Jean,
Leeloo is offering his (err... her) kits here. Haven't read it recently but they seem to be available. If she manages to learn English she might even tell you here 😉. But careful, She's a little...
Felix: not yet. I'm looking to buy something used for a while, might have to accelerate this "work stream" 😉.
Sven
Leeloo is offering his (err... her) kits here. Haven't read it recently but they seem to be available. If she manages to learn English she might even tell you here 😉. But careful, She's a little...
An externally hosted image should be here but it was not working when we last tested it.
😉😉)Felix: not yet. I'm looking to buy something used for a while, might have to accelerate this "work stream" 😉.
Sven
@Steen: the other thread is closed but I would like to say that I like your Pumpkin layout . From the inside It looks like an old Sansui amp. Nice! 🙂
I would do something similar but my transformers are much bigger and I have an additional PS. I will have to go for a two box solution.
Sven
I would do something similar but my transformers are much bigger and I have an additional PS. I will have to go for a two box solution.
Sven
Abraxas336 said:
you really don't need additional PSU
Shunty per channel is already insane overkill
anyway - whatever you do - keep Shunty pcb near
pcb
I'm sure I don't need it... but I have a redundand one here... and can it get insane enough?
An externally hosted image should be here but it was not working when we last tested it.
Do you remember Wolfgang "Pillendreher"s PSU? 😉Yes Sir!
Sven
Abraxas336 said:
agree - completely reasonable
I remember his PSU .....
once I had preamp NiCd charger
, with more TES than usual small tube power amp and with more iron than usual fifi SS amplifier ...everything is reasonable , if pleasure is result and cause
😉
Here we go again 🙂
I just fired up both Pumpkins. Im following Chokys procedure from the cook book. I am able to get offset between + and - outputs to zero. I am unable however to set the voltage between outputs and ground to zero. I can get them down to ~32V and then the voltage flips to -28V suddenly. I have to go some turns back to get it positive again but even if I am very sensitive I can not get closer to zero than abou 32V before it flips to negative. Any ideas?
Many Thanks
Sven
PS: Trimmer are Burns 3289 50R.
I just fired up both Pumpkins. Im following Chokys procedure from the cook book. I am able to get offset between + and - outputs to zero. I am unable however to set the voltage between outputs and ground to zero. I can get them down to ~32V and then the voltage flips to -28V suddenly. I have to go some turns back to get it positive again but even if I am very sensitive I can not get closer to zero than abou 32V before it flips to negative. Any ideas?
Many Thanks
Sven
PS: Trimmer are Burns 3289 50R.
ZM knows Bahnhof ......
what you have connected to Pumpie inputs ?
I mean - what sort of attenuator ?
what you have connected to Pumpie inputs ?
I mean - what sort of attenuator ?
*cough* ... do I need one? 
😀
Ok, you got me - i did not stick to cook book, I connected only the PSU on my "test rig", nothing else yet...
Sorry 😉
Sven
😀Ok, you got me - i did not stick to cook book, I connected only the PSU on my "test rig", nothing else yet...
Sorry 😉
Sven
Abraxas336 said:*cough* ... do I need one?
Ok, you got me - i did not stick to cook book, I connected only the PSU on my "test rig", nothing else yet...
Sorry 😉
Sven
that way - input gates are flying with ducklings in far away sunny bright sky ......
solder 22K from each input gate to gnd ; you can do that from bottom side of pcb
then try
later - you can leave these resistors permanently there
steenoe said:All that needs to be done, are all the internal connections...pheeew
Here is a detail shot of how the bearings are mounted.
🙂
Very nice. I'm trying to replicate this since I do not want my shafts to have play in the front plate. Did you glue the shafts in the bearings? How exactly does the mount work, I cant really tell from the pictures. is there a ring attached to the mount which then contains the actual bearing?
PS: I just went through 70+ pages of this thread. It is not exactly easy to extract the ~ 2 pages of valuable information it contains without missing stuff. 😀😀
I'd be interested in the results of Jacco/HB others (?) using the trimcaps. I went for a gain factor of 15 and used 3.3pF fixed caps. Does it make sense to switch to a trimcap?
Many Thanks
Sven
I used 3.3 +-0.5 pF and matched them to ~5%, that should do it, then. Chocky I also studied your very sophisticated drawing of the grounding scheme 😀. It is a coincidence but I will be using a TKD pot, too. The pot needs to be connected according to figure 1 in the attached picture. How do you connect grounds in the context of your grounding concept?
Thanks
Sven
Thanks
Sven
Attachments
Hello everyone,
After using the pre for a couple of weeks on my test rig I am kind of uncertain whether I will be able to set the offset to zero at all. My Q12/34 pairs are covered by a silicone tube cover, the whole Pre has been covered, too. I know it belongs into a real box and it will have a box, soon. But the offset stays not even close to +- zero after long hours of setting and re-adjusting while leaving the whole device powered for 5 days. Even a change in the room temperature messes up your offset and not only by a couple of 0.1V.
Question now is - how bad is a "not zero" offset. In the cook book replicated DC on the inputs is mentioned. I did not have any problems with noise while turning the pot. But I suppose that might be a problem for DC coupled sources?
If I put 10uF Caps in all 4 input signals I eliminate any DC coming out of the Pumpkin so thats not an issue anymore for other devices. The question is - does an "not zero" offset - even if no DC leaves the Pumpkin - compromise the sound quality somehow? If not I might go for some more caps and less trouble setting the offset.
