Kilowatt Plus. A DIY Power Amp Build.

[Chienmortbb]

The Connex modules do have a temperature output that makes it easier to monitor temperature and to turn on a fan if the temperature gets too high. I could add a fan circuit if needed and will leave space for it. 

[Chienmortbb]

Starting to look at the front panel and have come up against a problem with the VU meter. It is 80mm long, the same as the height of the enclosure but the mounting screws extend off the PCB. making a combined height of 84mm. So I either mount it horizontally or use a different VU meter. I could even use an analogue one like Ashdown.

 

 

Edited January 4, 2022 by Chienmortbb

[Chienmortbb]

Well what with the move, Covid and a new bamd this slipped on to the back burner but now I am back on it. I have drilled  the heatsink on one of the new modules and it is now installed. I have started the wiring. 

The mains wiring is done to one module. I tried to use the Faston connectors I had but they are too big and so I have had to order the correct ones. They will be here Monday or Tuesday then I can restart wiring and testing of the modules. 
 

Once the power amp modules are tested I can start on the wiring. More soon. 

[Chienmortbb]

I did not have much of a chance to do much today but I did a bit. If you look at the picture above, The left hand module in new and untested and the right hand one has lost all the screws that hold the mains cables.

 

So the first thing I did was to  replace the mains input socket on the RH module. All easy I thought. No chance. The pins were too big so I had to drill out the  holes. I was not sure whether the holes were plated through. So I had to malt sure the solder went right through. We will know tomorrow when I test it. 
 

I did test the other, newer module after rejigging and testing the mains wiring, Wiring was fine and the module worked fine. 
 

The new 4.8mm Faston connectors finally arrived this afternoon and I will start using them tomorrow. 

Edited May 12, 2022 by Chienmortbb

[Chienmortbb]

IAs you probably know by now, this project trundles on at its own pace. Today I wired up the amp modules to test that all was well. The protection lights for both modules came on and went off while the modules were settling down and a brief sound check on both was fine. As I was checking module B, I noticed that all the lights had gone out on module A. I checked everything But could not see the reason. Took it out and checked it out of the case.., all good but then when reinstalled it again was dead.  
 

Module A was the original module I bought and it has been on and out of the chassis, a new mains terminal block was fitted and it was the test module that has had lots of work done to it.I suspect it is something to do with the new mains terminal block.

 

So I got my drill out, drilled mounting holes on the spare module and that is now installed as module A. The original module has been put on the “look at later” pile.

All good now both modules working and now to start tha boring part, wiring. The switching arrangements are not that complicated but have added to the amount of wiring.  
 

I also need to make sure all the metal panels connect directly to earth. The black anodisation on the aluminium panels is not very conductive. 
 

I will take more pictures next time but it looks like a rats nest at the moment so that will wait. 

 

[Chienmortbb]

The speaker connections are done and I have tried to tidy them up with some cable ties. The cable is quite heavy duty as it carries the most current. The mains cable carries more power but you need thicker cable to higher currents. 

You might notice that the RED Speakon connector has two red cables. That is for Bridged operation where the +ve connection from both amps are used to drive the  speaker. Neutrik recommend that the 1+ and 2+ Terminals are used for bridged connection. This is to ensure that normal Speakon leads cannot connect to the amp in bridge mode. The thinking is that you have to know what cable to connect to get bridged operation but that installing a conventional Speakon cable would do no damage. 
 

The speaker cables should be twisted if possible but these are quite stiff and I can only get a couple of turns on them. Next to with up the inputs and switches. 

[Chienmortbb]

As with all these home brew projects, you are constantly re-evaluating the design and as Ivthink about the switch wiring, I realise that my thoughts were wrong. 

Bridging an amp  (or more correctly amps) require that two or more power amplifiers run in anti-phase. One amplifier will drive the +ve terminal of the speaker and the other will drive the -ve terminal of the speaker. By doing this we double the voltage swing across the speaker and potentially quadruple the power available. In reality most amplifiers will be currently limited, that is that they will only be able to supply a given amount of power and in most cases That would limit the increase in power to a factor of two.

Many of our favourite amps run bridged amps including the Ashdown RM range, Aquilar TH range and some GK amps like the MB200.

 

Of course there is no such thing as a free lunch and the increase in power comes with several negative including increased distortion. Luckily in most cases this is minimal and still well below what we could hear. 
 

Tfe problem with the Kilowatt design as shown in the  original wiring diagram is that the level or volume pots have to be set exactly by hand/eye to exactly the same level otherwise the distortion will rise considerably and one amplifier worked harder than the other. So I am now rethinking the wiring to take human error out of the equation.

