Welcome Guest! To enable all features please Login or Register.

Notification

Icon
Error

Login


2 Pages12>
Options
View
Go to last post Go to first unread
aos  
#1 Posted : Saturday, January 12, 2013 6:41:20 AM(UTC)
aos

Rank: Member

Groups: Member
Joined: 12/11/2012(UTC)
Posts: 18
Canada

I am getting DC offset on the output of Ventus EZ - both left and right. Currently only one channel's Ventus has connected input but both of them are showing large output offset. The one that is connected to Ivy 3 balanced out shows about 240mV while the other with nothing at input shows about 110mV. The input offset between + and - of the connected amp is around 1mV or less, and each of the inputs (+ and -) has their own individual offset to ground of about 4mV. That looks like pretty good offset to me.

I can't see why would this be happening as the output buffer is within the feedback loop and the gain is 1. The schematics is textbook balanced amp with equal impedance visible on both inputs. Both of my Ventuses are showing offset, whether connected to input or not, so it doesn't seem like I made a soldering error (there are barely any parts anyway).

Any ideas?

(I saw the 4 month old thread but there was no solution offered in there).
aos  
#2 Posted : Saturday, January 12, 2013 7:46:34 AM(UTC)
aos

Rank: Member

Groups: Member
Joined: 12/11/2012(UTC)
Posts: 18
Canada

Looking between Ivy 3 balanced outputs with an oscilloscope, I get 15-20mV pp 1.4MHz sine and a superimposed 66MHz 10mV pp sine. Both connected and unconnected Ventus EZ's have about 100mV p-p signal which is again combination of two or more sines and the dominant component is at 66MHz. Hard to say how much of this is my crappy measuring technique and probe and how much is actual HF noise. I guess the Ventuses might be oscillating, not sure why though.
aos  
#3 Posted : Sunday, January 13, 2013 7:09:32 AM(UTC)
aos

Rank: Member

Groups: Member
Joined: 12/11/2012(UTC)
Posts: 18
Canada

Ventus is definitely oscillating, I pulled one out of the box and connected it to my lab power supply. It is oscillating at around 69MHz producing about 120mV peak to peak pure sine at the output.
aos  
#4 Posted : Sunday, January 13, 2013 10:27:04 AM(UTC)
aos

Rank: Member

Groups: Member
Joined: 12/11/2012(UTC)
Posts: 18
Canada

I have a solution. Remove the CC1 capacitor. That stops the oscillation and gets rid of the DC offset. This capacitor isn't needed, the amp is compensated by CC2/CC3.
Russ White  
#5 Posted : Monday, January 14, 2013 1:32:01 AM(UTC)
Russ White

Rank: Administration

Groups: Administration, Customer
Joined: 10/24/2006(UTC)
Posts: 3,979
Location: Nashville, TN

Thanks: 25 times
Was thanked: 89 time(s) in 83 post(s)
Yes, CC1 cap is not intended for every config, and in some cases it can (and should) be ommited - it is there for those who wish to experiment.
aos  
#6 Posted : Tuesday, January 15, 2013 6:09:49 AM(UTC)
aos

Rank: Member

Groups: Member
Joined: 12/11/2012(UTC)
Posts: 18
Canada

It would probably be a good idea to remove the capacitor from the kit entirely or at least provide a note with it (or at least on website), especially since there is no manual for Ventus EZ.

It appears CC1 is only needed if the opamp is faster than the buffer but the LME49600 is extremely fast, never mind that it is configured for full bandwidth in Ventus. A lot of people won't be able to realize what is happening - I didn't either until I started reading datasheets, using the 'scope and started desoldering various stuff.
Russ White  
#7 Posted : Tuesday, January 15, 2013 12:55:40 PM(UTC)
Russ White

Rank: Administration

Groups: Administration, Customer
Joined: 10/24/2006(UTC)
Posts: 3,979
Location: Nashville, TN

Thanks: 25 times
Was thanked: 89 time(s) in 83 post(s)
It is there to form another pole for compensation. Remember that the kit can be configured a number of ways and with a number of different op-amps. That cap is required in some cases - but as you see, not in all. :)

I will make to mention it in the manual. That should be sufficient.
Russ White  
#8 Posted : Tuesday, January 15, 2013 1:04:54 PM(UTC)
Russ White

Rank: Administration

Groups: Administration, Customer
Joined: 10/24/2006(UTC)
Posts: 3,979
Location: Nashville, TN

Thanks: 25 times
Was thanked: 89 time(s) in 83 post(s)
What it really comes down to is if/how the op-amp is internally compensated.

