The rasberry pi dac hat alone and the B1 Korg preamp alone both hum equally ( ie if the preamp is not connected to source (dac) ). Both the pi and the B1korg use wallwart powersupplies. They have no main ground connetion. Only power and nautral ( or whatewer they are called in english 
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Yeah... I was afraid that it was a DIY DAC. They don't all play nice. The wall warts often have a connection from neutral on the mains to the "ground" on the output. Sometimes this connection is a wire. Other times it's a high-voltage ceramic capacitor.
If you have a power bank or battery pack that can supply the necessary power for the Rpi or Korg, you can try with that. That should get rid of the hum. In that case the solution may be a different power supply for the Rpi and/or Korg.
Tom
If you have a power bank or battery pack that can supply the necessary power for the Rpi or Korg, you can try with that. That should get rid of the hum. In that case the solution may be a different power supply for the Rpi and/or Korg.
Tom
Its not really a diy dac, but a dac hat for strawbery pi. I have used this for many years with out any issues. Just to try it I put a thermistor between powersupply ground and chassis gnd on the Mod86 ( like in my First Watt amps) but there was no change in hum.
I have several other amps that work ok in this system so I will use them for the time being. I have ordered new ICs and the main chip. Will see if some components are damaged. There is some grounding issue this amp does not tolerate that my other amps do.
I have several other amps that work ok in this system so I will use them for the time being. I have ordered new ICs and the main chip. Will see if some components are damaged. There is some grounding issue this amp does not tolerate that my other amps do.
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Personally, I would not do any chip replacement on the Modulus 86 until you first see if you can ID the grounding issue in the attached components.
Also, instead of using a thermistor, I would use a 35A diode bridge, with a capacitor, as shown in Nelson Pass's amp designs or on various diagrams available on the web.
Also, instead of using a thermistor, I would use a 35A diode bridge, with a capacitor, as shown in Nelson Pass's amp designs or on various diagrams available on the web.
I think the problem is at least related to the Mod86.
I used Hypex ncore nc400 monoblocks for many years in this system connected to this raspberry pi with Hifiberry dac, without any issues. I can use: a small hypex 30w amp, my First Watt F6 and Quiksilver Mid Mono EL34 monoblocks without issues. Haven't tried other amps. It has something to do with how the Mod86 balanced input tackles the RCA connection or possibly a component is damaged.
I might try a diode bridge and a capacitor as in the First Watt F5 turbo power supply. My First Watt F6 and M2 only use a thermistor. I also might try the Sowter trafo i use in the small hypex 30W amp for the RCA-Balanced connection.
I used Hypex ncore nc400 monoblocks for many years in this system connected to this raspberry pi with Hifiberry dac, without any issues. I can use: a small hypex 30w amp, my First Watt F6 and Quiksilver Mid Mono EL34 monoblocks without issues. Haven't tried other amps. It has something to do with how the Mod86 balanced input tackles the RCA connection or possibly a component is damaged.
I might try a diode bridge and a capacitor as in the First Watt F5 turbo power supply. My First Watt F6 and M2 only use a thermistor. I also might try the Sowter trafo i use in the small hypex 30W amp for the RCA-Balanced connection.
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You need to do a methodical approach to isolating the problem. Right now, it seems very scattershot (IMO). Another thing to consider is the interconnect cable connecting the Modulus86 to the component immediately before it; this would be especially true if you are using a pseudo unbalanced to balanced interconnect.
Good luck finding the problem.
Good luck finding the problem.
Thanks. Well I really haven done that much yet. Tested some amps in the same setup, wich are all ok. Soldered in the termistor, tried different interconnects. All of my stuff is RCA, not balanced. The simple qure is probably an isolation trafo from RCA to balanced. Im not going to change evrything else to satisfy the balanced topologi of the Mod86.
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In Post 5537 you stated that you have no hum when you short the inputs to the amp. As I then stated in Post 5540, this means the hum issue is not related to the amp. Randomly swapping ICs within the amp won't do any good. In fact it may do more harm as de-soldering the LM3886 can be pretty tricky to do without damaging the circuit board.
