Going Linear with the Caiman

[StanleyB]

I have been thinking of trying out a CB radio linear power supply on a Caiman just to see what the results would be like. CB radioes need extremely low noise linear power supplies or high current capability. Unfortunately the CB radios power supply are set at 13.8V. The Caiman needs 15V. But I realized that to set a linear power supply to an exact figure of 13.8V would mean that there had to be some sort of voltage preset in the case.
There are quite a few linear power supplies listed on eBay for CB radio, but Maplin also list a few and a new branch opened up about 10 minutes from my home a few months back. So off I went and grabbed myself one of THESE I grabbed the 3A version, which is all that would be needed for this application.

A quick look inside the unit reveals two pots.


The one on the left should be turned all the way clockwise in order to get it to output close to 15V.


WARNING NOTICE: : If you intend to try this mod, but you are not experienced with electrical safety procedures, make sure that the power supply is unplugged from the mains before you remove any screws on the case. Do not plug the power supply into the mains whilst the top cover on the power supply is unscrewed and removed!! Just turn the pot in the direction shown and that should be close enough to 15V.


I cut off the DC lead on an old TC-7510 power supply in order to make up the DC output lead from the modified CB radio power supply to the Caiman.

I tried out the linear power supply on the TC-7520 and Caiman, both in modded an unmodded state.
The bad news is that the Caiman power supply produced better results than the modded CB radio PSU when tried on an unmodified TC-7520 and Caiman.
The good news is that the modded CB radio PSU comes into its own with a Caiman fitted with the Murata regulators. A lower noise floor brought out some previous hidden detail in cymbals etc. There are more listening sessions to endure, but so far I am not disappointed with the £22 layout I made.

[leo]

Thats excellent Stan and its also cheap! Never actually thought of using a CB psu, nice thing is its ready cased etc

[chrism]

The Maplins bench supplies are a good way of trying out a basic linear supply (I had the 5v one for quite a while set at various voltages). The trafo is quite noisey though and the regulator very basic. The linear PS I have now uses a Toroidial 90 Va traffo, full wave rectifier, 10,000uf smoothing cap and a two stage regulator. This is much quieter than the Map's one and really helps give the Caiman a very "analogue" type sound.

Sounds really good with and without the Murata upgrade.

Regards

Chris

[Covenant]

This is the one I have been building:
http://cgi.ebay.co.uk/Variable-DC-Po...item41449a8f41
But my advice is DONT DO IT! By the time you add a decent toroidal transformer, case, switch, wire and other bits and pieces it costs in the region of £50. Stick with Stans suggestion.

[paul_cz]

Jerry,
can you provide us with some details about your PSU build? I just came along the same kit when I did some research for a DIY linear supply ... Would be interesting if you could share your experience in building it and listening to it.
-
Cherrs,
cz

[StanleyB]

I tested the power supply for noise on my scope, and at less than 10mV rms it is quieter than the 7812! The latter has between 30 to 70mV according to some datasheets.

Looking at the guts of the CBR PSU it should be quite an easy job to make improvements to its performance, which is already good enough for the job in hand. The internal PSU on the TC-7520 and Caiman does further regulation and noise filtering.

[Gazjam]

This is the one I have been building:
http://cgi.ebay.co.uk/Variable-DC-Po...item41449a8f41
But my advice is DONT DO IT! By the time you add a decent toroidal transformer, case, switch, wire and other bits and pieces it costs in the region of £50. Stick with Stans suggestion.

I've seen that PCB somewhere before Jerry....
Looks good!

[apmusson]

Stan.

I want to use the cable off an old 7520 wallwart power supply. Is there an easy visual way to tell which wires is should be connected to the +ve and -ve terminals?

Thanks

Ade

[chrism]

Take a look at this little beauty!

DAC Linear PS 002.jpg

Regards

Chris

[StanleyB]

Is there an easy visual way to tell which wires is should be connected to the +ve and -ve terminals?

The lead with the grey stripes is +V.