"so it must be something in the schematic"
No, it is highly unlikely to be something in the schematic. It is almost certainly something in the layout... the routing and connection order of grounds.
No, it is highly unlikely to be something in the schematic. It is almost certainly something in the layout... the routing and connection order of grounds.
An externally hosted image should be here but it was not working when we last tested it.
By arnoldc, shot with K750i at 2007-06-26
There is some hum which, when I touch the aluminum platter of the turntable goes away...
can't edit my previous post anymore...Anyway, I was going to ask how would the sound be affected by having 2M instead of 2M2 (I'm using Hi-Z version) for R5, and 7k5 for R3 and 2k4 for R2?
I also used 1uF 63V film cap for C3.
Diode bridge W02M.
This is supposed to be cheap right? 😀
What's your thought on the DF02M DIL bridge rectifier from General Semiconductors?
or these
Having the transformer right next to the amp is not ideal, as the inputs will pick up hum from the transformer. However this isn't the main problem ...
Are you testing this open, like in the photo, or do you have everything in a shielded case?
The grey wire attached to the board at the middle right hand side looks to be the ground. Is that correct? If so does it connect back to the turntable in any way?
/R
Are you testing this open, like in the photo, or do you have everything in a shielded case?
The grey wire attached to the board at the middle right hand side looks to be the ground. Is that correct? If so does it connect back to the turntable in any way?
/R
hi richard, yes i was testing it in the open. when the photo was taken it was actually playing.
yes, the white wire is ground and connected to the turntable ground.
how far should this small transformer be if it will be in the same case?
I plan on using this case - YM-130
yes, the white wire is ground and connected to the turntable ground.
how far should this small transformer be if it will be in the same case?
I plan on using this case - YM-130
Though you've followed the layout on the VSPS main page fairly closely, I suspect the trouble lies in the order the various returns connect to the power supply. Like the Gainclone the VSPS is an non-inverting stage, any kind of input-output coupling induces positive feedback.
The returns must connect to the ground plane in the following order: (this only applies to the dual opamp layout shown on the main VSPS page!)
input and R1
R2
output and R7 (also case connection and the ground wire to the turntable
output filter cap
regs
input filter cap
transformer
Give us a look at the underside of your board, please...
Richard
The returns must connect to the ground plane in the following order: (this only applies to the dual opamp layout shown on the main VSPS page!)
input and R1
R2
output and R7 (also case connection and the ground wire to the turntable
output filter cap
regs
input filter cap
transformer
Give us a look at the underside of your board, please...
Richard
Hi Richard, I'm at the office right now but I can tell you that the ground is like a T where the top of the T is where the input and output are connected and the neck of the T is where the other grounds are connected, so yes, it does not follow the recommended grounding
Will post picture when I get home.
Will post picture when I get home.
--"There is some hum which, when I touch the aluminum platter of the turntable goes away..."--
Had that too with vsps ultra. The toroid was about 35cm away of pcb, and pcb layed in an earthed tincan box.
Had that too with vsps ultra. The toroid was about 35cm away of pcb, and pcb layed in an earthed tincan box.
Hi Richard,
Here's the underside of the protoboard.
By arnoldc, shot with K750i at 2007-06-27
I want to make a PCB and I want it to be real small. I tried to stick to your grounding per original layout.
Can you give a quick look on this PCB please.
By arnoldc at 2007-06-27
Here's the underside of the protoboard.
An externally hosted image should be here but it was not working when we last tested it.
By arnoldc, shot with K750i at 2007-06-27
I want to make a PCB and I want it to be real small. I tried to stick to your grounding per original layout.
Can you give a quick look on this PCB please.
An externally hosted image should be here but it was not working when we last tested it.
By arnoldc at 2007-06-27
Hi,
Yeah, you've gone and done what I though you'd gone and done. Classic ground loop.
The output ground wires need to be disconnected from the sides of the "T" and attached to the point where the grounds of the two filter capacitors on the output of the regulators join up.
To be on the safe side, the ground wire to the turntable should be disconnected from from the top part of the "T" also and reconnected at the same point as the filter capacitors and ground wires now join up.
That should do the trick.
The best way to understand this is to focus on the return side of R2. Everything input-related has to be connected on one side of this point, output related else goes on the other side. Power supply stuff goes on the other side of that still. Screw that up and it will never work properly.
