Q405 Dual mono power suply

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31-Mar-2018 06:14 PM

CK

CK

Posts: 4

Hello Joost, hello Stefaan,
I have recently purchased and installed the "Dual mono power supply, M12566.19" in my 405, as well an Amplimo Toroidal Transformer 300VA, 2x35V.
At the left Speaker output (CB Nr 12565.5) I've measured around 0.1 V, as described in your "Quad 405 DIY upgrade illustrated guidelines V2.0".
At the right speaker output (CB 12565.3) I've measured for the time of about 4 seconds also around 0.1V but then the voltage rises to minus 4.4 Volts. Sometimes it has blown the time lag fuse of 1.6 Amps, as recommended by Amplimo. I think this happens when I repower the amp without emptying the 10'000 uF Caps fully, I am not sure about that though.
I have the original DIN-Connector and 2 new RCA connectors connected. Could that be a Problem?
A: Could you please let me know how I can solve that problem?
B: In the "Installation instuctions for the 405 Psu version 17 and 19" it is written "the green wire goes directly to the eyelet". As the new Toroidal transformer doesn't have this possibility to connect it to "T", how should I deal with that?
C: "Quad 405 Upgrade-kit with OPA604 v3 High-end-boards" is "in Stock 0". Is it still possible to order the boards?
I would greatly appreciate your advice,
yours sincerely,
Christian
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02-Apr-2018 08:38 AM

Joost Plugge

Joost Plugge

Posts: 953

First look at the data sheet of the transformer. You have to use the diagram for the double output voltage. Connect the yellow and blue wire to the chassis of the 405, use the eyelet for this. Then split the red and the grey wire by using the suplied yellow wire, to connect the ac to both the power supplies. Connect the ground of both power suplies to the chassis, now you have a double supply fed by only one AC transformer, also connect the speaker return wires to the chassis, both eyelets wil be occupied (6 wires). If there is still DC on one of the outputs, the board has a failure. Use a 2A slow main fuse, the start up current with such massive elco loading will be high. You can preorder the HE boards, I did send a new set of Pcb's to Stefaan.

Joost

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08-Apr-2018 12:14 AM

CK

CK

Posts: 4

Hi Jost,
thank you very much for your advice! I appreciate that very much, it worked very well.
I measure now 0.092 V and 0.84 Volt on the speaker outputs. I enjoy the improvement of the sound compared to with the normal power supply before. Much clearer, more details I have the impression.
Unfortunately I can hear a hum coming from the Amplimo transformer. There is no difference whether secondary windings are connected or not. At start-up the hum is first strong, and then gets weaker as the caps get loaded. The original Quad transformer didn't do that if I remember correctly. (Serial number 61'201). Is that normal? Is that because the windings are not cast in?
I could live with it as I can hear it only when I have my head near the 405.
Kind regards,
Christian
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08-Apr-2018 09:27 AM

Joost Plugge

Joost Plugge

Posts: 953

Both DC values are on the high side, do you use the Din connector or RCA chassis parts? If so, are the RCA chassis parts connected to the chassis? See the 405 upgrade manual for the details. I had several experiments with torodial transformers, they all hum. In a 606 I use a fully encapsuled transfo, and when you put your ear on the casing, the hum is there. Some transfo's are giving less hum, but a transfo is to expensive to buy a batch and select the best! As long as the hum is not noticable from your listening position, you have to live with it. Also the original 405 transfo's have a reputation for humming. Quad replaced the block transfo in a 606 with a torodial because of the hum problem. For the start up current you can buy a limiter, see the Amplimo site.

Joost

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