If you use a non-unity gain stable op-amp l(OPA637, OPA228 come to mind...) you will very likely need it - but the value will vary. :)

The position and the value are carry-overs from the original Ventus. They likely need to be tweaked depending on the parts used, gain, etc... Lots of variables.

Edited by user Tuesday, January 15, 2013 1:07:02 PM(UTC)  | Reason: Not specified

Jordo  
#9 Posted : Wednesday, April 3, 2013 9:14:55 AM(UTC)
Jordo

Rank: Member

Groups: Member
Joined: 12/7/2011(UTC)
Posts: 474
Location: Amsterdam

Thanks: 31 times
Was thanked: 4 time(s) in 3 post(s)
Hi all,

I'm still coping with a Left Right channel problem trough my Headphones.
Left is louder than Right.
If I mute the Left channel only the right channel can be heard trought the right speaker. So far so good.
If I mute the Right channel I can hear from what I believe is a mono signal but trough both speakers (left louder than right speaker though).

I have a Dual Mono BIII IVYIII setup.
Do you think this can occur due to the CC1?

Thx,

Jordo
Brian Donegan  
#10 Posted : Wednesday, April 3, 2013 3:01:43 PM(UTC)
Brian Donegan

Rank: Administration

Groups: Administration, Customer
Joined: 10/24/2006(UTC)
Posts: 2,868
Location: Massachusetts, USA

Thanks: 2 times
Was thanked: 141 time(s) in 134 post(s)
Originally Posted by: Jordo Go to Quoted Post
Hi all,

I'm still coping with a Left Right channel problem trough my Headphones.
Left is louder than Right.
If I mute the Left channel only the right channel can be heard trought the right speaker. So far so good.
If I mute the Right channel I can hear from what I believe is a mono signal but trough both speakers (left louder than right speaker though).

I have a Dual Mono BIII IVYIII setup.
Do you think this can occur due to the CC1?

Thx,

Jordo


I am guessing it's related to a configuration problem with either the Left channel DAC, or the wiring between the modules.
Jordo  
#11 Posted : Wednesday, April 3, 2013 3:40:34 PM(UTC)
Jordo

Rank: Member

Groups: Member
Joined: 12/7/2011(UTC)
Posts: 474
Location: Amsterdam

Thanks: 31 times
Was thanked: 4 time(s) in 3 post(s)
Hi Brian,

I have checked it over and over again.
I draw the signal lines for the Ventus directly from the same output as for the balance XLR outputs.

Here I have a Hookup Sceme.
The black grounding wires on the Jack should be on terminal 'T' i.s.o. 'S'

Edited by user Wednesday, April 3, 2013 3:42:38 PM(UTC)  | Reason: Not specified

Jordo attached the following image(s):
hookup sceme.png (253kb) downloaded 34 time(s).

You cannot view/download attachments. Try to login or register.
Brian Donegan  
#12 Posted : Wednesday, April 3, 2013 6:40:06 PM(UTC)
Brian Donegan

Rank: Administration

Groups: Administration, Customer
Joined: 10/24/2006(UTC)
Posts: 2,868
Location: Massachusetts, USA

Thanks: 2 times
Was thanked: 141 time(s) in 134 post(s)
What is the make/model of your headphone jack?
Jordo  
#13 Posted : Wednesday, April 3, 2013 7:34:18 PM(UTC)
Jordo

Rank: Member

Groups: Member
Joined: 12/7/2011(UTC)
Posts: 474
Location: Amsterdam

Thanks: 31 times
Was thanked: 4 time(s) in 3 post(s)
It's a Neutrik.
It's the NJ5FD-V 2x switching normalling stereo to be exact.
I removed Poles Tn and Rn while troubleshooring this problem so it can be considered as a NJ3FD-V Non switching Stereo model.

http://www.neutrik.com/e...4-vertical-jacks/nj3fd-v

Thx!

Jordo


Brian Donegan  
#14 Posted : Wednesday, April 3, 2013 8:29:30 PM(UTC)
Brian Donegan

Rank: Administration

Groups: Administration, Customer
Joined: 10/24/2006(UTC)
Posts: 2,868
Location: Massachusetts, USA

Thanks: 2 times
Was thanked: 141 time(s) in 134 post(s)
Originally Posted by: Jordo Go to Quoted Post
The black grounding wires on the Jack should be on terminal 'T' i.s.o. 'S'


I think the diagram in the picture is correct. Grounds to S, signals to R and T.

