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Glassware Aikido All-in-One (Octal) | ACF-2 Buffer
Glassware Aikido All-in-One (Octal) | ACF-2 Buffer
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Old 29th January 2019, 02:28 AM   #21
Steve Morley is offline Steve Morley  Canada
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Just be aware that if you connect two amps at once the load to the buffer will be the input impedances of the amps in parallel. So if both amps have a 50K input impedance your buffer will "see" 25K.
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Old 29th January 2019, 03:49 AM   #22
sunil is offline sunil  India
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Great point Steve. Thanks.

BASICS.....

Reckon I won't hear the difference in 3.18hz to 6.36hz

I got the ACF-2 working. There is a buzz though. The problem and solution is documented here

Waiting on the caps now...SIGH !

C4 now has two caps connected - the solution to the 'buzz' problem. Powered on without tubes but R7 on the left channel get really hot and starts to change to brown. Although R7 on the other channel gets hot, it does not get brown like this one. I've swapped out the R for a new piece and the same is happening. Looks like it is getting hotter than it is meant to handle.

I've attached the schematic from John's site.

What could be the problem, please help? I'm testing without tubes and have checked all the solder, which looks fine.

P.S: R4 & R7 set the HT+ power supply.
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File Type: jpg Aikido ACF-2.jpg (206.5 KB, 268 views)
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Old 12th February 2019, 01:57 PM   #23
kodabmx is offline kodabmx  Canada
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Glassware Aikido All-in-One (Octal) | ACF-2 Buffer
They shouldn't get hot at all if there are no tubes in it...
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Old 12th February 2019, 02:39 PM   #24
sunil is offline sunil  India
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Thanks Kodabmx. In that case I have a problem somewhere.

Looks like this has started after I put the fix for C4 twin caps. How do I troubleshoot ?

I'm reading ~182v before the resistors. R4 & R7 are 4.7K.

Last edited by sunil; 12th February 2019 at 02:43 PM.
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Old 13th February 2019, 01:52 AM   #25
alexcp is offline alexcp  United States
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Glassware Aikido All-in-One (Octal) | ACF-2 Buffer
Sunil, I am reposting you photo from the other thread.
Quote:
Originally Posted by kodabmx View Post
They shouldn't get hot at all if there are no tubes in it...
Looking at the schematic, with no tubes in sockets there are two ways R7 can get hot:

1. The cap between R7 and ground is reversed - that is, it has (-) going to the ground and (+) to R7 - and conducts DC current. It would be hot, too, and the voltage on it would be small. If there is enough current, the cap can even blow up. Did you get cap polarity right? Does R4 get hot/brown, too? It should stay cold if the other cap from the pair is connected correctly.

2. There is a short on the PCB somewhere, but it is difficult to say from the one picture provided. In this case, R7 would dissipate about 7W (182**2 / 4.7k).

Can you please check my two hypotheses and report back?
Attached Images
File Type: jpg Aikido ACF-2 -split C4 (S).jpg (159.0 KB, 243 views)
File Type: jpg Aikido ACF-2.jpg (206.5 KB, 238 views)

Last edited by alexcp; 13th February 2019 at 01:56 AM.
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Old 13th February 2019, 11:22 AM   #26
sunil is offline sunil  India
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Alexcp, thanks for the analysis.

Both caps have the -ve going to ground. I followed the instruction shown in the other thread.

Glassware ACF-2 Aikido hum problem

Like this.

Here's a pic.
Attached Images
File Type: jpg Aikido ACF-2 - Dual cap C4.jpg (131.1 KB, 179 views)
File Type: jpg Aikido-ACF2 - Dual cap Negative.jpg (760.4 KB, 152 views)
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Old 13th February 2019, 04:43 PM   #27
alexcp is offline alexcp  United States
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Glassware Aikido All-in-One (Octal) | ACF-2 Buffer
Quote:
Originally Posted by sunil View Post
Both caps have the -ve going to ground.
Here we go.

The cap between R7 and the ground should be reversed, and replaced with a new one. ACF-2 uses bipolar power supply, and R7 is the negative rail. The cap should have (-) connected to R7 and (+) connected to the ground.

Connected as is, the cap has reverse voltage applied to it. The dielectric of an aluminium electrolytic capacitor is made of a thin layer of aluminium oxide. When you reverse the voltage, the oxide becomes dissolved through electrolysis. This then allows current to pass freely between the two plates of the capacitor as they are submerged in conductive liquid, making it very low resistance between the two terminals instead of a capacitor. Wikipedia has additional detail if you're interested.

I posted this to the other thread as well, just in case.

Last edited by alexcp; 13th February 2019 at 04:52 PM.
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Old 13th February 2019, 05:44 PM   #28
sunil is offline sunil  India
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Thanks Alexcp. I will make the change.

You mention that the caps should be replaced. Does that mean I cannot rewire the existing cap with the right polarity ? Are the caps damaged having run them the way they are presently ?
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Old 13th February 2019, 06:54 PM   #29
kodabmx is offline kodabmx  Canada
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Glassware Aikido All-in-One (Octal) | ACF-2 Buffer
They CAN be damaged, but R7 is pretty large. They probably still work.
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Old 14th February 2019, 12:35 AM   #30
alexcp is offline alexcp  United States
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Glassware Aikido All-in-One (Octal) | ACF-2 Buffer
Quote:
Originally Posted by kodabmx View Post
They CAN be damaged, but R7 is pretty large. They probably still work.
You may be right - I have no hands on experience with that. Still, I'd change them, perhaps when a good replacement is available, to be on the safe side. Even if they work, they may be out of specs after 180V / 4.7k = 39mA flowing through them.
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