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  #1  
Old 3rd August 2021, 10:56 AM
rgccarter rgccarter is offline
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Default Coupling capacitor values

Hi

Looking to upgrade the orange drop coupling caps C11 on my newly acquired WD88VA and have a load of potentials lying around I could try.

From my knowledge the capacitance isn't to much of an issue as long as it's not below 0.01uf due to bass roll off?

So values of 0.47uf, 0.22uf - would be fine?

Would there be an upper limit? - I have some 3.3uf OIMP V-Caps as potential contenders.
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  #2  
Old 3rd August 2021, 02:00 PM
bob orbell bob orbell is offline
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Default Re: Coupling capacitor values

Looking to upgrade the orange drop coupling caps C11 on my newly acquired WD88VA why? Bob
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Old 3rd August 2021, 02:33 PM
rgccarter rgccarter is offline
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Default Re: Coupling capacitor values

To see if there is any noticeable difference to the sound for the better. I've done on previous amps with varying degrees of success.

+ I like to tinker.

Regardless of if I should or not. Would be interesting to understand if my assumptions above on values are true or not
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Old 3rd August 2021, 02:46 PM
bob orbell bob orbell is offline
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Default Re: Coupling capacitor values

Maybe you should ask the person that designed the WA88 he obviously calculated that .047uF was a good value for C11, yes change every value you like, it is your amplifier, but personally I would leave as is, as I have said in another thread, you would get a much more noticeable improvement by using better components on the HT power line like low ESR capacitors C12-13 and faster recovery diodes. Bob
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Old 3rd August 2021, 02:51 PM
rgccarter rgccarter is offline
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Default Re: Coupling capacitor values

Quote:
obviously calculated that .047uF was a good value for C11
I wasn't looking to change the values more about trying better quality components I have already - which are different values to what the circuit currently has. And from my understanding the value (as long as above 0.01uf) doesn't impact the design.

Quote:
you would get a much more noticeable improvement by using better components on the HT power line like low ESR capacitors C12-13 and faster recovery diodes. Bob
Already in hand, thnx
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  #6  
Old 3rd August 2021, 04:24 PM
Richard Richard is offline
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Default Re: Coupling capacitor values

Quote:
Originally Posted by rgccarter View Post
Hi

Looking to upgrade the orange drop coupling caps C11 on my newly acquired WD88VA and have a load of potentials lying around I could try.

From my knowledge the capacitance isn't to much of an issue as long as it's not below 0.01uf due to bass roll off?

So values of 0.47uf, 0.22uf - would be fine?

Would there be an upper limit? - I have some 3.3uf OIMP V-Caps as potential contenders.

C11 is not really what we'd think of as a coupling capacitor. C11 and R24 make an RC network across the output which shorts very high output frequencies to ground, to help stability, rather than having HF sent back in the global feedback network C10 R18. We're looking to limit the HF but not to roll it off audibly as, say, a larger cap value may do. Best left alone.

The coupling caps are C5 and C6. These work into R12, R13 and would affect the bass roll off frequency. 0.47uF into 220K gives a roll off at 1.5Hz. Double the cap will half the frequency and half the cap will double the frequency. So changing them to 0.22uF would raise the roll off to 3.3Hz and it may sound a little speedier and lighter. I wouldn't go much lower than 1.5Hz though as you may introduce low frequency instability as "motorboating".
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Old 4th August 2021, 06:52 AM
bob orbell bob orbell is offline
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Default Re: Coupling capacitor values

Well I could not have put it better Richard, as I said, why . Bob
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Old 4th August 2021, 10:27 AM
Richard Richard is offline
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Default Re: Coupling capacitor values

Thanks Bob. Itís also worth mentioning that roll-offs through the amp are cumulative. If the input signal has already been rolled off by an earlier stage it will still get rolled off some more by a too-high coupling later on. (A lower coupling will not get it back.)

These roll-offs may be caused directly on the signal, as in couplings, or indirectly by such as partial degenerative feedback caused by too-small cathode bypass capacitors on the earlier or later stages.
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  #9  
Old 4th August 2021, 12:35 PM
bob orbell bob orbell is offline
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Default Re: Coupling capacitor values

I don't want to sound harsh Richard but the first post of this thread, first line said to me, I haven't really got a clue, OK, we should try and help all members, as I will, but not too long ago a member decided to mess with a KAT6550 who did not listen to a word anyone said, the results were disastrous . Bob
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  #10  
Old 5th August 2021, 12:52 PM
bob orbell bob orbell is offline
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Default Re: Coupling capacitor values

Just been looking at this. About rgccarter
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words say a lot. Bob
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