Solid state amp for Pultec EQ..

[gyraf]

it won't work. You've already used the 0V once - the upper diode bridge will short AC. You need capacitor isolation (a'la tripler) to do this.

Jakob E.

 

[radiance]

So will it work if I loose the connection between point 3 on the upper rectefier and the center tap of the power transformer?

 

[gyraf]

No, then you loose the ability to have a common reference for the two supplies (grounds can't be connected). It's not easy to use a single-transformer for generating dual voltages. Look at Keith's version again..

Jakob E.

 

[radiance]

Capacitor isolation like this?

 

[gyraf]

Yes, I think that would do the trick. But you better check it in real-life yourself. Observe orientation of electrolytics. Current from the upper rail will depend on capacitor value (and mains frequency :razz: )

 

[radiance]

Thanks Jakob, I'm going to fiddle around a bit......see if it works.

 

[radiance]

Is the orientation of C3 and C4 in the obove scheme correct?
I suppose it is since I copied it from Ssltech's power supply (infact, it almost is Ssltech's power supply).

Still I don't understand why the electrolytics are positioned this way and not the other way arround. It just seems illogical to me.

 

[gyraf]

They're right.

The thing is, that when DC voltage builds up, it will be higher at the rectifier end (because we're aiming for a +voltage referred to transformer ground) than on the transformer end (that is AC only referred to ground)

Jakob E.

 

[Flatpicker]

[quote author="radiance"]@Flatpicker: I thought of puting those Haufe trannies behind the discrete opamp part. Anyway, maybe I just try both options (with and without the discrete opamp..)[/quote]?? If you put them behind (before?) the discrete amp, you won't have a balanced/differential output. By the way, it's not an op amp, just a multi-stage DC coupled amp. Personally I'd forget it and just use the Haufe trannies since you?ve got them. You will more than likely be feeding a much higher impedance than 600 ohms. Besides, it'll simplify your power supply.

 

[radiance]

Thanks to all.
@Flatpicker: What I ment was that I replace the 5532 opamp with the Haufe tranny/opamp (@the output stage) but you're right, I should forget about the "multi-stage DC coupled amp" and just use the Haufe trannies.
It's just that I have the "multi-stage DC coupled amp" almost finished and I want to use it. It's some kind of DIY syndrome I guess....(the parts I have laying around determine what the next project is going to be)

 

[Flatpicker]

[quote author="radiance"]Only thing is I started building the damn thing and have al the parts...[/quote]No problem... turn it into one of these: http://members.nuvox.net/~zt.robgrow/circuits/neve/neveba283.html

Add a gain switch, a couple of transformers and you've got yourself one of these: http://members.nuvox.net/~zt.robgrow/circuits/neve/nevemicpre.html

 

[radiance]

[quote author="radiance"]Capacitor isolation like this?

[/quote]

I build this power supply on vero board and after blowing a 125mA and a 500 mA fuse it works with a 1A fuse (connected to e 2 X 15V 1,6A toroid transformer). It gives +15V 0V -15V and +24V but I have nothing connected to it yet.
I have two questions:

1) what rating should the fuse be? I thought that with nothing connected to the power supply I could get away with a 125mA fuse but this seems not the case.

2) Does the 24V section give enough current to power 2 x this ? (only the make up gain section, not the 18V op amps) And how can I meassure this ?
(I guess the +/- 15V section will be ok, it's only the 24V I'm worried about)

 

[matthias]

hi,

why don't you use simply a 7815, a 7915 and a 7824...??

you could hook them up much more easily, just look at jakobs
power supply in the ssl schematic...

mat

 

[radiance]

[quote author="matthias"]hi,

why don't you use simply a 7815, a 7915 and a 7824...??

you could hook them up much more easily, just look at jakobs
power supply in the ssl schematic...

mat[/quote]

That's what I did :? Look at the scheme...

 

[matthias]

oops... sorry , I mixed it up with lm317.. because of the "adjust"...


but that's the way I'd do it...

use an 24V transformer and heatsinks on the 7815/7915

bigger power caps, and maybe protection diodes for the
regulators, if you like...

what do you think ??


mat

 

[radiance]

Yes, that's going to work as well and it saves me three cap's and a bridge rectefier.
It's just that I had this 15-0-15 toroid laying around that I wanted to use.
As a start I used SSL-Tech's power supply design(which gives 18-0-18 and 48).

The junk I have laying around makes me build thing's a certain way although I realise now that your way is probabely better. But on the other hand: if it works, it works, and my power supply works OK so far.

We'll see what happens if I hook everything up....

 

[radiance]

@Matthias: I had some problems with the Neve BA283 part from Steffen's solid state pultec which I'm building, and I thought it was because off my (weird) power supply. I build your version as well and it worked but it did not solve my BA283 problems.
What I did notice though was that with the 24-0-24 toroid connected, the 7915/7815's got really hot after a few minutes, with no load and with a very chunky heatsink connected.

 

[JLM Audio]

Steffen's pultec circuit has a part marked wrong. One of the two 1k resistors that sum at the gain pot should be 10k.

Also if reconfiguring the gain circuit it is best that this sum point feeds into a high input impedance amp for best results. So if going straight into the opamp reconfigure it to feed into the + input of a non inverting opamp stage and trim the gain using a pot on the negative feedback side of the opamp.

Joe

www.jlmaudio.com
[/quote]

 

[radiance]

[quote author="JLM Audio"]Steffen's pultec circuit has a part marked wrong. One of the two 1k resistors that sum at the gain pot should be 10k.

[/quote]

Thanks for pointing that out Joe!
Do you also happen to know which one off those two 1k resistors should be replaced with a 10k? Or should I pick one and see what sounds best....


Radiance

 

[JLM Audio]

Do you also happen to know which one off those two 1k resistors should be replaced with a 10k?

The bottom 1k which is inline with the wire coming from the join of the bass boost and Hi Cut pots should be 10k like a real Pultec.

Joe

www.jlmaudio.com