 

[JapanAxe]

Am I right in thinking that in bridged mode there is no earth connection to the speaker output because each terminal is fed by a ‘hot’ connection?

[nilebodgers]

The info I could find for those Connex modules was sketchy in the extreme, so no idea on the topology. Are they not already bridged internally like the Icepower 200/500/800w modules that almost everyone uses?

[Chienmortbb]

1 hour ago, JapanAxe said:

Am I right in thinking that in bridged mode there is no earth connection to the speaker output because each terminal is fed by a ‘hot’ connection?

Yes I originally did a long explanation of bridging but it looked so complex I deleted most of it. Yes is you like the amplifiers push and pull. One amp goes +ve while the second goes -ve. So the voltage swing is doubled. This should increase the power by 4 times but in reality two is usually the best you can do.

[Chienmortbb]

3 hours ago, nilebodgers said:

The info I could find for those Connex modules was sketchy in the extreme, so no idea on the topology. Are they not already bridged internally like the Icepower 200/500/800w modules that almost everyone uses?

They are based on the IR/Infineon IRS2092 mosfet driver chip. More information at https://www.infineon.com/cms/en/product/evaluation-boards/iraudamp7d/.

However they also include an integral Switch Mode Power Supply. Connex have been supplying  SMPS and amplifiers for years for the DIY audio market. They are a bit cagey about publishing too much about their designs as they say the do incorporate  proprietary circuits that make them a cut above the usual Chinese modules and they charge accordingly.

Edited May 29, 2022 by Chienmortbb
awaiting clarity, I may be wrong!

[Chienmortbb]

So the rethink about the wiring, it is going deeper than I had thought. I have two choices, either I change the wiring and accept that the volume or level controls are at max in bridge mode or accept that I am unlikely to need an amp outputting close to  1200W into 8 ohms. To achieve bridge mode while taking out the volume controls in bridge mode would require an inverter stage and this is a lot of fuss for something I will probably never need. However it may be possible using the DSP but the learning curve for the DSP is quite high  and I really need to have a working amp quite soon.

 

I am going to investigate and make a decision tomorrow. If I do decide to go deeper into DSP then there are other things may be possible.

 

[Chienmortbb]

3 hours ago, nilebodgers said:

The info I could find for those Connex modules was sketchy in the extreme, so no idea on the topology. Are they not already bridged internally like the Icepower 200/500/800w modules that almost everyone uses?

Many of the ICEPower modules are bridged for maximum power for example the ASX series as used by many, are really stereo modules that have been bridged for use in bass amps. Let’s take some examples. The Aguilar TH350 uses the 125ASX2 bridged to give a conservative 350 watt rating into 4 ohms. The 125ASX2 is rated at 125watts per channel into 4 ohms but bridged can achieve between 250-450 watts bridged depending on how you measure it and how you cool it. The. Same module is used in the. RM500 by Ashdown as far as I know and I’m that case they rate it at 450 watts. The TH500 uses the 250ASX2 module. The GK MB200 and several

of their 200 watt combos use the 50ASX2 module and all have to have have bridging circuits added to the preamp to achieve this. 
 

The 700 and 800 watt modules used by the like of Mesa etc. are not bridged, they use the later AS700 module that is a single ended module capable of 350/700 watts into 4/8 ohms.

 

 

 

 

 

[nilebodgers]

The 700AS1 is internally bridged according to the data sheet. It just isn’t explicitly split into stereo channels like the 125asx etc. (see https://doc.soundimports.nl/pdf/brands/ICEpower/700AS1/ICEpower700AS1_Datasheet_1_8.pdf page 22)

[Chienmortbb]

1 hour ago, nilebodgers said:

The 700AS1 is internally bridged according to the data sheet. It just isn’t explicitly split into stereo channels like the 125asx etc. (see https://doc.soundimports.nl/pdf/brands/ICEpower/700AS1/ICEpower700AS1_Datasheet_1_8.pdf page 22)

That shows the internal balanced input circuit but the output from that is single ended feeding the power amp. It could be that there is bridging going on inside the 700AS1 but as you say, the ASX range have two separate amplifiers that have to be fed antiphase signals.

[nilebodgers]

10 minutes ago, Chienmortbb said:

That shows the internal balanced input circuit but the output from that is single ended feeding the power amp. It could be that there is bridging going on inside the 700AS1 but as you say, the ASX range have two separate amplifiers that have to be fed antiphase signals.

In the output description it says “The output stage is a full bridge topology with a 2nd order filter.”.   That says it all, neither side of the speaker connection is a ground, both are signal (in antiphase).

