Contemplating using these transformers for my 686 build from RS.
RS PRO 230V ac, 2 x 25V ac Toroidal Transformer, 500VA 2 Output | RS Components
Is there any reason why I couldn't stack these one on top of the other in the case with a single bolt through both?
RS PRO 230V ac, 2 x 25V ac Toroidal Transformer, 500VA 2 Output | RS Components
Is there any reason why I couldn't stack these one on top of the other in the case with a single bolt through both?
kille99,
Stacking of toroidal transformers one on top of the other should be fine.
Only word of caution is do not in any way create a "shorted turn" installing the transformers in the chassis.
p.s. I clicked on the link for the transformers you are planning to get. Those are quite tall (65 mm) according to the product web page - does your case have required internal height for comfortably accommodating 2 of those stacked ?
Also the wires come out of the bottom, and the transformers are potted; there is a chance that the top of the bottom transformer might press the wires of the top transformer around its bottom edges.
And IIRC, for a stereo Mod-686 build, Tom advises a single 500VA unit.
Stacking of toroidal transformers one on top of the other should be fine.
Only word of caution is do not in any way create a "shorted turn" installing the transformers in the chassis.
p.s. I clicked on the link for the transformers you are planning to get. Those are quite tall (65 mm) according to the product web page - does your case have required internal height for comfortably accommodating 2 of those stacked ?
Also the wires come out of the bottom, and the transformers are potted; there is a chance that the top of the bottom transformer might press the wires of the top transformer around its bottom edges.
And IIRC, for a stereo Mod-686 build, Tom advises a single 500VA unit.
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According to RS support the wires come out the side with the top and bottom both flat.
The height isn't a problem, I have 155mm to play with.
The only other concern I have is the amount of weight 2 of these stacked is - 7kg - and what that would do to the 3mm aluminium base should I ever have to transport it and it gets dropped.
The height isn't a problem, I have 155mm to play with.
The only other concern I have is the amount of weight 2 of these stacked is - 7kg - and what that would do to the 3mm aluminium base should I ever have to transport it and it gets dropped.
killie99,
If you are building a stereo Mod-686, you do not need 2 x 500VA units - according to Tom's website, 1 x 350-500VA transformer with 2 secondaries (e.g 2 x 25V) is enough:
Modulus-686: 360W power amplifier achieving -120dB (0.0001%) THD – Neurochrome
If you are building a stereo Mod-686, you do not need 2 x 500VA units - according to Tom's website, 1 x 350-500VA transformer with 2 secondaries (e.g 2 x 25V) is enough:
Modulus-686: 360W power amplifier achieving -120dB (0.0001%) THD – Neurochrome
With heavy transformers, the optional "holey" plate the ModuShop offers starts to look like a good option. Alternatively, you could use an L or U shaped aluminum extrusion to stiffen up the bottom plate of the chassis.
I would probably put the transformers side-by-side rather than stacking them, though. Then make a mezzanine plate to go above the transformers and mount the power supply here. Just be careful not to create a shorted turn through the transformer.
Tom
I would probably put the transformers side-by-side rather than stacking them, though. Then make a mezzanine plate to go above the transformers and mount the power supply here. Just be careful not to create a shorted turn through the transformer.
Tom
See at the bottom here: Design Notes
Or read the design documentation for my Power-86 and/or Power-686...
Tom
Or read the design documentation for my Power-86 and/or Power-686...
Tom
And to avoid the shorted turn and yet let you fix a multi-kilogram transformer of an inconvenient shape (squat cylinder, no base plate with four convenient mounting holes a la E+I types) to the floor of your chassis, you typically need a mounting plate: a circular metal plate with a bolt-hole in its centre. If your transformer manufacturer gives you a mounting kit with plate and bolt, then that's great, else I've found such plates from RS Online. My transformer maker does not give such plates.
I sometimes feel it would be better to have either a metal case to cover the transformer and mount it (available in certain smaller sizes from eBay) or get metal brackets to straddle the transformer and bolt down on either side. Two such brackets at 90 degrees will hold the transformer down better than a central bolt and mounting plate will. But don't know any source of such brackets.
