Quad 405 complete upgrade kit questions

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08-Aug-2019 11:16 AM

Pholipe

Pholipe

Posts: 11

Hello,

I apologize to not be an electronicien, so I have some questions to be sure:

1\ C3 is removed but NOT replaced ?

2\ What do you mean by "decouple" ? Have you a schema of this operation (no picture in the documentation) ?"

3\ It is written in the pdf documentation: "Decouple D2 with a 2K7 resistor. ... Decouple D1 with a 100 nF capacitor."

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But I am lost because later on in your documentation and also in a recent former Forum's topic, they both mentionned:

- Documentation / Appendix 1_Photos: "Decouple caps for D1 and D2..." >style>

 - Forum : "The manual ... to solder a capacitor in parallel with the zeners (220µF in parallel with D1 & 100nF in parallel with D2)".

Many thanks in advance for your help.

Best regards

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09-Aug-2019 09:47 AM

EJP

EJP

Posts: 1677

1. Yes, C3 is not replaced. It is only there to stabilize the ancient op-amp. Not required on new ones.

2. 'Decouple' means 'connect to ground'. It is not correct to use it about a resistor: the instruction about the 2K7 resistor should read 'shunt', not 'decouple'. 'Shunt' would work about the capacitors you mention too. It just means 'in parallel with'.

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09-Aug-2019 11:47 AM

Pholipe

Pholipe

Posts: 11

Many thanks for your explanations.

My principal question was that for Zener D1: the texte in the guideline says to use a resistor 2K7 while in the same guideline (in Appendix photo's) and in one of a recent post of the forum (Quad 405 upgrade and Revision kits problems), it is mentionned to use a capa :" ...solder a capacitor in parallel with the zeners (220µF in parallel with D1 ...).

In my kit, I received a resistor and a capa and I stop at this step until I will be sure about what I have to do.

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10-Aug-2019 05:52 AM

EJP

EJP

Posts: 1677

Sorry, I don't do these instructions, but you can use either the 220uF capacitor or the 2K7 resistor. Not both.
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10-Aug-2019 11:52 AM

Pholipe

Pholipe

Posts: 11

It was exactly my question.

I needed to be sure that I correctly understood the guideline: why it can be either a resistor 2K7 or a capa 220uF for D1?

Many thanks for your help.

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10-Aug-2019 02:07 PM

EJP

EJP

Posts: 1677

The idea is to keep the squeal when the opamp shuts down out of the output stage. The 220uF capacitor manages that by keeping the opamp's power supply up long enough after power-down that the output stage shuts down first. The 2K7 resistor is copied from the 909: I believe the idea is the opposite, to shut down the opamp so quickly it won't squeal.
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13-Aug-2019 09:39 AM

Pholipe

Pholipe

Posts: 11

OK, I have completed replacements on ampli boards.

Except about their connectors ; the guideline says "Remove the old PCB connectors"but they are male ones and not part of the complete kit which contains females connectors. What I have to do ?

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13-Aug-2019 09:58 AM

EJP

EJP

Posts: 1677

Do nothing. Replacing these connectors is very tricky and rather risky, and the benefit if any isn't worth it.
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13-Aug-2019 11:01 AM

Pholipe

Pholipe

Posts: 11

So I only have to use new males connectors on new replacement cables.

Many thanks.

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