Dear Neurochrome Modulus-286 builders
After there is already a thread for the Mod-86 I thought for the sake of clarity I open a separate one for the Mod-286. Tom and / or the moderators please let me know whether you rather want that content somewhere else.
Other than that I am about to start my second ever Audio DIY project. I intend to build two Modulus-286 as Monoblocks to drive my KEFsR700 while being fed directly from the balanced output of my Auralic Altair.
The boards from Tom arrived in mint condition and I already got the parts from Mouser and therefore I am about to get started.
As I am new to SMD soldering, I got one of these practice kits on ebay, which Bill in another thread recommended and I watched some YouTube videos.
However I have my first choice to make. Which solder to use? Currently I have two solders at home. One with Pb another with Ag? I'd go with the Ag one or is the melting temp too high for some of the ICs?
Thx
SH
After there is already a thread for the Mod-86 I thought for the sake of clarity I open a separate one for the Mod-286. Tom and / or the moderators please let me know whether you rather want that content somewhere else.
Other than that I am about to start my second ever Audio DIY project. I intend to build two Modulus-286 as Monoblocks to drive my KEFsR700 while being fed directly from the balanced output of my Auralic Altair.
The boards from Tom arrived in mint condition and I already got the parts from Mouser and therefore I am about to get started.
As I am new to SMD soldering, I got one of these practice kits on ebay, which Bill in another thread recommended and I watched some YouTube videos.
However I have my first choice to make. Which solder to use? Currently I have two solders at home. One with Pb another with Ag? I'd go with the Ag one or is the melting temp too high for some of the ICs?
Thx
SH
Attachments
Practice kits are a good idea. Either solder should work just fine. It does take a higher temperature to do the Pb-free solder, but as long as your soldering iron has a way to adjust the temperature, you should be fine. The bigger heat risk is from bad technique -- heating for too long or repeated applications of heat. My own preference is for eutectic lead-bearing solder, like your Sn60Pb38Cu2 as it has worked well for me with less issues/hassles than the various Pb-free solders.
Tom has some good soldering info on his site.
Tom has some good soldering info on his site.
Thank you for starting a build thread. I'm looking forward to seeing your build develop.
As Brian mentions above, I have a small dissertation on how to choose solder on my website. You can find it here: https://www.neurochrome.com/choosing-solder/
Tom
As Brian mentions above, I have a small dissertation on how to choose solder on my website. You can find it here: https://www.neurochrome.com/choosing-solder/
Tom
Hi
Thanks for the soldering hints and also for pointing out Tom's article on that. Although I had read it before I had lost track as it is quite challenging as a noob to remember all the important things. So please bear with me.
So for today's progress. I started once more with my practice board to get the solder temps right and ended up with ca. 370-380degC. I have a digital temp controlled solder station but don't know how accurate the display really is. So don't take it for granted. As described within Tom's excellent description I started with the resistors. However I had to crank up the temp (430degC) considerably for the big resistor SMDs. I assume they and the pads draw more heat. At the end of the hour I had soldered the first three resistor values on both boards, checked them off in the BOM and on the package as they tested out ok.
Phew. Now off to dinner.
Please comment or had hints on my solder result. Not all is lost yet ;-)
Thanks for the soldering hints and also for pointing out Tom's article on that. Although I had read it before I had lost track as it is quite challenging as a noob to remember all the important things. So please bear with me.
So for today's progress. I started once more with my practice board to get the solder temps right and ended up with ca. 370-380degC. I have a digital temp controlled solder station but don't know how accurate the display really is. So don't take it for granted. As described within Tom's excellent description I started with the resistors. However I had to crank up the temp (430degC) considerably for the big resistor SMDs. I assume they and the pads draw more heat. At the end of the hour I had soldered the first three resistor values on both boards, checked them off in the BOM and on the package as they tested out ok.
Phew. Now off to dinner.
Please comment or had hints on my solder result. Not all is lost yet ;-)
Attachments
Last edited:
370 ºC (700 ºF) is about right for leaded solder. If you can't get the solder to flow well on the larger components at that temperature, try a larger tip before cranking up the temperature.
Looks like you need a bit more practice with the 0603 size if you plan to solder a lot of those. Thankfully, the MOD286 is 0805 or larger, with the exception of a small handful of diodes that are annoyingly small (SOD-123 package). I'd say do another row of 0805 and see if you can use slightly less solder and make it drape a bit better on the resistor terminals. You might need to hold the soldering iron on the resistor terminal for a second longer to make the solder drape nicely.
