Audio Dummy Load design and build
Vložit
- čas přidán 12. 07. 2024
- #diyelectronics #diyaudio Testing amplifiers can be a noisy business, with loud test signals adding an irritating distraction to an otherwise pleasant experience. If you want to test the amplifier at high output power, this can be quite impossible unless you have a sound-proof room sitting around.
This project provides the option of switching the signal either to a speaker, or to a dummy load made up of power resistors, which effectively provides the amplifier with the equivalent of a speaker at its output, but without the noise. The energy is converted to heat in the resistors instead of sound energy, so testing become much more pleasant.
The design aspect of this project is actually very simple, but the choice of modelling it first in Sketchup makes it much more interesting.
Hope you enjoy it.
You can now support the channel:
/ mcaldeira paypal.me/macaldeira
_____________________________________________________________
DIY TEST GEAR: The title says it all:
• Zener Diode Tester - P...
RESTORATION BUILDING BLOCKS: A series of videos showing detailed steps used the restoration process of tube equipment:
• How to safely check th...
HowTo's: Various videos on some simple techniques and projects:
• Extend tube radio FM b...
See also playlists on some other completed restoration projects.
PHILIPS BX750A:
• Philips BX750A tube ra...
TELEFUNKEN OPUS 2114:
• Telefunken Opus 2114 s...
SABA UW-175-Z 3D:
• Saba UW 175-Z 3D tube ...
GRUNDIG 1070:
• Grundig 1070 tube radi...
SCHAUB-LORENZ GOLDY 58 type 3020:
• Schaub-Lorenz Goldy 58...
BUSH VHF64:
• Bush VHF64 tube radio ...
GRUNDIG 3060A:
• Grundig 3060a tube rad...
TELEFUNKEN OPERETTE 8:
• Telefunken Operette 8 ...
GRAETZ SUPER 171W:
• Graetz Super 171W tube...
LOEWE-OPTA MAGNET 3737W:
• Loewe-Opta Magnet 3737...
BRAUN ATELIER 3:
• Braun Atelier 3
LOEWE-OPTA TRUXA STEREO 4741W:
• Loewe-Opta Truxa Stere...
GRAETZ COMEDIA 616:
• Graetz Comedia 616 tub...
SABA FREIBURG W2:
• Saba Freiburg W2 (WII)...
GRAETZ MUSICA 4R417:
• Graetz Musica 4R417 re...
You may also be interested in ...
CAPACITOR LEAKAGE TESTER:
• Capacitor leakage test... - Věda a technologie
Great how to video on making an expanded dummy load. Thanks.
Awesome project. Thank you for sharing it with us
pleasure
I definitely need a test panel like this to help neaten up my very messy workbench. Thanks for the inspiration.
Get on it. No excuses :)
Thanks for the great video! I have to admit that I gathered all the parts together and let it sit under my bench for about a year till I finally had a chance to work on it. Worth the wait though. Thanks for all the helpful info!
My pleasure
How cool and useful is that - well done sir. This is my next project
Enjoy.
Hello Sir great tool and inspiring video. Many thx !
Nice work! Awesome and clean build!
👍
That put my rats nest of wires and power resistors to shame. always intended to put it all in a case. Maybe the push I needed. Fantastic video and a nice use of graphical demonstrations. Keep them coming. Karl
Thanks Karl.
Nice job on the build and +1 on the use of SketchUP
Thanks.
A very useful and tidy way to switch between loads and speakers. Great video.
Thanks George.
Boo - Hi George regards Chris
@@allthegearnoidea6752 Hi Chris. Very tempted to follow Manuel and his design on this... also looking at the attenuator and the cap tester designs. My brain is a fixing one, you and Manuel are thinkers who can design stuff.
George Christofi I would like a high voltage capacitor tester would be really useful.
@@allthegearnoidea6752 just look in the videos on this channel. Manuel has a great design and really easy to implement.
Very clever and neat. If you play your cards right you could make a career in electronics 😆.
Saves a lot of bodging with clip leads every time something is on the bench.Great stuff.
Too late to make it a career :)
My labour costs would be astronomical!
Last year made my own (2 x) 2 x 4Ω dummy load. I avoided the switches by putting one extra input connector on the front, to have a mid contact between two 4Ω resistors.
The problem with the grounds can be made a bit safer by putting two 50mA Fast fuses in the negative of the BNC connectors.
