Switchable Hi-Z input impedance, how ? - Page 31 - diyAudio
Go Back   Home > Forums > Live Sound > Instruments and Amps

Instruments and Amps Everything that makes music, Especially including instrument amps.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 19th September 2012, 09:07 PM   #301
tinitus is offline tinitus  Europe
diyAudio Moderator R.I.P.
 
Join Date: Nov 2005
thanks guys

gain ?
not sure
right now I use a Creek headphone amp to drive my 2-channel power amp(stereo with Sanken outputs)
as high-Z 'buffer/preamp' in front it I only have a compressor with 12db gain
both are ste at around 12 o'clock', most of the time below, and rarely above
and thats a lot louder than I need
for very 'silent' practice I switch off the 12db gain from compressor

I forgot I also have small EQ on the mid
cheap digital crap thing
cant do without right now
bypassing it gives me very heavy loud low bass
fun sometimes
and matches some types of music
but mostly its a bit too much

hey, I have my proto/test preamp powered up now, +18.6V
  Reply With Quote
Old 20th September 2012, 08:29 AM   #302
tinitus is offline tinitus  Europe
diyAudio Moderator R.I.P.
 
Join Date: Nov 2005
Quote:
Originally Posted by shanx View Post
....consider adding bypass cap across the source resistor.
what size would you recommend ?

from I have read the bypass cap gives cleaner sound
I guess as a result of more even and controlled gain
on the backside, it should result in more unpleasant 'overdrive', but thats a guitar thing, and not sure I should worry about that

but I will experiment with that, thanks
  Reply With Quote
Old 20th September 2012, 02:33 PM   #303
shanx is offline shanx  Canada
diyAudio Member
 
Join Date: Dec 2010
Location: Quebec
If you are using a compressor with a 12 dB gain you may not need more gain there. If you were plugging the bass direct-in then you may want about a 6 to 12 dB gain to give a bit more drive to the tone stack and tubes. For bass you would use a larger bypass cap. Guitar stage typically 22 uF, 35 uF, but that is going to probably roll off your Lo Freq's way too much for a bass. You probably need to go to 100 uF or more to get full range of a bass.
  Reply With Quote
Old 20th September 2012, 02:34 PM   #304
shanx is offline shanx  Canada
diyAudio Member
 
Join Date: Dec 2010
Location: Quebec
Quote:
hey, I have my proto/test preamp powered up now, +18.6V
COOL!!!
  Reply With Quote
Old 20th September 2012, 03:18 PM   #305
tinitus is offline tinitus  Europe
diyAudio Moderator R.I.P.
 
Join Date: Nov 2005
just the power supply
but the rest is just the jfet, and resistors
that should be the easy part, I hope
  Reply With Quote
Old 20th September 2012, 03:27 PM   #306
shanx is offline shanx  Canada
diyAudio Member
 
Join Date: Dec 2010
Location: Quebec
I hope so too..I am working on a small guitar amp right now. Most of my time was spent on layout and mechanical build, drilling & mounting parts. I am more into getting the electronic components soldered in..anxious to finish the mechanical stuff.
  Reply With Quote
Old 20th September 2012, 04:24 PM   #307
tinitus is offline tinitus  Europe
diyAudio Moderator R.I.P.
 
Join Date: Nov 2005
you are welcome to upload all you want here

btw, I mounted a green LED with a bleed resistor
it works, and cool to watch it power down
and, on the open test amp, its probably good safety 'monitor'

on power up and watching LCD meter, it could look like its also do soft start function

btw, it was weird the first time I powered it up
I only had half voltage, or less
but also noticed the first cap had the full 18V
well, I had 1ohm resistors between all 4 supply cap
and guess what, the middle resistor was gone, defect
I removed all resistors, and everything worked
  Reply With Quote
Old 20th September 2012, 06:55 PM   #308
shanx is offline shanx  Canada
diyAudio Member
 
Join Date: Dec 2010
Location: Quebec
Thanks Tinitus, if I come up with any interesting ideas when building it, I will send them. My preamp section for now is 2 stages of jfet. I may add a 3rd stage for more gain. I will jumper in the bypass caps and see how it sounds with and without them. Please let me know if you try that also and how it reacts on bass frequencies.
  Reply With Quote
Old 20th September 2012, 08:20 PM   #309
tinitus is offline tinitus  Europe
diyAudio Moderator R.I.P.
 
Join Date: Nov 2005
will do
  Reply With Quote
Old 20th September 2012, 11:52 PM   #310
tinitus is offline tinitus  Europe
diyAudio Moderator R.I.P.
 
Join Date: Nov 2005
dont know if I should be happy or sad

happy because it works, and there is sound
but also sound that shouldnt be there....snerrring hummm

jfet is BL grade
drain resistor is 1.5K
source res is 15ohm
with modest voltage sag, it settled at 17.8V
I measure a little less than 9V across the drain resistor
and nothing when I measure across the source res
DC on output plugs is 'barely alive'

apart from the hum, very open and smooth midrange, none of the 'usual' harsness to hear at all

but the gain is excessive
with this alone between bass and poweramp, I can barely touch the onboard volume conrtrol on my bass

still work to do
but it works, thats something at least
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Switchable balanced / unbalanced input buffer nigeljking Analog Line Level 4 12th September 2011 12:03 PM
How to design input stage with specific input impedance/pot value mahleriana Tubes / Valves 0 16th November 2009 09:37 PM
Input Impedance Bengali Analog Line Level 7 15th August 2007 10:24 PM
Input impedance nhuwar Tubes / Valves 24 23rd July 2007 11:11 PM
Input pot and input impedance Bricolo Parts 1 19th March 2003 01:59 PM


New To Site? Need Help?

All times are GMT. The time now is 01:16 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2