Simple passive preamp. Neen some help in grounding. - diyAudio
Go Back   Home > Forums > Amplifiers > Solid State

Solid State Talk all about solid state amplification.

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 14th July 2007, 07:53 PM   #1
FaTTy is offline FaTTy  Russian Federation
diyAudio Member
 
Join Date: Mar 2007
Default Simple passive preamp. Neen some help in grounding.

Hi

I started to build passive preamp for my JLH monoblocks. It have only two functions :
- 4 way input selector on relays
- volume control on ALPS RK27 stereo pot
Simple at the first look, but not as is... So, i have some troubles with proper grounding. We have three ground lines, two signal and one power :
- left channel gnd
- right channel gnd
- relays feeding PSU's gnd
I think, that ground scheme sould be the same as on the attached pic. Is it a good way?

Thanks!

PS
Sorry if my english too hard to understand
Attached Images
File Type: gif grounding.gif (5.8 KB, 480 views)
  Reply With Quote
Old 14th July 2007, 08:37 PM   #2
TerryO is offline TerryO  United States
diyAudio Member
 
TerryO's Avatar
 
Join Date: Nov 2002
Location: Seattle,Wash.
I have a question: If you are constructing a passive preamp, what is the PSU gnd for? A true "passive" is TTBOMK little more than source selection switches and an attenuator. The use of relays and a PS suggests that you have, in reality an "active" preamp that is amplifying, or modifying in some way, the source signal.

Best Regards,
TerryO
__________________
"If you have to ask why, then you're probably on the right track."
quote from Terry Olson's DIYaudio Forum application
  Reply With Quote
Old 14th July 2007, 09:59 PM   #3
FaTTy is offline FaTTy  Russian Federation
diyAudio Member
 
Join Date: Mar 2007
Oh, i fogot about pcb. Here it is, see attach. Any comments?

TerryO
Maybe you right. Let it be active I thinked that passive volume regulator automatically makes my preamp passive...
Attached Images
File Type: gif pic.gif (22.4 KB, 411 views)
  Reply With Quote
Old 15th July 2007, 03:53 PM   #4
FaTTy is offline FaTTy  Russian Federation
diyAudio Member
 
Join Date: Mar 2007
Help needed... How to make proper grounding?
What can you say about my pcb?
  Reply With Quote
Old 16th July 2007, 04:23 PM   #5
Gordy is offline Gordy  United Kingdom
diyAudio Member
 
Join Date: Nov 2006
From the information that you have posted it seems as if you have a good understanding of the requirements.
  Reply With Quote
Old 16th July 2007, 04:35 PM   #6
Gordy is offline Gordy  United Kingdom
diyAudio Member
 
Join Date: Nov 2006
From the information that you have posted it seems as if you have a good understanding of the requirements.
  Reply With Quote
Old 16th July 2007, 04:40 PM   #7
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
Hi Fatty,
check all your sources that may get plugged into your pre-amp.
If any have the ground on the left channel connected directly to the ground on the right channel, then you will have a ground loop by connecting the L+R grounds together inside the pre-amp.
A loop will almost certainly cause hum on the affected inputs.
__________________
regards Andrew T.
  Reply With Quote
Old 16th July 2007, 06:04 PM   #8
diyAudio Member
 
Join Date: Jan 2006
Location: Virginia
Quote:
Originally posted by AndrewT check all your sources that may get plugged into your pre-amp.
If any have the ground on the left channel connected directly to the ground on the right channel, then you will have a ground loop by connecting the L+R grounds together inside the pre-amp.
A loop will almost certainly cause hum on the affected inputs.
This I don't understand. Most every source component I've been around has a common ground on its output. It's mandatory based on the powersupply grounding. The drawing posted is (in my obviously skewed view of the world) correct. I would be facinated by any description that justifies separating the grounds at the input and output connections of a preamp.

Any system comprised of multiple powered signal sources (and loads for them) needs a common reference point. The input/output connections at the preamp (in my experience) is it.

I don't normally feeled compelled to speak up anymore, but this post is likely to confuse many a DIYer without a challenge. They'll be chasing stability problems that are near unsolvable based on this.

Nothing personal, just a different point of view.

Mike.
__________________
"We are all agreed that your theory is crazy. The question which divides us is whether it is crazy enough to have a chance of being correct. " Niels Bohr
  Reply With Quote
Old 16th July 2007, 06:19 PM   #9
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
I would keep the pre-amp left and right completely separate.
__________________
regards Andrew T.
  Reply With Quote
Old 16th July 2007, 06:47 PM   #10
Gordy is offline Gordy  United Kingdom
diyAudio Member
 
Join Date: Nov 2006
Yes, I see what you mean Andrew. It is possible to separate Left and Right, and only bring them together at a link to the safety / chassis ground. It is also possible to switch the input source grounds too, so that the only source ground connected is the one of the source selected. However that may be getting too complicated for FaTTy.

What we can say is that although the design as presented is not optimal, it should work reasonably well.


Mike / Andrew... I think the forum needs a reference "how to ground your pre-amp" paper. Maybe when I get a spare week... unless you know of a ready-made paper / web link?
  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
Simple SE grounding -- metal spacers/standoffs? dogfish Tubes / Valves 4 26th June 2009 05:26 PM
Pass B1 Passive Buffer Preamp. A good and simple option for chipamps?. A Sanchez Chip Amps 5 2nd January 2009 06:34 PM
Grounding in a Passive Line Stage Zero Cool Solid State 7 12th March 2006 06:19 PM
Grounding Question on Simple System collinbd Multi-Way 0 30th November 2004 06:27 PM
APOX passive volume grounding tiroth Solid State 0 27th February 2004 06:53 PM


New To Site? Need Help?

All times are GMT. The time now is 07:01 PM.


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