The new "My Ref" Rev C thread

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#861
ben_lesmana said:
I think mostly are agreeing that the high is a bit 'over'. Its not harsh, or 'bad' its just 'more' than to my liking. I agree as well that the bass is 'less'. it sounds detailed, tight, but 'less'. This is why I would like to try out different caps. This is an excellent amp in any way, btw, what I said is purely my opinion.

What is the critical resistor that's in the signal path definitely should be upgraded?
Click to expand...

The Arcotronics R41 in C13 is particularly bass shy, if you remove it or use a better one you will hear also the muddy bass 😀

The resistors that are directly in the signal path are: R12,R13,R10,R7,R42

Remember that according to this post R42 is better if it's 47 Ohm.

Also the 0.1% R5, R6, R8 and R9 are in the signal path but probably the RC55Y are good enough, I've used CMF55 here.

Remeber also that R2 is better if it's 10K (Nelson Pass pointed the problem in this post and in this one you'll find the value)
 
#862
Allied has good selection of the Dale RN55 resistors. I just bought a few hundred at 3.6 cents each. Not bad. 🙂 They are not all that cheap, most are 12 cents which is less than Digikey by about 5 cents. But Allied also has a 25 dollar min order to avoid a 5 dollar surcharge. Anyway, if you plan on building a lot of chipamps you can get 1k and 10k and several other resistances for cheap cheap cheap.
Uriah
 
#863
Thanks for the encouragement and recognition, guys. I'll quit whining now.

I replaced all the resistors at once, so I can't describe which ones helped improve the sound the most. The parts are so inexpensive, it just doesn't make sense to try to save a few cents if you're taking the time to buy better parts and do all the work to replace them. The sonic contribution of resistors is controversial, but why not use a part that is constructed specifically for audio applications: PRP, available from Parts Connexion. Any quality part with tight tolerance would probably be adequate, however. I noticed some of the supplied Xicons were at the edge of being within tolerance, and that can't ever be the best situation.

Dario's recommendations, are, as usual, meaningful.

Peace,
Tom E
 
#864
Hello,

What is the suggested grounding for this amp? Reading the original My Ref thread, I read that we wire the input ground to 0V. Is this correct?

On one of the thread re. star grounding, they suggest we took the input ground, output ground, and PSU ground (is this the 0v?). This is done by the pcb if im not mistaken, should we do this again?

The reason why is that I have a slight hum on 1 of the channel, and dead silent in the other channel. What I did now, I connect the left input ground to the right input ground, it makes the noisy channel has less hum, but still noticeable when I put my ear in the tweeter.

I'm also using twisted pair for input, (From cat 5 cabling), is this ok in general? or using nice shielded cable is better.

Thanks for the help,
Ben
 
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#865
Before trying anything else I would try a second grounding on your input signal. For some reason when I did this my ground hum disappeared and you are not giving up safety this way.
The other thing I tried which also worked was to take a single bare wire and wrap it around all signal in and out grounds then take it to the star ground. Worked well but is not recommended by Twisted Pear.
Uriah
 
#866
Signal ground (RCA) should be isolated from the chassis and be terminated at the PCB.

There should not be any power ground touching the chassis.

Only the screws from the PCB mounts should contact the chassis.

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Once those conditions are met you can start trying to isolate the cause of the noise.

Is it a ground loop noise, 50 / 60 hz power hum noise, or general hiss / white noise?

You mentioned hum, but it is best to be specific and sure of the "type".

You can swap the incoming male RCA's to see if the noise follows to the other channel.

You can tie the 2 RCA grnds together in the chassis to see if that helps.

Personally I would have the RCA grnds tied together on the female jacks and then recheck the terminations at the PCB's.
 
#867
troystg said:
Signal ground (RCA) should be isolated from the chassis ......................

......................Personally I would have the RCA grnds tied together on the female jacks ...............
Click to expand...
Yes, that is Leach's option.
I use this for two channel amplifiers. A very short link between the earth straps on the isolated RCAs and a single wire back the the main audio ground. It's not perfect, but I find it's better than all the other options I have tried for reducing the majority of mains artefacts.
The single wire reduces the loop area of the input returns to reject most of the radiated field interference.
 
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#869
AndrewT said:
Yes, that is Leach's option.
I use this for two channel amplifiers. A very short link between the earth straps on the isolated RCAs and a single wire back the the main audio ground. It's not perfect, but I find it's better than all the other options I have tried for reducing the majority of mains artefacts.
The single wire reduces the loop area of the input returns to reject most of the radiated field interference.
Click to expand...

These are mono amplifier modules.
 
#877
Brian,
You have lost me.
A plurality of amplifiers/RCAs inside one chassis demands that at some point, channel grounds must be commoned.
A two channel amplifier has two speaker returns, two Zobel returns, two Power grounds, two Decoupling Grounds, two NFB returns, two signal returns, at least one PSU zero volts, a Safety Earth and maybe a few others.

Somehow, these need to be connected to a reference voltage.
 
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