Newbie: Max Power for Dynaco A-25?

[Brewdawg]

First post from newbie. After years of primarily using bluetooth & Bose Waves, preceded by middling surround systems, I craved a simple basic vintage setup for my home office- the way I listened to music in the 70's. Started researching "best" vintage speakers, and kept finding all the love for A-25's- much of it from this forum. So I found a near mint pair locally, and got a Sony STR-DH190. Yeah, it's not vintage, but I wanted the ability to play about 6,000 mp3's conveniently. And the Sony was the lowest cost with phono input to allow me resurrect my vinyl collection.

Anyway, I absolutely love the A-25's, really enjoying them, and they're better than I'd anticipated. But I know they can't handle 90wpc, so I'm asking how I can "safely" limit the power I use. It makes me nervous to start really cranking up the power on 50 year old speakers. So far, I've only briefly gone to about 50 on the receiver. How do you guys know how much power to apply to speakers rated lower than the power of the source?

I saw this in the 1975 Dynaco catalog. Should I install some sort of fusing to protect them when my IPA level gets too high, and I'm having too much fun?

 

[spark1]

The preferred method is judicious use of the volume control on your amp, combined with using your ears to warn you when the speakers are straining.

If this method will not meet your needs, here is a formula for calculating fuse value:

Square root of (desired wattage limit divided by 4x the rated impedance of the speaker).

Use a fast blow fuse, or consider use of a polyswitch.

BTW, if you are running an amp at more than 10-15% of its rated power on a sustained basis, it is almost assuredly clipping (distorting) the signal going to the speakers.

9 watts of continuous power into those speakers, assuming an 8-10 foot listening distance = approximately 92dB of output, with peaks over 100dB. That is VERY LOUD.

They can handle it (altho probably with some noticeable compression distortion), but your ears cannot.

 

[Brewdawg]

The preferred method is judicious use of the volume control on your amp, combined with using your ears to warn you when the speakers are straining.

If this method will not meet your needs, here is a formula for calculating fuse value:

Square root of (desired wattage limit divided by 4x the rated impedance of the speaker).

Use a fast blow fuse, or consider use of a polyswitch.

BTW, if you are running an amp at more than 10-15% of its rated power on a sustained basis, it is almost assuredly clipping (distorting) the signal going to the speakers.

9 watts of continuous power into those speakers, assuming an 8-10 foot listening distance = approximately 92dB of output, with peaks over 100dB. That is VERY LOUD.

They can handle it (altho probably with some noticeable compression distortion), but your ears cannot.

Okay, so the catalog says recommended 20-60W. If I wanted to limit them to 60, it'd be 8ohm, so 60/32 = 1.875. Sq. root is 1.37, so I'd get a fuse rated near that.
But after researching a little, I'm realizing fusing it is not a great idea. Not too foolproof, or even really advisable- especially for someone of my knowledge and electronics capabilities.
But I do appreciate the response!

 

[Dswankey]

.... finding all the love for A-25's...I found a near mint pair locally, and got a Sony STR-DH190......... I know they can't handle 90wpc... So far, I've only briefly gone to about 50 on the receiver.

Just my 2 cents, but I think you are over thinking this, you mention you are utilizing the speakers in a home office set up if so how loud are you actually listening to?

Most folks who aren't aware or don't know would be very surprised to learn how many wpc they are actually utilizing when listening at moderate levels.

I know and have read folks using 12 to 35 WPC tube amps.

Not knowing your particular receiver my guess is at the 9 o'clock position or even 12 o"clock position (based on 6 o'clock being no volume) on the volume dial you're not coming anywhere close to 60 and or 90 wpc

Curious, how did you determine that you'd briefly gone to about 50 wpc?

 

[Brewdawg]

Just my 2 cents, but I think you are over thinking this, you mention you are utilizing the speakers in a home office set up if so how loud are you actually listening to?

Most folks who aren't aware or don't know would be very surprised to learn how many wpc they are actually utilizing when listening at moderate levels.

I know and have read folks using 12 to 35 WPC tube amps.

Not knowing your particular receiver my guess is at the 9 o'clock position or even 12 o"clock position (based on 6 o'clock being no volume) on the volume dial you're not coming anywhere close to 60 and or 90 wpc

Curious, how did you determine that you'd briefly gone to about 50 wpc?

Mostly, I listen at low to moderate levels, but occasionally like it pretty loud, and just don't want to get too carried away on those songs I like really loud (Europa, The Rain Song, Can't You Hear Me Knocking, etc.) and cause damage. And you're right- I have no idea how much power is actually going to them. The receiver is a newer model, only made in the last year or two. The 50 I was referring to was the digital readout on the receiver, which goes from 1-73, then reads "max." It's 90wpc, and though I know very little about electronics, I'm sure there's not a direct linear relationship between the readings and the power delivered.

So, just trying to be cautious.

