The boards just looks a bit "messy" now as one resistor is a "normal" Vishay with color bands and all the others are the brown Vishay Dale RN55......will see if I can live with that
tl;dr - will a mix of 1/8W and 1/4W (Vishay RN55 and RN60) resistors be a proper choice for these circuits?
I am strongly considering the M2x as my first SS loudspeaker power amp build. I've read through this thread, and so far about 1/2 of the tea-bag thread along with the post of the original M2 schematic. I've also read the universal power supply threads / guides.
By the questions I ask, you can easily tell my level of knowledge. I am a new builder trying to learn. The build process has made me want to understand the "why" more. I had a blast building the WHAMMY, (enough to host a follow-up build party with 3 more people building). I want to try some new things.
I get thrown trying to determine "what specs REALLY matter" in the context of a specific circuit. When specs that are probably 2nd nature to seasoned builders are not mentioned, I get anxious.
I struggle through reading the volumes on whether or not to put a snubber in my power supply and if so, what value to use. It probably took me far longer than most of you to understand the monolithic rectifier (thanks @6L6) versus discreet components. I'm still not sure I understand how to determine the proper size for a power transformer, other than more is better (within reason and in consideration of space and EMI).
I'm not to the point where I can "try it and see". It's fear of expense and time lost and damaging a working circuit. Someone said something akin to "a day in the library saves a month in the shop" in a post. I agree. I'll do the work. I love learning more about all of this. I've spent probably 40+ hours reading just to decide if I'm ready to take this on. Bob Cordell's first chapter in his book is still a bit (a lot) over my head at the moment.
Enough of that nonsense... my first of what I'm sure will be many questions.
In the BOMs it says it will show a size (if important). I thought I had over-spec'ed resistors by choosing the Vishay/Dale "RN60 series" resistors vs. the RN55 series as an example. Even though Mouser categorizes some as 1/8 or even 1/10 W - the Spec sheet shows they are 1/4W at what I'd WAG would be higher than normal operating temp of 70C. I choose the tightest tolerances I could find within that series for both resistance change due to temperature fluctuation and resistance in general. Where I could not find a 60 series, I dropped to the 1/8W 55 series.
This is for all IPS boards and the main boards.
I am not to the level of understanding and confidence yet to calculate the power expected across each resistor in a larger circuit or even understand where we can deviate a few ohms or %.
Will the resistors I chose be sufficient? I ask b/c the Mouser link above shows 1/2W and 1/4W resistors when MPER was asking about a 37 ohm. The guide shows 1/2" between the pads, so I was picking the largest physical Vishay/Dale I could find to fit in the space with standard mounting against the boards (with the exception of the Austin where the guide specifically mentions vertical mounting). I won't be building that board for a while anyway most likely.
This is my paranoia until I learn more...
Thanks in advance. I'll keep my questions and the preamble shorter in the future.
BTW - I am not sure if it's proper to offer, but I'd be happy to document my build and note any questions / struggles / choices along the way in a separate thread if that would benefit others.
I am strongly considering the M2x as my first SS loudspeaker power amp build. I've read through this thread, and so far about 1/2 of the tea-bag thread along with the post of the original M2 schematic. I've also read the universal power supply threads / guides.
By the questions I ask, you can easily tell my level of knowledge. I am a new builder trying to learn. The build process has made me want to understand the "why" more. I had a blast building the WHAMMY, (enough to host a follow-up build party with 3 more people building). I want to try some new things.
I get thrown trying to determine "what specs REALLY matter" in the context of a specific circuit. When specs that are probably 2nd nature to seasoned builders are not mentioned, I get anxious.
I struggle through reading the volumes on whether or not to put a snubber in my power supply and if so, what value to use. It probably took me far longer than most of you to understand the monolithic rectifier (thanks @6L6) versus discreet components. I'm still not sure I understand how to determine the proper size for a power transformer, other than more is better (within reason and in consideration of space and EMI).
I'm not to the point where I can "try it and see". It's fear of expense and time lost and damaging a working circuit. Someone said something akin to "a day in the library saves a month in the shop" in a post. I agree. I'll do the work. I love learning more about all of this. I've spent probably 40+ hours reading just to decide if I'm ready to take this on. Bob Cordell's first chapter in his book is still a bit (a lot) over my head at the moment.
Enough of that nonsense... my first of what I'm sure will be many questions.
In the BOMs it says it will show a size (if important). I thought I had over-spec'ed resistors by choosing the Vishay/Dale "RN60 series" resistors vs. the RN55 series as an example. Even though Mouser categorizes some as 1/8 or even 1/10 W - the Spec sheet shows they are 1/4W at what I'd WAG would be higher than normal operating temp of 70C. I choose the tightest tolerances I could find within that series for both resistance change due to temperature fluctuation and resistance in general. Where I could not find a 60 series, I dropped to the 1/8W 55 series.