Jordo  
#15 Posted : Wednesday, April 3, 2013 8:37:10 PM(UTC)
Jordo

Rank: Member

Groups: Member
Joined: 12/7/2011(UTC)
Posts: 474
Location: Amsterdam

Thanks: 31 times
Was thanked: 4 time(s) in 3 post(s)
Yes you are correct.
I remembered there was a fault in the scematic but I already seem to corrected it.
The picture asside is contra. That was confusing me earlier too.

S is the Sleeve. That is how it's wired up.

So if everything is correct in theory and CC1 does not have to be removed for my setup... Wat is going wrong here than?
I must mention that if I connect the LH channel without the RH, all is good. (LH channel trough the LH channel and dimmable)
If I do the same with the RH channel all the same for the RH channel.
But together seems to be a problem.

The only thing the two channels share is the ground at 'S'....

Thx,

Jordo
Brian Donegan  
#16 Posted : Thursday, April 4, 2013 6:48:24 PM(UTC)
Brian Donegan

Rank: Administration

Groups: Administration, Customer
Joined: 10/24/2006(UTC)
Posts: 2,868
Location: Massachusetts, USA

Thanks: 2 times
Was thanked: 141 time(s) in 134 post(s)
Can you disconnect both R and L from the headphone jack, then measure continuity between T and R on the jack, with and without the headphone plug inserted.
Russ White  
#17 Posted : Thursday, April 4, 2013 11:21:07 PM(UTC)
Russ White

Rank: Administration

Groups: Administration, Customer
Joined: 10/24/2006(UTC)
Posts: 3,979
Location: Nashville, TN

Thanks: 25 times
Was thanked: 89 time(s) in 83 post(s)
I would omit CC1
Jordo  
#18 Posted : Friday, April 5, 2013 2:18:31 PM(UTC)
Jordo

Rank: Member

Groups: Member
Joined: 12/7/2011(UTC)
Posts: 474
Location: Amsterdam

Thanks: 31 times
Was thanked: 4 time(s) in 3 post(s)
If I meassure between "T" and "R", so only with the grounds connected to both boards, I read an infinite resistance.
With the headphones connected (Plug inserted in the Jack) I read about 39 Ohm.

The headphone itself is 75 Ohm if I meassure L and R on the Plug of the headphone.

Also with the grounds disconnected (so the Jack completeley disconnected) I get the same readings. Infinate and 39 Ohm.

All the units (LH + RH Ventus, LH + RH IVY, LH+RH Placid HDBP and HD etc) are interconnected trough ground.

I will cut the CC1 out if you say so Russ.
I also do not have CC2 and CC3 installed.

Many thanks to both!

Jordo
Jordo  
#19 Posted : Sunday, April 7, 2013 9:54:04 AM(UTC)
Jordo

Rank: Member

Groups: Member
Joined: 12/7/2011(UTC)
Posts: 474
Location: Amsterdam

Thanks: 31 times
Was thanked: 4 time(s) in 3 post(s)
Russ, Brian,

I think I might have found wat was causing this behaviour.
Somehow I misinterpreted the connections on the Jack.

Last night when I was taking a good (fresh) look again at the contacts of the Jack I noticed that S and R must have been cross connected. So The RH channel was connected with the ground of th headphone.
I cannot see why I missed this over and over again.
This also might explain the 38 ohm between the channels. The resistance between the both channels should be 75 ohm and that is equals approximately two times 38 ;)

I do have CC1,2 and 3 omited from the boards. Still ok?

For now I do not have my amplifier in operation due to the Teleporter modification.
As soon it will be ready to test (with good results I hope) you will be informed.

Thx,

Jordo
Brian Donegan  
#20 Posted : Monday, April 8, 2013 4:10:20 PM(UTC)
Brian Donegan

Rank: Administration

Groups: Administration, Customer
Joined: 10/24/2006(UTC)
Posts: 2,868
Location: Massachusetts, USA

Thanks: 2 times
Was thanked: 141 time(s) in 134 post(s)
I think you do want CC2 and CC3 installed.
Rss Feed  Atom Feed
Users browsing this topic
GuestUser (2)
2 Pages12>
Forum Jump  
You cannot post new topics in this forum.
You cannot reply to topics in this forum.
You cannot delete your posts in this forum.
You cannot edit your posts in this forum.
You cannot create polls in this forum.
You cannot vote in polls in this forum.