 

[spark1]

Mostly, I listen at low to moderate levels, but occasionally like it pretty loud, and just don't want to get too carried away on those songs I like really loud (Europa, The Rain Song, Can't You Hear Me Knocking, etc.) and cause damage. And you're right- I have no idea how much power is actually going to them. The receiver is a newer model, only made in the last year or two. The 50 I was referring to was the digital readout on the receiver, which goes from 1-73, then reads "max." It's 90wpc, and though I know very little about electronics, I'm sure there's not a direct linear relationship between the readings and the power delivered.

So, just trying to be cautious.

As I said earlier, if you are even pushing ten watts of continuous power, they will be painfully loud in a small to mid-sized room.

Generally, continuous power is the concern.

 

[whoaru99]

If something doesn't sound quite right turn it down. That one simple thing will nearly always keep you out of trouble, which is pretty good because, IMO, the only 100% guarantee is never use them.

 

[Dswankey]

I think you'll be fine as long as you're not "cranking it up" for extended periods.

 

[Brewdawg]

Thanks guys, makes me feel a little more comfortable. Makes sense. Maybe this is incorrect, but I guess for ballpark reference, I could remember about how loud my Pioneer SX-450 (15wpc) from college days would be at full volume, and I guess I'd rarely, if ever, get that loud.

While you're all being so helpful, let me ask another question. Not sure if I'm supposed to start another thread, but: I have a sub from a surround system I'm no longer using. My receiver is just 2 channel, no sub output. The sub has no high level inputs, so I'm not sure if there's a way to play around and try it with this system?

 

[spark1]

You can use something like this:

https://www.crutchfield.com/S-hZllZ...t6iDCXtvwVqYjaL1YtAHAVS1IAr9QTdkaAmjXEALw_wcB

It converts higher-voltage speaker-level output (using the B outputs from your receiver) to a lower-voltage line-level signal, with which you can feed the subwoofer's line-level inputs. Many subwoofers offer both speaker-level and line-leve inputs, while some only offer line-level inputs.

Russound is a reputable manufacturer. There may well be less costly versions of this relatively simple device.

By the way, you might want to trim the bare ends of your existing speaker wires so they can be more fully inserted into the receiver's terminals. Leaving so much exposed copper creates a higher potential for a short circuit.

Another BTW; the loudness produced by a given amount of power is a function of the speaker's sensitivity...which can vary quite widely. With the same speaker, a 15 watt amp will be just as loud as a 150 watt amp, up until the point at which the 15 watt amp runs out of power.

 

[whoaru99]

Just FYI/FWIW, if you wish to pursue use of the speaker level to line level converter, just be advised if your receiver puts A+B in series (some do, most do not) it will not work connected to the B terminals, and you'll think something is broken. Nothing broken, just means you have to put those connections in parallel off the A terminals (at the amp or at the speakers, no matter either way).

 

[Brewdawg]

Thanks, I may look into that. After getting more speakers for the workout room, so I can move the Tailgater to the garage. And upgrading my phono cartridge.

And I knew someone would point out the exposed wire! Thought I'd remembered the receptacle being deeper back in the day when I stripped them, and got in a hurry to hear the speakers, so I didn't go back and cut them. When I saw it, I almost trimmed them before taking the pic.

 

[MaxP]

How big is the space? I have a small home office where o use a pair of KLH6s powered by a Marantz 2216 - that’s a whopping 16 WPC and in the small space it can get plenty loud without pushing hard.

 

[Brewdawg]

How big is the space? I have a small home office where o use a pair of KLH6s powered by a Marantz 2216 - that’s a whopping 16 WPC and in the small space it can get plenty loud without pushing hard.

16' x 25', 9' ceiling, speakers on the long wall. Yep, I'm gathering from the responses that I'm not likely pushing wattage as high as I'd thought I might be.

 

[spark1]

Thanks, I may look into that. After getting more speakers for the workout room, so I can move the Tailgater to the garage. And upgrading my phono cartridge.

And I knew someone would point out the exposed wire! Thought I'd remembered the receptacle being deeper back in the day when I stripped them, and got in a hurry to hear the speakers, so I didn't go back and cut them. When I saw it, I almost trimmed them before taking the pic.

Your amp (receiver) appears to have a fairly limited power supply. So, if you want to connect a second set of speakers to it, I would recommend that you only run one pair at a time...A or B, not A and B.

 

[Brewdawg]

Your amp (receiver) appears to have a fairly limited power supply. So, if you want to connect a second set of speakers to it, I would recommend that you only run one pair at a time...A or B, not A and B.

Yeah, I wasn't clear in my post- I won't be running more speakers on this receiver, except maybe a sub down the road. For the other room, I'll use my old Kenwood VR-507 surround receiver for now. But I'll want to get a bluetooth for it so the wife can play from her phone, too.

Do you know if there's significant performance (not feature or range) difference between something like these? I don't really see any of them talking about any sort of specs, unless you get into the $100+ range, and I don't really need audiophile quality to run on the treadmill. And it would likely be a waste with my level of system anyway. I'm thinking of just trying the cheap one to see, but...thought I'd ask.