Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Solid State Talk all about solid state amplification.

Nominal Vpp amp output across home theater speaker exceeds 100V
Nominal Vpp amp output across home theater speaker exceeds 100V
Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 17th June 2017, 08:10 PM   #1
bobakrep is offline bobakrep  United States
diyAudio Member
 
Join Date: Sep 2014
Location: suburbs of Houston
Default Nominal Vpp amp output across home theater speaker exceeds 100V

In preparation to replace my excellent B&K 200.2 amplifier powering my two Martin Logan ReQuest left/right speakers, with a DIY amp that has been in progress for a while (just for fun/bragging rights), I decided to measure the B&K's output swing across a speaker in various movie and musical passages, and see how big of a peak I might run across.

I hooked up my Rigol oscilloscope to the speaker +/- terminals, after checking the black terminal's resistance to ground to ensure I wasn't doing something bad by hooking up the O-scope's ground terminal (appears it was either floating or close enough to ground not to matter).

First I just turned on the TV and watched a movie, with the scope set to measure VV-max and VV-top, and a cursor set at +/- 32V rails, my originally planned amp rails. Even though it was a loud action movie, I never saw the signal go above +/- 18V. No problem!

Second, I decided to try a blue ray. I selected The Hobbit 1, because the beginning with the Dragon attack (spoilers!) has some very loud and impressive audio sequences. Then I really cranked up the volume, louder than I typically make it, but at a level I have heard before, many times for parties or demonstrations to friends.

Unfortunately I started seeing some huge peaks during this sequence, one of which was about 100Vpeak to peak! I managed to capture on screen a +/- 49V transient.

Worse, the Martin Logan reQuests have a very low impedance at high frequencies, nearing 1 Ohm.

So, needless to say I'm now having 2nd thoughts if I should follow my original plan to swap from the B&K to a DIY amp, especially since my original plan was to use 2 or more LM3886s-based amps in parallel. I was thinking 2 or more LM3886 should be able to handle the current, plus I could remove the shunt between the tweeter and panel, and amp each separately to reduce current further... but now I'm thinking even if I can source enough current, there will be some slight clipping at very high listening levels.

Any advice? Any chance since I'm using a digital O-scope with edge triggering it's somehow lying to me/I've measured it incorrectly? Is clipping at those levels going to be audible or missing the edge of that peak actually won't matter much?

(BTW for the home theater I also have 6 other speakers powered by a Proceed AMP5)
  Reply With Quote
Old 17th June 2017, 08:53 PM   #2
bobakrep is offline bobakrep  United States
diyAudio Member
 
Join Date: Sep 2014
Location: suburbs of Houston
Default Oscope capture

Click the image to open in full size.
  Reply With Quote
Old 17th June 2017, 09:32 PM   #3
vzaichenko is offline vzaichenko  Russian Federation
diyAudio Member
 
vzaichenko's Avatar
 
Join Date: Jan 2010
Location: Moscow, Russia
Nominal Vpp amp output across home theater speaker exceeds 100V
Well, 100Vpp = 50Vp = 35.46V RMS
That equals to 157W RMS @ 8 ohm load

Pretty much OK for both B&K 200.2 and the speakers.
Rather loud though
__________________
If you can't explain it simply, you don't understand it well enough (c) Albert Einstein
VIRTUAL ZERO distortion AUDIO
  Reply With Quote
Old 18th June 2017, 12:34 AM   #4
bobakrep is offline bobakrep  United States
diyAudio Member
 
Join Date: Sep 2014
Location: suburbs of Houston
Yes, fine for the B&K. But not really my question, which was about switching to an LM3886 based amp.

Loud but not unpleasant. My room is pretty over the top, and big. 35x20 non rectangular, with ~40% upholstered walls, stadium seating, stage, etc. mix of absorbtive and diffraction treatment, staggered stud construction, blown in acoustic foam on all sides 1 foot thick etc.
  Reply With Quote
Old 18th June 2017, 12:50 AM   #5
vzaichenko is offline vzaichenko  Russian Federation
diyAudio Member
 
vzaichenko's Avatar
 
Join Date: Jan 2010
Location: Moscow, Russia
Nominal Vpp amp output across home theater speaker exceeds 100V
LM3886 will not give you enough swing at the output.

