All these National chipamps are current crippled.
They need to use power reduction arrangements to drive 4ohms loads.
As such they need the same power reduction when bridged into 8ohms loads.
That ruins much of the benefit that the higher output voltage could bring.
And it gets even worse trying bridged into 4ohms loadings.
They need to use power reduction arrangements to drive 4ohms loads.
As such they need the same power reduction when bridged into 8ohms loads.
That ruins much of the benefit that the higher output voltage could bring.
And it gets even worse trying bridged into 4ohms loadings.
R12 is part of the RF attenuation input filter.
You can vary this a lot. I recommend you experiment with the RC combination to see how low in frequency you can take this filter and still maintain the full treble response to your speaker/ears.
R37 is the noise shaping of the chipamp to stabilise it at high frequency when it has been set to low gain.
The RC inserts a pole+zero to change the HF gain of the amplifier and thus keep the stability margins at HF.
The value may have a small tolerance and still work, but as recommended above keep the value until you know that a different value performs better.
E24 series resistors is the standard range stocked by virtually all retailers of 1% metal film leaded resistors. At that value the standard E24 values are 3k0, 3k3, 3k6 & 3k9.
If your retailer does not stock all those E24 values then find a new retailer.
You can vary this a lot. I recommend you experiment with the RC combination to see how low in frequency you can take this filter and still maintain the full treble response to your speaker/ears.
R37 is the noise shaping of the chipamp to stabilise it at high frequency when it has been set to low gain.
The RC inserts a pole+zero to change the HF gain of the amplifier and thus keep the stability margins at HF.
The value may have a small tolerance and still work, but as recommended above keep the value until you know that a different value performs better.
E24 series resistors is the standard range stocked by virtually all retailers of 1% metal film leaded resistors. At that value the standard E24 values are 3k0, 3k3, 3k6 & 3k9.
If your retailer does not stock all those E24 values then find a new retailer.
jwjarch My-Ref Build
Finally getting around to populating my boards from GB#10. Going pretty well so far. Trying to keep soldering temp in check with my cheap iron. Fingers crossed they fire up when I get to the transformer wiring.
A few questions/observations:
1. As tempted as I am to throw in the OPA827 right away, I'm going to stick to the BOM and get this pair of My-Ref's working first. Then I can play around later.
2. For the Wima MKP's, the datasheets state expressly that MKP's are bi-polar caps. I've seen a few times in this thread that there is a supposed directionality to the MKP's. Does direction REALLY have an effect on these or not? I may have soldered them is backwards but I would like to avoid rework if possible.
3. For R37 I used the 3K3 SMD. I have 3K3 RN55's that I could use here too. Would it be worth trying the RN55 in this position? I would have to bend the leads a little funky but I could make it work. Curious to know people's thoughts on this.
Finally getting around to populating my boards from GB#10. Going pretty well so far. Trying to keep soldering temp in check with my cheap iron. Fingers crossed they fire up when I get to the transformer wiring.
A few questions/observations:
1. As tempted as I am to throw in the OPA827 right away, I'm going to stick to the BOM and get this pair of My-Ref's working first. Then I can play around later.
2. For the Wima MKP's, the datasheets state expressly that MKP's are bi-polar caps. I've seen a few times in this thread that there is a supposed directionality to the MKP's. Does direction REALLY have an effect on these or not? I may have soldered them is backwards but I would like to avoid rework if possible.
3. For R37 I used the 3K3 SMD. I have 3K3 RN55's that I could use here too. Would it be worth trying the RN55 in this position? I would have to bend the leads a little funky but I could make it work. Curious to know people's thoughts on this.
Get the basic amps to work before attempting mods. You will very impressed with the sound.
There are a few people who believe that parts direction makes an audible difference. Most people cannot detect it in this or any other device. You will be very impressed with the sound whichever way they're installed.
RN55 is a nice resistor but nothing special. The SMU's are also very good. You will be very impressed with the sound.
Do you have your faston tabs soldered under the board? Hard to tell from the pics. Never seen that before. I bet soldering outputs directly to the board, from either side, would make more improvement to the sound than any of the other changes you are considering.
Peace,
Tom E
There are a few people who believe that parts direction makes an audible difference. Most people cannot detect it in this or any other device. You will be very impressed with the sound whichever way they're installed.
RN55 is a nice resistor but nothing special. The SMU's are also very good. You will be very impressed with the sound.
Do you have your faston tabs soldered under the board? Hard to tell from the pics. Never seen that before. I bet soldering outputs directly to the board, from either side, would make more improvement to the sound than any of the other changes you are considering.
Peace,
Tom E
Hi Tom. Thanks for the info. Other than the MKP's I've followed the direction on all other components. I can't wait to hear them.
Yes, I soldered the fast-ons to the bottom of the board and will run my wires to the underside to clean up the look of the final amp. Eventually I'll probably solder directly to the board.
Yes, I soldered the fast-ons to the bottom of the board and will run my wires to the underside to clean up the look of the final amp. Eventually I'll probably solder directly to the board.
MKP are non polar. Polypropylene is one of the few plastic dielectric that is truly non polar.
Some circuits are intolerant of interference impinging on big components.
Some of these circuits benefit by placing the OUTER foil of a rolled capacitor at the lower impedance of the two connections.
The OUTER foil acts like a enclosing screen for the inner foil connected to the higher impedance.
Is your MKP a rolled construction, or a folded construction?
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1. As tempted as I am to throw in the OPA827 right away, I'm going to stick to the BOM and get this pair of My-Ref's working first. Then I can play around later.
Wise choice, IMHO.
All film caps are bipolar, it means that they work as supposed either way but this doesn't mean that they will behave exactly in the same way, simply similar enough according a tolerance.
Wound capacitors usually have an 'outer-foil' and so noise pickup will change according mounting direction.
Yes, it REALLY sound a bit different, nevertheless film caps are delicate so if you're not confident on reworking leave them as they are, it will still sound fantastic.
I will not use any other through hole resistor than metal foils there unless they're 5mm lead spacing, it's a delicate part of the circuit and IMHO long leads are not advisable in that position.
Nevertheless a RN would sound better in an ideal world of very short leads.
If you mean plain My_Evo Rev A (no R39, no C10, R3=0.33R), I will use that compensation scheme, it simply sounds better.
I missed it!
It looks like I will wait to have something more to order...
Thanks Dario. I'll leave the MKP's alone for now so I don't risk any damage. And I'll save up for some Z-Foils for R37 eventually.
I should have also mentioned I'm building these with the Evo-A mod as well. Seemed to be the way to go.
Good to know there's another group buy going! I'm thinking about 2 more kits for a future active 4-way speaker project. In general, has anyone used the My-Ref in a multi-way project? Any thoughts on that? I'm a little concerned the wattage would be too small for any large woofers. Please re-direct me to the appropriate thread if this info already exists. Thanks!
I should have also mentioned I'm building these with the Evo-A mod as well. Seemed to be the way to go.
Good to know there's another group buy going! I'm thinking about 2 more kits for a future active 4-way speaker project. In general, has anyone used the My-Ref in a multi-way project? Any thoughts on that? I'm a little concerned the wattage would be too small for any large woofers. Please re-direct me to the appropriate thread if this info already exists. Thanks!