You're doing well so far, though. Good call on getting one of those SMD practice boards. They're only a buck or two on eBay.
Tom
Looks like you need a bit more practice with the 0603 size if you plan to solder a lot of those. Thankfully, the MOD286 is 0805 or larger, with the exception of a small handful of diodes that are annoyingly small (SOD-123 package). I'd say do another row of 0805 and see if you can use slightly less solder and make it drape a bit better on the resistor terminals. You might need to hold the soldering iron on the resistor terminal for a second longer to make the solder drape nicely.
You're doing well so far, though. Good call on getting one of those SMD practice boards. They're only a buck or two on eBay.
Tom
Yes, Pb-free solder melts at a higher temperature than SnPb types. I've seen recommendations in the 750-800F range (400 - 425C). It varies depending on the alloy, so check the solder manufacturer's datasheet. As Tom said, for physically larger components you should use a bigger tip to allow more heat flow to the part. Just cranking up the temperature of a tiny tip is not the way to get there.
I had to consult my own website to get the melting points of the lead-free solder with Ag. 
It melts at around 225 ºC - about 50 ºC higher than leaded solder. I'd crank the soldering iron up to 425 ºC. Or consider switching to 60/40 or 63/37 leaded solder. They're a lot easier to work with. It also looks like you have some Sn/Pb/Cu available. I'm not familiar with that alloy, but you could try it out.
Edit: A quick Wikipedia read reveals that the 60/38/2 Sn/Pb/Cu alloy increases the hardness of the solder joint and prevents the molten solder from dissolving the metals in the joint. It should behave like 60/40 in actual use. It enters the plastic region at 183 ºC and melts at 190 ºC. I'd use a 370 ºC iron with that.
Tom
It melts at around 225 ºC - about 50 ºC higher than leaded solder. I'd crank the soldering iron up to 425 ºC. Or consider switching to 60/40 or 63/37 leaded solder. They're a lot easier to work with. It also looks like you have some Sn/Pb/Cu available. I'm not familiar with that alloy, but you could try it out.Edit: A quick Wikipedia read reveals that the 60/38/2 Sn/Pb/Cu alloy increases the hardness of the solder joint and prevents the molten solder from dissolving the metals in the joint. It should behave like 60/40 in actual use. It enters the plastic region at 183 ºC and melts at 190 ºC. I'd use a 370 ºC iron with that.
Tom
Last edited:
Wow. You guys are great. Thank you so much. The Sn/Pb solder I had already for years and I am used to it and it's easy to work with. I guess I run a few more practice rounds on the tryout board and see if I can get more proficient with the Ag solder.
BTW. I am using currently a 0.6mm chisel shaped soldering tip. Should I get a bigger one for the larger parts?
Do you think I have to redo the already soldered parts? Is there a way to salvage or improve the joints? Or would I only make things worse by subjecting these parts to heat again?
BTW. I am using currently a 0.6mm chisel shaped soldering tip. Should I get a bigger one for the larger parts?
Do you think I have to redo the already soldered parts? Is there a way to salvage or improve the joints? Or would I only make things worse by subjecting these parts to heat again?
Last edited:
I wouldn't bother with redoing anything on the practice board. If you've started soldering the Modulus-286, I'd take a close look at the solder joints. If they look good - i.e. are shiny in appearance and drapes nicely on the component terminals - I wouldn't bother redoing anything. However if the solder balls up on the component terminals, I'd wick up the solder using de-solder braid (Solder Wick is one brand name) and redo the joints. You'll probably find that there's enough solder to hold down the component once you've wicked up "all" the solder. That's fine. Wick up as much as you can and re-solder.
It's probably overdoing things to rework the solder joints, but then again you're spending a good chunk of time and money. It's more fun to have the project work from the start so it seems wise to spend a little time up front.
Tom
It's probably overdoing things to rework the solder joints, but then again you're spending a good chunk of time and money. It's more fun to have the project work from the start so it seems wise to spend a little time up front.
Tom
62/37/1Cu is the eutectic and it melts/solidifies @ the same 183degreesC as the 63/37 eutectic.
The extra copper helps prevent copper going into solution. Especially useful for copper tips of soldering irons (some times sold as SavBit).
