms. Do not connect an 8 ohm load along with a 4 ohm or 16 ohm load in the jack. This procedure halves the reflected impedance of each and will not allow ideal operating conditions. If you are using more than one speaker, they must be the same impedance. For example, use two 4-ohm speakers or two 8-ohm speakers. Never use two different speaker impedances - you should not mix and match. The maximum number of speakers you can safely connect is 2. Always ensure that the speaker impedance matches the correct impedance selection, since this amp is designed to be played “wide open.” Mismatching impedances from a lower tap to a higher speaker impedance stresses the amp more than going into a lower impedance mismatch and can cause arcs on the tube sockets, failure of power tubes, or even failure of the output transformer. Confirm that the speaker cabinet you are using matches to the correct speaker jack on the back of the amp. For the 4 OHM and 8 OHM speaker jacks, a second cabinet may be plugged into the “EXT” (Extension) cabinet. Note: The total speaker impedance must be determined before connecting to the speaker jacks.

In particular:

Use the extension speaker jack for adding a like speaker load, being careful to calculate the total impedance for the two loads. For example, two 16 ohm loads would total 8 ohms and two 8 ohm loads would total 4 ohms.

and

Note: The total speaker impedance must be determined before connecting to the speaker jacks.

To me, that sounds like the same situation as the HXDA - the pairs of outputs are in parallel. So if Boogie is running two 8-ohm speakers, he is actually presenting a total load of 4 ohms to the amp, when plugged into the pair of 8-ohm jacks. Which apparently is preferred over presenting too high a load, as dmatthews noted previously:

Mismatching impedances from a lower tap to a higher speaker impedance stresses the amp more than going into a lower impedance mismatch and can cause arcs on the tube sockets, failure of power tubes, or even failure of the output transformer.

Which seems to be what this bit says right before the above quote, also found in the other manual:

Always ensure that the speaker impedance matches the correct impedance selection, since this amp is designed to be played “wide open.”

So PRS designed the amp to push current, and it gets really grumpy if it can't push as much as it is configured for.

 

[shinksma]

Just heard back from PRS Customer Service (Thanks Matt!).

As I thought, the pairs of jacks are in parallel, and if I wanted to add an external cab I would move the 16 ohm internal speaker plug to the 8 ohm jack and then plug in a 16 ohm ext cab into the other 8 ohm jack.

i.e. speakers are parallel, total load should equal 4 or 8 ohms if using those pairs.

If I had just a single 8 ohm speaker, I would plug it into one of the 8 ohm speaker jacks (presumably not the one that says EXT, though I don't know if it really matters).

So I notice that PRS 2x12 cabs are always 8 ohm (at least, all the ones I have seen, both on the PRS site and in used classifieds etc), whereas the 1x12 is 16 ohm. And the 4x10s are 8 ohm, while the 4x12 is 16 ohm.

Obviously the 2x12s are therefore two 16 ohm speakers in parallel, and there is no way to reconfigure that to a 16 ohm load without swapping speakers.

Anyone ever come across a PRS 2x12 that was 16 ohm?

I suspect I'll be getting a 1x12 extension cab. Eventually...

 

[dmatthews]

Just heard back from PRS Customer Service (Thanks Matt!).

As I thought, the pairs of jacks are in parallel, and if I wanted to add an external cab I would move the 16 ohm internal speaker plug to the 8 ohm jack and then plug in a 16 ohm ext cab into the other 8 ohm jack.

i.e. speakers are parallel, total load should equal 4 or 8 ohms if using those pairs.

If I had just a single 8 ohm speaker, I would plug it into one of the 8 ohm speaker jacks (presumably not the one that says EXT, though I don't know if it really matters).

So I notice that PRS 2x12 cabs are always 8 ohm (at least, all the ones I have seen, both on the PRS site and in used classifieds etc), whereas the 1x12 is 16 ohm. And the 4x10s are 8 ohm, while the 4x12 is 16 ohm.

Obviously the 2x12s are therefore two 16 ohm speakers in parallel, and there is no way to reconfigure that to a 16 ohm load without swapping speakers.

Anyone ever come across a PRS 2x12 that was 16 ohm?

I suspect I'll be getting a 1x12 extension cab. Eventually...