[nekomatic]

I’m no PA guru but I find it hard to imagine the use case where you need to put 1200 W into a single load but couldn’t split the load across two channels instead. 

[Chienmortbb]

9 hours ago, nekomatic said:

I’m no PA guru but I find it hard to imagine the use case where you need to put 1200 W into a single load but couldn’t split the load across two channels instead. 

I was starting to think that way. The easiest and most sensible course is to abandon the bridge mode possibly utilising the switch as a stereo/dual mono switch.

[Chienmortbb]

11 hours ago, nilebodgers said:

In the output description it says “The output stage is a full bridge topology with a 2nd order filter.”.   That says it all, neither side of the speaker connection is a ground, both are signal (in antiphase).

Well spotted, I missed that.  However unlike the ASX series modules, the circuitry is built on the board so it does not need external bridging circuits.

Edited May 30, 2022 by Chienmortbb

[Chienmortbb]

Looking back at the reat panel, I now have  redundant holes, the Stereo/Bridge swith and the Bridged Speakon in the centre.

 

I have decided to put a grille over the two holes that will act as the air inlet for a small fan. The white writing will be covered by black paint as the text is all engraved and filled with white paint currently. The amplifier modules have a temperature monitoring pin each, such that I can turn a fan on, only if the temperature rises too far.

Edited May 30, 2022 by Chienmortbb
add info

[Chienmortbb]

One of the lessons from this little blip is firstly to to get your design down on screen and/or paper before committing to any hardware and secondly to read datasheets properly. Each hole in the panel  costs money so I have wasted a few £s there.

 

On the subject of the panels, I may have already mentioned it but the holes to attach the IEC/Switch/fuse module to the panel were threaded. As a result there is no need for a nut on the inside. The extra cost was 11p per hole (£0.11). The cost of doing all the screw holes would have would have been about £2.50. It has cost more than that to buy nuts so it was a false economy to not get all the holes threaded.

[itu]

10 hours ago, Chienmortbb said:

...get all the holes threaded.

It is easy to make threads, but not so easy to make them straight...

[Chienmortbb]

I decided to collect my thoughts by tidying the wiring diagram so here is Version 1.1. I have converted it to an image so it shows up on here. I have one more major decision to make, whether to include a level meter on the front. Nearly all power amps do and I have two options, one is a bar type display but that is 80mm long so would only fit horizontally. The other uses 5 standard LEDS and is more than good enough to see whether the amp is being over driven. I might get two prototype front panels made and then decide or I might just draw it and make a decision from the line drawings. Anyway here is the version 1.1 interconnection/wiring diagram.

 

Edited June 5, 2022 by Chienmortbb

[Chienmortbb]

I am going to do soak testing when I can locate my dummy loads. I plans to test over a long period at 50 watts continuous and the diagram below shows how it will be wired, There will be no ancillary components or circuits, just the power amps. 50 watts has been chosen as amps are rarely driven flat out, all the time, and that is the power of my dummy loads at the moment.

 

 

 

 

 

[Chienmortbb]

It occurs to me that I have not shown the full spec of the IRS500SMPS modules.  I will post it start as well as it was an omission. The datasheet is being updated as we speak but here are the main points are shown below.

 

• Output Power: 542W at 4Ω, or 306W at 8Ω, with max. 0.1% THD+N, @230V supply voltage.
• Output Power: 525W at 4Ω, or 302W at 8Ω, with max. 0.1% THD+N, @120V supply voltage.
• Output Power on 2R load: 468W @ 1% THD+N, current limited, supplied at 230V or 120V mains voltage.
• Audiophile sound Quality: 0.01% THD+N at 378W at 4Ω or 198W at 8Ω @230V or @120V mains voltage.
• Maximum Output Power: 637W at 4Ω, or 357W at 8Ω, with max. 10% THD+N, @230V supply voltage.
• High efficiency: Up to 87.4% @500W on 4Ω, or up to 89.6% 300W at 8Ω with 230V mains supply voltage.
• Idle Power consumption: Muted: 2.5-3W; Un-Muted without Input Signal: ~8W.
• Full Protection set included: Short-circuit, over-current, over-temperature.
• Sensitivity: 1.5V for 500W on 4Ω or 1.64V for 300W on 8Ω rated output power. Amplifier gain is 29.81.
• Can be feed either with Balanced or Unbalanced Input signal, and a simple 3 pins Volume Potentiometer can be connected directly to the IRS500SMPS Audio Amplifier Module dedicated pins.
• Mute control, Status and Temperature feedback pins for controlling the amplifier status within the system.
• Compact size 150x50mm, and 37mm tall.