Pumpkin preamp - More Boring Making Thread

[Variac]

well great! we need to make more Pumpkins!! ZenMod will be soooo sad..

Wait! I have another question: does an F4 used single ended and one used balanced have the same gain? I guess so...?.........

[carpenter]

Originally posted by mpmarino


Yes but you'd then have a amp that would strain to run a 8r load ...No?

I don't think it's a strain--not if the driver is a 110db 1w1m horn. I get 2 amps total bias, not 6 (which is what the midbass units will have per pcb). The overall wattage output is down, but that's what I want.

[Zen Mod]

jeeeeeeeeeeeez!!

god mornin' to all, you are all drekin' nutz!!

seems that nobody in fact read all these crazy threads ...

it will be hard to cover all issues from last posts ......

woodie :

That makes sense, too. Is there a way to have a low wattage, yet good sounding, balanced-mono F4?

Reduce bias, have fewer fets to make it simpler?

go to page one or two of F4 thread and look my mini F4 variant - for 16 ohms ; crank bias to 1A and you'll be good for at least 8W/8E in A class
like you said

CY :

Why don't you switch grounds on that chicken scratch?

why should I ? for unbal conversion ? use XLR with shorted 1 and 3 ......
if you mean - switching just ground on used input ( all inputs always connected to signal rails) ........ I'm not so hysteric regarding little takamisawa relays in signal path ....... this is no Blowtorch ,and never will be

greedy danske :

Yes, you can tell me, what about -in connection when running unbalanced ?
As i see it, you are going to short pin 1 and pin 3 on XLR input's for running unbalanced input.
But when attenuator is placed somewhere at coax (russian?) cable the -in on pcb arent shorted anymore.
The shortning will be, whatever the attenuator is set to somewhere between 0 --> 10kohm in my situation ?

I assume that this is intented to be used with 4channel attennuator, so this is relavant for me to know...

yes - it's intended to use 4 channel attenuator ; not exactly twice teuerer than simple stereo but certainly better and more versatile .
on input where 1 and 3 are shorted in XLR source's cable , lower leg of attenuator is shorted automatically , so you have plain stereo 2 channel pot automatically

Lyyyykkkkkkkkkk - what you must do now is - see what you have on output of between + and gnd ,WITHOUT - shorted to gnd


you can use Pumpkin's output unbalanced - WITHOUT - shorting minus leg to gnd , but with somewhat lesser gain ........ comparing to "properly" terminated output

in that case you can one can use one routing to balanced amp (say for mids) and other routing ( just from positive leg and ground of Pumpkin's output) to unbalanced amp (say for highs) ;
IF - I repeat - IF gain for tweet amp is adequate , everything is solved .
if not - only solution is two additional main boards but - it's completely possible to feed 4 main boards from two Shunty boards ........... if ya are cheapskate ,as I am ........
unfortunately - there is no free lunch in some things ..............


I hope that I cover everything ....... good enough

[carpenter]

I have IRF9630 and Fairchild 630 Fets. I'm going to try with these first. They have half the Ciss of stock Fets. 1 amp bias is well within their range.

Choky, I do remember something about your smaller version. Perhaps this is why the idea comes to mind.

Thanks guys.

[carpenter]

Choky, I went to page one of F4 thread. Yes, there is your drawing, and best of all, it stuck in my brain--even though I couldn't remember where, why, whom, or how.

That's what I'm planning to do.

[mpmarino]

go to page one or two of F4 thread and look my mini F4 variant - for 16 ohms ; crank bias to 1A and you'll be good for at least 8W/8E in A class

Sorry to beat a dead horse - But what I am saying is that the above configuration will only be 16 ohm stable when BRIDGED. Right?


ZM - I was joking about the grounds.... I forgot the

[Zen Mod]

Originally posted by mpmarino


Sorry to beat a dead horse - But what I am saying is that the above configuration will only be 16 ohm stable when BRIDGED. Right?


.........

not right ;

[Zen Mod]

Originally posted by mpmarino


Bad Choky, your killing me

just crank bias........... what else?

[lykkedk]

on input where 1 and 3 are shorted in XLR source's cable , lower leg of attenuator is shorted automatically , so you have plain stereo 2 channel pot automatically

If you look at a potmeter from (bottomview) left leg is 'input'
Middle leg is 'output'
Right leg is 'GND'

If i look at attenuator connection for -in it's like this right ?
XLR input pin 1 goes to Right leg (GND)
(XLR input pin 2 is for +in)
XLR input pin 3 (-in) goes to Left leg (input)

Output from attenuator (wiper) is middle leg... Soo if you short pin 1 and 3 in XLR input, you will short the resistor''coil'' inside the potmeter. This seem's to be OK, in theori... BUT... I tried to hook it up, with my ohmmeter, and no-mater how i do it, there will be in area of 2-2,5k resistance when wiper crosses middle of potmeter
This mean's that when using in real life (this is ehh ? )... when volumecontrol is near middle posistion, there will be some resistance between -in and GND.
If you meassure on potmeter, in normal use, this problem is not there ofcause.

Proberly this don't mean anything, but it's worth consider doing something about when making an inputselector i think ?

ZenMod you proberly have an explanation for this! Am i right ?

Lyyyykkkkkkkkkk - what you must do now is - see what you have on output of between + and gnd ,WITHOUT - shorted to gnd

With my ~20dB gain setting on ...
Input with 2vac sine = 30v out -out leaved open...
Input with 2vac sine = 45v out -out shortned to GND...

[Zen Mod]

Originally posted by lykkedk


If you look at a potmeter from (bottomview) left leg is 'input'
Middle leg is 'output'
Right leg is 'GND'

If i look at attenuator connection for -in it's like this right ?
XLR input pin 1 goes to Right leg (GND)
(XLR input pin 2 is for +in)
XLR input pin 3 (-in) goes to Left leg (input)

Output from attenuator (wiper) is middle leg... Soo if you short pin 1 and 3 in XLR input, you will short the resistor''coil'' inside the potmeter. This seem's to be OK, in theori... BUT... I tried to hook it up, with my ohmmeter, and no-mater how i do it, there will be in area of 2-2,5k resistance when wiper crosses middle of potmeter
This mean's that when using in real life (this is ehh ? )... when volumecontrol is near middle posistion, there will be some resistance between -in and GND.
If you meassure on potmeter, in normal use, this problem is not there ofcause.

Proberly this don't mean anything, but it's worth consider doing something about when making an inputselector i think ?

ZenMod you proberly have an explanation for this! Am i right ?



With my ~20dB gain setting on ...
Input with 2vac sine = 30v out -out leaved open...
Input with 2vac sine = 45v out -out shortned to GND...

lykk

what's count here is that minus leg of signal is grounded , not gate of fet .

so - everything is OK

tnx for measuring these combinations ....... you know that I'm still Pumpkinless