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A possible approach to adding a silent start/shutdown to the ACA
A possible approach to adding a silent start/shutdown to the ACA
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Old 15th September 2018, 05:45 PM   #21
Mark Johnson is offline Mark Johnson  United States
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A possible approach to adding a silent start/shutdown to the ACA
I prefer not to connect the relay contacts in series between the amplifier and loudspeaker.

I prefer a parallel connection, which means that during normal operation when the amp is playing music, the relay contacts are not in-circuit. Just my personal preference.

Is my preference related IN ANY WAY to the failed output relay contacts on my Carver receiver, which I and many many other people had to repair? Mmmm, could be.

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Old 15th September 2018, 07:01 PM   #22
Mooly is offline Mooly  United Kingdom
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A possible approach to adding a silent start/shutdown to the ACA
The idea of applying a short across the output at power on and power off could be viable.

A check of the supply current of the ACA working into a shorted load is shown below. This was with an input signal that would drive the amp to clipping being applied. The peak current in this condition levels out at around 900ma per channel. So no problems as far as the PSU is concerned.

A possible approach to adding a silent start/shutdown to the ACA-aca-25r-jpg

To simulate a mechanical relay I used a voltage controlled switch and set the properties at 1000meg off resistance and 0.01 ohm on resistance. Just as with the photovoltaic coupler, there is an unexpected glitch at power off. A mechanical relay that has its power removed will short the speaker as quickly as the contacts can close... which in practice should be plenty quick enough. The moment power is removed under full drive is also shown below.

A possible approach to adding a silent start/shutdown to the ACA-aca-26r-jpg

A possible approach to adding a silent start/shutdown to the ACA-aca-27r-jpg

A practical version would need the comparator output interfacing to the relay via a suitable drive transistor for which I often find the 2N7000 FET (or similar) to be a useful device.

A possible approach to adding a silent start/shutdown to the ACA-aca-28r-jpg
Attached Images
File Type: jpg ACA 25R.jpg (89.0 KB, 623 views)
File Type: jpg ACA 26R.jpg (101.3 KB, 382 views)
File Type: jpg ACA 27R.jpg (63.4 KB, 380 views)
File Type: jpg ACA 28R.jpg (131.3 KB, 394 views)
Attached Files
File Type: asc ACA1 plus Shorting Speaker Relay.asc (5.6 KB, 3 views)
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Old 16th September 2018, 12:30 PM   #23
eddyvb is online now eddyvb  Belgium
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Or something with 1 or 2 555’s? Maybe using the S/R pins something can be done with 2 relays. 1 for the power and 1 for the LS. ACA powerswitch is now driving the 555 iso the power line. ACA power switch ON, first power relay, later LS relay. ACA power switch off, first LS relay, next power relay.
(The Arduino mentioned a few posts back is the easiest way, but it brings a potential noise source in the ACA box.)

Last edited by eddyvb; 16th September 2018 at 12:33 PM.
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Old 16th September 2018, 03:42 PM   #24
optimationman is offline optimationman  United States
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Default Can not explain

I had ugh, a long time ago(38 yrs ago), a SS Dynaco with a big turn on thump. I know this problem.

I also have built an ACA, but use a linear PS. With 91db speakers there is no turn on/off thump. However I first started with a set of CPU PSs and never had the turn on/off thump? I switch the PS ac on/off.

The only minor deviation from the "normal" components is using a MKC input cap instead of the normal silmic.

just a thought......
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Old 16th September 2018, 08:17 PM   #25
Bare is offline Bare  Canada
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Hmm I have /had a Dynaco st120.. it featured that turn "thump' and a just as concerning turn off piston action on my 94 db drivers.. grrr.
Did finally fix it. Can't remember how tho.
Notwithstanding that it was a Genuinely Bad sounding amp.
That! remains as memorable.
Are these ACA Noises Only associated with using SMPS ?

Last edited by Bare; 16th September 2018 at 08:24 PM.
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Old 17th September 2018, 01:08 AM   #26
optimationman is offline optimationman  United States
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Default Ops

I forgot one other change I made to the original circuit. I did raise the input impedance up to 28k to accommodate a tube preamp.
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Old 17th September 2018, 10:12 AM   #27
Danger Mouse is offline Danger Mouse  Germany
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Quote:
Originally Posted by Bare View Post
...Are these ACA Noises Only associated with using SMPS ?

I would think so.


I`ve build an ACA with an ZEN like regulated PSU (Articles at Firstwatt.com)
and have not seen such Problems.
No turn on or turn off thumb.
Speakers where 91db/8ohm this time.



So try a ZEN PSU. Maybe this would help too.
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Old 17th September 2018, 04:06 PM   #28
Bare is offline Bare  Canada
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Ahhh.. thank you. If that's the case.. then it's as simple as using a linear (DIY Store) PS rather than the laptop smps things ?
Seems Too easy
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Old 18th September 2018, 10:28 AM   #29
albertNL is offline albertNL  Australia
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A possible approach to adding a silent start/shutdown to the ACA
Quote:
Originally Posted by RafaPolit View Post
Albert, that is 'my type of hammer' also!

Wouldn't you be afraid that the 'noisy' arduino could affect the highly-sought-after clean supply?
The current used by the arduino are very small. According to this site 54mA. A Solar Powered Arduino Uno

I am not sure how much "arduino"-noise would get through the diodes used to drop the PSU voltage to arduino acceptable levels (or how much noise the diodes themselves introduce for that matter).

Radiation is another matter. If it turns out to be a problem, the arduino itself could be positioned so it does not radiate to the ACA circuitry (in a small metal box for shielding?).

The relay will use power while the ACA is in the stable phases (i.e. when you are listening). The relay can be placed anywhere, but probably close to the speaker terminals (with short leads) would be best. I have no idea if a relay pollutes the supply or radiates much noise.

If only things in the analog world were as simple as in the digital world haha Click the image to open in full size.
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Old 18th September 2018, 10:41 AM   #30
Mooly is offline Mooly  United Kingdom
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A possible approach to adding a silent start/shutdown to the ACA
Thinking about this a bit more... for those of you using the SMPS there could actually be far simpler ways of creating a silent start up (that's probably the easy bit) and also (with a bit of thinking outside the box) a silent shutdown.

The shorting relay across the output has to be silent at power on. It can't be anything else. That means a simple single transistor such as a 2N7000 FET powering the relay, and with a simple R/C delay on the gate would work. That is your silent switch on.

The relay closing when the ACA is switched off has to be accomplished very quickly. One possible approach could be to use a low voltage relay (5 volt) with appropriate Zener in series with the coil. As soon as the supply falls a little the relay will drop out shorting the speaker.

The above would be a unique (bit reliable) one off solution to the ACA using its recommended SMPS given that the SMPS output is both very tightly defined and that it will fall very quickly once the mains input is removed.
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