Quad 66 Hybrid Elements

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06-Dec-2010 03:06 PM

Tim H

Tim H

Posts: 4

Many thanks to Stefaan et al for the advice and comments concerning i.c's for the 66. I have now completed the project, and am delighted with the results.

However, having replaced the op. amps. with Burr Brown types, and the selector and switch i.c's with Maxim devices, it would appear that the multiple surface mount 4051's, used in the two hybrids per channel, form the weakest links in the audio chain. It would clearly be folly to attempt to replace these chips with higher quality types without access to highly specialised equipment - and possibly not even then! Thus my 'solution' is to leave well alone. I would be interested to learn of the experts' views and approach to this problem.
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06-Dec-2010 04:18 PM

Thierry

Thierry

Posts: 94

Hi,

I have dealt with much smaller footprint ICs that the 4051, i.e. the AK4393 in the VSOP28 package. I fee at ease with this - mostly because I have the appropriate equipment which is an hot air station - but I would strongly advise you to NOT fiddle your pride and joy. It takes some training, including try and error, before achieving a perfect job without ending with lifted pads or a destroyed PCB.

If you feel brave enough and really want to do it get some old computer motherboard or extension cards and train yourself  unsoldering something similar until you succeed.

I published some hints here :   

http://www.dcx2496.fr/cms2.php

And here's an example of VSOP28 package removal and refitting :  http://www.dcx2496.fr/newdacs.php

Good luck,

Thierry

[URL]http://www.dcx2496.fr/cms2.php[/URL]

[URL]http://www.dcx2496.fr/newdacs.php[/URL]




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07-Dec-2010 04:23 AM

EJP

EJP

Posts: 1412

The 4051s aren't in the audio chain. They provide logic switching to control the 4066s, which are in the audio chain.

Esmond Pitt
Dada Electronics Australia
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07-Dec-2010 10:38 AM

Tim H

Tim H

Posts: 4


Esmond, the 4051's to which I am referring are not those on the mother board providing logic signals, but the five mounted on the volume hybrid and the two on the tilt/balance hybrid which Quad refers to as 'stepped controls (fixed resistors and cd4051 i.c's.' As such, they are surely carrying the audio signal and switching it to varying degrees of attenuating resistors, etc.? The circuit diagram, on which the hybrids are represented by variable resisors, with control lines in, not out, would appear to confirm this.

Thierry, many thanks for your helpful hints on soldering these devices. However, it is not working with s.m.d's which worries me, but the fact that these are mounted not on standard p.c.b. material, but on the thin plastic of the hybrid, into which the other components are formed. Thus the potential for damage seems so much greater.
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14-Dec-2010 02:29 AM

EJP

EJP

Posts: 1412

Sorry, you are right, I am crazy. There is a range of MAX4051 which have the same advantages over the CD4051 as the MAX4066 has over the CD4066: much lower on-resistance and much lower THD. We can supply these. You don't need any special equipment: just desolder the existing 4051s, fit 16-pin DIP IC sockets, solder them up, and slot in the MAX4051s. Very similar to replacing CD4066s, and I've done hundreds of those.

Esmond Pitt
Dada Electronics Australia
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14-Dec-2010 01:12 PM

Tim H

Tim H

Posts: 4

Esmond, that's exactly what I've done with the 4051 which acts as an input selector, and is in DIP format. However, as I mentioned to Thierry, the eight 4051 i.c's per channel on the volume and balance/tilt hybrids are surface mount, and the substrate is the thin plastic of the hybrids - hence my reluctance to intervene.

(These i.c's aren't individually shown on the circuit diagram, but are mentioned in the legend at the bottom of the page, and can be seen in profile on the later plan view of the audio boards.)

 
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14-Dec-2010 02:58 PM

Thierry

Thierry

Posts: 94

Tim,

Any maintenance shop equiped with even an entry level hot air station like the one I use (  http://www.dcx2496.fr/outils.php , middle of the page) will be able to tackle the job for you.

Soldering new chips isn't really difficult either. Go on youtube.com  and search the words "SMD soldering"

Thierry
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15-Dec-2010 02:02 AM

EJP

EJP

Posts: 1412

Sorry Tim, I am crazy again, I was thinking of the 66pre which I have just been inside, where they are DIP-14. Manual SOIC soldering is possible, I've done a bit, but it is certainly no joke and not to be contemplated without a steady hand, a fine solder tip, and a good lens.

Dada Electronics Australia
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18-Dec-2010 04:47 PM

Stefaan

Stefaan

Posts: 563

There is a good High-end alternative in DIP-package for the TL074 available in the Webshop now:

http://www.dadaelectronics.eu/shop/components/ics/analog-ics/lm4974-hifi-quad-opamp-national-semiconductor

Stefaan
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