What you did, adding a speaker connection, is a very good idea, I did not see that one.
And nice way to finish the front, but I hope that it will stand the test of time.
Thanks Eric. It has so far. Looks and works very well. Obviously I’ve thought of a few mods to do, as can be expected. One is never fully satisfied :)
And commenting is made so easy these days :)
Very useful and nice design. I watched you using it in the last video and searched for a video where you built it (I only recently joined the channel you know ;-) Funny that you mentioned Dave's video because it happens to be the first recommended video after watching this one ...
👍
An addition I would add would be grommets for the Resistor wholes in the chassis.
Great video
Thanks
M, thanks for your videos that are very informative. A tip: Try printing your labels in reverse on the overhead plastic. Then with an iron, heat the plastic with the toner against your face plate. If you get it to the right temp (I think its 175-215C) it will fuse to your chassis. You can then spray it with a sealer like clear lacquer.
I’ve tried that, but more often than not I made a mess of it as the aluminium is painted and it melted the paint 😊
@@electronicsoldandnew
So sorry to hear that. Most of my stuff is brushed or anodized aluminum. Toner will start to fuse at 230F. Lacquer melts at 200F so I see your issue. I have made it work but its probably my iron and I keep it moving. I have used paint. Rustoleum has hi-temp pain that is good to 1200F that works great. Powder coating is good to well over 400F.
👍
Smart looking front panel. Your projects always look great. Lately I’ve been using PCB CAD software and sending them out for manufacture. In my case kicad and jlcpcb. If you are creating pcbs anyways this is a pretty good way to go plus there are other advantages electrically as well.
I agree. I’ve done a few videos using jlcpcb. Very happy with those guys.
I’m specifically talking about using them to create front panels
Dennis Ryan : Oh, I see. Misunderstood that.
I´ve also built a similar dummy load; but with a different scope connection: The plus AND minus have BNC-connectors, so i can connect a scope without grounding the minus - but i need a scope with two channels in differential mode.
For a stereo application i need therefore a 4 channel scope; two of them for the left and two of of them for the right channel.
The ground of the scope for all four inputs has to be connected to the ground of the amplifier.
That's a very complete system. I don't normally need that much detail, so this one works fine for me. For now anyway :)
Do I hear guitar pedals? That looks so cool. Both builds do really. Thanks for sharing your knowledge and craftmanship.
Yes, I’ve designed an built pedals and also tube guitar amps. I have a friend in Braga who is a blues guitarist that has one of my amps, which I simply could not insult with my level of playing. He truly does it justice!
Mr Caldeira, you rock. Maybe not literaly but for sure in figurate speech. And I once took a peek at your guitar in one of your videos and it sure looks cool.
Awesome
👌
Really nice build looks great! I built one very similar on my channel but i added a low level sampling port for supplying a PC sound card. Now i did plan on doing a video showing how to use free PC based tools for making amplifier measurement. I dont know if you have looked at using PC software for amplifier testing but there are some great tools for free. Im no expert on amplifier testing but I bet you could do a good video on this . I am also really sold on 3D CAD but I am using Fusion 360 as it can do tool paths for my CNC machines. But i did use Sketch up for a while and had no complaints. I also noted you used wire wound resistors some of the audio guys moan about using none inductive loads but I havent found any problems and its not like we are doing lab measurement. I did buy some much larger ceramic load resistors from china with a much higer power rating but not got around to building it as yet. I really could do with building a much small dummy load for low power testing. I really like your from panel looks great. This is the unit I built czcams.com/video/lQMm0RcI6k0/video.html.
I’ve seen yours and liked it. I wanted to do the “modular” version to clamp on my shelves, hence the rather strange design chassis-wise.
I’ve used AudioAnalyser before with my PC and it is really great. I used it mainly for testing the response of a bunch of guitar pedals I did, but have not tried it on amplifiers yet. I know there are a lot of other, and probably better, systems available, so I’ll have to look into it.
Fusion 360 looks good, but as I don’t own a CNC I’ve not tried it yet. So much to learn, so little time :)
Electronics Old and New by M Caldeira Yes not enough time in the day. Thanks for sharing always enjoy watching construction projects like yours thanks for sharing.
Great job ++++ :-)
Thanks
Great looking gear, you are doing what most forget thought out and coherent design (seems you learned the hard way ;)
I probably never have the use for it but i would build it anyway just be course of the looks of it and you never know what repairs end up on the desk.
