LM3886 based 8 Channel amps for linkwitz Orion

[ST7677]

Originally Posted by Michael Bean

Here's what I think would be a good way to go. First build a normal stereo amp as I previously said to gain knowlege and experience, that amp should be built with the idea of eventually using it in the big project. After you get that accomplished and have a good feel for what it takes, proceed onward with the rest of the project. Andrew recommended building your amps in separate stereo and monoblock boxes which is generally a good idea, it will keep construction complexity down and makes the inevitable troubleshooting much easier. But one way I differ from Andrews' suggestion would be to build a two channel amp for the woofers and a three channel amp for the mid and tweeters for each stereo side, in other words, two amplifier boxes for each channel for a total of four for the whole project instead of the six that four stereo and two monoblcks would require. Here's a block diagram for clarity:

Mike

Hi Mike,
Thanks for taking time to draw this out.

I would like to understand what causes the improvement in sound. What is the logic behind this - crosstalk, voltage drop across channels on power surge, etc?

If I know the factors involved I can knowingly decide which approach to take for my design - 1 chassis, 2 chassis, 4 chassis or 6 chassis. Else it is just following someones recommendation without knowing the rational, hope you understand.

Regards

[Michael Bean]

It's not really a matter of improving sound per se, rather the avoidance of degrading sound quality. Due to the way the sound spectrum is generally apportioned, the woofers and mid range drivers will draw the most current from the amps, and the tweeters much less. So it makes sense to put the two woofer amps together in one box with a single power supply (both amps will be passing identical signals so they won't interfere with each other), and the mid and tweeter amps in another box sharing a single power supply (tweeter amps won't have much current draw and generally won't have as high of a signal level, so there won't be any problem sharing a power supply with the mid amp). And as I already stated, dividing amps into several boxes will make construction and troubleshooting easier. Keep in mind that the more complex something is, it's more likely there will be problems, and more difficult to work with. Another factor to consider is cost. Generally the boxes, heatsinks and hardware will be the most expensive items, followed by power supply components, and lastly the electronics.

Mike

[kevinahcc20]

Originally Posted by ST7677

Hi Kevin,
Did you try running the woofer with 50W single channel before you made it in bridge? If so did you find it inadequate?
Is there a perceptible difference in running the woofer 50W (single channel) or 100W bridge?

Finally have you made any adjustment to the ASP for dealing with higher power woofer channel? I guess it would lead to 3db gain in woofer channel.

Thanks

I originally powered my Orions with two 4 channel amps rated at 60 WPC & in this configuration the woofers were driven by 1 channel each. In this configuration it was possible to get clipping of the woofer channels although it required very bass-heavy program material and at listening levels much higher than I would typically use. The move to 100 WPC on the woofers eliminated this issue for me and the overall sound quality was improved.

There is no change to the ASP required but you must carefully balance the gain of each amplifier channel (single or bridged), so your amp should include a gain adjustment pot. I do this by starting with a tone at the W-M crossover frequency into the ASP and adjusting the gain of each woofer and midrange channel for an output voltage that corresponds to a gain of 26dB (SL's recommended level) with a tolerance of +/- 0.1dB. Once these are set move to a tone at the M-T crossover frequency and match the gain of the tweeter amps to the same gain value as the midrange without changing the previously set midrange gain! For this you will need a stable tone generator (I use a modified Heathkit IG18) and a good multimeter preferably with 4 1/2 digits and frequency and true RMS voltage measurement (I use a BK Precision 2834).

Finally before you dive in you may want to consider buying an amp (I know - heresy on a DIY forum). Similar to the ATI amp that SL recommends the Sonance 1250MKII amp I bought retails for $1700 new. But they regularly show up on eBay and Audiogon (unlike the ATI 1260) and the winning bid is typically around $500 (I paid $525). I suspect you will have a tough time keeping your parts expenditure under this level (chassis & heat sinks are the big hitter) and, as many others have commented, this is a huge undertaking for a 1st DIY build. Either way good luck...it will be worth the journey!