The PCB layout you have is correct. I'd tidy it up so there are no <90 angles in the region near C2, and increase the width of the power supply tracks as much as possible but it will work fine just as you have it above.
Richard
Yeah, you've gone and done what I though you'd gone and done. Classic ground loop.
The output ground wires need to be disconnected from the sides of the "T" and attached to the point where the grounds of the two filter capacitors on the output of the regulators join up.
To be on the safe side, the ground wire to the turntable should be disconnected from from the top part of the "T" also and reconnected at the same point as the filter capacitors and ground wires now join up.
That should do the trick.
The best way to understand this is to focus on the return side of R2. Everything input-related has to be connected on one side of this point, output related else goes on the other side. Power supply stuff goes on the other side of that still. Screw that up and it will never work properly.
The PCB layout you have is correct. I'd tidy it up so there are no <90 angles in the region near C2, and increase the width of the power supply tracks as much as possible but it will work fine just as you have it above.
Richard
Richard, would you think there'd be any benefit in changing out the OP27 or 37 for OP627 or 637? (in VSPS)
Fran
Fran
Hi Richard, after re-routing the ground the hum is still there. I think I should make a version on PCB now.
An externally hosted image should be here but it was not working when we last tested it.
on a tiny 2" x 1.5" PCB 😎
No hum, no noise!
I'm deeply satisfied with the sonic quality of this little phono amp, I decided to sell my Musical Fidelity X-LP 😀
I have a cheap Audio Technica CN5625AL which sounded rolled off and somewhat boring with the X-LP. With the VSPS it now has more extension and detail (all along I thought the cart was flawed) and now has the fun factor. Great!
Thank you Richard for everything.
ps.
The PCB layout I posted prior has a flaw, I'll post the correct one.
That's great!
I was kinda depressed that my suggestions for rerouting your previous version failed. In theory it should have converted the layout into the exact equivalent to the circuit board you just made.
However on a crowded veroboard and multiple fixes there is always the risk of burnt out components, bad solder joints, shorts and capacitative noise coupling.
Happy to see the new PCB worked out.
Richard
PS. I give up .. what was the mistake on the PCB layout you posted earlier?
I was kinda depressed that my suggestions for rerouting your previous version failed. In theory it should have converted the layout into the exact equivalent to the circuit board you just made.
However on a crowded veroboard and multiple fixes there is always the risk of burnt out components, bad solder joints, shorts and capacitative noise coupling.
Happy to see the new PCB worked out.
Richard
PS. I give up .. what was the mistake on the PCB layout you posted earlier?
Hi Richard, I need your help!
I loaned my VSPS to a friend and after hours of using it, he said his SS integrated amp died.
I took the VSPS home and found 100mV DC on the right output. Before I used it, I checked DC and was below range of my DMM (0.0 reading in mV range)
What would have caused DC to suddenly appear?
I'm sad for my friend's amp
I loaned my VSPS to a friend and after hours of using it, he said his SS integrated amp died.
I took the VSPS home and found 100mV DC on the right output. Before I used it, I checked DC and was below range of my DMM (0.0 reading in mV range)
What would have caused DC to suddenly appear?
I'm sad for my friend's amp
I can only assume one of the output capacitors (C3) failed: it is impossible for DC voltage to be on the output otherwise.
100mV is about the normal offset for the opamp output before C3. So I dont think the VSPS is broken, you just need to replace C3 in both channels with something you trust not to fail.
What are those yellow caps you are using for C3? They look to be 63V film types, but given the small size that would mean they are only about 0.2 uF...
/R
PS. 100mV DC on the inputs should not cause an amp to fail. The worst that should happen is it blows a fuse. The reason C3 is there is to protect the speakers in the rare case that the amplifier is direct coupled from input to output.
100mV is about the normal offset for the opamp output before C3. So I dont think the VSPS is broken, you just need to replace C3 in both channels with something you trust not to fail.
What are those yellow caps you are using for C3? They look to be 63V film types, but given the small size that would mean they are only about 0.2 uF...
/R
PS. 100mV DC on the inputs should not cause an amp to fail. The worst that should happen is it blows a fuse. The reason C3 is there is to protect the speakers in the rare case that the amplifier is direct coupled from input to output.
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