Understanding speaker impedance and Ohm's? 4-16 Ohms? In specific the SET 400.

AvsFan · « **on:** 27 Jul 2020, 09:47 pm »

I am buying some new speakers that are 100% opposite of what I have been dealing with when it comes to my Magnepan's. Going from 4ohm, 86db and extremely current and power hungry Magnepan's to ZU Audio, 16ohm and 101db speakers.

How do amps work going the other way? In specific the SET400?

So if at 8ohms it makes 200 watts per channel and at 4ohms it doubles that, at 16ohms is it half of 200? I am confused.

Thanks.

srb · « **Reply #1 on:** 28 Jul 2020, 12:28 am »

It depends on the amplifier topology and design, for example, many amplifiers that have output transformers or autoformers may output the same power at 4Ω, 8Ω and 16Ω and I've seen a few Class D designs also output similar wattages at different impedances.

But in general theory, many direct coupled or capacitor coupled Class AB amps I've come across will output ~ 50% power at 16Ω vs 8Ω. However, the difference between a 86dB speaker and a 101dB speaker is 15dB, corresponding to a ~32X power difference.

So even if your available power to the high sensitivity speaker is cut in half, the power requirement of the new speaker is cut by 32X and your new combination would be like having a 16 times more powerful amplifier!

charmerci · « **Reply #2 on:** 28 Jul 2020, 01:26 am »

Seems like a bit of overkill. Just get a SET120.

srb · « **Reply #3 on:** 28 Jul 2020, 01:35 am »

I was assuming that the SET 400 was already powering the Magnepans.

AvsFan · « **Reply #4 on:** 28 Jul 2020, 01:52 pm »

Quote from: srb on 28 Jul 2020, 01:35 am

I was assuming that the SET 400 was already powering the Magnepans.

No. Digital Amplifier Company Golden Cherry Monoblocks. Moved my Maggie's to the theater room and will power with them.
So still looking at something for the Zu's. And have ALWAYS wanted to try AVA electronics.

AvsFan · « **Reply #5 on:** 28 Jul 2020, 02:04 pm »

Quote from: charmerci on 28 Jul 2020, 01:26 am

Seems like a bit of overkill. Just get a SET120.

Absolutely NOT overkill. I am currently powering my ZU Audio Dirty Weekends with my DAC Golden Cherry monoblocks putting out about 200 watts per channel. Every time I have stepped up in both power and quality, the ZU's have responded with terrific sound. They like power.

avahifi · « **Reply #6 on:** 28 Jul 2020, 03:21 pm »

Our SET 400 will put out over 100W/ch into your 16 ohm Zu speakers. Much more then enough and the amp will be running Class A almost all of the time too.

It is a great match.

Frank

AvsFan · « **Reply #7 on:** 28 Jul 2020, 05:30 pm »

Quote from: avahifi on 28 Jul 2020, 03:21 pm

Our SET 400 will put out over 100W/ch into your 16 ohm Zu speakers. Much more then enough and the amp will be running Class A almost all of the time too.

It is a great match.

Frank

Thanks for the input Frank. So I did have a question. ZU Audio offers snub speaker loading resistors. Looks like they have 5, 10 and 25ohm resistors. Would this help give me more out of the SET 400?

https://www.zuaudio.com/diy/loading5r

https://www.zuaudio.com/diy/loading25r

https://www.zuaudio.com/diy/loading10r

avahifi · « **Reply #8 on:** 28 Jul 2020, 08:40 pm »

No. The SET 400 is happy with a 16 oh load. I am not sure how those “snub speaker resistors” are used. If in series with the speaker wire they will reduce the damping factor of the system and reduce bass control. If in parallel then the resistors will just eat up amplifier power. I see no useful purpose.

Correct me if I am wrong about this.

Frank0

AvsFan · « **Reply #9 on:** 28 Jul 2020, 09:31 pm »

Quote from: avahifi on 28 Jul 2020, 08:40 pm

No. The SET 400 is happy with a 16 oh load. I am not sure how those “snub speaker resistors” are used. If in series with the speaker wire they will reduce the damping factor of the system and reduce bass control. If in parallel then the resistors will just eat up amplifier power. I see no useful purpose.

Correct me if I am wrong about this.

Frank0

This is why I ask the pro's.

Another amp builder said the exact same thing. They see no useful purpose.

mick wolfe · « **Reply #10 on:** 29 Jul 2020, 06:44 pm »

https://www.cnet.com/news/high-expectations-for-a-low-power-audiophile-amplifier/

Here's an opinion from Nelson Pass ( another amplifier designer of note) who had no problem recommending "snubbing" resistors with a Zu speaker and one of his amps. You can also go to the Zu site under DIY and see chart/graphs that clearly show the effects of the snubbing resistors on each of their models. You might also note that this applies strictly to Zu speakers, so those not familiar might find this use of resistors a bit unconventional.
In your case with an amplifier that can comfortably do 100 watts into 16 ohms they certainly would seem unnecessary, but don't dismiss their value in every case. As always YMMV.