[ST7677]

Originally Posted by kevinahcc20

I originally powered my Orions with two 4 channel amps rated at 60 WPC & in this configuration the woofers were driven by 1 channel each. In this configuration it was possible to get clipping of the woofer channels although it required very bass-heavy program material and at listening levels much higher than I would typically use. The move to 100 WPC on the woofers eliminated this issue for me and the overall sound quality was improved.

Thanks Kevin, this is one of the most helpful information.
I thought that 50-60w would be inadequate for the woofer channel, but you have confirmed the same.

Originally Posted by kevinahcc20

Finally before you dive in you may want to consider buying an amp (I know - heresy on a DIY forum). Similar to the ATI amp that SL recommends the Sonance 1250MKII amp I bought retails for $1700 new. But they regularly show up on eBay and Audiogon (unlike the ATI 1260) and the winning bid is typically around $500 (I paid $525). I suspect you will have a tough time keeping your parts expenditure under this level (chassis & heat sinks are the big hitter) and, as many others have commented, this is a huge undertaking for a 1st DIY build. Either way good luck...it will be worth the journey!

Frankly speaking DIY process of building something in itself is great fun, learning and satisfying experience.
Plus, I would like to build an amp that by itself is better than an ATI or Sonance or any other commercial amp costing 5 times more

The amp budget is $1000 to $1500, depending on what configuration I take. I believe that is a lot of money to build a high quality chip amp!

I am a hardcore DIYer and have done many complex projects in my first attempt (though not in this space), so I am determined and confident enough to pull it off.

[ST7677]

Originally Posted by AndrewT

One 5channel amp dedicated to each Orion is far more likely to sound better than 12 or 16chipamps in a common chassis.

Personally I would build stereo amplifiers.
One stereo amp to the tweeter pair. One stereo amp to the woofer pair.
One monoblock to the Mid driver.
Total amp requirement for the 10driver Orions: 4 stereo amps and 2 monoblocks.

Originally Posted by Michael Bean

Andrew recommended building your amps in separate stereo and monoblock boxes which is generally a good idea, it will keep construction complexity down and makes the inevitable troubleshooting much easier. But one way I differ from Andrews' suggestion would be to build a two channel amp for the woofers and a three channel amp for the mid and tweeters for each stereo side, in other words, two amplifier boxes for each channel for a total of four for the whole project instead of the six that four stereo and two monoblcks would require. Here's a block diagram for clarity:

Mike

I have been reading up on this on forums and have got mixed opinions.

The positives of a separate power supply, seems to be...
+ Freedom from interconnected Audio Grounds (what does this mean???)
+ Less Crosstalk between channels - more stereo seperation leading to better imaging and depth
+ Don’t fight with other channel during intense musical passages, specially for low frequency
+ Provides greater dynamic range
+ Shorter speaker wire (but longer interconnects - they need to be balanced)
+ More audiophile gadget appeal - means highend serious business

Negatives being...
- More expensive - cost of extra chasis, transformer, rectifiers, etc
- Grounding issues
- More space requirement to house the extra chassis
- More weight


Where as Douglas Self, who is a good authority on Audio Amplifiers has following to share

In a multichannel amplifier, the power supply will fall into one of three types. In order of increasing cost, and allegedly decreased interaction between channels, these are:

1. The transformer, rectifiers, and reservoir capacitors are shared between channels.
2. Each channel has its own transformer secondary, rectifiers, and reservoirs. There is a single transformer but only the core and primary are shared.
3. Each channel has its own transformer, rectifiers, and reservoirs. Nothing except possibly the mains inlet and mains switch are shared.

In reality the only interaction experienced with (1) and (2) is a variation in maximum power output depending on how the other channels are loaded. With competent design signal crosstalk via the power supply should simply not happen.

The above leads me to believe the following in order of increasing expense and diminishing returns...
1. Common PSU (Power supply unit)
2. Separation of left vs right channel PSU
3. Separation of woofer PSU from Tweeter and Midrange PSU (as suggested by Mike)
4. Separation of all channels PSU on all sides (as suggested by Andrew)

[pacificblue]

The first thing you should do is to buy the Orion construction kit. It contains all the information you need to build the speaker and the cross-over plus the PCB for the latter.