I sometimes feel it would be better to have either a metal case to cover the transformer and mount it (available in certain smaller sizes from eBay) or get metal brackets to straddle the transformer and bolt down on either side. Two such brackets at 90 degrees will hold the transformer down better than a central bolt and mounting plate will. But don't know any source of such brackets.
Hi all, I'm relatively new to diy audio and in the process of building a 686.
Tom pre populated the boards, I'm just doing final assembly into a modushop case.
I've the amp up and running..it sounds superb apart from an annoying low level crackle noticeable at very low volumes or when nothing playing.
Its coming from both speakers,. Ive tried swapping mains cables and preamp inputs ..no change.
Its likely a dodgy solder joint or lead internally. Any tips on where to start? Im guessing not the boards themselves as these were tested by Tom. I think Tom is off camping this week so thought I would ask you seasoned builders!
Tom pre populated the boards, I'm just doing final assembly into a modushop case.
I've the amp up and running..it sounds superb apart from an annoying low level crackle noticeable at very low volumes or when nothing playing.
Its coming from both speakers,. Ive tried swapping mains cables and preamp inputs ..no change.
Its likely a dodgy solder joint or lead internally. Any tips on where to start? Im guessing not the boards themselves as these were tested by Tom. I think Tom is off camping this week so thought I would ask you seasoned builders!
Tom,
In the documentation you mention using the non-isolated version of the LM-3886 if you are running regulated 36V rails. I am going with an Antek 22V transformer for now. I may want to upgrade to a 25V Antek in the future. Would it be best if I used the non-isolated LM-3886 over the isolated version? Currently placing my order for the LM-3886 (including the replacement for my shorted out Mod-86 board) and just wanted to be sure.
On the heat sink, does it matter where the the LM-3886’s are mounted? Centered, lower third, or upper third. I was going to mount them flush to a 5U heatsink instead of at right angles using your brackets.
In the documentation you mention using the non-isolated version of the LM-3886 if you are running regulated 36V rails. I am going with an Antek 22V transformer for now. I may want to upgrade to a 25V Antek in the future. Would it be best if I used the non-isolated LM-3886 over the isolated version? Currently placing my order for the LM-3886 (including the replacement for my shorted out Mod-86 board) and just wanted to be sure.
On the heat sink, does it matter where the the LM-3886’s are mounted? Centered, lower third, or upper third. I was going to mount them flush to a 5U heatsink instead of at right angles using your brackets.
If you plan to upgrade to ±36 V rails (so use a 2x25 VAC transformer), I would build the amp with the LM3886T, thermal pads, shoulder washers, etc.
Heat rises. It's a gravity thing... But it also conducts through metal. So my recommendation is to mount the LM3886es roughly 1/3rd up on the heat sink.
PSA: Buying the LM3886 directly through TI is often cheaper than through Mouser, especially for the LM3886T. TI charges $6.99 flat rate shipping and ships by FedEx. I just ordered 500 of them for the upcoming MOD686 build.
Tom
Heat rises. It's a gravity thing...
But it also conducts through metal. So my recommendation is to mount the LM3886es roughly 1/3rd up on the heat sink.PSA: Buying the LM3886 directly through TI is often cheaper than through Mouser, especially for the LM3886T. TI charges $6.99 flat rate shipping and ships by FedEx. I just ordered 500 of them for the upcoming MOD686 build.
Tom
Hello,
I need some advices regarding PSUs for Modulus-86 and Modulus-686 :
What is the best choice for Modulus-86 - for a 8 Ohms driver - between :
- 2 mono blocks with each 1 toroid 160VA 2x25V + 2 double rectifiers bridges with fast schottky + 2x 10.000uf per rail (so 40.000uF per block)
- 1 stereo block with 1 SMPS300RE 36V from Connex ?
What is the best choice for Modulus-686 - for a 8 Ohms driver and 2 heatsinks with a thermal resistance of 0.45 K/W each - between :
- 2 mono blocks with each 1 toroid 450VA 2x24V + 2 double rectifiers bridges + 3x 15.000uf per rail (so 90.000uF per block) ?