You mentioned paralleling them for higher current capability. Having constant R load - in order to make the load demand more current - you need to swing higher voltage (Ohm's law ).

If you'd like to be able to drive kind of the same 100Vpp peaks into your speakers, you need to have at least +/-60V rails in your DIY amplifier. And enough output current capability for providing at least 200W per channel with no artifacts.
__________________
If you can't explain it simply, you don't understand it well enough (c) Albert Einstein
VIRTUAL ZERO distortion AUDIO
  Reply With Quote
Old 18th June 2017, 02:18 AM   #6
mt490 is offline mt490
diyAudio Member
 
Join Date: Jun 2010
If you could do BTL with paralleled chips (LM3886) on both sides then you would be able to get closer to what you originally had.

But it hardly seems like the 'right' solution.
  Reply With Quote
Old 18th June 2017, 02:47 AM   #7
PRR is offline PRR  United States
diyAudio Member
 
PRR's Avatar
 
Join Date: Jun 2003
Location: Maine USA
> B&K 200.2 amplifier

That's 350W in 4 Ohms.

It would take a silly stack of 68W LM3886 to equal it.

> My room ...big. 35x20 ... ~40% upholstered walls, ...absorbtive ..treatment, ...blown in acoustic foam on all sides 1 foot thick etc.

That's a big hole to fill with sound. At a guess, it is 10X more sound-suck than a typical living room; and modern cinema sound may peak louder than many musics. So for hi-fi speakers it would be quite reasonable to supply 1,000 Watts minimum. Way past LM3886 turf.
  Reply With Quote
Old 18th June 2017, 03:16 AM   #8
mt490 is offline mt490
diyAudio Member
 
Join Date: Jun 2010
Quote:
Originally Posted by PRR View Post
and modern cinema sound may peak louder than many musics.
I would say actually that this is not a may but a will.

I refer to the THX cinema volume levels as a reference for what you might want if you might aim for a cinema experience. It peaks at 105dB at the listening position per each front main channel. To put that in perspective the total (incl surround and LFE) system would supposedly be able to replicate the reality of a small petrol whipper snipper being used in the same room. Whether you want the whipper snipper or the sound in the room, is up to you
  Reply With Quote
Old 18th June 2017, 05:41 AM   #9
JMFahey is offline JMFahey  Argentina
diyAudio Member
 
JMFahey's Avatar
 
Join Date: Mar 2009
Location: Buenos Aires - Argentina
Now that you built your LM3886, use it.
It will play good, just not that loud.

And for your next project, build a discrete mp with +/-70V rails

Do not waste time parallelling, bridging or both, with chipamps.

The beauty of chipamps is simplicity, plus they sound good ... within their limitations.

Once you need 2 or 4 of them, you start approaching discrete amp complexity, so, what´s the point?
__________________
Design/make/service musical stuff in Buenos Aires, Argentina, since 1969.
  Reply With Quote
Old 18th June 2017, 08:31 AM   #10
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
The only purpose of all these PA100, BA100, BPA300 topologies is to sell more chipamps and make more profit for NS/Ti.

If one needs more current than a single chipamp can supply, then use a more appropriate topology.
__________________
regards Andrew T.
Sent from my desktop computer using a keyboard
  Reply With Quote

Reply


Nominal Vpp amp output across home theater speaker exceeds 100VHide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
cheap home theater speaker dave123 Multi-Way 5 3rd April 2016 08:18 PM
Looking for home audio / home theater speaker DIY or not? qualm Multi-Way 17 26th March 2012 03:30 PM
Best style of speaker for HOME THEATER hawkson Multi-Way 50 12th April 2011 07:48 PM
Another Home theater speaker thread... Tristanc1 Multi-Way 4 31st May 2007 07:23 PM
Ultimate home theater speaker gaff Multi-Way 2 11th November 2003 05:38 PM


New To Site? Need Help?

All times are GMT. The time now is 05:37 PM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 15.79%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Copyright ©1999-2017 diyAudio
Wiki