Would a "cheap" battery powered oscilloscope be good enough to show what you need on those BNC's?
I mean, there is nothing much above 100kHz worth looking at and you won't have to be concerned about grounding anything, as you mentioned, it is you hearing that will do the final testing.
A battery powered scope is ideal - actually one per channel, but that is getting expensive.
@@electronicsoldandnew I am not sure what is needed to do the measurements but could something like this be good enough?
www.banggood.com/Original-JYETech-DSO138-DIY-Digital-Oscilloscope-Unassembled-Kit-SMD-Soldered-13803K-Version-p-984002.html?rmmds=search&cur_warehouse=CN
Great video as usual! But I probably would have done the circuit slightly differently, with the second resistor between the +input and the common contact of the speaker/off/dummy switch. And I would have made the impedance selector short that resistor. That way you can switch impedance regardless of whether you're using the speaker or the dummy resistors. And especially for tube gear, higher impedance is sometimes necessary, isn't it?
I think I get your idea. However, if I see it right you would have 8 ohms ir 16 ohms to choose from. Maybe I didn’t get it right. Not sure.
@@electronicsoldandnew Yes. I forgot to mention I might have used 4 ohm resistors but in my experience, most equipment that can use 4 ohms will work fine with 8 ohms, but not the other way around. And some old equipment might need even higher impedance.
Now that I think about it, I might do it even more differently: I would connect your second resistor to the common pin of the double-throw switch (so that it can be used with the speaker too), and I would put two banana plug sockets in series with the entire circuit, with a switch to bridge the plugs or open the circuit (I'd probably make that a protected switch so it can't be operated accidentally). Maybe I'd even put that on the "ground" side.
I might add some neon lighs on the ground side too, to warn against "hot ground".
Nice design, but may i give a suggestion ?
Place the powerresistors inside the housing, that way you don't have to make holes in te back, and also,
you can place a small fan (40x40x10) on one side of housing and use the housing as a airduct and lett the warm/hot out on the opposite side.
The only minor to this, is that the fan needs a 5V or 12V powersupply.
Good suggestion. However, I don’t normally test high power for any length of time so the heating has never been an issue for me. Outside, the cool somewhat by convection, and I don’t see them anyway.
Who knows, maybe there will be a version 2 soon:)
another excellent video project,i have the parts just gotta get off me butt and build it,my only scope is a 1962 HP 130C which apparently will do XY mode,will that work for L and R channel viewing? im pretty green at electronics only a few years of electronics in high school and tinkering around blowing things up and shocking myself..
If it’s a two channel scope it should work fine.
Great video! Love your channel. I'm planning to build a dummy load too.
Soon I'll start restoring a Grundig 5195 Stereo, which has 3 output transformers and 4 speakers if I remember correctly. Does this mean that I would need more than 2 dummy loads in order to not damage my output transformers? One per transformer or one per speaker?
My latest series on the Grundig 4006 has exactly the same output arrangement. You’ll need to place a dummy load across each output transformer, but it can be a simple 4 Ohm resistor, as I have done in mine.
@@electronicsoldandnew Thanks!
My workbench is starting to look a lot like yours :) thanks for all your help with diy test equipment. Just one question, I use my scope (same as yours) when doing alignments, is it normal for the signal voltage to the scope to drop when you switch to dummy load? I inserted a 1vrms test signal into the input of the audio dummy load and on speaker setting all good, but as soon as I switch to dummy load the voltage reading drops dramatically. Thanks again.
You can get a small drop, but it should not be too significant. Test the resistances at the input to confirm that all is well.
To minimize the possible damage and havoc that may be caused by accidental loops to earth ground via the scope earth ground, or the interconnection of the amps negatives via any instrument attached to both channels at the same time, I would consider a small fast blowing fuse in the negative lead to the BNC connectors...
That is a great idea. The scope should measure signals with only minimal current draw, so that would probably save some grief. I’m going to do that.
Great ideas, would appreciate if you could suggest a value for the fuse.
100mA should be enough
I was wondering about this very point - thanks for raising it.
Very beautiful and sufficticated job. I'm interested on technics of making the labels on the face plate. Can you please explain how you did that? Can you please give links for the material? Thanks!