This is for all IPS boards and the main boards.
I am not to the level of understanding and confidence yet to calculate the power expected across each resistor in a larger circuit or even understand where we can deviate a few ohms or %.
Will the resistors I chose be sufficient? I ask b/c the Mouser link above shows 1/2W and 1/4W resistors when MPER was asking about a 37 ohm. The guide shows 1/2" between the pads, so I was picking the largest physical Vishay/Dale I could find to fit in the space with standard mounting against the boards (with the exception of the Austin where the guide specifically mentions vertical mounting). I won't be building that board for a while anyway most likely.
This is my paranoia until I learn more...
Thanks in advance. I'll keep my questions and the preamble shorter in the future.
BTW - I am not sure if it's proper to offer, but I'd be happy to document my build and note any questions / struggles / choices along the way in a separate thread if that would benefit others.
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#469 was posted in August 2018, (barely) within the range I thought I remembered: "last summer".
Congratulations on finding the answers you sought.
You could buy 1/4w Xicon or Yeago resistors for about 10x less than the Dale and have similar performance. The Dale are used in the kits and in the guides for the simple reason that 1) if properly oriented, the values are readable on internet photos, 2) those values are clearly written on the side, no need to try to decipher the color code on a background color that makes it nigh impossible to read in photos, and 3) they are really, really, really good resistors.
But make no mistake, they are chosen for ergonomic reasons. Resistors make very little difference in sound, particularly in this circuit where the transformer has such an outsized influence on its personality.
But make no mistake, they are chosen for ergonomic reasons. Resistors make very little difference in sound, particularly in this circuit where the transformer has such an outsized influence on its personality.
For those who have numerous Tucson boards containing different IC opamp types, allow me to suggest a fun little listening experiment.
Choose two different opamp types to compare, let's hypothetically say uA741 and OPA604. Put your two uA741 Tucson boards in one paper bag and put your two OPA604 Tucson boards in a second paper bag.
Ask a trusted person to do the following while you are in another room. Amazon link to colored dots
Now you've got two red-dot-Tucsons which use one opamp, and two green-dot-Tucsons which use the other. You don't know which is which. You are "blind" to the identities of the boards.
Install them in your M2x and listen for however long you wish. Are there any sonic differences between the red Tucsons and the green Tucsons? Big or small differences? Do you have a strong preference? No preference? etc.
When you've made your final judgments, remove the dots. Are you surprised?
By the way there is a sale of blank Tucson boards going on at the link below. People are buying ten blank Tucsons (for ten dollars), I assume they plan to perform experiments and listening comparisons.
FS: M2x daughter cards, type "TUCSON"
In case it isn't obvious, you need to do this with four Tucson PCBs that all use the same IC package. Otherwise the package type will reveal the chip identity. Use four DIP-8s, or else four SOIC-8s, but don't mix the two. If socketed DIPs, use the exact same socket types on all four boards. Gold/NoGold, milled/pressclips, etc.
Choose two different opamp types to compare, let's hypothetically say uA741 and OPA604. Put your two uA741 Tucson boards in one paper bag and put your two OPA604 Tucson boards in a second paper bag.
Ask a trusted person to do the following while you are in another room. Amazon link to colored dots
- Choose a bag at random
- Open the bag and remove the two PCBs
- Put a red colored dot over the IC on one of the PCBs
- Put a red colored dot over the IC on the other PCB
- Set those aside
- Open the other bag and remove the two PCBs
- Put green colored dots over the ICs on each of those PCBs
Install them in your M2x and listen for however long you wish. Are there any sonic differences between the red Tucsons and the green Tucsons? Big or small differences? Do you have a strong preference? No preference? etc.
When you've made your final judgments, remove the dots. Are you surprised?
By the way there is a sale of blank Tucson boards going on at the link below. People are buying ten blank Tucsons (for ten dollars), I assume they plan to perform experiments and listening comparisons.
FS: M2x daughter cards, type "TUCSON"
In case it isn't obvious, you need to do this with four Tucson PCBs that all use the same IC package. Otherwise the package type will reveal the chip identity. Use four DIP-8s, or else four SOIC-8s, but don't mix the two. If socketed DIPs, use the exact same socket types on all four boards. Gold/NoGold, milled/pressclips, etc.
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Mark, and @6L6. Both of you are a wealth of knowledge. Not only that, you share it freely. Again - and again.