- 2 mono blocks with 2 chinese SMPS 32V like fluid's one : https://www.diyaudio.com/forums/ven...er-amp-extremely-low-thd-119.html#post5996456 ?
- 1 stereo block with 1 SMPS2000R 26V from Connex ?
Many thanks !
I need some advices regarding PSUs for Modulus-86 and Modulus-686 :
What is the best choice for Modulus-86 - for a 8 Ohms driver - between :
- 2 mono blocks with each 1 toroid 160VA 2x25V + 2 double rectifiers bridges with fast schottky + 2x 10.000uf per rail (so 40.000uF per block)
- 1 stereo block with 1 SMPS300RE 36V from Connex ?
What is the best choice for Modulus-686 - for a 8 Ohms driver and 2 heatsinks with a thermal resistance of 0.45 K/W each - between :
- 2 mono blocks with each 1 toroid 450VA 2x24V + 2 double rectifiers bridges + 3x 15.000uf per rail (so 90.000uF per block) ?
- 2 mono blocks with 2 chinese SMPS 32V like fluid's one : https://www.diyaudio.com/forums/ven...er-amp-extremely-low-thd-119.html#post5996456 ?
- 1 stereo block with 1 SMPS2000R 26V from Connex ?
Many thanks !
Not all Chinese SMPS are the same, the ones I used (and another member used the same ones in their build too) are built very well and the main components seem to be of a high standard. I have quite a few of these and I have had no issues with any of them but I don't run them 24/7 either.
I have not seen any others that look anywhere near as good. If you can't get good quality ones I would look at the other options.
I would scrap the Schottky diodes. They're not a good tool for the job. You can read more details on that here: Taming the LM3886 Chip Amplifier: Rectification and Snubbers – Neurochrome. What you want is soft recovery diodes with a low reverse recovery charge.
Either supply will be fine for the Modulus-86. I do have a slight preference for the SMPS due to size and weight reasons.
0.45 K/W is not enough for a Modulus-686 amp running beyond ±26-27 V. If you choose to squeeze the heat sink size that hard, I suggest that you fit the heat sink with a temperature sensor and rig it to shut the amp down when the temperature exceeds 60-65 ºC.
My personal preference for an SMPS at that voltage would be a pair of Mean Well RPS-400-27-C. In fact, that's what I used in my Modulus-686 builds. They work great!
If you don't like the Mean Well units, I'd go with a transformer-based solution. 2x22 VAC @ 400 VA.
I just posted a page on my amplifier recommendations on my website this morning. You will probably find it insightful: Choosing Your Neurochrome Amplifier.
Tom
From Orion Pluto users group, there was considerable discussion on the maximum power that was needed for the two woofers. This is the definitive post:
"The whole power requirement paradigm for typical box woofer/subwoofer usage is turned on its head with these Linkwitz systems.
Remember, the drivers are operating in (pretty much) free air. There is also considerable low frequency equalization applied. This means the drive voltage decreases at a steep rate as you go higher in frequency.
At 20Hz the L26 drivers can be driven to Xmax with 36 volt peaks. That corresponds to an amplifier with a rated 8 ohm power of 80wpc. (And because of the equalization 20Hz is worst-case.)
So, for typical usage, an amplifier rated at anything higher than 70wpc is providing gravy.....and potentially hazardous gravy.
The watchword is that you can easily fry the bass drivers by feeding them with too much power.
Craig
"The whole power requirement paradigm for typical box woofer/subwoofer usage is turned on its head with these Linkwitz systems.
Remember, the drivers are operating in (pretty much) free air. There is also considerable low frequency equalization applied. This means the drive voltage decreases at a steep rate as you go higher in frequency.
At 20Hz the L26 drivers can be driven to Xmax with 36 volt peaks. That corresponds to an amplifier with a rated 8 ohm power of 80wpc. (And because of the equalization 20Hz is worst-case.)
So, for typical usage, an amplifier rated at anything higher than 70wpc is providing gravy.....and potentially hazardous gravy.
The watchword is that you can easily fry the bass drivers by feeding them with too much power.
Craig