[kklee]

I hadn't retested the new HV PS with all my headphones, but my modded prototype amp seems to be fine with Grado SR-225's, HD-600's and ATH-W1000's. I get a little bit of hiss at max volume, with a DAC connected.

The only headphones that exhibited hiss were Shure SE530's, which is expected due to their sensitivity.

I'm running my home-made PCB for the HV-PS at 90V. I pulled all of the old HV PS parts from the prototype board and added a couple of jumpers to re-route the HV. The HV PS PCB is sitting right next to the SOHA-II and the wires connecting the two boards are about as short as I could make them. I layed out the connections on the HV PS PCB to match up with this mounting position and didn't make any special considerations for noise in the layout. If I remember correctly, I used the spec'd parts for everything.

The second amp I made for a co-worker doesn't exhibit any hiss either. The only differences in this build were different coupling cap's and no protection circuit.

 

[bmwpowere36m3]

Quote:

Originally Posted by runeight /img/forum/go_quote.gif The SOHA II that is implemented on the board is shown on the website under SCHEMATICS. This implementation, with the trimpot, should give you a range of B+ from about 55V to 95V. Maybe a bit higher than 95V.

So that's a yes to Ferrari's original HV PS design and ~95V. To achieve higher B+ would require a modifed HV PS & voltage multiplier, correct?

What about any useful mods besides those listed in the "tweaks" section and boutique components?

 

[Uncle Bob]

Quote:

Originally Posted by runeight /img/forum/go_quote.gif Oh, reading your post again, even thought one pin on each of the regs is grounded, the metal tabs on the regs should not have continuity to the heatsinks.

Sorry for the delay in replying. On the 7815 regs, the centre pin is designated 'ground' and has continuity to the metal tab. As the pcb links the heatsink pins to ground as well as the centre pin, there is necessarily continiuity between regulator tab and heatsink via the pcb traces - or am I confused somehow?

On the 7915 reg, the centre pin also has continuity to the metal tab but this pin is designated 'input'. In this case the heatsink and regulator tab have no continuity when mounted on the pcb.

 

[runeight]

Quote:

Originally Posted by bmwpowere36m3 /img/forum/go_quote.gif So that's a yes to Ferrari's original HV PS design and ~95V. To achieve higher B+ would require a modifed HV PS & voltage multiplier, correct? What about any useful mods besides those listed in the "tweaks" section and boutique components?

That's a yes to the HV design that the prototype team worked out, including Ferrari's excellent suggestion to use the HV regulator. You can add more stages to the HV mulitplier to get higher voltages. Each stage causes some amount of degradation to the output of the multiplier and reduces the current supply capability. However, I don't think that one more stage will matter too much. I think that Ferrari actually proto'd this up a while back.

As voltages go up, of course, cap voltages need to go up with them and the BC transistors in the input stage should probably be changed to higher voltage PNP transistors.

I have to let the other builders suggest the mods because my amp is stock.

 

[runeight]

Quote:

Originally Posted by Uncle Bob /img/forum/go_quote.gif Sorry for the delay in replying. On the 7815 regs, the centre pin is designated 'ground' and has continuity to the metal tab. As the pcb links the heatsink pins to ground as well as the centre pin, there is necessarily continiuity between regulator tab and heatsink via the pcb traces - or am I confused somehow? On the 7915 reg, the centre pin also has continuity to the metal tab but this pin is designated 'input'. In this case the heatsink and regulator tab have no continuity when mounted on the pcb.

Yes, this is correct Uncle Bob.

 

[Alcaudon]

Just another question about grounding.....

I was planing to build a DIY full wood enclousure for this project, using just an aluminium bottom panel, will this be enough for grounding issues? I can make an aluminium rear panel too if it helps, but I certainly would like to use wood for everything else.

And...... what about going full wood?

 

[runeight]

MHO is that a single bottom metal ground panel will be sufficient, particularly if you connect it to the line ground. However, as you know, the wood does not provide any EM shielding for the rest of the amp.

You might get away with all wood because the board has a full ground plane. You'll just have to try it out.

 

[Alcaudon]

Thanks for the answer runeight!

Quote:

Originally Posted by runeight /img/forum/go_quote.gif MHO is that a single bottom metal ground panel will be sufficient, particularly if you connect it to the line ground. However, as you know, the wood does not provide any EM shielding for the rest of the amp.

That's what i thought, however I just wanted to be sure. And about EM shielding, I was planing a dual case solution for this project, taking transformer far away from signal, and hope not to have any other noise source near

. Maybe I could add some shielding material, like conductive foam or rubber or something like that...... but I will have to build the case and see how it turns out

.

Thanks!

 

[bmwpowere36m3]

what's the status on the Prod PCB boards? Also to run high-current heaters from my understanding you need a 1.5A trafo, removing R3P, and a bigger heatsink for H-. If I were to run 300mA tubes later on, would I need to replace the R3P? Any recommends switches to run for the heater headers (DPDT).

 

[holland]

yes to r3p, trafo, heatsink. you don't need to replace r3p if you're sinked properly. the regs do generate a good amount of heat, the most heat on the board. I'm considering opening some holes in my case above the regs.

switches should be in the bom. because of the way the switches work, it's reversed from the silkscreen.

 

[TimmyMac]

Quote:

Originally Posted by Alcaudon /img/forum/go_quote.gif Just another question about grounding..... I was planing to build a DIY full wood enclousure for this project, using just an aluminium bottom panel, will this be enough for grounding issues? I can make an aluminium rear panel too if it helps, but I certainly would like to use wood for everything else. And...... what about going full wood?

I built a Bijou case of wood, with plate steel top and bottom. Works great - but I mounted the tubes and transformer up top to keep heat down.

 

[bmwpowere36m3]

Quote:

Originally Posted by holland /img/forum/go_quote.gif yes to r3p, trafo, heatsink. you don't need to replace r3p if you're sinked properly. the regs do generate a good amount of heat, the most heat on the board. I'm considering opening some holes in my case above the regs. switches should be in the bom. because of the way the switches work, it's reversed from the silkscreen.

Yes there's a main power switch in the BOM but no switch for the heater circuit instead it uses headers and pins.

 

[runeight]

Right. No heater switches on the main BoM. However, on the PS Parts list page on the website, at the very bottom, there are some part numbers for switches that should fit the footprint.

And another reminder that the switches work opposite to the jumpers so the board markings are reversed when using a typical switch.

 

[Uncle Bob]

Progress report - I know it's slow, but I keep being told to clear the kitchen table

Anyway it appears the ps section is now running OK, I get the following voltages

TL+ 14.9V
TL- -16V
TH -12.4V
TB+ 123.5V

TB+ seems a little high, is this within an acceptable range to proceed to the next step?

 

[runeight]

Great. Are you sure about TL- ? Is it too high and out of spec for the regulator if it is really making 16V.