Pumpkin preamp - ordered by Steen , official making thread

Jump to Latest
#2,643
Zen Mod: Many thanks for such a detailed answer.

Zen Mod said:


:Pumpkin: was primary made for F4 in balanced config ; even if most important goal was to squeeze every possible volt from balanced F4 , little pumpie is surprisingly good even in lower gain settings ( adequate for F5 , which needs no more than few volts at input for full blast ) .
I dunno for Impasse , which is certainly one hell of a preamp for same role - driving balanced buffer , how is acting in less demanding role - idling with just few volts at output . you must ask SY about that .
Click to expand...

I had completely missed the line on the front of the cook book that clearly says "Super Symmetric BALANCED Line Amplifier" (It's pretty obvious looking at the circuit, too, now it's pointed out...) :ashamed: This would mean TWO stereo F4s following it, correct? This is out of the question for reasons of $$$ unless I find four large heatsinks somewhere... At least here in Brazil these are easily the most expensive thing to buy, so I can't do two F4s until my children grow up and get jobs...

Is it possible to build the Pumpkin in unbalanced form, or does that defeat the purpose? (The schematic shows +in, -in, +out and -out... If I only do the part which links +in and -out will that give me a single-ended inverting line amp?) If the Pumpkin is not appropriate, does anyone have another suggestion of a SS circuit?


1. yes - one Shunty for two Pumpies , with better heatsinking than for 2+2
4E7 is old European trick to confuse boyz from other side of Big Splash :clown: ........ same as you boyz wrote uuF , driving us nutz :rofl:
but - 84Vst means 84V center tapped on both sides of silly ocean 😉 , and you can imagine it as twice 42Vac
Vin at J1 and J2 are points for connecting DC pos & neg supply , in case that you already have adequate voltages ( from power amp PSU , for instance ) so there is no need for additional rectifying with internal Pumpie's Graetz bridge .
Click to expand...

OK, that's all clear. (I should have known 84Vct meant center-tapped... pretty obvious really)


2. in most cases - volume pot is going BEFORE gain stage ; both Impasse and Pumpie don't need any sort of buffer before them ...... and God forbid after them . that's pure redundancy .
Click to expand...

Maybe I wasn't quite clear. I'd like to do another B1 anyway, but it seems unnecessary to spend on volume pots (to get good ones I'd have to import, which means $$$$) for the B1, and others for the other preamps. If I connect the output from the B1 to the input of the Impasse or Pumpkin (forgetting the problem of balanced/unbalanced for the moment) you are saying that the B1 buffer is not necessary, but does it actually do any harm? To the sound, I mean (My guess is no). If it doesn't then I can build a B1, with volume pots and switched inputs and so forth, and if I build various gain stages then none of them need (expensive) volume pots.... which means more fun for me at less cost... 😎


3. you can use for heatsinks even plain sheets of Al or Cu . but - at least from my experience - for dumpster dive approach in making singing gadgets , you must have pretty much more experience than you have - at least according to your questions ;
don't take that even slightly as insult - nobody is born knowing everything ..... but Pumpie is everything but simple ;
it is simple - just 4 active parts per channel , counting it even in balanced mode ....... but rest is pretty complicated , in case that you don't have enough understanding of each part functionality ...... and in that case - everything is simple 😉
Click to expand...

I wasn't insulted at all - just grateful to get answers to my (sometimes stupid) questions...


4.
edit:
I had impression that I wrote pretty clear Cook Book ; did you read it ?
Click to expand...

I took a look through it, yes, but as usual found I needed to know about 10% more than I do to understand it - hence my post. (It would have helped if I'd read the front cover, of course.... :ashamed:) This isn't at all a criticism of your Cook Book (which seems pretty thorough) but is the same thing I find with everything on the net. With a little more experience this should solve itself... After all, I have three reasons for doing diy audio:

1. To get better-sounding music at a reasonable price

2. To learn something along the way

3. To have fun

Any project I do has to satisfy at least two of these...

In any event, many thanks for your answers.

Cheers
Nigel
 
#2,644
Zen Mod said:


ya teasing me - as always 😉
Click to expand...


wasn't someone around here working on a more light emitting version of the F4?

As to a single toob, something like this I suppose is what you're thinking:

tube_unity-gain_buffer.png
 
#2,645
luvdunhill said:



wasn't someone around here working on a more light emitting version of the F4?

...
......
Click to expand...


regarding "tube F4" - take almost any PP toob amp , strip anything in front output tube's grids , and you have what's called in ancient times "booster amp" .

I remember ( I read that , certainly wasn't around when actually they made them :devily: ) sissy WE booster amps with VT4C in PP , where two worn ones were used as diodes in PSU ....... off course - they had input xformer , in role of voltage step up and phase splitter ;
off course - phase splitter was needed in case that you use your eeny weeny SE amp for driving the beast

nothing new under the Sun ........ except stronger Coppertone eevry year .... :rofl:

luvdunhill said:

...