I just printed on an overhead transparency sheet, and glued it on the front. Nothing complicated.
wonderful Craftspersonship thanks for sharing : )
Cool video. I was thinking of making one myself but version 1 was not much good as the resistors at 1Khz were very inductive giving me ridiculous output level powers.
Would it also be worth putting resistors in circuit with the scope BNC sockets to reduce the possibility of high currents flowing down the scope leads. Scope has no load so readings should not be effected.
I’ve never had a problem with the scope leads, but if you put resistors in you have to realise that that resistor will become added to the scope input resistance do your readings will be slightly off.
I'm building a similar dummy load. I was concerned about blowing up my 'scope, especially as I can be absent minded. So I only used one BNC, plus a dpdt switch to choose the left or right channel.
That will help keep it safer. However, you still connect the speaker’s negative to earth, and if the signal generator negative is also earth, you need to remember that as well.
I'm just a few years into my electronics tinkering, so still learning. Can't the blown-up o-scope situation almost always be avoided by simply plugging the unit under test into an isolation transformer?
It seems like the danger with the BNC, one per channel or otherwise, would be grounding one half of a bridged amplifier and blowing up the amp. In this situation, if one is really set on using BNCs, I guess you could add a ground lift switch then connect the scope ground terminal to the proper ground reference point in the amp (amp chassis)? Probably better/more simple to just use the scope probe and remember not to use the BNC in this case (and minding the ground connection of the probe to the proper point, i.e., not across the speaker terminals in a bridged amp).
I guess, long story short... As is mentioned in the video, make sure black actually equals ground before connecting the scope ground to it via BNC or probe ground lead, or any test equipment ground lead for that matter.
Nice job! Wish I could get my simple front panels to look as good without going to the trouble of getting full-sized self-adhesive laser sticker sheet (strangely hard to get here). Mine always suffer from the glue being visible through the sheet, so I'm curious what glue you used?
Also, with respect to the common scope ground shorting out bridged &/or other floating/isolated outputs, I wonder if a 10:1 twin-T or twin-Pi attenuator between the dummy load & each BNC would provide enough isolation? By my rough calcs it should provide several hundred K of resistance between the scope ground & each channel - which I'd expect to be plenty - and the scope readings will still be correct when set to 10:1.
The sheets I previously used were the ones that you mentioned - self-adhesive laser sticker sheets. I also have a problem finding them now, and had a slight mishap with the ones I did find. They melted and nearly messed up the printer (they were labelled as laser, so I don’t understand why this happened).
I used a spray glue from 3M, which worked quite well here, much to my surprise.
As for the bnc problem: if a balanced pi or T attenuator were to be used, I would imagine one would choose the impedance as 1M (same as present scope impedance within 1:1 probe) with 20dB attenuation. I’m not sure what happens when the grounds of the two amp outputs are in fact the same ground point. You will effectively be shorting the two attenuator’s grounds at both ends and I’m not sure what the attenuation would then be. Perhaps you could give me your opinion.
I’d also like your opinion on simply adding a 100n cap from bnc ground to speaker ground.
Sorry Jim. Forgot to mention that when I did the guitar pedals with the self-adhesive film, I got to see the glue on light background. This ended when I painted the enclosure grey and then stuck the film onto it. On a white background, I think I’d have the same problem.
@@electronicsoldandnew Thanks Manuel, I think I used 3M 77 or 90 glue on off-white which was fairly visible; might try a grey/darker bg net time. And yes to the melting problem - Brother printer, by any chance? They apparently use a higher temp than others, which is why I've been wary of changing to a generic-type sheet (had to fix one once when a friend bought the same printer as me & tried to use standard OHP laser sheets in it - several hours of swearing later, ...)
Yup, voltage-wise, 10:1 = 20dB, and 1M to match scope. Good point about the case where both ends are connected to ground though - didn't think of that! I had considered an isolating cap; I guess my main objection was that I'm an mostly an RF guy & don't like putting reactive components in strange places where they're not necessary. Nothing wrong with it for AF though, but I'd be tempted to (a) make it as large as possible (at least in the uF range) to pass low freqs, and (b) suitably voltage-rated since even a transistor amp could put 50v-100v or more across it. That'd suggest a plastic film cap, and I'd also be tempted to fuse/PTC it just in case.
