Confused...
guys, did you read the build guide or at least the BOM?
Vishay Dale RN55 are the through hole resistors in BOM, available from Mouser...
BOM
Build Guide
BTW I subscribe to this:
guys, did you read the build guide or at least the BOM?
Vishay Dale RN55 are the through hole resistors in BOM, available from Mouser...
BOM
Build Guide
BTW I subscribe to this:
While we are talking about resistors, I have been reading up on resistors and their effects. Based on my reading, R13, the input impedance resistor may be worth looking at.
The idea is that, since it runs from input to ground, it sees the entire input signal and any noise or distortion that is introduced will be amplified through the system. Measurements show that resistor noise increases with voltage drop across the resistor and with resistance value of the resistor. Since R13 is 100k, it is likely one of the highest resistor sources in the amplifier.
Of course, some would argue that any noise or distortion from a resistor is small compared to the noise and distortion from active elements and that may be true. But, with the exception of bulk foil resistors, industrial and military resistors are all relatively affordable, choosing a good resistor makes sense to me.
Jac
The idea is that, since it runs from input to ground, it sees the entire input signal and any noise or distortion that is introduced will be amplified through the system. Measurements show that resistor noise increases with voltage drop across the resistor and with resistance value of the resistor. Since R13 is 100k, it is likely one of the highest resistor sources in the amplifier.
Of course, some would argue that any noise or distortion from a resistor is small compared to the noise and distortion from active elements and that may be true. But, with the exception of bulk foil resistors, industrial and military resistors are all relatively affordable, choosing a good resistor makes sense to me.
Jac
Thanks, this is useful. I recently replace the 12K Susumu feedback resistor with a Z foil and was very impressed, but in the other important positions I already have Vishay Dales. I'm currently thinking I'll hold back for a while, and spend my budget on other things, such as some nice NE123W midranges .....
Sorry Dario, I have not read the BOM lately. Nice to see we agree on this "value" part. You specify RN55, but I have found any of the Vishay/Dale series sound good. Mouser stocks thousands.
Spartacus, that NE123W is the midrange I have recently installed in my MTM's. It is an amazing driver, so much better than the poly cones I had in there previously. The voices have finally come "out of the box" and now I can easily discern things like the subtle differences between resistors (and, more importantly, violins!). Like the Z-foils, the NE123W is worth the premium price if you can afford it.
Peace,
Tom E
Spartacus, that NE123W is the midrange I have recently installed in my MTM's. It is an amazing driver, so much better than the poly cones I had in there previously. The voices have finally come "out of the box" and now I can easily discern things like the subtle differences between resistors (and, more importantly, violins!). Like the Z-foils, the NE123W is worth the premium price if you can afford it.
Peace,
Tom E
Yes I saw in another thread that you were using these. I'm currently using Tangband W4-1337s as midranges, which are good but have a slightly hard sound due to elevated odd harmonics. The NEs seem good replacements, or possible SB12s.
Whatever impedance that is driving the amp will be in parallel with R13, so should mitigate many effects of the large value of this resistor.
The largest voltage will be across the 12K feedback resistor. Something else, that came out of a chat with George, was that any distortions/noise from the feedback network (R7, R10 and C9) will be amplified by the open loop gain of the amplifier, so in the ball park of 100,000 in this case. Therefore, higher feedback amplifiers such as the MyRef should be more sensitive to the quality of the feedback network than lower feedback amps.
Actually R13, R12, C12 form an input impedance curve. This curve is close to the curve of lots of cable.
Sorry to ask about something that has been discussed before in this thread, but i can't find it... 
Can someone please explain the proper way to ground heatsinks?
I mean:
- which heatsinks
- connected where and how
- proper wiring
- proper earthing (if needed)
and so on.
Thanks very much in advance!!!
Can someone please explain the proper way to ground heatsinks?
I mean:
- which heatsinks
- connected where and how
- proper wiring
- proper earthing (if needed)
and so on.
Thanks very much in advance!!!
Luca72c
I found in my notes only this info about grounding of the LM's heatsinks:
post #2207
It would be great to hear some comments from gurus.
I found in my notes only this info about grounding of the LM's heatsinks:
post #2207
It would be great to hear some comments from gurus.
Luca,
I think Tom is telling why you aren't getting much response. Back in the FE RC days, Dario added a place to ground the heatsinks for those who were having hum problems. If I recall correctly, only builders with very efficient speakers were seeing any hum. For most of us, there hasn't been a need to ground the heatsinks, so we don't know the proper way.
The link from alexwey is to a response from George. Hopefully, he has more insight.
Ok, thanks. I'm not having hum problems and my LM heatsinks are part of the chassis.
I just thought that was a more proper grounding technique.
If you aren't having hum issues, I think you are good to go.
I've actually done it both ways, but no hum in either case. It might be my speakers aren't efficient enough. Anyway, the only reason I grounded the heatsinks was because they were part of the case. I didn't do it to fix any noise.
Jac
I've actually done it both ways, but no hum in either case. It might be my speakers aren't efficient enough. Anyway, the only reason I grounded the heatsinks was because they were part of the case. I didn't do it to fix any noise.
Jac
then, be careful: it's quite likely that your chassis is already connected to ground somewhere. If it is, adding any other connection to ground would create a "ground loop", which would create troubles.
BTW: what George (Joseph K) was talkin' about was not hum pickup, but the risk of (high frequency) oscillations due to the stray coupling of the 3886 with the (floating) heatsink on which it is mounted. In turn, (sometimes) this may (indirectly) result in the amp producing an audible "hum" (but it would not be that the problem...).
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HSGND
The heatsink, if not grounded, is another possible source of hum.
You will not hear that unless you have very sensitive speakers, like 94 dB and up.
Most builds will have the heatsink already grounded since it will be part of a grounded metallic chassis.
The HSGND pad should be used ONLY in case the heatsink is not already grounded, like when using a plastic or wood chassis or when the heatsink is insulated from the grounded chassis.
The heatsink, if not grounded, is another possible source of hum.
You will not hear that unless you have very sensitive speakers, like 94 dB and up.
Most builds will have the heatsink already grounded since it will be part of a grounded metallic chassis.
The HSGND pad should be used ONLY in case the heatsink is not already grounded, like when using a plastic or wood chassis or when the heatsink is insulated from the grounded chassis.