I have enjoyed starting to understand some of the "why's" that go into part selections separate from bare specs. The great news is that I'm strictly an enjoy the tunes type of guy. If there is a "known" benefit with a very small risk or adding or over-spec'ing a relatively small value part, then it will go into my builds as a newcomer. When building the WHAMMY, I loved having the values visible on the resistors (as did the guys that came for the build party).
Plus *cough* when I may need some further assistance, the values can show clearly in a pic. I read through many build experiences (one here) that showed how easy it can be to mis-stuff even by the most conscientious of builders. I don't know the bands off the top of my head, but I've become proficient at reading the values from the Dales.
@RafaPolit - re-reading your posts has been great. Please know your willingness to ask questions helped another newcomer. We have some similar goals. I too want to experiment with as many deigns as practical while re-purposing parts using a modular approach.
Now onto sourcing the BOM for the power supply, finding a soft-start, and finding a transformer / chassis, wire etc etc. Man, this is fun!
I have enjoyed starting to understand some of the "why's" that go into part selections separate from bare specs. The great news is that I'm strictly an enjoy the tunes type of guy. If there is a "known" benefit with a very small risk or adding or over-spec'ing a relatively small value part, then it will go into my builds as a newcomer. When building the WHAMMY, I loved having the values visible on the resistors (as did the guys that came for the build party).
Plus *cough* when I may need some further assistance, the values can show clearly in a pic. I read through many build experiences (one here) that showed how easy it can be to mis-stuff even by the most conscientious of builders. I don't know the bands off the top of my head, but I've become proficient at reading the values from the Dales.
@RafaPolit - re-reading your posts has been great. Please know your willingness to ask questions helped another newcomer. We have some similar goals. I too want to experiment with as many deigns as practical while re-purposing parts using a modular approach.
Now onto sourcing the BOM for the power supply, finding a soft-start, and finding a transformer / chassis, wire etc etc. Man, this is fun!
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I'm really glad! As I said, I have this feeling that I not always come out as I intended... even after almost a year Mark remembers me as the one that "did not want to make the decisions himself".
So I really appreciate your words.
I never managed to buy the PCBs, shipping costs were prohibitive (specially for the large case). Now that the Audio Store has new shipping methods, I'll look again into re-starting this project.
I'll be following your adventure here, so please keep us posted!
Best regards,
Rafa.
Please feel free to DIY the amp however you like and, most importantly, have fun doing it! It might be useful for you to know that both 6L6 and I have built working M2x amplifiers, and neither of us included an explicit soft start PCB or output muting relay in our builds. In fact I would say that the great majority of finished M2x amplifiers that are posted to this thread, don't include either soft start PCBS or output muting. The Inrush Current Limiter parts (CL-60 on Nelson Pass's PSU schematic), plus the very very slow wake-up of the M2x power output stage, are more than adequate. An external "soft start" PCB doesn't make things much better.
It's certainly not a bad idea to include either one, and both are at least somewhat useful functions. (Plus, they're fun!) I am only passing along a smidgen of anectdotal evidence that they don't seem to be absolutely necessary in an M2x. Your finished amp will play beautiful music even if you decide not to include them.
Conventional wisdom / audio lore holds that soft start usually isn't necessary until the power transformer rating exceeds 750VA or 800VA. Which is a lot bigger than any sane person would choose for an M2x power transformer.
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Words of experienced members! Don't make it more complicated than necessary.
My M2X plays wonderful without any protectioncircuit or softstart (only the CL60). This amp shows absolutely no misbehaving for months now.
Only one thing - wonderful music!
At the moment with my Balanced Zen Line Stage in front. Also great combo.
Mark Johnson and 6L6 - a big THANK YOU!
Greets
Dirk
My M2X plays wonderful without any protectioncircuit or softstart (only the CL60). This amp shows absolutely no misbehaving for months now.
Only one thing - wonderful music!
At the moment with my Balanced Zen Line Stage in front. Also great combo.
Mark Johnson and 6L6 - a big THANK YOU!
Greets
Dirk
You guys are fantastic, thank you for the added advice and information supporting it.
Some of this information comes easily to me, and some will take some repetition. I was looking to re-confirm the specs and find some alternatives on resistors. These are things I am sure you guys do without expending much mental energy every day. If I learn to do it properly it will stick. So, I make the effort. In looking at the Vishay data sheets for the RN series and the CMF series, it specifically uses the following language
"Vishay Dale Model CMF is also available as Military Qualified Styles RN and RL. See Vishay Dale’s CMF (Military RN and RL) datasheet (www.vishay.com/doc?31027) for the MIL-SPEC ratings / attributes. (Except for marking, the Industrial and Military versions are exactly the same)." Emphasis mine.
