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Old 21st August 2013, 10:34 AM   #3241
Neville is offline Neville  United States
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Quote:
Originally Posted by Salas View Post
You can, its only they get a bit hot. If you see any suspicious dc offset wandering apply a copper foil tape linking the group of 4 tops and fold its edges up and back to the middle so it helps with dissipation.
Ah ok so it acts as a heatsink I was going to tap off the terminal blocks and use that source to drive fans blowing across mosfets and their heatsinks, maybe i can direct it in such way that they also target the jfets?

Thx again Salas !
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Old 21st August 2013, 11:38 AM   #3242
Salas is offline Salas  Greece
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Better avoid forced cooling. It can be uneven. Motors can send back EMI to the audio PSU. Use an independent 78XX chip for a fan if it will be mandatory.
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Old 21st August 2013, 12:42 PM   #3243
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Quote:
Originally Posted by Erlend Sæterdal View Post
No serious listening tests has proven that.

What you use to insulate the devices from the heatsink is largely immaterial. The improvement comes from keeping the devices cool. OK mica works better as a thermal conductor than silicon rubber but to say that the mica makes for a better sound is very misleading and not entirely accurate.
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Old 21st August 2013, 02:04 PM   #3244
AndrewT is offline AndrewT  Scotland
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If modulation of the device junction temperature can lead to poorer sound performance, then it follows that excessive and avoidable modulation of device temperature will result in a poorer sound performance than when a device is held at near constant temperature.

Whether Mica, or filled rubbers, or Kapton, or other/s will give excessive temperature modulation is up for argument.

That excessive temperature modulation can cause sound performance degradation is, in my view, not up for argument. I am not referring in this situation to reduced reliability affecting sound output.
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Old 21st August 2013, 02:07 PM   #3245
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Exactly. It's got nothing to do with what you use as an insulator but all to do with keeping the devices at a lower stable temperature. Using big heatsinks with no insulator will keep everything cooler.

In the B1 everything is pretty stable. The B1 itself draws only a minimal load compared to the shunt regulation. There are not going to be any transient loads.

Last edited by KatieandDad; 21st August 2013 at 02:11 PM.
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Old 21st August 2013, 02:20 PM   #3246
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Next we will see that using steel bolts in an aluminium enclosure will cause noise due to differential metals.

BUT, using copper bolts to attach the devices to the heatsink might help get heat away from the device and into the heatsink.

Last edited by KatieandDad; 21st August 2013 at 02:23 PM.
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Old 17th September 2013, 09:28 AM   #3247
Corpius is offline Corpius  Netherlands
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Default Coupling capacitors

I think that I need some coupling caps on the outputs of my DCB1 because both my power amps have no coupling caps in the inputs. Just to be on the save side. Maybe I will make some DC coupled outputs and some without DC coupling in case I don't need them. I'll see.

this is what Salas wrote some time ago
My amps are both a 100K Zin amps. According to the Z-Cap website I can go down to a value as low as 0.80uF for my 100K Zin amps and have an optimal low frequency response at 20Hz. They even state that this is better than having higher value caps and thus having a lower optimal frequency response (Hz) and risking that some phase anomalies may introduced into the signal. Is this correct and how does this work? Just trying to understand... Lower values coupling are generally much cheaper, so please let it be correct

I also read some things about using a resistor between the coupling caps and GND. So,
  • where do I need to put these resistors, before or after the caps?
  • Is there a way to calculate the right values for these resistors depending the the value of the caps or perhaps the input impedance of the power amps?

Do I need to put the caps as close to the DCB1 outputs as possible or is it OK to put them at the RCA chassis connectors?

Sorry of all these questions..
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Old 17th September 2013, 09:46 AM   #3248
AndrewT is offline AndrewT  Scotland
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Check what happens with your power amp first.
How much does the output offset vary (or not) when different input resistances are connected.
Try zero ohms, try infinite ohms (open input), 220r (to mimic DCB1).

I have standardised on ~90ms for the high pass filter on all my power amps. It did not take long to swap the blocking capacitors to discover what I could not hear as any further improvement.

Your 100k for Zin and 0.8uF equates to 80ms, so is likely to be as low as you need to go.

BTW,
keeping the same capacitor and varying the Zin by adding a second 100k (to Signal Ground) to give 40ms High Pass then adding 51k for 20ms and then adding 24k for 10ms allows you to compare the effect of different input filters.
You could make the added resistor switchable.
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Old 17th September 2013, 10:15 AM   #3249
Salas is offline Salas  Greece
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1uF standard value capacitors work fine for coupling to 100K in practice IMHO. That is for plastic film. For electrolytics as couplers there are bass region THD issues due to their losses with rising signal level that is why you may spot up to even 220uF or 470uF in some professional audio preamps. Especially when they have EQ options like in studio mixing desks.
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Old 18th September 2013, 08:56 PM   #3250
Corpius is offline Corpius  Netherlands
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Quote:
Originally Posted by AndrewT View Post
Check what happens with your power amp first.
How much does the output offset vary (or not) when different input resistances are connected.
Try zero ohms, try infinite ohms (open input), 220r (to mimic DCB1).

I have standardised on ~90ms for the high pass filter on all my power amps. It did not take long to swap the blocking capacitors to discover what I could not hear as any further improvement.

Your 100k for Zin and 0.8uF equates to 80ms, so is likely to be as low as you need to go.

BTW,
keeping the same capacitor and varying the Zin by adding a second 100k (to Signal Ground) to give 40ms High Pass then adding 51k for 20ms and then adding 24k for 10ms allows you to compare the effect of different input filters.
You could make the added resistor switchable.
I can try varying with different input resistances to see how both my amps behave on the outputs, but I'm not entirely sure what I should do with the measurements. Please explain.

Quote:
Originally Posted by Salas View Post
1uF standard value capacitors work fine for coupling to 100K in practice IMHO. That is for plastic film. For electrolytics as couplers there are bass region THD issues due to their losses with rising signal level that is why you may spot up to even 220uF or 470uF in some professional audio preamps. Especially when they have EQ options like in studio mixing desks.
I was also thinking of using 1uF caps, Mundorf Evo Oil caps to be exact. My diy headphone amplifier has some Nichicon muse ES 470uF electrolytics in the signal path. They are bypassed by some 0.22Uf Spraque Vitamin Q's. This is a good sounding combination. I still have some of the Nichicon's left so I can compare them to fi the Mundorf's when I decide to use coupling caps.
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