The tweeter is a 6 Ohm model and paralleling them brings the impedance down to 3 Ohm. The woofers are 4 Ohm models and quite current hungry due to their high moving mass. There is a reason why Linkwitz himself recommends solid state amps for the task.

If you still want to try it with chip amps, follow Andrew's advice and build a mono- or stereo amp first. If you succeed, you can add more channels by Copy-&-Paste. If you don't, you cut your losses.

[ST7677]

Originally Posted by pacificblue

The first thing you should do is to buy the Orion construction kit. It contains all the information you need to build the speaker and the cross-over plus the PCB for the latter.

The tweeter is a 6 Ohm model and paralleling them brings the impedance down to 3 Ohm. The woofers are 4 Ohm models and quite current hungry due to their high moving mass. There is a reason why Linkwitz himself recommends solid state amps for the task.

If you still want to try it with chip amps, follow Andrew's advice and build a mono- or stereo amp first. If you succeed, you can add more channels by Copy-&-Paste. If you don't, you cut your losses.

Hi Pacificblue,
That is already agreed based on suggestions from Andrew and Mike, I will make 1 mono channel first, experiment with it and fine tune the circuit before building rest of the amps. Makes perfect sense.

But I still need to decide on the over all amp design and configuration. Building one channel will still not allow me to decide on those aspects - like single PSU or multiple one, how many chassis, etc.


Tweeter is 6 ohm but on the frequency range it operates on it dips down to 5 ohm (speaker has variable impedance based on the frequency).

Woofers are Peerless 830452 and each one is 8 ohm impedance. I am building Orion 3.3 ver.

Though I have not bought the Orion construction plan yet, but I have gone through the whole site to understand the project. With Construction plan, it should be a simple project to build. Moreover, Linkwitz doesn't provide any additional information on amplifier design in that plan. All amplifier requirements are mentioned in his public webpages and FAQ section.

Thanks,

[AndrewT]

Originally Posted by AndrewT

Only after all that, can you make an informed decision on whether a 3 channel or 5 channel or 16 chipamp version of the amplifier can be built to meet the Orion's requirements

You cannot make an informed decision until after you have informed yourself !

[kevinahcc20]

Originally Posted by ST7677

Though I have not bought the Orion construction plan yet, but I have gone through the whole site to understand the project. With Construction plan, it should be a simple project to build.

ST7677,

I am a pretty accomplished woodworker and have done a fair bit of electronics DIY and I would describe Orion as a straightforward but hardly simple project. A lot depends on how basic or exotic your choices are in materials, details and finishes on the cabinets. If you are going for painted MDF that helps alot but if your tastes are more toward solid woods with inlays, etc that's a lot tougher - and more fun! The ASP is simple enough to assemble but you will encounter some challenges in finding all of the tight tolerance film caps as that is an area of ongoing flux. Overall though your planned amp project is likely a good bit tougher than the speaker system.

[ST7677]

Originally Posted by kevinahcc20

ST7677,
I am a pretty accomplished woodworker and have done a fair bit of electronics DIY and I would describe Orion as a straightforward but hardly simple project. A lot depends on how basic or exotic your choices are in materials, details and finishes on the cabinets. If you are going for painted MDF that helps alot but if your tastes are more toward solid woods with inlays, etc that's a lot tougher - and more fun! The ASP is simple enough to assemble but you will encounter some challenges in finding all of the tight tolerance film caps as that is an area of ongoing flux. Overall though your planned amp project is likely a good bit tougher than the speaker system.

Hi Kevin,
Planning to use plyboard wood for the orion construction.
I have not decided on the final finish, but most likely it will be mix of clear lacquered Veneer with inlays, and duco paint (automotive finish).
I hear that with (latest DIY) 3.3version upgrade Linkwitz has revised the ASP components list to what is available today (as many of the earlier parts list were not available any more).
New Orion ASP PCB boards are also expected this month which are slightly simpler to assemble and offer more options.

With the circuit diagram, construction plan and PCB boards directly from Linkwitz and support from Orion forum, I am pretty comfortable with the Orion. I am only worried about the amps. I want pretty much the best that can be done with LM3886s

PS: Wishing happy independence day to all Indian