As to a single toob, something like this I suppose is what you're thinking:
......
Click to expand...

I'm usually known as someone who's not thinkin' too much :rofl:



I'll be back later , to respond to njepitt's saga .......... :clown:
 
#2,649
njepitt said:
Zen Mod: Many thanks for such a detailed answer.



I had completely missed the line on the front of the cook book that clearly says "Super Symmetric BALANCED Line Amplifier" (It's pretty obvious looking at the circuit, too, now it's pointed out...) :ashamed: This would mean TWO stereo F4s following it, correct?

exactly


Is it possible to build the Pumpkin in unbalanced form, or does that defeat the purpose? (The schematic shows +in, -in, +out and -out... If I only do the part which links +in and -out will that give me a single-ended inverting line amp?) If the Pumpkin is not appropriate, does anyone have another suggestion of a SS circuit?

it's pretty much possible - best way is build it as original , then just use it in form you need it - if you read end of cookbook , you'll see that you can connect it in any way you need ( both input and output in both balancced or unbalanced , with slight trick used ofr rare needs of using in same time balanced and unbalanced output scheme

....



Maybe I wasn't quite clear. I'd like to do another B1 anyway, but it seems unnecessary to spend on volume pots (to get good ones I'd have to import, which means $$$$) for the B1, and others for the other preamps. If I connect the output from the B1 to the input of the Impasse or Pumpkin (forgetting the problem of balanced/unbalanced for the moment) you are saying that the B1 buffer is not necessary, but does it actually do any harm? To the sound, I mean (My guess is no). If it doesn't then I can build a B1, with volume pots and switched inputs and so forth, and if I build various gain stages then none of them need (expensive) volume pots.... which means more fun for me at less cost... 😎

buffer does some harm in this hypothetical case , even in case that you use most sophisticated one ; they're always visible/hearable in circuit ...... sometimes they give benefits , but in this case not
you can place both Pumpie and B1 in one case , and use one volume pot for both , taking their outputs to adequate power amps - if yo have multiamp on mind

...


\
1. To get better-sounding music at a reasonable price

2. To learn something along the way

3. To have fun


that last one is certainly most important factor ..... even if first two are completely sane 😉


Any project I do has to satisfy at least two of these...

In any event, many thanks for your answers.

Cheers
Nigel
Click to expand...


I placed my reply inside your post ..... too lazy to struggle with multiple quote

😉
 
#2,652
R13,R18,R22

I nead a hint concerning R13,R18,R22:

Can I use 47.5ohm instead of 47ohm for R13,R18,R22?

I have a problem to purchase 47ohm resitors in the quality I use for the other resitors.
Or is it better to use lower quality with 47Ohms?

Marcel
 
#2,655
you'll have to ask prayers from Pumpkin Pope Zen Mod.

In other news, I'm considering raising input on F4 to 200K. I think this mod is a worthy thing to mention in Cookbook, assuming Pumpkin is okay with this change and there are no changes that need to be made on the Pumpkin side.
 
#2,656
400 said:
Tolerance is 0,5%.
So they can have max. 47.74.
So the difference can get max. 0,27ohms.

Can I do this???
Click to expand...

yup
R13 & R18 - whatever you have - between plain short and 82E
it will dictate output impedance of :Pumpkin:
R22 +/- 10% , just because there is pot in series


luvdunhill said:
you'll have to ask prayers from Pumpkin Pope Zen Mod.

In other news, I'm considering raising input on F4 to 200K. I think this mod is a worthy thing to mention in Cookbook, assuming Pumpkin is okay with this change and there are no changes that need to be made on the Pumpkin side.
Click to expand...


Pumpkin will be bored same with 200R as with 200K



in later case you can decrease output caps on Pumpie to 430nF

:rofl:

or even better - leave Pumpie as is , and save these Jfets on F4 input for something else ;
there is somewhere sketch of F4 without them .....
 
#2,659
Stupid question

Zen Mod said:



:rofl:

I hope that you bought few male (heiss) ones , for outputs ............
Click to expand...

OK, I realise this may be an absurdly stupid question..... I just came back from buying some hardware for putting my Pumpkin together, and was faced with choosing female and/or male XLR sockets to mount on the back panel for inputs and outputs - and looking at them I realised I had no idea which should be used for which.... Now I'm back home I found the post I quoted, which says the outputs (to power amp) should be male sockets, and presumably female for inputs. (In this case from DAC, most likely...) SO: why this way round instead of the other?

(Oh, and apparently I guessed wrong and will have to change some males to females... oh well... )

Cheers

Nigel
 
You must log in or register to reply here.
Top Bottom