Cap Question for SSL 9k

[Andy Millar]

Thanks for that Simon - what were we on in those days! I'd forgotten quite how bizarre (but very good) that circuit was. It was mostly designed by an interesting Californian called Dave Mate (who may even be still at SSL?), with just a bit of input from me, I think originally for the ARC console.

The only important spec for the TL052 is the offset voltage and current, both of which had to be as low as possible. No audio passes through these at all - they are only to generate a DC 'servo' voltage to avoid the need for output coupling capacitors (Dave hated coupling capacitors!). There probably are much better devices around now.

At first glance I don't think any of the capacitors are very critical for type in terms of audio performance (except the 2u2 input caps), most of them are there to achieve a dead flat high frequency response - we're talking 200kHz not 20kHz so any effects a dodgy dielectric produces should only be of interest to highly trained bats. As suggested the smaller ones should be ceramic. The 470n can be anything you like - they're to produce the DC 'servo' voltages so they don't pass audio. The 330pf and 470pf I probably would use some sort (any sort) of plastic film type, but to be honest I would be very surprised if anyone noticed if they were ceramic. But I'll have a bit more of a think when I'm awake.

 

[gltech]

Thanks Andy!

Does anybody know where you can online-order Rubycons?

Glenn

 

[Andy Millar]

The 3p3s, 10ps and 100ps don't need to be NPO/COG, any old ceramic will do, for highest performance the others up to 470p could be. (Because NPO/COG capacitors are very stable with temperature this stops any high frequency phase differences between the two halves of the balanced channel. But it is probably me being a bit perfectionist!)

In answer to the question way above, the reason for using ceramics is (to put it simply) they keep their capacitance up to very high frequencies - well into the MHz - and the challenge with 5534s is to stop them turning into radio transmitters which is what the really small value capacitors are for. Otherwise ceramics are dreadful for audio due to their distortion, but this is only a problem if the capacitance is starting to have an effect seriously down into the audio band, which none of these are.

 

[Flatpicker]

All this talk about the MAT-02s being expensive got me to thinking about using discrete transistors instead. Looks like you could match up a pair of decent low noise bipolars and thermal-couple them (if that is even necessary) with some epoxy or something? Probably wouldn?t be worth the trouble for one or two, but if you were going to build several, it might be worth looking into.

Anyhow, as I was inspecting the PC board layout and exploring this possibility last night, I noticed a discrepancy between the layout and the schematic. It appears that R108/C83 are reversed, and that R72/C59 are reversed. I?m at work right now and don?t have time to search the META so I apologize if this has already been covered, but figured I should mention it in case it wasn?t. I assume the layout is correct since everyone?s boards seem to be working?

 

[zitoune]

Thanks Andy for the caps !

For the 2u2 in the input and after the firts ne5534, which good quality capa should be used ?
Elna, Panasonnic,Rubycon ...?

 

[Guest]

I used these

2U2 - Wima - that fit 63v from Farnell
http://uk.farnell.com/jsp/endecaSearch/partDetail.jsp?SKU=1006054&N=401
You may need to drill the holes a bit wider to fit the thicker wires

 

[Andy Millar]

The manufacturer doesn't matter, the important thing is a high quality dielectric such as polypropylene, PPS or polyester. PPS is probably the best, but I'd be surprised if anyone can hear the difference between any of these three. Those Wima Polyesters from Farnell would be fine. And, of course, they don't have to be 63V, but you probably won't find a lower voltage and higher would be a bit big. Have fun!

 

[muadgil]

Hello
About those blocking caps. Could I use 10uF ones instead of 2u2, or will it change something, like undesirable filtering, lower impedance or else?
I'm asking that because i can't find polypropylenes or polycarbo that fit the PCB, but i can have good electrolytic caps dedicated to audio applications, but minimum 10uF.
That kind of obsession (caps quality) probably makes you laugh Andy, but I'm so excited building this pre with my little hands that i want to give it the best i can. :grin:

Thanks
Gilles

 

[zitoune]

Thanks !

And what about the use of polarized electrolitics cap ? It's not recommanded ? it's not better for audio (elna audio caps : SILMIC, Serafine, purecap..)

Mudagil >> i think if we use 10u insteed of 2.2 will change the input impedance and frequency of the filter..

Mais je suis pas sur !! peut etre que ca changera pas !

Thanks a lot for your help !

 

[muadgil]

Hi
Zitoune> There is no problem to use polarized caps like ELNA or BGate at these places (blocking, and after the 5534), it was confirmed in another topic.
But about the blocking one, Bgate makes 2u2, but only 50V, which quite short regarding 48V. And Elna makes 63V, but at 10uF minimum.

By the way, I just found that cap (polypropylene 2u2/250V), which is quite big, but has long legs, so we could fit it in the PCB.
http://www.bmm-electronics.com/Product.asp?Product_ID=4150
Don't you think it could be a good solution?

 

[zitoune]

Elna make 2u2 in 100 V... it's not good ? it's preferable 63 V ??

 

[muadgil]

Elna make 2u2 in 100 V

I think it would be perfect :grin: . There's no problem to use a 100V here.
But where did you found it? I haven't seen it at Selectronic.

 

[zitoune]

I foud this in the elna catalog...

But i dont know if electrolitics cap for audio (slimic, purecap..) are better then PPS, polipropylene , polystirene caps. Andy seen to say no.

Anyone can confirm this ?

we should prefer goog electrolitic such as elna slimic or use film capacitors (PPS, polypro..) ?

Thanks a lot

 

[Andy Millar]

Electrolytic/tantalum caps (whether polarized or not) do have a distortion problem, by the way they are built their performance will be different at different voltage levels. It depends how 'golden ears' you want to be about it. In all the stuff I build now (for myself) I use electrolytics, but if I was building for someone else I would avoid them if I could.

I would say that if you want to experiment then try 10u (or whatever) electrolytics, and if it sounds good don't worry! But the idea of the circuit was to allow us to use the smallest value cap that we could, so that we could use plastic film types, and the low risk option for ultimate performance is to use these.

(By the way Giles, quite right - the whole point of building stuff yourself is that you can get it as good as possible! Manufacturers try to shave every penny off the cost of their components that they can.)

 

[dubwarrior]

what kinf of ceramic caps are good for those compensation caps?

I think ceramics are need for

C73
c74

C46
c47

C64
C65

C48
C93
C94

am i right wqith those caps as ceramics?

The other i woudl take some film ones, maybee wimas.

Are this good
http://www.banzaimusic.com/5-0mm/

Or should i use other ones?

Regards