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THOMO

Parallel resistor -what is the function?

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What would be the reason for  R5- in this crossover -a 3 ohm resistor in my case.A value which seems hardly worth bothering with if it is only there for attenuation?

image.png.54293047ce4470a0bf9752bf36522d67.png

 

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What would be the reason for  R5- in this crossover -a 3 ohm resistor in my case.A value which seems hardly worth bothering with if it is only there for attenuation?
image.png.54293047ce4470a0bf9752bf36522d67.png
 


My hunch is it’s a Zobel network rather than a pad.

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The parallel capacitor makes the low pass filter steeper.

 

Their choice of capacitor makes a peak in the response around 1khz ... and the peak was a little bit too big for them, so they added the small resistance.

 

 

C5+R5 disconnected

101840246_ScreenShot2018-07-24at20_14_20.png.9ef0f6cc6eb91d2313a265a226a33715.png

 

C5=20uF  R5=10 ohm

169846606_ScreenShot2018-07-24at20_14_34.png.b7959e9375046d99138e84d79e961fa9.png

 

C5=20uF  R5 = 2 ohm

1094401803_ScreenShot2018-07-24at20_15_00.png.1944691159f3252ec3d8c40bf09ae891.png

 

 

C5=20uF  R5 = 1ohm

426358703_ScreenShot2018-07-24at20_15_07.png.73d219a7757e1ef976885cfced4345de.png

 

C5=20uF  R5 disconnected

 

332166864_ScreenShot2018-07-24at20_20_45.png.92a5aa227efa6c4f2ef9513c7dc2da23.png

 

Edited by davewantsmoore

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Yes possibly a Zobel to flatten impedance of the woofer although the normal  Zobel seems to have the resistor before the capacitor.

I have tried with and without it and can't really say which I prefer.Seems to sound a bit more open and dynamic without but  perhaps I get a bit more overlap without it.?The crossover is about 200 Hz .

Sometimes the cure is worse than the problem?

 

 

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2 minutes ago, THOMO said:

I have tried with and without it

The resistor?   Have a look at the last two charts.

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12 minutes ago, davewantsmoore said:

The resistor?   Have a look at the last two charts.

Yes the resistor.

The schematic is not what I have-I just used it as an example.

 

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On ‎24‎/‎07‎/‎2018 at 6:46 PM, THOMO said:

Yes the resistor.

The schematic is not what I have-I just used it as an example.

 

Then why not provide the actual schematic in question for an informed comment or comments?

 

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On 24/07/2018 at 6:32 PM, davewantsmoore said:

 

 

8 hours ago, Monkeyboi said:

Then why not provide the actual schematic in question for an informed comment or comments?

 

I am unsure about doing that because it is probably not for public use.You have to purchase the kit to get the design.Which is fair enough.I am a bit sensitive about that sort of stuff as I have had some of my furniture designs copied .

It is actually an add on for a two way design to convert it to a three way.

 

Edited by THOMO

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What we saw in my simulation of the filter from post #1 is potentially relevant here.   A small value resistor, can have a not-insignificant effect.  You will need to understand the circuit before you can tell - or ask the designer.

 

The speaker impedance is also relevant (but unknown).  However, if this is some sort of "mid woofer", then the impedance likely doesn't make a ton of difference to the resistor effect around 1khz  (in the example from post #1)

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I asked the designer about it and he said the change was fine from an impedance perspective and if I preferred the sound that way then go with it.

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30 minutes ago, THOMO said:

I asked the designer about it and he said the change was fine from an impedance perspective

Sounds like you asked a 'leading question'  ;)

 

I wouldn't expect any impedance consequence.... and of course, it's up to you whether to keep the change.

 

I would have though he could say what the difference would be.   eg. like a chart provided above  (or a description of it, like "a dB or so more, for an octave either side of 1khz")

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3 hours ago, THOMO said:

 

I am unsure about doing that because it is probably not for public use.You have to purchase the kit to get the design.Which is fair enough.I am a bit sensitive about that sort of stuff as I have had some of my furniture designs copied .

It is actually an add on for a two way design to convert it to a three way.

 

A printed circuit board layout, a chassis design, a loudspeaker box design, furniture designs and can be protected by patents, but also in common law as intellectual property (copyright) as for instance product labels and logos.  Schematics however AFAIK can't be protected by patents or copyright.  Been down this path before.  You could try contacting the kit designer and asking why the resistor is there and the significance of its ohmic value, however IMHO without the parameters of the driver one can only theorise in general terms as to its exact purpose.

 

Given that it is an "add-on" to convert a 2 way design into a 3 way design, no doubt modifications to the existing passive crossover networks would be required.  The only reason I can think of is it in conjunction with the capacitor is to attempt to "flatten out" the impedance of the driver from the crossover's perspective.  

