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Old 16th May 2019, 04:51 AM   #1861
6L6 is offline 6L6  United States
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Quote:
Originally Posted by MEPER View Post
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 :-)

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Old 16th May 2019, 05:18 AM   #1862
MEPER is offline MEPER  Denmark
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Nice cat!
I had 33k RN55.....which probably also will work…..but 39k was closer…..so technical reasons……won…..over "look" :-)
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Old 16th May 2019, 11:41 AM   #1863
ItsAllInMyHead is online now ItsAllInMyHead
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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.

Last edited by ItsAllInMyHead; 16th May 2019 at 11:51 AM. Reason: Adding comment re: Pics and build
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Old 16th May 2019, 01:45 PM   #1864
ItsAllInMyHead is online now ItsAllInMyHead
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Quote:
Originally Posted by ItsAllInMyHead View Post
I ask b/c the Mouser link above shows 1/2W and 1/4W resistors when MPER was asking about a 37 ohm.
Sorry, it was Elwood asking. Editing was locked after I noticed.
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Old 16th May 2019, 01:57 PM   #1865
Mark Johnson is offline Mark Johnson  United States
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The same question was asked last summer here on this thread. A member from South America wanted someone to tell him exactly what wattage resistors to buy, and why. He did not want to make the decisions himself. If I remember correctly, there were quite a few responses.

Last edited by Mark Johnson; 16th May 2019 at 01:59 PM.
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Old 16th May 2019, 01:58 PM   #1866
ItsAllInMyHead is online now ItsAllInMyHead
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Mark, thanks. I've read the thread from end to end and clearly missed it. I'll take another look.

While I'm at it - Thank you for making this project possible and (potentially) practical for me.

Last edited by ItsAllInMyHead; 16th May 2019 at 02:01 PM.
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Old 16th May 2019, 02:58 PM   #1867
ItsAllInMyHead is online now ItsAllInMyHead
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AHA! I clearly overlooked it. After re-reading again from the beginning, I found the relevant info beginning around post #469. Pasted into my build notes and updated in my BOM.

Thank you!
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Old 16th May 2019, 03:16 PM   #1868
Mark Johnson is offline Mark Johnson  United States
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Quote:
Originally Posted by ItsAllInMyHead View Post
.. I found the relevant info beginning around post #469.
#469 was posted in August 2018, (barely) within the range I thought I remembered: "last summer".

Congratulations on finding the answers you sought.
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Old 16th May 2019, 03:17 PM   #1869
6L6 is offline 6L6  United States
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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.
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Old 16th May 2019, 04:07 PM   #1870
Mark Johnson is offline Mark Johnson  United States
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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
  1. Choose a bag at random
  2. Open the bag and remove the two PCBs
  3. Put a red colored dot over the IC on one of the PCBs
  4. Put a red colored dot over the IC on the other PCB
  5. Set those aside
  6. Open the other bag and remove the two PCBs
  7. Put green colored dots over the ICs on each of those PCBs
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.

Last edited by Mark Johnson; 16th May 2019 at 04:09 PM.
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