Perfect! Glad you got the right info for your amp. I'll be interested to learn more about how/why PRS states that an equal or greater impedance is worse than equal to lesser.
This is what I was taught...
https://music.stackexchange.com/que...-amplifier-output-with-a-16-ohm-cabinet#31160

http://www.tdpri.com/threads/running-a-16-ohm-speaker-to-a-8-ohm-output.455392/

Or response #3 here
http://www.tdpri.com/threads/min-8-ohm-into-a-16-ohm-cabinet.620860/

But as we all know, you learn something new every day, and I'm all ears!

 

[Boogie]

But, it sounds to me like PRS changed the design of their pairs of output jacks to be in parallel, vs series for the Super Dallas, assuming Boogie's statement is accurate.

Your logic is fairly sound, except for when you look at the 4 ohm jacks: parallel wiring would yield a 2 ohm load that is simply not a tap on that transformer. So, even if the the 8 ohm jacks are wired in parallel, the 4 ohm should not. That’s the operative term...should. My amp is a CAD creation and has several customizations so it may not be representative of the norm or average PRS config. To know for sure, you have to open the amp and trace the wiring.

 

[shinksma]

Your logic is fairly sound, except for when you look at the 4 ohm jacks: parallel wiring would yield a 2 ohm load that is simply not a tap on that transformer. So, even if the the 8 ohm jacks are wired in parallel, the 4 ohm should not. That’s the operative term...should. My amp is a CAD creation and has several customizations so it may not be representative of the norm or average PRS config. To know for sure, you have to open the amp and trace the wiring.

I think the amp is not intended to have two 4-ohm speakers plugged in. The 4 ohm jacks would be used by two 8 ohm speakers, or just one 4 ohm speaker. The 8 ohm jacks are used by two 16 ohm speakers, or just one 8 ohm speaker, and the single 16 ohm jack is for one 16 ohm speaker.

 

[Deleted member 5962]

Perfect! Glad you got the right info for your amp. I'll be interested to learn more about how/why PRS states that an equal or greater impedance is worse than equal to lesser.
This is what I was taught...
https://music.stackexchange.com/que...-amplifier-output-with-a-16-ohm-cabinet#31160

http://www.tdpri.com/threads/running-a-16-ohm-speaker-to-a-8-ohm-output.455392/

Or response #3 here
http://www.tdpri.com/threads/min-8-ohm-into-a-16-ohm-cabinet.620860/

But as we all know, you learn something new every day, and I'm all ears!

Me too. I've always read that you can go higher with the speakers/load than what the amp output is, but not lower unless expressly stated by the designer. This is news to me too. I have a "little above average" understanding of this stuff... but obviously not enough to grasp this concept... hmmm

 

[dmatthews]

Me too. I've always read that you can go higher with the speakers/load than what the amp output is, but not lower unless expressly stated by the designer. This is news to me too. I have a "little above average" understanding of this stuff... but obviously not enough to grasp this concept... hmmm

Yup...
I gotz no problem being wrong, I just wantz to know why!

 

[dsenoj]

I think the amp is not intended to have two 4-ohm speakers plugged in. The 4 ohm jacks would be used by two 8 ohm speakers, or just one 4 ohm speaker. The 8 ohm jacks are used by two 16 ohm speakers, or just one 8 ohm speaker, and the single 16 ohm jack is for one 16 ohm speaker.

This matches my understanding from the manual.

I've wondered whether I could use my PRS 2x12 cabinet with my Sweet 16 and Archon 25 combos. The combos have a 16 ohm 12" speaker while the 2x12 is 8 ohms. Normally I think it would be a bad idea to use a 16 ohm speaker in parallel with an 8 ohm cabinet. But since the 2x12 is two 16 ohm 12" speakers in parallel, I'd effectively have three 12" 16 ohm speakers in parallel giving a 5.3 ohm load. It seems like I should be able to use this and select a 4 ohm load on the amp. I'll email PRS before I actually try this though.

 

[shinksma]

This matches my understanding from the manual.

I've wondered whether I could use my PRS 2x12 cabinet with my Sweet 16 and Archon 25 combos. The combos have a 16 ohm 12" speaker while the 2x12 is 8 ohms. Normally I think it would be a bad idea to use a 16 ohm speaker in parallel with an 8 ohm cabinet. But since the 2x12 is two 16 ohm 12" speakers in parallel, I'd effectively have three 12" 16 ohm speakers in parallel giving a 5.3 ohm load. It seems like I should be able to use this and select a 4 ohm load on the amp. I'll email PRS before I actually try this though.