 

I am saddened to read that some of your furniture designs have been copied without your consent.  :(  Some person or persons obviously admire your designs and has chosen to capitalise on them.  If there is any consolation, I'm quite sure whoever it is they aren't putting in the same passion or craftsmanship you probably would into the pieces.

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On 27/07/2018 at 11:03 AM, THOMO said:

I asked the designer about it and he said the change was fine from an impedance perspective and if I preferred the sound that way then go with it.

Like people have suggested over on DIYA .... don't fall into the "less components colour the sound less" trap for this one .....   I'm not saying that isn't true .....  but you're not auditioning that in a fair apples/apples way here.   What you're hearing is the cutt-off shape of the crossover filter changing.   (ie. a slight peaking before the rolloff in the sim above)     To tell you more about exactly what actual change you're listening to, will need to know the deets (driver, filter, and even maybe cabinet shape).  :) 

 

 

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10 hours ago, davewantsmoore said:

Like people have suggested over on DIYA .... don't fall into the "less components colour the sound less" trap for this one .....   I'm not saying that isn't true .....  but you're not auditioning that in a fair apples/apples way here.   What you're hearing is the cutt-off shape of the crossover filter changing.   (ie. a slight peaking before the rolloff in the sim above)     To tell you more about exactly what actual change you're listening to, will need to know the deets (driver, filter, and even maybe cabinet shape).  :) 

 

 

The whole crossover seems wrong anyway.I have had to change the high pass crossover point to avoid an obvious overlap and it is still not right anyway-probably because it was really designed for a 4 ohm woofer and the SB driver is 6 ohms [although that driver was suggested and measured].It needs more inductance-or if I am being really honest a fourth order crossover.My job today is to change the 5mH inductor on the woofer to 7.8 mH and see if that helps.It should.

 

Edited by THOMO

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On 24/07/2018 at 7:53 PM, THOMO said:

Bakoon

Oh.  This is potentially a big factor.

 

Being a 'current source' amplifier (one with a large output impedance) it will not drive speakers to the frequency response that (most) manufacturers expect.

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3 hours ago, THOMO said:

The whole crossover seems wrong anyway

Almost certainly was designed for a "voltage output" amplifier (like almost every typical SS amplifier).

 

Most tube amps are somewhat current source amplifiers (they have a few ohms output impedance, as opposed to the almost zero for a typical SS amplifier).   Your amplifier has an output impedance which is much(!) higher.    This is a very large part of the reason why you find the amplifier sounds "different" (as it is producing a completely different response from most speakers - vs a more 'normal' amp)

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I have tried a range of different amps .The 35 watt Bakoon which is SS but unusual,the 150 watt Usher which will drive anything, a 50 watt SS, and a 40 watt gainclone and the problem is pretty consistent in them all.

I am yet to try a valve amp on them but suspect it will not be a great combination.

 

I suppose the room could be a factor but I have had a lot of speakers in there and it seems pretty neutral.Although none from memory with a crossover around 200Hz-more like 500-750Hz.

 

 

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6 hours ago, THOMO said:

... and the problem is pretty consistent in them all.

Do you mean the problem you mentioned about the crossover seeming all wrong, with too much overlap, etc.?    This (too much overlap, crossover looks all wrong) would be exactly the comment I would expect if driven from a current source amp like the bakoon.

 

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48 minutes ago, davewantsmoore said:

Do you mean the problem you mentioned about the crossover seeming all wrong, with too much overlap, etc.?    This (too much overlap, crossover looks all wrong) would be exactly the comment I would expect if driven from a current source amp like the bakoon.

 

No and most unlikey.I have heard Bakoons driving all sorts of speakers including difficult ones like Magicos  with no sign of any frequency anomalies other than those which would apply to any amp with similar power [some of them a low powered].They are not like SET amps or many  PP valve amps in that regard-and I have owned plenty of them.

They may prefer 8 ohm rather than sub 4 ohm speakers I suppose but for the more powerful ones that is not an issue either.

 

Changing the inductor on the low pass from  5mH to 7.7mh has made a big improvement .My guess is that it was designed specifically for the alternative suggested driver which is 4 ohms.A rough estimate is that it was crossing at 300 Hz instead of 200 hz .Which accounts for the overlap but it also seemed to be triggering some sort of resonance-either cabinet or cone or perhaps a bit of both.

The kit using the 4 ohm woofer would probably be fine but people have built it with the 6 ohm woofer and I do not understand how they could think it was OK.The designer has had serious health problems so that might account for that oversight I suppose.He did a brilliant job on the two way section.

Edited by THOMO

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1 hour ago, THOMO said:

No and most unlikey.I have heard Bakoons driving all sorts..

That's interesting.  It is not my understanding of the bakoon amplifier.

 

1 hour ago, THOMO said:

They may prefer 8 ohm rather than sub 4 ohm speakers I suppos

I don't see why....

 

 

Note - I don't think that's a bad thing (the way the bakoon amp works wrt to being a current source), quite the opposite.... but it will have these issues with frequency response.

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