You have a ground loop. The sure-fire way to get rid of that is to use the differential input on the Modulus-86. You can use a line transformer like the Jensen JT-11P-1 or an active circuit like my Universal Buffer. You can also try grounding your sources. Ground the power supply for your Raspberry Pi for example.
You can also try lifting the ground on the MOD86. I.e. remove the connection from chassis to ground. The 'nice' thing to do then would be to add a diode bridge so you still get a modicum of safety earth protection.
Fact is that grounding is a mess in single-ended circuits and any solution will be half-baked compared to just using differential signalling like they do in the PRO world.
Tom
You have a ground loop. The sure-fire way to get rid of that is to use the differential input on the Modulus-86. You can use a line transformer like the Jensen JT-11P-1 or an active circuit like my Universal Buffer. You can also try grounding your sources. Ground the power supply for your Raspberry Pi for example.
You can also try lifting the ground on the MOD86. I.e. remove the connection from chassis to ground. The 'nice' thing to do then would be to add a diode bridge so you still get a modicum of safety earth protection.
Fact is that grounding is a mess in single-ended circuits and any solution will be half-baked compared to just using differential signalling like they do in the PRO world.
Tom
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Hi Tom, yes it is related to the input. Specifically the RCA stuff with floating ground and the Mod86. However my other amps which are not balanced are ok, even the Nc400 ( balanced) was ok with my dac for several years ( one of the switching power supplies in one monoblock gave out after 8-9 years of constant use. I will buy another one some day, there is a lot left in the Nc400s).
I can put in a diode bridge and cap (I have the components) in addition to the thermistor I added between chassis to lift from the chassis ground (it should at least not affect the sound). If that does not help a isolation transformer is next.
All my IC are in sokets, the LM3886 is the last ting I would try to change anyhow.
I play around with many things so I dont think Ill go fully balanced yet
My current project is a pair of 350L boxes for som JBL2242s to supplement my Altec A5s in my main system ( where the Mod86 did well for several months). Ill probably use an inexpensiv Crown on the 18” basses or fix my Nc400.
I can put in a diode bridge and cap (I have the components) in addition to the thermistor I added between chassis to lift from the chassis ground (it should at least not affect the sound). If that does not help a isolation transformer is next.
All my IC are in sokets, the LM3886 is the last ting I would try to change anyhow.
I play around with many things so I dont think Ill go fully balanced yet
My current project is a pair of 350L boxes for som JBL2242s to supplement my Altec A5s in my main system ( where the Mod86 did well for several months). Ill probably use an inexpensiv Crown on the 18” basses or fix my Nc400.
I recommend building the Modulus-86 exactly like that. Put XLR connectors on the chassis and use pseudo-differential cables if you need to connect RCA sources. That gives you the option of switching to balanced interconnects once you get a source that supports that.
If you do choose to implement the Modulus-86 with RCA inputs, use RCA connectors that have the shell isolated from the chassis.
Tom
If you do choose to implement the Modulus-86 with RCA inputs, use RCA connectors that have the shell isolated from the chassis.
Tom
That it is.
Thank you for your feedback.Of the 1k+ boards sold since its launch in 2014, I can count on two hands the number of builders who have had issues with their builds. That's a pretty good track record!
The issues have been related to accidentally swapped parts, forgetting to stuff all the parts, reversed polarity on polarized parts, and the occasional swapped polarity on the power supply. There's been the occasional dry solder joint as well.
Tom
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B+D Enterprises has the LM3886 at non-ripoff prices even though everybody else is out of stock: LM3886TF
I've dealt with B+D in the past for obsolete parts and have always received good parts.
Just thought I'd let you know in case you're not willing to wait six weeks for Mouser to get the parts in stock.
Tom
I've dealt with B+D in the past for obsolete parts and have always received good parts.
Just thought I'd let you know in case you're not willing to wait six weeks for Mouser to get the parts in stock.
Tom