When I review the specs, the RN series data sheet shows RN60s as 1/4W at 70C and a cross reference to the corresponding CMF60 as the global style. The CMF series data sheet shows that CMF60s are 1W rated at 70C. It shows the CMF 50s are 1/4W. Mouser lists them all over the place (very rarely matching the data sheet). It looks like in some cases Mouser lists the rating from the 70C rating, sometimes from the 125C rating, and sometimes neither. I tried to match them by the dimensions on Mouser, but I have no idea what the single source of truth is... I thought it'd be the data sheet, but....
One of many things is definitely true and likely multiple - one Vishay data sheet is wrong, both Vishay data sheets are wrong, Mouser is wrong / has bad data, I can't read a data sheet properly, I need a drink.
These are the frustrations of a noob... <end rant>
Once again - Thank you both for clear and concise guidance and pointers to information that is helpful to learn rather than frustrating as #@!#
I'll work it out, but any pointers are always well-received and will be reciprocated in beverages of your choice if I get to burning amp.
Edited to confirm the two truths in bold... I read the wrong CMF data sheet. I was reading "CMF Industrial" vs. "CMF Military" I won't confirm Mouser's data peculiarities.... but I'l say it's a rumor from an unconfirmed source.
Some of this information comes easily to me, and some will take some repetition. I was looking to re-confirm the specs and find some alternatives on resistors. These are things I am sure you guys do without expending much mental energy every day. If I learn to do it properly it will stick. So, I make the effort. In looking at the Vishay data sheets for the RN series and the CMF series, it specifically uses the following language
"Vishay Dale Model CMF is also available as Military Qualified Styles RN and RL. See Vishay Dale’s CMF (Military RN and RL) datasheet (www.vishay.com/doc?31027) for the MIL-SPEC ratings / attributes. (Except for marking, the Industrial and Military versions are exactly the same)." Emphasis mine.
When I review the specs, the RN series data sheet shows RN60s as 1/4W at 70C and a cross reference to the corresponding CMF60 as the global style. The CMF series data sheet shows that CMF60s are 1W rated at 70C. It shows the CMF 50s are 1/4W. Mouser lists them all over the place (very rarely matching the data sheet). It looks like in some cases Mouser lists the rating from the 70C rating, sometimes from the 125C rating, and sometimes neither. I tried to match them by the dimensions on Mouser, but I have no idea what the single source of truth is... I thought it'd be the data sheet, but....
One of many things is definitely true and likely multiple - one Vishay data sheet is wrong, both Vishay data sheets are wrong, Mouser is wrong / has bad data, I can't read a data sheet properly, I need a drink.
These are the frustrations of a noob... <end rant>
Once again - Thank you both for clear and concise guidance and pointers to information that is helpful to learn rather than frustrating as #@!#
I'll work it out, but any pointers are always well-received and will be reciprocated in beverages of your choice if I get to burning amp.
Edited to confirm the two truths in bold... I read the wrong CMF data sheet. I was reading "CMF Industrial" vs. "CMF Military" I won't confirm Mouser's data peculiarities.... but I'l say it's a rumor from an unconfirmed source.
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Do what I do: buy metal film resistors and try very hard to find the value you need in a 600 milliwatt (0.6W) rated metal film resistor. If that's unavailable or ridiculously expensive, buy 500 milliwatt (0.5W) rated metal film resistor in the value you need. If no can do, drop down to 250 milliwatt (0.25W) metal film and for resistances less than about 10K, ask expert circuit designers whether a 250 milliwatt resistor in position Rnnnn is dangerous or safe.
Math problem: the total supply voltage (pos rail to neg rail) in an M2x amplifier is about 46 to 50 volts. What's the lowest resistor value you can apply 46-50 volts across, and have a power dissipation less than 175mW or 200mW?
Thought problem: what is the relevance of the math problem above?
_
Math problem: the total supply voltage (pos rail to neg rail) in an M2x amplifier is about 46 to 50 volts. What's the lowest resistor value you can apply 46-50 volts across, and have a power dissipation less than 175mW or 200mW?
Thought problem: what is the relevance of the math problem above?
_
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cubicincher, excellent!
We don't often connect resistors directly between the positive rail and the negative rail, so the calculation represents a worse-than-reality scenario. But it does tell us that resistors greater than about 12.5K generally don't need to be rated more than 250 mW in an M2x and other amps having plus/minus 23V to 25V power supplies.
We don't often connect resistors directly between the positive rail and the negative rail, so the calculation represents a worse-than-reality scenario. But it does tell us that resistors greater than about 12.5K generally don't need to be rated more than 250 mW in an M2x and other amps having plus/minus 23V to 25V power supplies.