You must shorten the inputs, otherwise I got the full swing too and could not adjust...
And you will never get away the drift completely, I suppose that is the price for the good sound..
Better good sound than no drift.
I suppose the same drift is in Nelsons X0.2 and even in the original UGS3/4 and that could be one reason Nelson uses caps for in and output.
DIY people seem to put to much emphasis on an extreme low offset, I suppose Nelson takes more care for the sound.
And high bias produces air circulations that are not easy to control.....
I hope I am at least partially right.....
And you will never get away the drift completely, I suppose that is the price for the good sound..
Better good sound than no drift.
I suppose the same drift is in Nelsons X0.2 and even in the original UGS3/4 and that could be one reason Nelson uses caps for in and output.
DIY people seem to put to much emphasis on an extreme low offset, I suppose Nelson takes more care for the sound.
And high bias produces air circulations that are not easy to control.....
I hope I am at least partially right.....
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An externally hosted image should be here but it was not working when we last tested it.
The Pumpkins under build. 2 x Pumpkin + 2 x Shuntky.
I've got an odd arrangement of transformers due to what was in the scrap bin. I had 2 x 20-0-20V 50VA EI transformers. These have been arranged to give 40-0-40V at 50VA which is perfectly sufficient for the Pumpkin / Shuntky pair.
Zen Mod has been ever so helpful during the build. Unfortunately Czech PCBs weren't the best quality but I got it all working with less than £1.00 worth of component failure due to the PCBs.
Zen Mod is now looking at a better supplier, so hopefully the lessons that I learnt will become history.
The odd trapezium arrangement around the heatsinks is purely intentional. The heatsinks that I bought from Germany had fin spacing that was too big for the holes in the PCB. This resulted in the heatsinks being unattached to the PCB and easilly bent. In time this would have resulted in lead failure to the components on the heatsinks. The easiest cure for this was to tie the heatsinks together with a cord. A more elegant solution might have been plastic strips but, what the hell, thuis is the DIY world.
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Hi Andy,
I could not see the picture .... On my iPad. Did you load it correct?
I had the same problem, I had to resolder the feet of the semiconductors some times because the weight of the heatsinks loosened connection over the time.
40v is enough and you get less heat problems, I started with 50V and had many difficulties....
I hope shortcutting the inputs will help you to fiddle W2 to the correct position.....
Zen is an incredible helpful guy and such a luck for us......
I could not see the picture .... On my iPad. Did you load it correct?
I had the same problem, I had to resolder the feet of the semiconductors some times because the weight of the heatsinks loosened connection over the time.
40v is enough and you get less heat problems, I started with 50V and had many difficulties....
I hope shortcutting the inputs will help you to fiddle W2 to the correct position.....
Zen is an incredible helpful guy and such a luck for us......
An externally hosted image should be here but it was not working when we last tested it.
This image might work.
Although each heatsink is electrically isolated from the devices attached to it. I have placed a layer of PVC tape between them to prevent contact between them. I am trying ever so hard to prevent any path for "Ground Loop". There is always a possibility that the heatsinks may contact the Upper Ground Plane of the PCB.
No they are 50VA. They may be 50VA per winding which would make them 100VA but I dont think so.
Well, I powered up the Pumpkins and my first impression is NOISE, NOISE and more NOISE.
And I'm not talking about pleasant MUSIC.
Both Pumpkins are working and producing very pleasant music BUT, and its a BIG BUT.
With the source turned OFF all I can hear is white noise and general "popping". This disappears when I disconnect the XLR connectors from the back of the pre-amp.
The cables are connected so that I can use an unbalanced RCA input into the XLR connectors, i.e pins 1 and 2 (+In and GND) are shorted together. The output is not shorted, just taken from the -Out and GND.
If I waggle the input XLRs the noise comes and goes. These are all good quality new connectors.
I can see in the photo that the LEFT / RIGHT - RED / BLACK connectors are wrong but this wont make any difference.
Please excuse me if I've got the XLR pin numbers wrong. I call PIN 2 the CENTRE connection and pins 1 and 3 the + and - balanced inputs.
The GREY wire you can see is not connected to anything, its just holding the heatsinks together.
And I'm not talking about pleasant MUSIC.
Both Pumpkins are working and producing very pleasant music BUT, and its a BIG BUT.
With the source turned OFF all I can hear is white noise and general "popping". This disappears when I disconnect the XLR connectors from the back of the pre-amp.
The cables are connected so that I can use an unbalanced RCA input into the XLR connectors, i.e pins 1 and 2 (+In and GND) are shorted together. The output is not shorted, just taken from the -Out and GND.
If I waggle the input XLRs the noise comes and goes. These are all good quality new connectors.
I can see in the photo that the LEFT / RIGHT - RED / BLACK connectors are wrong but this wont make any difference.
An externally hosted image should be here but it was not working when we last tested it.
Please excuse me if I've got the XLR pin numbers wrong. I call PIN 2 the CENTRE connection and pins 1 and 3 the + and - balanced inputs.
The GREY wire you can see is not connected to anything, its just holding the heatsinks together.
Zen_Mod suggests fitting 2.2uF caps in line with each of the +/- inputs. I'll give it a go and report back.
You will notice that I have no input selector or volume controls fitted. These are external. So effectively all I have is a resistor connected across the - input and 0V and the + input is shorted to 0V.
There is a LOT of "SHOT" noise that I can't seem to find where it is coming from.
The same leads with my Borbelly pre-amp are silent so I find it difficult to fault the interconnects ??????
You will notice that I have no input selector or volume controls fitted. These are external. So effectively all I have is a resistor connected across the - input and 0V and the + input is shorted to 0V.
There is a LOT of "SHOT" noise that I can't seem to find where it is coming from.
The same leads with my Borbelly pre-amp are silent so I find it difficult to fault the interconnects ??????
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I have no idea where your noise is coming from....
I remember there was a difference in sound when I went out unbalanced and did or did not connect the unused output to ground....
I liked more the sound when the unused output was grounded, had more body...
maybe grounding the unused output stops oscillation...
I would try a provisory direct RCA to one of the inputs of pumpkin and ground the other...
something seems to oscillate ......
sometimes shunty oscillates, but you have the problem in both channels... and only when connected, what is your source?
and normally XLR for in and output are inverse and your "special" connecting with center (ground) in the middle is done in your system with consequence and there is no other commercial part that uses the normal pin order?
I remember there was a difference in sound when I went out unbalanced and did or did not connect the unused output to ground....
I liked more the sound when the unused output was grounded, had more body...
maybe grounding the unused output stops oscillation...
I would try a provisory direct RCA to one of the inputs of pumpkin and ground the other...
something seems to oscillate ......
sometimes shunty oscillates, but you have the problem in both channels... and only when connected, what is your source?
and normally XLR for in and output are inverse and your "special" connecting with center (ground) in the middle is done in your system with consequence and there is no other commercial part that uses the normal pin order?
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well - you must read Cook Book , I already covered that
you can choose any possible combination of inputs/outputs
but - when grounding one leg ( either in or/and out) , most usual way is to ground negative one
that way - if nothing else , you're avoiding confusion in signal wiring
- just imagine music studio where techies , working in different shifts , choose different signal legs for grounding .....
you can choose any possible combination of inputs/outputs
but - when grounding one leg ( either in or/and out) , most usual way is to ground negative one
that way - if nothing else , you're avoiding confusion in signal wiring
- just imagine music studio where techies , working in different shifts , choose different signal legs for grounding .....- Status
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