So I have a Harman Kardon 930 vintage receiver in which I'd like to replace a phono stage with something modern.
I can fit Muffsy or Richard Murdey's VSPS in the place of the original phono PCB. The problem is new phono stages require bipolar +/- 9-18 V DC (Muffsy) or +/-12-18 V DC (VSPS) and the old phono stage is supplied by just +20 V DC.
The space inside HK930 is tight and I didn't find a new power transformer for phono stage that fits. The HK power transformers have 29-0-29 V and 6.3 V secondaries. There's also +/- 41 V DC that powers output stage.
How can I use what is there to get a bipolar DC for a new phono stage? It's enough space inside HK for a regulator board or two; however, if going this way I'd strongly prefer a PCB or a kit rather than a breadboard-based one.
Any help and inputs are greatly appreciated
I can fit Muffsy or Richard Murdey's VSPS in the place of the original phono PCB. The problem is new phono stages require bipolar +/- 9-18 V DC (Muffsy) or +/-12-18 V DC (VSPS) and the old phono stage is supplied by just +20 V DC.
The space inside HK930 is tight and I didn't find a new power transformer for phono stage that fits. The HK power transformers have 29-0-29 V and 6.3 V secondaries. There's also +/- 41 V DC that powers output stage.
How can I use what is there to get a bipolar DC for a new phono stage? It's enough space inside HK for a regulator board or two; however, if going this way I'd strongly prefer a PCB or a kit rather than a breadboard-based one.
Any help and inputs are greatly appreciated
I just made +/- 16v from +/- 39v for an opamp in a Denon.
I have spare transistors and more of the resistors involved. I used the Denon's already supplied 1uf 50v caps on the output side, and the 220uf caps are very very common sizes.
Denon 250III drawing anyone?
If you don't have such things around, I could bundle some up. I have 1uf poly's in the post, leaving just the 220s to find yourself.
Edit: It seemed every time I looked at a denon schematic, There was such a regulator set in play. Different transistors in use, and different resistors for different supply voltages. It was a very common circuit though. iirc the 350 model had 41v rails and it's 17v output went off driving other regulator circuits for lower voltages. It must of had a reasonable current output
Oh.. it's the pma 355uk, 41.5v rails down to 16v rails. Perfect?
HiFi Engine - Owners and Service Manuals
I have spare transistors and more of the resistors involved. I used the Denon's already supplied 1uf 50v caps on the output side, and the 220uf caps are very very common sizes.
Denon 250III drawing anyone?
If you don't have such things around, I could bundle some up. I have 1uf poly's in the post, leaving just the 220s to find yourself.
Edit: It seemed every time I looked at a denon schematic, There was such a regulator set in play. Different transistors in use, and different resistors for different supply voltages. It was a very common circuit though. iirc the 350 model had 41v rails and it's 17v output went off driving other regulator circuits for lower voltages. It must of had a reasonable current output
Oh.. it's the pma 355uk, 41.5v rails down to 16v rails. Perfect?
HiFi Engine - Owners and Service Manuals
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Oh, missed a post. I found most boards using voltage regulators had a 30v input limit. Only £2.50 but no use. At 12 components it's not a bad job on veroboard, but somebody could have a board etched out for the job. They didn't pass by this week though.
Edit: This is the cheap board. Has rectifier but those regs are 35v max. However, how big is a tiny transformer really? edit: 40x40x35mm
LM7815 + LM7915 +-15V Dual Voltage Regulator Rectifier Bridge Power Supply Module | eBay
This reg will need further looking at. Arcam choose to use a lot of regs not diode/transistor arrangements. Their drawings might help you clean up the output of the £2.50 board. As it is it's not ready for a good phono board, surely
Edit: This is the cheap board. Has rectifier but those regs are 35v max. However, how big is a tiny transformer really? edit: 40x40x35mm
LM7815 + LM7915 +-15V Dual Voltage Regulator Rectifier Bridge Power Supply Module | eBay
This reg will need further looking at. Arcam choose to use a lot of regs not diode/transistor arrangements. Their drawings might help you clean up the output of the £2.50 board. As it is it's not ready for a good phono board, surely
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How about using the Muffsy PSU with the +41V DC?
Skip all the stuff that I crossed out, and connect DC as shown. (Do not connect +/- 41V, only the +41V and GND.)
This will give you +/-15V DC output. Be careful to not connect the Muffsy PSU GND to the existing GND. That's easily done at the RCA connectors/through the chassis or similar.
Skip all the stuff that I crossed out, and connect DC as shown. (Do not connect +/- 41V, only the +41V and GND.)
This will give you +/-15V DC output. Be careful to not connect the Muffsy PSU GND to the existing GND. That's easily done at the RCA connectors/through the chassis or similar.
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...or a DC-to-DC converter. This will give you an isolated (meaning you can connect the GND from this to the existing GND with no ill effects, unlike the example with the Muffsy PSU) +/-12V sufficient to power either the Muffsy or the VSPS:
Something like the the WRD241212YS-2W will accept 18-36V DC input, and gives you +/-12V DC out at some ~80 mA max.
Here's how you hook up the thing (and yeah, the WRD isn't really that big):
Something like the the WRD241212YS-2W will accept 18-36V DC input, and gives you +/-12V DC out at some ~80 mA max.
