909 Question R16/R17

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21-Sep-2017 04:17 PM

CBK

CBK

Posts: 24

Does anyone know are the standard resistors for R16/R17 FLAMEPROOF?

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22-Sep-2017 03:14 AM

EJP

EJP

Posts: 1376

There's nothing to suggest that in the service manual.
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28-Sep-2017 04:45 PM

CBK

CBK

Posts: 24

Random question, which has better DC stability between OPA627 and LME49710? (i'm aware none are ideal but would still appreciate an answer).

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29-Sep-2017 02:08 AM

EJP

EJP

Posts: 1376

The OPA627 is ten or more times the price of LME49710 and the performance is not nearly as good.

I consider it obsolete.
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29-Sep-2017 05:15 PM

CBK

CBK

Posts: 24

Will LME49710 function in a 909? Not sure if it's a dual or not? I would really like to try it out just for the hell of it. I'm NOT fussed about power up or down pops/noises (as i'm using a passive pre-amp that may be less likely anyhow), but i would be concerned if insertion of this opamp makes the 909 unstable and likely to cause damage ect. Any thoughts?

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30-Sep-2017 03:43 AM

EJP

EJP

Posts: 1376

There is no point in putting a high-quality op-amp into a 306, 606, 707, or 909. In these amplifiers it only acts as a DC servo, with a bandwidth limited to 14Hz. The audio signal doesn't go through it.
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30-Sep-2017 11:09 AM

CBK

CBK

Posts: 24

I hear what your saying, but if one was compelled to try it, would LME49710 function without issues? (apart from startup noises).

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30-Sep-2017 12:28 PM

EJP

EJP

Posts: 1376

But you aren't 'compelled to try it'. You already have a working op-amp in there which has never been known to fail.
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30-Sep-2017 12:53 PM

CBK

CBK

Posts: 24

EJP, I know for a fact you really know your stuff, and i have a lot of respect for your knowledge and on this particular subject, certainly many people would agree with you. 

However this can be a contentious subject, and I've read on various forums numerous people who have used other opamps in the 909 and swear that sound has improved, and i'm talking about numerous people here (at least half a dozen who are independent of each other and on different sites ect). 

I am aware sometimes psychology can play a role in "imagined differences that aren't really there ect", however i genuinely don't believe that is what is happening with these people who swear to have heard differences in changing opamps in the 909. 

I have cut and paste many quotes from these people that i saved on my computer, and am happy to paste those here if you would be interested to read them. The idea of being able to hear differences around DC servos is contentious, but based on all the comments i've read i'm inclined to think there's something in it and i would like to try for myself. 

My only concern is, is it safe to do so? Can it cause the amp to overheat, break or malfunction in some way?


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03-Oct-2017 12:02 PM

Joost Plugge

Joost Plugge

Posts: 920

Hello,

Also on this forum there are numerous post's about changing the DC control loop op-amp in a 306/606/707/909/510/520 and the rest. The answer from DaDa people, like me, is always thesame and consistant. Your original question is ansered by EJP. I suggest we stop the discussion right here.

Joost Plugge

DaDa Engineering

Moderator of the forum

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13-Oct-2017 08:38 AM

Eric

Eric

Posts: 45

I am curious, people say R16/R17 have "pluggable" wirewound resistors, and these have solid metal connections not the traditional wire. Is the purpose of the metal here is create space between the board and resistors, or is the metal acting like heatsink?
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13-Oct-2017 09:18 AM

Joost Plugge

Joost Plugge

Posts: 920

The metal 'leg' is there to add some stifness to the resistor, otherwise it would be a wobly affair at those heights. The distance is neccesary for the heat transfer. In the first versions of the 405 you will see the results of direct placement on the circuit boards, a burned pcb and brittle pcb tracks. We use normal wire wound resistors in those positions in a 405, but they are placed closer to the boards to prohibit the wobly behauviour but far enough from the boards to prevent burning issues.

Joost Plugge

DaDa Engineering

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13-Oct-2017 10:25 AM

Eric

Eric

Posts: 45

So you use the regular wirewound for these positions?

Could you please provide me the link to the dadashop? 

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13-Oct-2017 11:28 AM

Joost Plugge

Joost Plugge

Posts: 920

http://www.dadaelectronics.eu/shop/components/resistors/wirewound-power-resistors/560r-4w-wirewound-welwyn

At your service!

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14-Oct-2017 11:49 AM

Eric

Eric

Posts: 45

Can 1% be used instead of 5% for these? Just curious how come Quad didn't use 1%?

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14-Oct-2017 10:53 PM

Joost Plugge

Joost Plugge

Posts: 920

R16/17 sets the bias current for Tr7, no 1% neccesary, but it does not harm.

Joost Plugge

DaDa Engineering

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16-Oct-2017 02:22 PM

Eric

Eric

Posts: 45

Are you saying there is no technical advantage using 1% here?

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16-Oct-2017 04:00 PM

Joost Plugge

Joost Plugge

Posts: 920

No, if the bias current is at a certain level, a few percent lower or higher does not make a differance. So Quad and we use 5% resistors.

Joost Plugge

DaDa Engineering

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