AvsFan · « **Reply #11 on:** 30 Jul 2020, 12:25 am »

Quote from: mick wolfe on 29 Jul 2020, 06:44 pm

https://www.cnet.com/news/high-expectations-for-a-low-power-audiophile-amplifier/

Here's an opinion from Nelson Pass ( another amplifier designer of note) who had no problem recommending "snubbing" resistors with a Zu speaker and one of his amps. You can also go to the Zu site under DIY and see chart/graphs that clearly show the effects of the snubbing resistors on each of their models. You might also note that this applies strictly to Zu speakers, so those not familiar might find this use of resistors a bit unconventional.
In your case with an amplifier that can comfortably do 100 watts into 16 ohms they certainly would seem unnecessary, but don't dismiss their value in every case. As always YMMV.

Thanks for the info. It's a good read. Tommy said that there is no need. I am not using them on my current Dirty Weekends and will try the new ZU's without them as well. If I feel the need to, or just simply want to try it, will for sure give my opinion.

Yeah, I was on the phone with Gerrit and we went over that chart. Very useful and helpful information if you want to try to match your amps butter range.

mick wolfe · « **Reply #12 on:** 30 Jul 2020, 03:03 pm »

No prob. I believe the resistors are a worthy experiment considering that they're inexpensive and only take seconds to install. (or remove if you find they don't have a positive effect)

dB Cooper · « **Reply #13 on:** 30 Jul 2020, 05:59 pm »

I'm with charmerci, the SET120/Zu combo would be capable of reaching ear-bleeding levels; what do you need the 400 for? Save the money.

I will note that Frank van Alstine is a highly regarded designer with decades of experience but you can make your own choice whose advice to take. Certainly you'd be less likely to need the 'snubbers' with the 120 and save $$$ in the process vs the 400. The choice is yours.

dB Cooper · « **Reply #14 on:** 30 Jul 2020, 06:00 pm »

accidental dupe

AvsFan · « **Reply #15 on:** 30 Jul 2020, 07:50 pm »

Quote from: dB Cooper on 30 Jul 2020, 05:59 pm

I'm with charmerci, the SET120/Zu combo would be capable of reaching ear-bleeding levels; what do you need the 400 for? Save the money.

I will note that Frank van Alstine is a highly regarded designer with decades of experience but you can make your own choice whose advice to take. Certainly you'd be less likely to need the 'snubbers' with the 120 and save $$$ in the process vs the 400. The choice is yours.

Less likely to need the snubbers with the 120 compared to the 400?

Why is that? The 400 is pretty much just a more powerful version of the 120 right?

charmerci · « **Reply #16 on:** 30 Jul 2020, 08:18 pm »

Quote from: AvsFan on 30 Jul 2020, 07:50 pm

Less likely to need the snubbers with the 120 compared to the 400?

Why is that? The 400 is pretty much just a more powerful version of the 120 right?

No, the 120 is a less powerful version of the 400! (That's what Frank says, as the 400 was designed and made before the 120.)

mick wolfe · « **Reply #17 on:** 30 Jul 2020, 11:38 pm »

Correct me if I'm wrong, but the 120 into a 16 ohm load would yield only 30 watts per channel. Plus it may not be as comfortable with a 16 ohm load. If the OP doesn't want to fiddle with snubbing resistors, he's already been told the 400 is comfortable driving a 16 ohm load and putting out at least 100 watts per channel. Maybe I'm reading between the lines, but seems like this is the power range/headroom he's looking for.

charmerci · « **Reply #18 on:** 31 Jul 2020, 12:56 am »

Quote from: mick wolfe on 30 Jul 2020, 11:38 pm

Correct me if I'm wrong, but the 120 into a 16 ohm load would yield only 30 watts per channel. Plus it may not be as comfortable with a 16 ohm load. If the OP doesn't want to fiddle with snubbing resistors, he's already been told the 400 is comfortable driving a 16 ohm load and putting out at least 100 watts per channel. Maybe I'm reading between the lines, but seems like this is the power range/headroom he's looking for.

I used to own a 25 y.o. 60 watt AVA amp with a 86db efficient speaker and man, it never ran out of power and those speakers got loud!!!

The SET is a much more modern design. I wouldn't be worried.

AvsFan · « **Reply #19 on:** 31 Jul 2020, 03:39 am »

Quote from: mick wolfe on 30 Jul 2020, 11:38 pm

Correct me if I'm wrong, but the 120 into a 16 ohm load would yield only 30 watts per channel. Plus it may not be as comfortable with a 16 ohm load. If the OP doesn't want to fiddle with snubbing resistors, he's already been told the 400 is comfortable driving a 16 ohm load and putting out at least 100 watts per channel. Maybe I'm reading between the lines, but seems like this is the power range/headroom he's looking for.

You're reading everything correct.
Headroom is EXACTLY what I am looking for. I was a little confused by the earlier statement by DB Cooper, saying the 400 would need the snubbing resistors more than the 120. I wasn't really following that.

I have ran the ZU's with 60 watts of power before and it's not enough. The ZU's love heavy doses of power and current.