Here's how you hook up the thing (and yeah, the WRD isn't really that big):
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The 40x40x35 mm will fit; however, it needs to be shielded since the only place I can install within the chassis is near FM Multiplex and Power amp boards (red areas at the first pic). Anyone knows where to get small metal boxes that could be used as shields? I have MuMetal but I don't think it's possible to wrap the small transformer in it reliably.
Shielded Hammond transformers such as this BA2DA (Mouser 546-BA2DA) 120V primary/10V secondary/ 500 mA will be fine but it's too big. Overall, despite of its size, the HK930 has very few free space on a chassis.
Shielded Hammond transformers such as this BA2DA (Mouser 546-BA2DA) 120V primary/10V secondary/ 500 mA will be fine but it's too big. Overall, despite of its size, the HK930 has very few free space on a chassis.
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Great idea, thank you! I found several like this in Mouser.
I also found some AC to DC power converter such as this RECOM RAC04-12DC/277-E. Input 80 V AC to 305 V AC, output +/- 12 V DC with 166mA current in each channel. It mounts through hole as the one you suggested; can install it on a breadboard; however, it also needs to be shielded since tuner boards near it are sensitive to EMI noise.
Any experience with such AC to DC converters?
I also found some AC to DC power converter such as this RECOM RAC04-12DC/277-E. Input 80 V AC to 305 V AC, output +/- 12 V DC with 166mA current in each channel. It mounts through hole as the one you suggested; can install it on a breadboard; however, it also needs to be shielded since tuner boards near it are sensitive to EMI noise.
Any experience with such AC to DC converters?
...or a DC-to-DC converter. This will give you an isolated (meaning you can connect the GND from this to the existing GND with no ill effects, unlike the example with the Muffsy PSU) +/-12V sufficient to power either the Muffsy or the VSPS:
Something like the the WRD241212YS-2W will accept 18-36V DC input, and gives you +/-12V DC out at some ~80 mA max.
Here's how you hook up the thing (and yeah, the WRD isn't really that big):
Found a WRD051212YS-2W DC to DC converter that takes 4.5-9 V DC as input and outputs +/- 12 V. The input I can get from the 6.3 V AC HK power transformer winding; in one of two transformers such winding is not used at all.
I can find a rectifier PCB module that gives 7-7.5 VDC at the output (with the load) and feed this into WRD051212.
Is this a good idea?
I can find a rectifier PCB module that gives 7-7.5 VDC at the output (with the load) and feed this into WRD051212.
Is this a good idea?
The 20 V DC is there; it's used for powering up the preamp section of the receiver, the FM multiplex board and the phono stage. I always thought it's better to separate power supplies; in some fancy gear phono stages have their own power supply or even power transformer.
The converter you recommended is the easiest option to get +/- DC for the phono stage. I'd like to see if a fancier option, 6.3 V AC conversion with something like "1N4007 AC-DC Converter 12V 1A Full-bridge Rectifier Filter Power Supply Module" from eBay into that 4.5-9 V DC to +/- 12 V MICRODC converter, is viable.
By the way, where did you get the MICRODC converters? Didn't find any at the Web available.
The converter you recommended is the easiest option to get +/- DC for the phono stage. I'd like to see if a fancier option, 6.3 V AC conversion with something like "1N4007 AC-DC Converter 12V 1A Full-bridge Rectifier Filter Power Supply Module" from eBay into that 4.5-9 V DC to +/- 12 V MICRODC converter, is viable.
By the way, where did you get the MICRODC converters? Didn't find any at the Web available.
Too many to list, here's a starting point:
DC DC Converters | Power Supplies - Board Mount | DigiKey
These are isolated, so you are in effect separating the power supplies. And why put a lot of resources into a separate rectified DC when these have in the ballpark of +/-50 mV ripple? The ripple can be lowered somewhat, check the datasheets.
DC DC Converters | Power Supplies - Board Mount | DigiKey
These are isolated, so you are in effect separating the power supplies. And why put a lot of resources into a separate rectified DC when these have in the ballpark of +/-50 mV ripple? The ripple can be lowered somewhat, check the datasheets.
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My question was where I can find this specific MICRODC converter that you recommended. I found a lot of other converters at Mouser but the MICRODC is nowhere to be found.
And for the converters I did find, it's not very clear even after reading datasheets how to connect them to the phono stage.
And for the converters I did find, it's not very clear even after reading datasheets how to connect them to the phono stage.
I couldn't find that specific one either, it's been four years or so since I bought it.
Find one with suitable in and output voltages, and I'll look at the datasheet for you.
Most of these are actually easier than the one I showed you, since they have +, - and GND outputs instead of the Microdc's 2x +12V.
Find one with suitable in and output voltages, and I'll look at the datasheet for you.
Most of these are actually easier than the one I showed you, since they have +, - and GND outputs instead of the Microdc's 2x +12V.
Just in terms of ground loops though, no?
It still demands power from a circuit that's all cleaned up for another purpose. Even two separate secondary windings isn't really a separate supply, as pulling from one, effects the flux round the other. It's only when an item uses the mains input that it's honestly separate. As the mains is a very sturdy supply. Hopefully.
I like the proper board someone posted. Lots of big caps, and likely what the amp was using to meet its spec
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