I would always use the eutectic to avoid the pastey region where movement during cooling can damage the joint.
Another very useful eutectic is the 62/36/2ag 179degreesC
The silver content lowers the melting temp very slightly and gives some extra strength to the joint, but it's main attribute is reducing solubility of the silver from silver plated wires/leads.
The extra copper helps prevent copper going into solution. Especially useful for copper tips of soldering irons (some times sold as SavBit).
I would always use the eutectic to avoid the pastey region where movement during cooling can damage the joint.
Another very useful eutectic is the 62/36/2ag 179degreesC
The silver content lowers the melting temp very slightly and gives some extra strength to the joint, but it's main attribute is reducing solubility of the silver from silver plated wires/leads.
Last edited:
I dug up the data sheet of the non lead solder I am using (see first post). Sn95Ag4Cu1. It is eutectic and the high silver content lowers the melting point to 217degC which is in the ballpark of the lead based solders (183deg C)
http://www.stannol.de/fileadmin/Service/Dokumente/Dokumente_TDB/SB/TDB_ME_FLOWTIN_TSC_EN.pdf
Anyhow. Let me draw some conclusions for me from this interesting discussion:
- Eutectic is preferable
- Don't crank up the heat too much but look into a tip with more mass (also to avoid brownish color of flux core residues)
- Read Tom's article for details
- Practice
Therefore I think as the solder is ok I just need to practice some more with the SMD board and possibly get a higher mass tip for the bigger solder tasks.
http://www.stannol.de/fileadmin/Service/Dokumente/Dokumente_TDB/SB/TDB_ME_FLOWTIN_TSC_EN.pdf
Anyhow. Let me draw some conclusions for me from this interesting discussion:
- Eutectic is preferable
- Don't crank up the heat too much but look into a tip with more mass (also to avoid brownish color of flux core residues)
- Read Tom's article for details
- Practice
Therefore I think as the solder is ok I just need to practice some more with the SMD board and possibly get a higher mass tip for the bigger solder tasks.
Last edited:
... some more practice and some 15 more resistors soldered today. Definitely getting better... other than that, no built topics to contemplate today.
Therefore let me go back way to the beginning of all that and share my selection decision for the Mod286.
Selecting a DIY Amp.
My selection criteria was to get two mono amps with balanced inputs which measure excellently and which had received great reviews from the community since as with most DIY projects, it is hard to organize a listening test beforehand. THD+N <0.0005% was convincing for me. Especially as I plan to build the amps with the optional 20dB gain, which should bring further improvement over the standard 26dB.
The KEFs R700 are specified for 8ohm (although stereophile measurements show impedance as low as 3.2ohm)
https://www.stereophile.com/content/kef-r700-loudspeaker-measurements
The 60 W (8 Ω), 100 W (4 Ω) of the Mod286 in mono config together with the ca 87dB sensitivity of the speakers should give me about 85dB with 2watts at my ca 3m listening distance.
Peak SPL Calculator
Tom also has an article about selecting power supplies considering the crest factor of music on his web site
https://www.neurochrome.com/wp-content/uploads/2014/10/ClassAB_Calculator.xlsx
Here I have a question. Given the above setup and the above average 85dB SPL. Would my two Mod286 mono give me enough peak power to play music with a 20dB crest factor?
Therefore let me go back way to the beginning of all that and share my selection decision for the Mod286.
Selecting a DIY Amp.
My selection criteria was to get two mono amps with balanced inputs which measure excellently and which had received great reviews from the community since as with most DIY projects, it is hard to organize a listening test beforehand. THD+N <0.0005% was convincing for me. Especially as I plan to build the amps with the optional 20dB gain, which should bring further improvement over the standard 26dB.
The KEFs R700 are specified for 8ohm (although stereophile measurements show impedance as low as 3.2ohm)
https://www.stereophile.com/content/kef-r700-loudspeaker-measurements
The 60 W (8 Ω), 100 W (4 Ω) of the Mod286 in mono config together with the ca 87dB sensitivity of the speakers should give me about 85dB with 2watts at my ca 3m listening distance.
Peak SPL Calculator
Tom also has an article about selecting power supplies considering the crest factor of music on his web site
https://www.neurochrome.com/wp-content/uploads/2014/10/ClassAB_Calculator.xlsx
Here I have a question. Given the above setup and the above average 85dB SPL. Would my two Mod286 mono give me enough peak power to play music with a 20dB crest factor?