@@electronicsoldandnew After a bit more thought & a quick simulation: 100nF/0.1uF would be fine; the -3dB point would be down around a couple of Hz, and flat within a fraction of a dB from 10Hz or so up.
Thanks for the excellent video. Quick question... do I have it right that if I put my DMM across the positive and negative contacts of one of the BNC terminals, that it will read 8 Ohms?
8 or 4, depending on the respective switch.
@@electronicsoldandnew nice! I think I'm going to just do 8 ohm - as opposed to 4 and 8 ohm - as it's what I have on hand.
👍
How long did it take to draw this in Sketchup? It looks amazing but I really think I lack the patience needed to learn how to use Sketchup and then actually use it unless it's absolutely necessary.
Once you learn how to use the software, about 30 minutes. It really is useful.
@@electronicsoldandnew Thanks - that's encouraging. Many people praise Sketchup. I guess I should try it.
I realize you want to fit the space and minimize components, but I wonder if you used an audio matching transformer at each input how well it would work. I think it would keep from grounding the amplifier output with the scope leads.
That would prevent shorting, but would also suppress dc offset information as well as any oscillations that may exist beyond the limits of the transformer’s response.
I agree that an audio isolation transformer can be a nice feature for testing some amplifiers, bridged outputs can be a real pain in the bum.
Just watched this and will prob build one myself. Just wonder regarding the common ground when connected to the oscilloscope - would some capacitors between the BNC ground tag and the circuits reduce some of this issue ? Hhhmmm I am of two minds on that. Blocks any DC component, but the AC could still be an issue. Oh and Aliexpress has a wide range of 50W and 100W resistors, (assuming you are not allergic to 'Uncle Ali'.)
No allergies here 😊
The D.C. blocking cap will do the trick, but will affect the frequency response a bit. I’ve got so used to being careful that I don’t worry about it anymore.
Good tutorial. Thx. One question about resistors power demand. How to size power of resistors. Just 1:1 RESISTOR VS AMP@8ohm so having 50 W@8ohm amp should I go for 50 W resisitor or oversize them 50-100% so eg 100W. Does exist any kind of rule here ? Thx. Marek
Always oversize. I’d go for at least 150% of my max expected power, and even then I’d keep the test times at full power short.
I decided to go for 100W with possibility to install extra heat sink - radiator- Thx.@@electronicsoldandnew
Which SketchUp version are you using? Shop? Pro????
Neither of those. I use the free online version. Don't need anything else for now.
Do you have a link to the sketchup component templates you used?
BNC - Banana sockets switches etc.
afraid not.
Hi,
Are the resistors non-inductive? Do I need them to be?
Thanks in advance,
Sean
Preferably, but not too critical for most purposes.
@@electronicsoldandnew
Thank you. What made me question it is, that when I look on eBay for 8 ohm dummy loads, most say, "for tube amps". The ones that don't say that, say "non-inductive".
Excuse my rookie question. I had a hard time seeing the positive speaker out terminal connection point. Is it connected to the lower terminal on the switches (same side as the other connections)?
Not sure I understand your question. Follow the schematic at 14:40 and then check connections with a multimeter.
I believe I understand from your schematic, just double checking. There are 6 posts on the switches for L & R, I believe you are using 3 posts on one side, corrects?
Can’t remember now. It’s been a while since I did that project.
Given that your BNCs are going to a high impedence device why don't you put a capacitor from -ve to bnc ground? Then you can monitor both channels without shorting the -ve lines. You can have a switch across the cap for DC monitoring
That eliminates the possibility of seeing any DC offset, which is sometimes useful. You could put in a cap which can be shorted if needed, so yours is a good idea.
@@electronicsoldandnew
Thank you for your reply. I have recently made a dummy load system with caps in the BNC grounds and it works well. For DC or low impedence test gear I have a shorting switch on them. I had the idea from "xraytonyb".
Can this circuit be used for guitar amp applications?
Sure. I use it often. As it stands it can emulate 4 and 8 Ohms.
i would stick to using a cro probe with the earth wire not used it what i use
Can I use single string wire?
Yes you can. Just use one that is at least 1mm diameter.
I'm trying to replicate this for myself... but I cannot think of why there needs to be an "OFF" position. What is the use case for wanting to bring a signal into this device and not use the dummy or speaker setting? I'm sure there is a reason... it is just eluding me at the moment. Thank you sir!
This setting is to be able to monitor it on the scope with no load.
