Demian:
Thanks for sharing this.
I'm curious - I didn't think those old Supertex VN1306 were Depletion Mode MOSFETs. Assuming they really are not, how does the front-end diff amp in the "DMA-50 driver revised" bias up properly? I would have expected some high IDSS JFET like a pair of J111 as cascodes instead for this kind of cascode configuration ...
Thanks for sharing this.
I'm curious - I didn't think those old Supertex VN1306 were Depletion Mode MOSFETs. Assuming they really are not, how does the front-end diff amp in the "DMA-50 driver revised" bias up properly? I would have expected some high IDSS JFET like a pair of J111 as cascodes instead for this kind of cascode configuration ...
Sorry about the oversight. I am using depleation mod gets now. I just sailed past that detail. I have not looked at this stuff closely since the 1990's. Fortunately my amp has been working fine since then.
You have the full Crosby mod. There are possibly other areas to tweak but not many and not much ROI for huge effort.
The Crosby mod started with the active regulator for the input/driver circuit. I believe there was also a seperate always on supply for the regulator. (There is in the DMA 50 mod) Then additional caps and component tweaks on the modules. Since it used very premium parts initially there is not a lot to upgrade.
The backlight is an electrolumincent panel. An LED backlight for a display would be the best modern option. This may be a "direct fit" option: https://www.adafruit.com/product/625
The Crosby mod started with the active regulator for the input/driver circuit. I believe there was also a seperate always on supply for the regulator. (There is in the DMA 50 mod) Then additional caps and component tweaks on the modules. Since it used very premium parts initially there is not a lot to upgrade.
The backlight is an electrolumincent panel. An LED backlight for a display would be the best modern option. This may be a "direct fit" option: https://www.adafruit.com/product/625
Thanks,do you have information to implement the always on regulator supply,as the driver / regulator power is switched on at the same time as the output power supply….
Thanks for the info. for luminescent display I’ll order one…
Thanks for the info. for luminescent display I’ll order one…
Hi,working on building up the spectral DMA power supply,do you have a figure for the max voltage to the output section….
Currently running 48 vdc +/- …I have a pair of 1000va 25volt transformers,want to use them since it’s no money out,can the output section handle the increase….25 volt in series,50 volt,so,would be 68.7….you had referenced to 50 vdc for full output,48 vdc works fine though,but present supply is a single 500va transformer feeding both boards……
Currently running 48 vdc +/- …I have a pair of 1000va 25volt transformers,want to use them since it’s no money out,can the output section handle the increase….25 volt in series,50 volt,so,would be 68.7….you had referenced to 50 vdc for full output,48 vdc works fine though,but present supply is a single 500va transformer feeding both boards……
Damien,I have a question about setting offset on each side,I need to know the purpose of the resistors that are raised on the edge of each board,also,how can I assure accurate offset,as being BTL,it seems possible to adjust each board individually up or down…I am able to easily set offset,but am I being accurate…bias also is stable,both sides sitting at 100mv
Tha amp is dead quiet,dynamic and sweet….finished with dual 300va at 10000uf at 62vdc for inputs,dual 800va 55,000uf at 50vdc on outputs….Dave
Tha amp is dead quiet,dynamic and sweet….finished with dual 300va at 10000uf at 62vdc for inputs,dual 800va 55,000uf at 50vdc on outputs….Dave
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The goal is to set the offset to zero +/- 10 mV or so. it won't be super stable and its DC coupled to your source device can affect things. Having both a few millivolts off of zero will not have any negative effects. its more important that the voltage across the load is zero. I'm delighted its all working for you.
Damien,yes the amp works amazingly well.as I stated,I feel the need to understand some of the mods,what are the stand-off resisters do,is this an aspect of the Crosby mods,if so,how do I verify it..….is there a way to clarify the zero set points of the input boards,so I can know the effects of setting offset…..I’m thinking I’m not expressing what I’m asking to do….Dave