Thanks
Sven
After using the pre for a couple of weeks on my test rig I am kind of uncertain whether I will be able to set the offset to zero at all. My Q12/34 pairs are covered by a silicone tube cover, the whole Pre has been covered, too. I know it belongs into a real box and it will have a box, soon. But the offset stays not even close to +- zero after long hours of setting and re-adjusting while leaving the whole device powered for 5 days. Even a change in the room temperature messes up your offset and not only by a couple of 0.1V.
Question now is - how bad is a "not zero" offset. In the cook book replicated DC on the inputs is mentioned. I did not have any problems with noise while turning the pot. But I suppose that might be a problem for DC coupled sources?
If I put 10uF Caps in all 4 input signals I eliminate any DC coming out of the Pumpkin so thats not an issue anymore for other devices. The question is - does an "not zero" offset - even if no DC leaves the Pumpkin - compromise the sound quality somehow? If not I might go for some more caps and less trouble setting the offset.
Thanks
Sven
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It limits the output voltage swing, which shouldn't be a problem here.
As sources tend to be low impedance, and the input offset is not - no problem.
Some people out there put extra DC on their coupling caps (by means of a battery), because it is said to sound better. Considering that, some offset won't hurt 😀.
Bigger caps won't help anything. They just shift the lower cutoff frequency to even lower values.
Thanks Holger.
As for the caps - I didn't say bigger, I said more 🙂. Specifically 4 additional decoupling caps in signal +/- (both channels) between pot and Pumpkin inputs according to cook book. But if I do not have problems with the pot and DC on the Pumpkin inputs is no problem for sources it might not be necessary even if the offset is lets say 5V?
Thanks
Sven
Mhh... starting from PSU voltage? With my "settings" gain factor is 15, voltage swing afaik 20V max? So lets say 36V PSU voltage, some more regulation, at what offset does it become an issue?
As for the caps - I didn't say bigger, I said more 🙂. Specifically 4 additional decoupling caps in signal +/- (both channels) between pot and Pumpkin inputs according to cook book. But if I do not have problems with the pot and DC on the Pumpkin inputs is no problem for sources it might not be necessary even if the offset is lets say 5V?
Thanks
Sven
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If you have 5 Volts of offset, your output voltage maximum will be 5 Volts less.
There's no relation between the value of the coupling caps (input or output) and the offset's amplitude. Go with the values ZM suggested on the input and you'll be fine, doesn't matter how much offset you have. I would not triy to omit those caps on the input, as you will run into cracking noise problems sooner or later - not necessarily related to the input offset voltage.
There's no relation between the value of the coupling caps (input or output) and the offset's amplitude. Go with the values ZM suggested on the input and you'll be fine, doesn't matter how much offset you have. I would not triy to omit those caps on the input, as you will run into cracking noise problems sooner or later - not necessarily related to the input offset voltage.
Hi Holger,
vielleicht müssen wir wegen der Kondensatoren mal Deutsch reden 😀😀
Ich beabsichtige nicht irgendwelche Werte zu verändern oder Kondensatoren wegzulassen. Ich bezog mich auf diese Aussage im Kochbuch:
Normalerweise sind doch gar keine Kondensatoren im Input oder schnalle ich da was nicht...
Wie auch immer, das betrifft nur den "Absolute Offset". Den habe ich ohnehin einigermaßen erträglich hinbekommen, was ich für sehr schwierig halte ist der "Andere Offset" 😀😀😀.
Und da verstehe ich dich so, dass es außer der reduzierten maximalen Ausgangsspannung des Kürbis keine weiteren negativen Begleiterscheinungen gibt?
Danke!
Sven
(Sorry guys, back to English 😉)
vielleicht müssen wir wegen der Kondensatoren mal Deutsch reden 😀😀
Ich beabsichtige nicht irgendwelche Werte zu verändern oder Kondensatoren wegzulassen. Ich bezog mich auf diese Aussage im Kochbuch:
Normalerweise sind doch gar keine Kondensatoren im Input oder schnalle ich da was nicht...
Wie auch immer, das betrifft nur den "Absolute Offset". Den habe ich ohnehin einigermaßen erträglich hinbekommen, was ich für sehr schwierig halte ist der "Andere Offset" 😀😀😀.
Und da verstehe ich dich so, dass es außer der reduzierten maximalen Ausgangsspannung des Kürbis keine weiteren negativen Begleiterscheinungen gibt?
Danke!
Sven
(Sorry guys, back to English 😉)
Hi Sven,
da steht: Wenn du Offset am Ausgang hast, dann wirstdu auch welchem am Eingang haben, der wird nach vorne weitergereicht, reduziert um den Gegenkopplungsfaktor. Und wenn Offset am Eingang da ist, brauchst du Koppel-Cs am Eingang, sonst wird's hässlich, wenn du an der Lautstärke drehst.
Du hast Offset am Ausgang, ergo brauchst du Koppel-Cs am Eingang.
da steht: Wenn du Offset am Ausgang hast, dann wirstdu auch welchem am Eingang haben, der wird nach vorne weitergereicht, reduziert um den Gegenkopplungsfaktor. Und wenn Offset am Eingang da ist, brauchst du Koppel-Cs am Eingang, sonst wird's hässlich, wenn du an der Lautstärke drehst.
Du hast Offset am Ausgang, ergo brauchst du Koppel-Cs am Eingang.
Richtig.