Last edited:
20dB = Factor 10. Why do I need factor 100, that is 200W for music with a crest factor of 20dB? Is it because energy requirement scales with the second power?
Also assuming 2W on average gives me the desired average SPL. Wouldn't a crest factor of 20dB (100x) not also mean that 2W/50x is the lowest and 2w x 50 = 100W is the highest power requirement and not 200W?
Can one mono Mod286 deliver a peak power of 200W? I would assume that 7A max peak current with +-28V rail voltage = 196W might just get it there?
Please correct my thinking.
Thx
SH
Last edited:
Andrew thanks for clarify the first question.
The answer to second questions is "no". I think I was able to answer that one myself by looking up the definition of the crest factor in wikipedia. CF = Ppeak^2/Paverage (which also answers question one, actually) and therefore 200W would be required assuming 2W is the Paverage.
With the third question I am still struggling and I think what confuses me is the disctinction between Paverage, P RMS and Ppeak of an amplifier (e.g. Mod286). I have re-read the section on output power and supply design on Tom's webpage
https://www.neurochrome.com/taming-the-lm3886-chip-amplifier/
but somehow I don't get my head around it.
The mono Mod286 gives out 50W at 8ohm or 100W at 4ohm with +-35V rail voltage (output voltage power supply Vcc) according to the table at the very beginning of the section "Output Power". However when using the approximating formula P=Vcc^2/2/SpeakerImpedance and plugging in 35V and 8ohms, P=76W.
Where am I wrong? What is the short term peak output power of the mono Mod286 for 8ohm speakers (50W, 76W, other value?) available to reproduce the loudest tone in a music with 20dB crest factor?
Thanks for bearing with me.
SH
Last edited:
power of a sinewave is the average. Paverage, but because that never changes we shorten it to P and everyone knows we mean Paverage.
Prms does not exist.
Ppeak is a specific power at ONE instant in time. I would refer to it as instantaneous peak power.
One can specify the power at any instant in time, not just at the peak.
Amplifier output powers are averages.
a.) Some could be for long term averages that are reliable in that they do not take the amplifier devices beyond a safe operating temperature.
b.) Or they could be shorter term, say typically 100ms to 10seconds. I use this to measure the maximum unclipped output power into a resistive test load. my 2seconds or so is just long enough to check the signal is still unclipped on the scope and just long enough to allow the DMM to measure the average voltage across the load and re-scale that to an equivalent Vrms.
c.) Or a very short term typically at very low duty cycle to ensure the main smoothing capacitors do not discharge. This style of measurement allows manufacturers to specify an increased maximum power output that may mimic the transient signals one gets from high crest factor audio.
The supply rail voltage is not the same as the amplifier output voltage.
35Vdc >< 35Vpk
An output rail to rail opamp cannot achieve that. It might get the peak output voltage to within a few dozen millivolts of rail voltage when output currents are low (for an opamp), but this loss gets worse as current is increased (lower load impedance).
A power amplifier behaves similarly. There are some that get quite close to supply rail voltage (a cfp is an example that can be engineered to achieve near rail to rail - car amplifiers often fall into this category). But many lose 3Vloss to 6Vloss through the amplifier when driving rated resistive load.
In addition there is PSU voltage sag under load. This can be another 3Vsag to 8Vsag
So a power amplifier running on +-35Vdc, when there is no output current, could end up with supply rails that have sagged to 32Vdc to 27Vdc.
Then one takes into account Vloss and the maximum output could be anywhere from 29Vpk to 22Vpk
Now put that into the standard power formula
P = Vpk^2 / Rload / 2 and you get maximum power anywhere from 52.5W to 30.2W into 8r0 (a range of 2.4dB)
The current capability of both the amplifier and the PSU have a big effect on the maximum output power into the rated load.
It was to hide this failing that the HiFi industry invented the IHF (very short term) maximum power output test.
And then the midFi and PMPO jumped on this manipulation of test results to claim stupid powers that draw in the gullible.
Prms does not exist.
Ppeak is a specific power at ONE instant in time. I would refer to it as instantaneous peak power.
One can specify the power at any instant in time, not just at the peak.
