#26 pre amp

[Brouilly]

Hi Ale,

So are you just using one Salas board for both chanels, then an individual CCS VR per side?

How does it perform and sound compared to no SSHV?

Charlie

[andyjevans]

Just a recap on filament cables. For a 1 metre run twisted pair screened it looks like DMX512 which is 22AWG, 7/30 or 7/.025mm. This is overall screened. It's used extensively for digital lighting and uses 5 pin XLRs, with pin 1 ground as usual and 2+3, 4+5 for the pairs. I'm thinking this is a good solution. Belden 8723 is widely available too and is individually screened with a drain wire. Also OK if you decide on 22AWG which should be OK for short runs. Data says 22AWG is 1 amp cable but also 7 amps in equipment.

20AWG would probably be nicer - haven't found anything commonly available for that.

[mogliaa]

Originally Posted by CSlee

Hi Ale,

So are you just using one Salas board for both chanels, then an individual CCS VR per side?

How does it perform and sound compared to no SSHV?

Charlie

Yes, only one. Channel separation is from CCS onwards.
Compared to previous incarnation: In my first version of 26 I had an SSHV1 regulator in place. This preamp is quieter, less microphonic but this is due to filament starvation. Bass is deeper and overall tone is rich and pleasant. I need to listen to it more!

I will do some tests when I get the chance to so can show the performance of the regulators, etc.
Ale

[Vinylsavor]

Hi Andy,

I typically use umbilicals with 5, 7 or 10 wires (depending on amp) with 1 mm2 cross section which is about AWG17. This is available with screen from a local store. They even have thicker wires. But you probably won't be able to fit such a cable into XLRs

Best regards

Thomas

[king4joy]

For HV umbilicals...personally I would pay more attention to the insualtion rating of the wire (and the connectors) used b/4 anything else......for HV I use only Teflon insulated wires......no???

[Vinylsavor]

Hi!

Of course the voltage rating needs to be adequate. I considered that as a given. With the voltages in a 26 preamp that should normally not be a problem. The umbilical I use is good for over 600VDC. In amps with higher voltages I make the umbilical myself with double or even triple insulated wires for the HV.

Best regards

Thomas

[andyjevans]

On a whim I decided to upgrade the PSU for my preamp. What a difference! Better detail and tone. I used a large EI 240-200v transformer I had on the shelf. This whole PSU feeds a VR150 voltage reg. Moral of the story - don't neglect the PSU. I should know this. All the caps are polypropylene motor runs. The diodes are UF4007. I suppose I could find something more sophisticated for those, but that was what I had in stock.

[disco]

Originally Posted by andyjevans

... What a difference! Better detail and tone...

Just curious -as your new setup is quite elementary*- with what are you comparing?

You're stabilising the HT with a gas tube. One of the advantages of an electronic regulator is in the strong reduction of the influence the PS has on stages with low PSRR. It's not sacred because every power supply (even the battery) has internal resistance and impedance, interacting with the audiosignal imposed on the HT. The amount of the interaction however differs, freeing the bandwith of interest from phase behaviour.


* To reduce the ripple voltage it's more effective to first use a RC filter and next a LC filter. See if you can improve with that in PSUD.

[andyjevans]

I attach the old PSU - it's actually pretty similar. I can only think that the AZ1 mesh is making some sort of difference - smoother treble and a bit more refined sounding. I heard that on previous occasions when I made the switch. On the other hand, the 80 is no slouch.

Up to now the PSU has been driving a VR150 which feeds the circuit. Actually the preamp now uses 4P1L not 26, but it's in filament bias as well.

Next I inserted a DN2540 before the VR150 in place of the dropper resistor for the VR150. I did this in the 80 PSU, and this PSU now has even more detail than the AZ1 PSU without a DN2540. However, I'm not convinced about the tone in the mids and treble.

It's starting to sound like an active load again - tried that with IXYS and found it a bit bright and tiring. Yes - bass is better, detail is better. I heard that before. But I'm hearing something else - is it possible that the DN2540 is compressing the sound somehow? How could that happen?

Andy

[andyjevans]

After comparative listening I decided I preferred the VR150 with a DN2540 or IXYS 10M45 CCS, and with a mesh AZ1.

I went back and used this arrangement with my original 26 preamp, which has the two Hammond 156C plate chokes and teflon FT-2 output caps. It's still good, but I miss the treble sparkle of the 4P1L into LL1660/18mA. This may be the capacitor coupling. The mids and bass are fine.

But I have the hummmmm back again with the Hammond chokes. Has anyone using these managed to get them free of hum, and if so how? I'd really like to know!!

Andy