Those 33000uF caps might come in Handy!!

[primalsea]

I'm building a new preamp, nothing complicated, just a buffered volume pot. I plan to use single opamp chips with 1 for each channel before the pot and the same again after the pot.

For the power supply I intend to have an RC filter of a 2 ohm resistor and a 15000uF cap connected to a bridge rectifier. There will be 2 of these one for + and one for - V. Then the caps will be connected to more RC filters of another 2 ohm resistor and a 33000uF cap. There will be 4 of these one for each + & - V of each channel. The supply voltage will be about +/- 8V ish DC.

My question is, is that abit OTT I do intend to have dc outlets from the preamp to power my unbuilt active filter so it will need abit of welly. However my choice of caps is govened by the fact that I managed to pick up 4 33000uF 10V, 20A caps for £1 and salvaged 2 15000uF caps from old equipment.

A quick simulation shows that the supply rails will take a few seconds to reach full potential. I hope this will mean no power up thumps from the opamps, negating the need for a relay circuit. Also if the simulation is correct the rails will be very smooth so good chance no voltage regulators needed either.

However if I can get sonic results just as good by using smaller caps and not having to cram them in a small box its worth thinking about.

Has anyone here made a unfeasibly large PSU for a preamp. Can you advise if it was worth it???

Kind regards
Paul

[Stocker]

Only if it will also power the power amp...

[Nelson Pass]

Originally posted by primalsea
Has anyone here made a unfeasibly large PSU for a preamp. Can you advise if it was worth it???

Abso******inglutely

[Praudio]

Hope the transfo is in major league, my latest preamp was with a 8A transfo!

[cowanrg]

hehe. goto my site and click on the BOSOZ project. it uses an 800va xformer for the pre-amp circuit. a little bit overkill, but why not???

http://www.cowanrg.mesanetworks.net/projects/

[GRollins]

I used to have about 250,000 to 300,000uF on my Threshold amps. Bloody marvelous. Preamps? Well, lemme see...I haven't gotten into the area you're talking about yet as far as the sheer number of uF, but in terms of Joules of storage, I've done a bit of extreme work.
As we speak, I have an entire case of caps coming in for use in a mega-amp project. That's 36 units of 68,000uF. That's in addition to a distributed capacitance final bank with 2200uF situated next to each output device. I can't wait.
In other words...go for it.
You're not alone.
You just thought you were.

Grey

[wigginjs]

OT:

cowanrg, those Aleph 2 cases look REALLY amazing, did you do that metal work yourself?

[cowanrg]

thanks! i didnt do the work, i had a CNC shop do it. the back case will be redone here soon. i decided against a standard box case and will be doing a CNC'ed case as well.

[primalsea]

Thanks for that all.

Actually I think I miss-calculated the effective capacitance for the simulation using Duncan Amps PSU Desinger. The resistors can be made alot smaller, probably sub 1 ohm values and still give a smooth supply with ripple in the single millivolt range. So the simulations says anyway.

I plan to have the rails reach full potential after about 5 seconds. I'm hoping he slow raise in the rails will mean no opamp thumps at power on.

Do I guess correct??

Also I intend to strip this preamp right down to basics. I found that most switchs I used for source selection have terrible amounts of crosstalk. I thought about using buttons activating relays. Then I thought again. I usually listen to either records or CDs and its not a labour of love to just turn the various sources on or off as required. So no source selector on this amp!!

Just thought i'd throw that one in as well

Paul

[janneman]

Originally posted by primalsea
[snip]I usually listen to either records or CDs and its not a labour of love to just turn the various sources on or off as required. So no source selector on this amp!!
[snip]Paul

Paul,

Be carefull with that. Switching a source off but leaving it connected may influence the sound from the active source. The impedance that the off source presents to the active source is undefined and may be low or non-linear or both.
A good selector switch would avoid this. I have used Pickering 101 series (UK) relays in the past with undetectable crosstalk.

Jan Didden