Amplifier output powers are averages.
a.) Some could be for long term averages that are reliable in that they do not take the amplifier devices beyond a safe operating temperature.
b.) Or they could be shorter term, say typically 100ms to 10seconds. I use this to measure the maximum unclipped output power into a resistive test load. my 2seconds or so is just long enough to check the signal is still unclipped on the scope and just long enough to allow the DMM to measure the average voltage across the load and re-scale that to an equivalent Vrms.
c.) Or a very short term typically at very low duty cycle to ensure the main smoothing capacitors do not discharge. This style of measurement allows manufacturers to specify an increased maximum power output that may mimic the transient signals one gets from high crest factor audio.
The supply rail voltage is not the same as the amplifier output voltage.
35Vdc >< 35Vpk
An output rail to rail opamp cannot achieve that. It might get the peak output voltage to within a few dozen millivolts of rail voltage when output currents are low (for an opamp), but this loss gets worse as current is increased (lower load impedance).
A power amplifier behaves similarly. There are some that get quite close to supply rail voltage (a cfp is an example that can be engineered to achieve near rail to rail - car amplifiers often fall into this category). But many lose 3Vloss to 6Vloss through the amplifier when driving rated resistive load.
In addition there is PSU voltage sag under load. This can be another 3Vsag to 8Vsag
So a power amplifier running on +-35Vdc, when there is no output current, could end up with supply rails that have sagged to 32Vdc to 27Vdc.
Then one takes into account Vloss and the maximum output could be anywhere from 29Vpk to 22Vpk
Now put that into the standard power formula
P = Vpk^2 / Rload / 2 and you get maximum power anywhere from 52.5W to 30.2W into 8r0 (a range of 2.4dB)
The current capability of both the amplifier and the PSU have a big effect on the maximum output power into the rated load.
It was to hide this failing that the HiFi industry invented the IHF (very short term) maximum power output test.
And then the midFi and PMPO jumped on this manipulation of test results to claim stupid powers that draw in the gullible.
Last edited:
Wow... Andrew thanks a lot... I got it. The Vloss I believe is about 2.6V in the specific case of the LM3886, as described in Tom's article.
Therefore I conclude, following the data provided on the mono Mod286, that the Mod286 is capable to provide 50W max. into 8ohms for prolonged (>10s) signals at that level.
Coming back to the initial question, how much power does music with 20dB CF require -> Factor 100 above the Paverage. Does the CF definition assumes prolonged peaks at the maximum level and therefore requires an amplifier to be capable to provided sustainable power at the factor 100 or would an amp, which is capable to continusly putting out 50W also be able to put out 200W for lets say the 10-100ms of a drumbeat?
Assuming the above being correct, the mono Mod286 with its 50W (8ohms) let's you listen to 20dB CF music at an average level of 0.5W, which in my case (87db speakers) would result in an average listening SPL of 77dB?
Assuming "only" average CF of 14dB it gets better (thanks to the parabolic nature of the correlations) -> Factor 25, that is 50W / 25factor = 2W average listening level, which results in an avg. SPL of 83dB (which is plenty loud for my purposes, I guess). Especially as the loudest tone would come across with 50W equalling a whopping 97dB SPL!!!
All in all I am super excited to finish the two Mod286 and actually do some real listening, get my own loudness impression and see how theory compares to reality...
Therefore I conclude, following the data provided on the mono Mod286, that the Mod286 is capable to provide 50W max. into 8ohms for prolonged (>10s) signals at that level.
Coming back to the initial question, how much power does music with 20dB CF require -> Factor 100 above the Paverage. Does the CF definition assumes prolonged peaks at the maximum level and therefore requires an amplifier to be capable to provided sustainable power at the factor 100 or would an amp, which is capable to continusly putting out 50W also be able to put out 200W for lets say the 10-100ms of a drumbeat?
Assuming the above being correct, the mono Mod286 with its 50W (8ohms) let's you listen to 20dB CF music at an average level of 0.5W, which in my case (87db speakers) would result in an average listening SPL of 77dB?
Assuming "only" average CF of 14dB it gets better (thanks to the parabolic nature of the correlations) -> Factor 25, that is 50W / 25factor = 2W average listening level, which results in an avg. SPL of 83dB (which is plenty loud for my purposes, I guess). Especially as the loudest tone would come across with 50W equalling a whopping 97dB SPL!!!
All in all I am super excited to finish the two Mod286 and actually do some real listening, get my own loudness impression and see how theory compares to reality...
Last edited:
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.