dynaudio bm15a amplifier modification

[jamescarter1982]

hi everyone u have a pair of dynaudio bm15a that ive never quite been happy eith the sound of . I also own the passive version of this monitor that sounds great . the passive has a different tweeter with a short waveguide with I think helps along with a diff crossover frequency .
I came up with the idea of using the amplifier and bass driver and trying to lower the crossover frequency to say 300htz and using an avi nunuetron which I really like as the mid and trebble in a 3way speaker
I can make a new cab and have a umik if I need it for measurements I also have the schematic and wondered if someone could help me identify the crossover and weather it could be altered and if not if I could insert my own active crossover pre power amplifier on the plate amp .
I've been told that the amplifier is good quality and I'd like to reuse it if I can
mines the mk2 thanks if anyone can help

 

[MaxwellsEq]

If you are happy to learn through experimentation, and are prepared for disappointment and even accept that you may end up with component parts with little residual value, then try a few things. You may be extremely fortunate and the whole solution comes together well and measurements support this. However, I think it's far more likely that this won't deliver satisfactory results. There are a lot of interactions in speaker design beyond drivers, crossovers and cabinets and achieving the sweet spot where positives outbalance negatives is tough to do.

But as I say, if you are happy to write off the value of the component parts in order to experiment, you could have a lot of fun and may even have success.

 

[jamescarter1982]

yeah I've had a lot of use from the monitors already so they don't owe me anything .
where should I start learning to read the schematic I suppose would be a good start then I can try and figure out what does what .
I'm quite practically minded but still find it a bit daunting

 

[LTig]

yeah I've had a lot of use from the monitors already so they don't owe me anything .
where should I start learning to read the schematic I suppose would be a good start then I can try and figure out what does what .
I'm quite practically minded but still find it a bit daunting

Read the book The Art of Electronics by Horowitz/Hill. It's written in a very understandable language. An older edition like the 2nd suffices since the speakers use analog electroncs only from 2002 or earlier (I have own I can sell since I bought the 3rd edition and don't need both).

However chances are almost zero you could make them better. Since frequency response is the biggest factor in sound quality I suggest to play with a software EQ first to find an EQ setting you prefer over flat. If you succed then you could just use this setting as is, or connect a cheap hardware EQ in front of the speakers. Chances to implement this EQ setting using the current design are also close to zero since you can only modify the parameters of the crossover but not the design itsself.

 

[jamescarter1982]

thanks all.vwry good pionts .
worst case I can make something else like you say the eq would be a good place to start . amd help me narrow down what i dont like about them .if I could tap into the plate amp with my own active crossover like xkitz or similar I could implement any crossover point I wanted making use of just the amplifier itself . I have the book thank-you though appreciate the offer I keep meaning to get round to reading it .
I kind of know where your coming from but then again this website is full of people who have achieved a lot without the budget of these big companies who seem to put out some inherently flawed designs knowing up until now they were somewhat safe the measuring equipment being out of reach of most of their customers
.

Read the book The Art of Electronics by Horowitz/Hill. It's written in a very understandable language. An older edition like the 2nd suffices since the speakers use analog electroncs only from 2002 or earlier (I have own I can sell since Ibought the 3rd edition and don't need both).

However chances are almost zero you could make them better. Since frequency response is the biggest factor in sound quality I suggest to play with a software EQ first to find an EQ setting you prefer over flat. If you succed then you could just use this setting as is, or connect a cheap hardware EQ in front of the speakers. Chances to implement this EQ setting using the current design are also close to zero since you can only modify the parameters of the crossover but not the design itsself.

 

[LTig]

if I could tap into the plate amp with my own active crossover like xkitz or similar I could implement any crossover point I wanted making use of just the amplifier itself .

As I see it those two points are the + inputs of U4 (tweeter) and U6 (woofer) - in theory, since you need some passive circuitry in front like a DC blocking cap and a 47k resistor to ground.

 

[jamescarter1982]

brilliant thank-you. I hoped I might be able to do it in a way that was reversible. I'll start reading the book snd see where it goes .

 

[justjason]

hi everyone u have a pair of dynaudio bm15a that ive never quite been happy eith the sound of . I also own the passive version of this monitor that sounds great . the passive has a different tweeter with a short waveguide with I think helps along with a diff crossover frequency .
I came up with the idea of using the amplifier and bass driver and trying to lower the crossover frequency to say 300htz and using an avi nunuetron which I really like as the mid and trebble in a 3way speaker
I can make a new cab and have a umik if I need it for measurements I also have the schematic and wondered if someone could help me identify the crossover and weather it could be altered and if not if I could insert my own active crossover pre power amplifier on the plate amp .
I've been told that the amplifier is good quality and I'd like to reuse it if I can
mines the mk2 thanks if anyone can help

It is easier if you break things down, for example

On the HF input side - you can break down the parts like this

You have a basic band pass ( H.P + L.P) at the start, then a 2nd order active high pass filter followed again by a band pass ( H.P +L.P)
Now take each of those blocks and put them through a online calculator and see what is going on. I am not doing anyone's homework, that is left for you to do, but just to get you started - the first H.P has a 3dB roll off at about 1kHz.

