909 resistors

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20-Feb-2018 12:16 PM

Eric

Eric

Posts: 53

Joost can you advise which resistors are in the signal path of the 909 (which resistors are most important for the sound). 

R1 & R2? Any others?

Thankyou

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21-Feb-2018 02:16 AM

EJP

EJP

Posts: 1511

As we say, everything is in the signal path, although in the 909 you can exclude R5,6,25 and the op-amp and C3 as they only deal in infrasonics.

But if you're hoping to hear startling improvements by changing a few resistors you're in for a disappointment. Any damage done by R1 is undone by R24, for example.
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21-Feb-2018 08:48 AM

Eric

Eric

Posts: 53

ok i see. I also curious whats the standard "parts per million" (PPM) for the metal film resistors in the 909?

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21-Feb-2018 09:45 AM

EJP

EJP

Posts: 1511

PPM of what? Temperature coefficient? Voltage coefficient? Noise coefficient?
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22-Feb-2018 04:21 AM

Eric

Eric

Posts: 53

Sorry i mean temperature coefficient. Any idea what is the temperature coefficient of the metal film resistors in the 909?

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22-Feb-2018 06:08 AM

EJP

EJP

Posts: 1511

No I don't, but I will bet it is standard, and it also doesn't matter in the least because it is well ventilated. The only significant heat is developed across R24 and it is 2.5W rating.
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22-Feb-2018 07:26 AM

Eric

Eric

Posts: 53

What would be considered the standard temperature coefficient ppm for metal film in audio gear?

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23-Feb-2018 01:25 AM

EJP

EJP

Posts: 1511

I can only say again that it doesn't matter. It isn't specified in the service manual, so Quad don't care.

I just went through the exercise of selecting through hole fixed resistor, metal film, 1% tolerance, 0.5W, 22K at two different suppliers and in both cases there were only two choices of tempco. I don't know why you're worrying about it.
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23-Feb-2018 11:47 AM

Eric

Eric

Posts: 53

Im not worried or anything was just curious in audio gear what the average temp co was for metal film. 

I would really love to ask when i want to change PSU caps, do i need to de-solder any wires? I can see the wires on the side boards have spades, so disconnecting those should be easy, but what about the power cables that run from the circuit breaker to the transformer PCB? Do those need to be de-soldered to take out the whole transformer board?

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23-Feb-2018 11:59 PM

EJP

EJP

Posts: 1511

No. You have to remove both the bottom and the strap thing that goes around, and then undo the four screws that hold down the PCB. Then with great care you can kind of turn it enough so you can get at the underside. Putting the screws back is fun too ;-)
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24-Feb-2018 12:30 AM

Eric

Eric

Posts: 53

But the power cables are soldered to the transformer pcb board on one end and on the other they connect direct to the circuit breaker.

Does the circuit breaker end of the cable have spades or something?

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24-Feb-2018 01:31 AM

EJP

EJP

Posts: 1511

I don't have one to look at right now but I have never had to disconnect any power cables when changing 909 PSU capacitors. Turning the PCB is tight all right but it can be done.
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25-Feb-2018 12:05 PM

Eric

Eric

Posts: 53

Thankyou. Also can i ask is it safe to use  a 100V electrolyte capacitor for C7? (instead of 63).

Can using higher voltage shorten the life of the cap here, or maybe cause capacitance to go down more quickly over time?

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25-Feb-2018 11:37 PM

EJP

EJP

Posts: 1511

It won't do any harm, but why? It will cost you a lot more, and possibly be too big for where it has to go. There is no advantage. If you want an improvement, raise its value to 100uF. There's a small improvement in LF distortion.
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26-Feb-2018 11:45 AM

clearsound

clearsound

Posts: 27

Hi Eric,

just for your info - the 909 PSU PSB needs to be removed to get to the solder connections for the Caps as these are on the underside of the PCB. Esmond is correct there are 4 screws securing it but on mine two of these were partially / completely obscured by the transformer. The transformer is again attached by a single bolt - this locates in a welded nut on the underside of the PSU PCB bracket ( which is held in the box by the 4 screws). The transformer sits on a bitumin (?) 'washer' which will have hardened over the years and  can effectively glue the transformer to the PCB, so take care removing it if you decide to do the job. All this is made more problematic by the lack of room - which may necessitate further removal of parts.

Coupled with this is the chance that your choice of replacement caps will be of a different pin configuration. Even the ones listed on the webshop are - theres a blog on here about it. Have a search and a read if you haven't already done so.

Also I'd recommend downloading the 606 upgrade manual from here - its got some good info on the 909 if I remember correctly.

Depending on your skill level and where you are in the world - you might want to contact Joost and see what the cost for completeing this work would be? He's done a fair amount of work for me in the past on both my 34's and 909's and I think his rates are very reasonable. He's a busy guy though so you might need to give him time to complete the work.

Hope this helps

Joe

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26-Feb-2018 02:44 PM

Eric

Eric

Posts: 53

Thankyou clearsound much appreciated. So i presume the whole transformer ect has to be removed to access the PSU solder connections right? I had a looked at the upgrade manual but couldn't find any detailed instructions regarding this. Thanks again : )

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26-Feb-2018 03:12 PM

clearsound

clearsound

Posts: 27

Hi Eric,

pretty much, yes, the mains switch connections can be left on as you can remove the case around it.But you have to have access to the whole of the underside of the board. Depending on how much you're used to doing it can be a real squeeze with the amplifier boards in place. Replacing the PSU board would be expensive but Dada do a replacement including transformer. Hence my suggestion to send it to Joost. They're still expensive amps so you want to make sure its done properly. 

Regards

Joe

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26-Feb-2018 03:15 PM

clearsound

clearsound

Posts: 27

Sorry last post should have included:

If the transformer damages the pcb when you try to remove it  ( It can be really attached) - Dada do a replacement.

J

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