Ah, yes, that makes perfect sense. I guess this is sort of a "bonus" feature so you don't have to hook the scope directly up to the outputs of the DUT. Thank you sir! @@electronicsoldandnew
Pleasure
@@electronicsoldandnew One follow-up question though... if you take the Off / Pass-thru option, wouldn't you need to be extremely careful of what goes to the scope so you don't damage it or possibly even damage the amplifier outputs? Sorry for my confusion... I'm just having a hard time trying to mentally picture where all the power/heat will go if it is not routed through the resistors. Thank you again sir.
Nevermind... I found out that the worry only applies to tube amps where the output transformer could be damaged without a load. This, apparently, does not apply to solid state amplifiers.
Thanks for the video. I have 2 dummy loads of 4.2 and 8.4 ohms, can I use for load testing of 4 and 8 Ohms? What's the maximum tolerance? Thanks.
Those are fine. The actual “resistance” of speakers is very imprecise, and also frequency dependent, so you are Ok with those values.
@@electronicsoldandnew thank you.
Hi, I know this is an old video but if someone come across this post can you tell the correct name for the On-Off-On (6 post) and On-On (4 post) switch. Trying to build this.
Double pole double throw, and double pole single throw. However, the best designation is exactly what you have: on-off-on and on-on.
@@electronicsoldandnew Every Switch I look up using DPST 4 post On-On (Amazon & Digikey) the product description says On-Off. Is this the same switch?
@@electronicsoldandnew weird, just got off the phone with Digikey and no such thing as a DPST, On-On with 4 post. They all have 6 post.
I had bought two 500 watt wire wound. I've hit a stump on how the design would go. I was wanting to put two 8 ohms in series for 16 ohms and like you're doing here for 8 and 4. I'd love to have the non inductive to build my design. In series or parallel the wattage capabilities would increase to 1000 watts I think no matter what the ohms would be.
That is one really large dummy load!
The power handling is the sum of the resistors, yes.
Can anyone come up with a “not too ridiculously complicated “ way to add a 16 ohm load capability to this gentleman’s fine dummy load circuit? I’ve been beating my head trying to come up with a reasonable circuit but adding the 16 ohm into the mix has baffled me. I figure I’ll probably have to install a rotary switch to facilitate all 3 resistor loads.
Now that would be interesting with a toggle switch 😃
I hope someone answers because I’m curious too.
😕 Darn! I was really counting on you to come up with a solution....now I’m going to have to figure it out myself...lazy boy that I am!
@@electronicsoldandnew I have added an extra 8R resistor with another toggle switch, which gives the options of 4, 8, 12 or 16 ohms, utilising the two switches
👍
Well but it may be dummy load but only to signals like 1 kHz to which apparently speaker may behave like resistance. For sure it is not 8 ohms for speaker 8 ohms. . Resistance of 8 ohms speaker driver is about 6,4 ohms. and speaker column impedance may vary from 3 ohms to 25 ohms depending on chosen frequency. So I think it may be enjoyable to make measurements with computer which so many people discovered in last decade but it gives misleading knowledge.
I agree. However, using a resistive (non-inductive) load is standard practice for amp testing. You always have to consider the issue you mention.
@@electronicsoldandnew I think we should not push to measure things which in practiced way cannot be measured. .
Hi, maybe you can have a look at this dummy load it's in Dutch www.circuitsonline.net/schakelingen/90/audio/luidspreker-dummyload.html
Very interesting. I guess you would get a more accurate response from the amp as it takes into consideration the varying impedance characteristics of a real loudspeaker. However, for most simple purposes, the resistive load is enough. For me anyway.
The Lout and Rout have not 8 Ohms. They have what the amp has as the output-resistance. :-)
And the Dummy-R's have to be cooled with a fan, when you use the full load at them.
An old problem, what i have, is, how is a REAL loudspeaker compareable with this dummy-R.
If you measure the R, you get 8 ohm. If you measure the LS, you get what? No, no 8 Ohm.
Yes, of course, i know, the LS is completely an inductive coil. The dummy-R is from resistive wire.
Both parts have completely different behavior over the frequency-area. How does this effect
the output of the amp? I never saw a dummy-load, which works like a real LS. How i wrote, MY problem. :-))
True. But for most simple test purposes, this method has served me well.
In the end, it's the ears that will have to do the final testing.