 

[jamescarter1982]

It is easier if you break things down, for example

On the HF input side - you can break down the parts like this

View attachment 293470
You have a basic band pass ( H.P + L.P) at the start, then a 2nd order active high pass filter followed again by a band pass ( H.P +L.P)
Now take each of those blocks and put them through a online calculator and see what is going on. I am not doing anyone's homework, that is left for you to do, but just to get you started - the first H.P has a 3dB roll off at about 1kHz.

thank-you that is very helpfull and gives me a good starting point . would you suggest looking at that that the filters are stacked to create a steeper crossover filter ? I remember in the literature it talks of 30db filters . please can I ask are active crossovers working in smartly the same way as a passive filter only using smaller components or diff comments to do the job of an lcr filter .
now that you've started breaking it down it doesn't seem so completely impossible thank-you!!
my idea was to find a suitable crossover piont in software and then alter the one on the plate amp to reproduce it

 

[justjason]

would you suggest looking at that that the filters are stacked to create a steeper crossover filter ?

Yes and no.
Your passive filters are there to confine the frequency to useful values that the active crossover can work with. There is also impedence matching and a few more things going on. It will also provide a steeper cut off. Those after the active crossover are doing a similar job, but filtering out any unwanded stuff that may be coming out of the op amp

 

[jamescarter1982]

OK thank-you I think I understand . so they are passive line level crossovers in front and after an active crossover using opamps ? where would you suggest starting to understand this stuff the art of electronics as earlier mentioned ?
ima carpenter by trade so used to reading plans and quite practical this just seems such a massive subject to try and understand

 

[justjason]

The best advice I can give is focus on breaking things down into small chunks, the smaller the better. Once you have chunks, google all you can to understand the small chunk you are looking at. Unless you want to dive into full design from scratch complex projects, you dont really have to understand everything, just the basic logic how stuff works. The rest is for later.
In the beginning everything seems like complete magic, but after a while, you start to see the building blocks and understand the basic functions. Like every thing - practice makes perfect.

 

[DSJR]

Do be warned as regards the AVI NuNeutrons - This model was tested along with other monitors of twenty odd years back and this included the ATC 20ASL pro's (which measured similarly to Amir's sad test of the 19V1). The NuNeutrons have a 'Linn Kan' response, 50Hz to just over 1kHz rising in a straight line 10dB or more from 100 to 1kHz approx, the tweeter then set at the nominal 500Hz level

https://dt7v1i9vyp3mf.cloudfront.net/assetlibrary/n/ns10m.pdf?jQWj8tYIeZeymRCNXitG9Qfwq9mLf1t0=

 

[jamescarter1982]

thank-you for the advise justjason and thanks for the link dsjr I haven't seen that test .
I must say that I really like the sound of them and any abnormalities I could iron out with dsp anyway .
guess it goes to show you like what you like I've owned the mackie 824mk2 and didn't like the sound of those from the first time I turned them on and they're quite highly rated

 

[MaxwellsEq]

You can learn some simple "rule of thumb" heuristics quite quickly. For example, Ohm's law turns out to be essential in pretty much all electronics work. If you fix electronic equipment, you get used to mentally dividing the object in half, testing one half and then dividing the problem again until you are down to a few parts that could be responsible for the failure.

If you want to design electronic systems, you need more formal knowledge. The further you dig in, the more you need to understand mathematics. However, these days, with spice-like simulators freely available, you can learn a lot through trial and error, without spending any money!

Electronics is a discipline that takes time to master. No-one has ever mastered it in a few months, but you can get proficient through reading and experimenting. The book "The Art of Electronics" is the best I've come across. It might be worth picking up a second hand copy.

 

[jamescarter1982]

You can learn some simple "rule of thumb" heuristics quite quickly. For example, Ohm's law turns out to be essential in pretty much all electronics work. If you fix electronic equipment, you get used to mentally dividing the object in half, testing one half and then dividing the problem again until you are down to a few parts that could be responsible for the failure.

If you want to design electronic systems, you need more formal knowledge. The further you dig in, the more you need to understand mathematics. However, these days, with spice-like simulators freely available, you can learn a lot through trial and error, without spending any money!

Electronics is a discipline that takes time to master. No-one has ever mastered it in a few months, but you can get proficient through reading and experimenting. The book "The Art of Electronics" is the best I've come across. It might be worth picking up a second hand copy.

thank-you . this is something Iver always been interested in . from a young age ... I'm nor sure why I have put off studying it I think that it has been a bit daunting for me but I think I'll read a little bit of that book every night and try and unpick the schematic as suggested above . then I can make a plan and see if it's doable for me !!

 

[MaxwellsEq]

thank-you . this is something Iver always been interested in . from a young age ... I'm nor sure why I have put off studying it I think that it has been a bit daunting for me but I think I'll read a little bit of that book every night and try and unpick the schematic as suggested above . then I can make a plan and see if it's doable for me !!

I started experimenting with speakers and radios when I was about 7. I continued doing that for years. I left secondary school with good grades in mathematics and physics. I then did an electronics degree before spending all my working years in engineering roles.

If it had been available (and I could have afforded it), much of The Art Of Electronics would have been suitable for me from about 12 to 15 years of age. If you struggle with it, you might find it helpful to brush up on high school mathematics and physics.

 

[LTig]

I started experimenting with speakers and radios when I was about 7. I continued doing that for years. I left secondary school with good grades in mathematics and physics. I then did an electronics degree before spending all my working years in engineering roles.

Same here, but I started at 10.

If it had been available (and I could have afforded it), much of The Art Of Electronics would have been suitable for me from about 12 to 15 years of age. If you struggle with it, you might find it helpful to brush up on high school mathematics and physics.

Absolutely. This book is a true gem, and when I discovered it I felt that my life as a youth would have been much easier with this book.