NEW  Matt presents bias and operation data for the 6V6 tube in SE operation - 6V6 Single-Ended (SE) Ultra Linear (UL) Bias Optimization.

DIY Audio Projects Forum

Welcome to the DIY Audio Projects Message Forum. Use these forums to discuss Hi-Fi audio and to share your DIY Audio Projects. Registration is free and required to post messages and view the file attachments. Registration will only take a minute and registered users do not see any advertisements. After you have completed the online registration process, check your email (including spam/junk folder) for the verification email to activate your account. New members are under moderation - so your posts will not be visible until approved by a moderator. See the Read Me 1st, Forum RULES and Forum FAQ to get started on the forum.

 It is currently 24 Oct 2020, 16:04

 All times are UTC - 6 hours [ DST ]

 Page 1 of 1 [ 5 posts ]
 Print view Previous topic | Next topic
Author Message
 Post subject: LM3886 example circuit questionPosted: 30 Nov 2010, 21:12

Joined: 28 Oct 2010, 00:11
Posts: 26
In the LM3886 circuit diagram below Cs connected to V- shows + on the ground side.
I'm a bit confused by this? Perhaps it's because I'm a tad confused
by V+ and V- to begin with. I did manage to build the power supply
circuit and it's showing about 57v DC between V+ and V- from an EI
transformer that's putting out 20v - 0 - 20v. Can someone describe what's
actually going on here?

http://diyaudioprojects.com/Chip/LM3886 ... 886_CA.htm

Top

 Post subject: Re: LM3886 example circuit questionPosted: 30 Nov 2010, 22:43

Joined: 24 Jun 2010, 00:48
Posts: 788
Location: Christchurch, NZ
Hi,

The connection is correct. The negative (-) supply is connected to the negative leg of Cs. If you reverse the polarity, you'll get a blown cap.

V+ and V- is a dual supply which means that half the voltage is measured when referenced to ground. Using your voltmeter under Volts reading, connect the negative probe to the ground, and positive probe to V+. You should read (57/2 = 28.5V DC).

Similarly, connect the positive voltmeter probe to the ground, and negative probe to V-. You should get 28.5V DC.

The advantage of dual power supply is that in most cases, no output capacitor is needed (as can be seen from the diagram). This can be a blessing and a curse, as if the chip fails and DC is present on the output, the speakers will be fried.

_________________
Kind Regards,
Dinesh

Some of my diy audio projects:

Top

 Post subject: Re: LM3886 example circuit questionPosted: 01 Dec 2010, 18:32

Joined: 28 Oct 2010, 00:11
Posts: 26
Thanks for the response.

I went out and double checked my pre rectified AC and post rectified DC readings.

From the EI transformer I'm seeing 39.4v between the two outer taps
and 19.7v between either of the outer taps and the center tap.

Taking readings from the taps to ground I get
Right tap: 23v, Center tap: 14.7v, Left tap: 6v.
Not sure if those values are worthwhile at all.

When I move to the rectified DC output I see 52v between V+ and V-
If I measure between V+ and ground I see 19.1v, V- and ground
shows -19.1v.

There's roughly 7v missing if I should be seeing 26v between V+ and ground.

Note that between the transformer and the DC circuit, I connected the
left and right taps to the bridge rectifier as shown. I wasn't exactly
sure what to do with the center tap as it's not exactly shown in the
diagram, so I connected it directly to the chassis ground, which is
connected to the ground pin on my mains plug.

Any suggestions on where my 7v has gone? Could the chassis/ground
be floating at 7v hence accounting for the differential when measuring V+
against ground?

Top

 Post subject: Re: LM3886 example circuit questionPosted: 01 Dec 2010, 22:18

Joined: 24 Jun 2010, 00:48
Posts: 788
Location: Christchurch, NZ
skatefriday wrote:
Taking readings from the taps to ground I get
Right tap: 23v, Center tap: 14.7v, Left tap: 6v.
Not sure if those values are worthwhile at all.

Something isin't right. Do not proceed yet, could be risky.
Can you post a picture?

_________________
Kind Regards,
Dinesh

Some of my diy audio projects:

Top

 Post subject: Re: LM3886 example circuit questionPosted: 02 Dec 2010, 13:34
 Editor

Joined: 28 May 2008, 21:53
Posts: 4591
Yes, something is wrong. Also, before hooking up these sorts of amplifiers to speakers make sure to check that the DC offset.
Cheers

_________________

Top

 Display posts from previous: All posts1 day7 days2 weeks1 month3 months6 months1 year Sort by AuthorPost timeSubject AscendingDescending
 Page 1 of 1 [ 5 posts ]

 All times are UTC - 6 hours [ DST ]

Who is online

Users browsing this forum: No registered users and 13 guests

 You cannot post new topics in this forumYou cannot reply to topics in this forumYou cannot edit your posts in this forumYou cannot delete your posts in this forumYou cannot post attachments in this forum

 Jump to:  Select a forum ------------------ DIY Forums    Vacuum Tubes / Thermionic Valves    Solid State / Op-Amps / Chip Amps / Class-D    Speakers, Subwoofers and Headphones    Audio Sources and Signal Processing    Audio Cables and Power Cords    DIY Radio    DIY Electronics and Components    Chassis, Wood/Metalworking and Tools Hi-Fi and Audiophile Forums    Hi-Fi Equipment and Audiophile Talk    Audiophile Music and Audio Rooms    For Sale / Wanted / Group Buys    Off-topic and Introductions    Site Updates, News and Announcements