Hmm. Electrical-circuit-wise, your theory looks sound. But they seem to recommend against this. If you put two 2x12 ext speaker cabs that were 8 ohms each into the 4 ohm jacks, you'd be loading the amp correctly. And that would just happen to be four 16 ohm speakers in parallel. Hmm.

I am curious what they might say - the only thing I can think of is the bit where they say to not present too high a load for the desired impedance, and maybe 5.3 is too high for 4, even if the actual impedance at any one time might vary drastically from that nominal value due to frequency content of the signal provided.

 

[Deleted member 5962]

Yup...
I gotz no problem being wrong, I just wantz to know why!

Me too. Well, I have a problem with being wrong. That's why I stated that I only had a little above average knowledge. When it comes to this stuff, there are plenty of things I "know" and plenty of things I have some understanding but not enough that there can be different answers. What interests me about this particular one is, I've been messing with, modding, building, playing electronics since I was a teenager, and this is the first time I've heard this. I'm more interested in WHY it's the case, since it's certainly not the norm.

 

[Deleted member 5962]

Hmm. Electrical-circuit-wise, your theory looks sound. But they seem to recommend against this. If you put two 2x12 ext speaker cabs that were 8 ohms each into the 4 ohm jacks, you'd be loading the amp correctly. And that would just happen to be four 16 ohm speakers in parallel. Hmm.

I am curious what they might say - the only thing I can think of is the bit where they say to not present too high a load for the desired impedance, and maybe 5.3 is too high for 4, even if the actual impedance at any one time might vary drastically from that nominal value due to frequency content of the signal provided.

If you've ever seen a real impedance chart on a speaker, it's much different than most would think. The guy from Celestion who posts at TGP one time put up a chart of a particular Celestion speaker to indicate just how "nominal" that rating is. An 8 ohm speaker was (while back, trying to remember, but...) over 13 ohms at some frequencies. Resonant peaks are a whole nother thang, and then the speakers environment (cab... sealed, ported, open back, cab size etc.) all affect it's damping and how that reflects back to the OT... blah blah blah... sorry for rambling

 

[shinksma]

If you've ever seen a real impedance chart on a speaker, it's much different than most would think. The guy from Celestion who posts at TGP one time put up a chart of a particular Celestion speaker to indicate just how "nominal" that rating is. An 8 ohm speaker was (while back, trying to remember, but...) over 13 ohms at some frequencies. Resonant peaks are a whole nother thang, and then the speakers environment (cab... sealed, ported, open back, cab size etc.) all affect it's damping and how that reflects back to the OT... blah blah blah... sorry for rambling

Indeed, that's what I meant! Here is the freq response and impedance vs freq char Eminence has for one of their typical speakers (Legend 1275):

http://www.eminence.com/speakers/speaker-detail/?model=Legend_1275

You can see the big wall-o-impedance at 110 Hz or so, and the wobbly response growing from 8 ohms to ~27 ohms from 400 Hz through 6 kHz (at which point it the sensitivity is getting too low to matter).

 

[dmatthews]

Everybody's geeking!

 

[Boogie]

Here’s some affirmation.
I stand corrected. The 4 ohm jacks (on the left)are, indeed, wired in parallel, as are the 8 ohm (middle pair). PRS does it differently from Mesa/Boogie on the Mark series, which should come as no surprise. I’ve only ever used the 16 ohm and a single 8 ohm.

 

[László]

I’m stupid, so I keep it simple. One cab.

And even then sometimes I plug into the wrong jack on the amp.

 

[Deleted member 5962]

I used to have all 1x12 cabs so I could mix and match speakers to taste. Now I have two 2x12 cabs, the PRS pine and the Mesa vertical recto cab, plus 5 other 1x12 cabs with various speakers. I just got a Thiele cab with Celestion C90. Might get a Warehouse 12L for that. Right now it's stacked under a 1x12 recto V30 cab and the Mark V25. That stack sounds nice and I want to try it with the Archon.

I wandered off topic. Somebody help me find my way back.

 

[shinksma]

Here’s some affirmation.
I stand corrected. The 4 ohm jacks (on the left)are, indeed, wired in parallel, as are the 8 ohm (middle pair). PRS does it differently from Mesa/Boogie on the Mark series, which should come as no surprise. I’ve only ever used the 16 ohm and a single 8 ohm.

Thanks Boogie! Nicely detailed shot.

Looks like a soldering iron got a little too close to the upper left corner of the far left jack housing!

 

[László]

Looks like a soldering iron got a little too close to the upper left corner of the far left jack housing!

They do that so you know a machine didn’t make it.