Hardware humming on the GREY SP 1200 !

[12bitski]

hi ,

lately a friend of mine installed the newest version of the HXC ref F on one of his original GREY SP 1200s .

he called me and told me that he has an heavy hummin in his audiopath now. we doubt, that it could be the HXC that causes this problem.

when he installed it on his second grey SP 1200, he got the same problem. First I told him, that it must be a problem in his wireing.

then we tried something: we took off the screws the HXC was assembled to the body of the SP 1200 and see what, the humming was gone.

now we got to find a way to isolate the ground of the HXC and the SP 1200´s body. we thought about to use zip ties through the screwholes to fix it. but i guess, that´s not "the" best sulution

Someone with the same experience?

I installed the HXC on a BLACK SP 1200 lately (but not the latest HxC ref F model) , and it seems to work like it should.

Is it a slightly difference between the latest rev F models or might it be the difference between the GREY and the BLACK model of the SP 1200?

[12bitski]

Ok, I think, I found the problem.

There´s a connection between the HxC-case and the 0V (ground) of the Floppydrive-Powerconnection (the inner pins on the power con.).

I checked the original Floppydrive, if the case is connected to the 0V (ground) of the 5V supply. And it´s not.

So I checked the HxC circuit board. First I thought it might be the display, but it´s not. It´s the buttons in the front.

So, if you concern this humming problem on your SP1200 since you built in the HxC ref F try this:

Take off the circuit board of the HxC and the displaycable (be carefull here not to damage the flatcable) and try to isolate the metal of the buttons in the front with isolate-tape.

Just to be sure, I will do this modification on all HxC Ref F I build into machines (S950, MPC 60, SP 1200) to avoid problems related to this.

I´ll post pics in the next post.

[12bitski]

Here we got some pics:

[12bitski]

Isolate-tape installed.

Problem solved

Now you can reassemble it.

[Jeff]

mhh very interresting. And this surprise me because i thought that all drive case are connected to the power supply ground.
Can you check the old drive case - gnd power supply connection ?

[Jeff]

I just tested some of my floppy disk drive :
6 have the case connected to the ground.
2 don't have the connection.

[12bitski]

the one we got here, doesn´t have this connection.

i built in the HxC into the Black version of the SP 1200 and there wasn´t a problem in the audio path. i guess it´s because of the more modern powersupply in the black model

it occures with the old grey model.

ok, just checked the drives i got here from different devices.

S950: not connected
SP1200 (grey or black model) : not connected
MPC 60: not connected
Studio 440: connected
MPC 3000 : connected
Akai S6000: connected

[khayoz]

I had a similar problem in the past with my Akai MPC 3000 with original floppy drive, one day it just started to hum and it took me many hours/days before I found the problem.. The screws on the bottom of the MPC that hold the floppy drive was loose, I tightened them up and the hum disappeared!

So if anyone else have problem with earth hum check this!

P.s. posted this on mpc-forums.com back then.

[12bitski]

I had a similar problem in the past with my Akai MPC 3000 with original floppy drive, one day it just started to hum and it took me many hours/days before I found the problem.. The screws on the bottom of the MPC that hold the floppy drive was loose, I tightened them up and the hum disappeared!

So if anyone else have problem with earth hum check this!

P.s. posted this on mpc-forums.com back then.

That confirms, the MPC 3000 needs the connection, whereas the MPC 60 doesn´t and the SP 1200 neither

Interesting is, that also the S950 drive doesn´t have the connection. But I couldn´t find a earth-hum problem here. To be save, I´ll also do the modification on the Hxc unit in the S950.

I´m glad that it´s the buttons in the front, what produces the connection and not the display. The buttons are easy to modify and isolate, but the display had been more complicate.

[winsten]

Hi,

are the hxc pre drilled to fit any sp1200 , as I do not own power tools nor do I want to use sticky tape?

Thanks

[12bitski]

The humming appears when you install the drive by screws as you will get a metal connection between the cases.

If you installed the HxC with doublesided tape into the HxC , you won´t get a humming as the cases are isolated through the tape.

Another way to isolate the cases from each other is to use M3 plastikscrews. When you do so, i recommend also to put some isolation tape to the bottom of the hxc case to avoid a metal connection with the bottom of the SP 1200.

Meanwhile, when you buy a HxC Rev F there are 4 holes predrilled where they ought to be to fit into any unit, but they are not tapped yet.

There´s a alternate idea of installing the HxC case to the SP that we haven´t tried yet. Use ties like instead of screws.

just take two ties for each hole. I will try later this afternoon and post some pics. That way you won´t need to tap the holes and won´t need to buy plasticscrews , but have the same effect. No metalconnection between the cases.

[winsten]

The humming appears when you install the drive by screws as you will get a metal connection between the cases.

If you installed the HxC with doublesided tape into the HxC , you won´t get a humming as the cases are isolated through the tape.

Another way to isolate the cases from each other is to use M3 plastikscrews. When you do so, i recommend also to put some isolation tape to the bottom of the hxc case to avoid a metal connection with the bottom of the SP 1200.

Meanwhile, when you buy a HxC Rev F there are 4 holes predrilled where they ought to be to fit into any unit, but they are not tapped yet.

There´s a alternate idea of installing the HxC case to the SP that we haven´t tried yet. Use ties like instead of screws.

just take two ties for each hole. I will try later this afternoon and post some pics. That way you won´t need to tap the holes and won´t need to buy plasticscrews , but have the same effect. No metalconnection between the cases.

Hi thanks for the input,

So on the og sp1200 your saying that you would need to insulate bottom with black insulation tape of the hxc and to stop any sort of hum or would you also need to tape the area around the 3 buttons as seen in your screen shots?

also you mentioned m3 size screews, how about the length 10mm/20mm/6mm what would do.

Lastly are you saying the hxc is predrilled to fit the sp1200? are the pre drilled holes in a optimal position?

do you have a picture of how well the hxc lines up in the sp1200 using the predrilled holes?

Thanks again for taking the time to post back.

[12bitski]

So on the og sp1200 your saying that you would need to insolate bottom with black insulation tape of the hxc and to stop any sort of hum or would you also need to tape the area around the 3 buttons as seen in your screen shots?

Just if you don´t isolate the area around the buttons you will need to find another way to break the groundconnection.
If you isolate the area arround the buttons, you´re fine. No need to do more. But some people are afraid of taking off the HxC mainboard.
As soon you isolate the buttons, the groundconnection is interupted. Means, you can install the HxC case by screws to the unit. No more isolation needed.

also you mentioned m3 size screews, how about the length 10mm/20mm/6mm what would do.

I guess the screws shouldn´t be too long. 6mm should be fine. 20mm could be too long.

Lastly are you saying the hxc is predrilled to fit the sp1200? are the pre drilled holes in a optimal position?
do you have a picture of how well the hxc lines up in the sp1200 using the predrilled holes?

Optimal position now, like on original floppydrives! I Don´t have pics.

[spmac]

Hi all ...just got the emulator direct from Lotherak, good service. Gonna fit it to my OG grey SP1200 over the next few days.

Does it still need this mod of has the issue been addressed?

Cheers in advance for any help

[winsten]

Hi all ...just got the emulator direct from Lotherak, good service. Gonna fit it to my OG grey SP1200 over the next few days.

Does it still need this mod of has the issue been addressed?

Cheers in advance for any help

pics would be awesome,

im about to order my hxc's also.


did your come with threaded holes to mount into the og screw holes instead of using tape?