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Old 20th October 2018, 10:23 AM   #21
Rudi_Ratlos is offline Rudi_Ratlos  Germany
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James, I have in the meantime drawn a layout for "one-half of a bridged ACA" (according to your proposals) and have already soldered and listened to a prototype of it.

I am driving this ACA from a 24VDC regulated PSU, consisting of a 2x19VAC/160VA torroid, full bridge-rectifier (mounted on the heatsink), 10mF reservoir caps
and LM1084 regulator, adjusted to 24VDC.
I would never think about driving a ClassA AMP from a SMPS.

This ACA alone already plays beautifully, but I would like and bridge it , same as you did.
Can you please tell me, how to proceed with ACA#2?

For the ACA#2 I need an inverse input-signal (which can be derived from the output of ACA#1).
Is a "bridging resistor" (value: 68,1K, from where to where?) all that I need?
Don't I need a resistor-divider (same like in feedback)?

Once I am done with my "bridged-ACA", I will happily send you a pair of my PCBs.

Best regards - Rudi_Ratlos
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File Type: jpg SNV34510.JPG (549.4 KB, 690 views)

Last edited by Rudi_Ratlos; 20th October 2018 at 10:26 AM.
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Old 20th October 2018, 06:19 PM   #22
Nelson Pass is offline Nelson Pass  United States
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I printed out ACA1.6 schematics in two formats, attached here.
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File Type: gif aca16 sch.gif (109.0 KB, 754 views)
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Old 20th October 2018, 06:27 PM   #23
Zen Mod is offline Zen Mod  Serbia
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how's that nobody asked for SUSY ACA ?

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Old 20th October 2018, 07:04 PM   #24
Dennis Hui is offline Dennis Hui  Canada
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Quote:
Originally Posted by Zen Mod View Post
how's that nobody asked for SUSY ACA ?

Bad ZM!
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Old 20th October 2018, 08:41 PM   #25
Zen Mod is offline Zen Mod  Serbia
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it's not trivial , but certainly easier than it looks

tired two cells ..... maybe later tonight , when I allow some caffein to lift me up .....
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Old 20th October 2018, 09:28 PM   #26
TungstenAudio is offline TungstenAudio  United States
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Rudi, glad you are moving forward with your own mods to the ACA. I have not seen another build using integrated regulator ICs for the 24V power. To make a bridged amp, you just need to add the 68.1 kOhm resistor from the left (–OUT) terminal to the right (+IN) input. This is commonly done through a switch as shown in Step 38 of the excellent Amp Camp Amp V1.6 Build Guide by 6L6. Note that it is also necessary to tie the two (+OUT) terminals together with a heavy piece of wire, which is also shown. These steps may be easier if the two boards are in one chassis.

The speaker wires will then be connected as shown in Step 54, with the black (–) wire connected to the left (–OUT) terminal, and the red (+) wire connected to the right (–OUT) terminal.
Now you need to build two more boards the same way for the other channel of your stereo system.


I have been quite happy with the sound of my bridged ACAmps powered by the kit SMPS power supplies. I must admit that I was skeptical at first, and some of my capacitor upgrades were intended to address any residual noise issues that may have been caused by the little brick supplies. Regardless, the system sounds quite fine, and I'm currently pursuing some other builds.
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Old 20th October 2018, 11:46 PM   #27
JSA1971 is offline JSA1971  Canada
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Quote:
Originally Posted by Zen Mod View Post
how's that nobody asked for SUSY ACA ?

SUSY ACA PLEASE!!
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Old 21st October 2018, 12:53 AM   #28
TungstenAudio is offline TungstenAudio  United States
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Quote:
Originally Posted by Zen Mod View Post
how's that nobody asked for SUSY ACA ?


No doubt there are a myriad of mighty wackoo ideas to try.
I already have schematics for a higher voltage ACA with IRFP150s and a cascoded input follower, an ACA with double IRFP240s in the output, and one with an FET cap multiplier on the power rail.
How about an ACA headphone amp or an ACA-X (or is that X-ACA)? Certainly there must be a Son of ACA, Babelfish ACA and a Bride of SoACA! Should keep the Greedy Boyz busy for a little while.
Among other things, I'm working on an ACA with a Zen V4 input buffer. I've got a few ZVP3310A and ZVN3310A Fets to play with. You know, just in case the 2SK170s get scarce.
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Old 21st October 2018, 10:58 AM   #29
anotherJoachim is offline anotherJoachim  Germany
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Hello

i am rather a newbie in such things, so maybe you could give a little help to me

Quote:
Originally Posted by TungstenAudio View Post
I changed the input resistor R11 to 20k and the feedback resistor to 90.9k.
So now R11 is 20k and R12 is 90.9k?

Quote:
Shortly after making this change, I also added a 2.0 Ohm resistor in parallel to R3 and R4,
Hmmm... so now we have
0.68R II 2R II 0.68R -> 0.291R
Or
0.68R II 2R II 2R II 0.68R -> 0.254R

Maybe better said, did i need *one* 2Ohm resistor or *two*?

thanks Joachim
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Old 21st October 2018, 07:00 PM   #30
xrk971 is offline xrk971  United States
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Nice work, Rudi!

I like this layout and use of integrated VR.

Click the image to open in full size.

Although I find SMPS followed by DC-DC step up and then a cap multiplier and a CRC works great and sounds great too. Many folks are doing this with the MoFo I think as the DC-DC has adjustable output and you can set the final voltage to whatever suits you.
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