electro-music.com   Dedicated to experimental electro-acoustic
and electronic music
 
    Front Page  |  Articles  |  Radio
 |  Media  |  Forum  |  Wiki  |  Links  |  Store
Forum with support of Syndicator RSS
 FAQFAQ   CalendarCalendar   SearchSearch   MemberlistMemberlist   UsergroupsUsergroups   LinksLinks
 RegisterRegister   ProfileProfile   Log in to check your private messagesLog in to check your private messages   Log inLog in  Chat RoomChat Room 
Live streaming at radio.electro-music.com

  host / artist show at your time

poster

Please visit the chat
 Forum index » DIY Hardware and Software » MusicFromOuterSpace.com designs by Ray Wilson
Debugging MFOS panning mixer…
Post new topic   Reply to topic Moderators: dnny, Uncle Krunkus, v-un-v
Page 1 of 1 [12 Posts]
View unread posts
View new posts in the last week
Mark the topic unread :: View previous topic :: View next topic
Author Message
hedefalk



Joined: Aug 29, 2017
Posts: 49
Location: Stockholm, Sweden

PostPosted: Thu Sep 28, 2017 7:36 am    Post subject: Debugging MFOS panning mixer… Reply with quote  Mark this post and the followings unread

Newb alert here.

I'm just starting out building my diy eurorack thingie.

Second module I'm building is a simplified version of Ray Wilson's panning mixer. I've just taken two channels and stripped the entire FX bus. That leaves me with just 4 TL07 opamps and two 386n-4's so I figured I would just use a TL074CN as opposed to using 4 TL071's as schematic says. So first question, is this a bad idea in any way? Leakage?

Second question, is there something that I'm missing in believing I could just strip it to use only the circled parts here in the schematic:


After breadboarding it half decently I built it on a breadboard-like proto board and I'm currently debugging it. Seems like first stage buffers are fine but something weird happens with the signal at the pan stage (pans seems to not work correctly)

I've checked everything I can think of offline with a digital meter and I'm currently debugging with a cheap scope hooked up, but I'm really out of ideas what to check for.

Any pointers are highly appreciated, like a standard checklist to go through or anything…

…while writing this, I was gonna do list of my observations and doing that I found that there's most likely just something wrong with the pan pots and I had turned the panel wiring for the main phones level the wrong way.

Ok, having fixed the phones level I now just have to fix the pan's. I guess I have a little bit of distortion due to that, signal's being too strong since the grounding via pan wiper is gone, but my biggest concern is a white noise bright hizzing I have in the phones that is entirely unrelated to the turn of any pots, both input gain and also master headphone level.

I would think that this is coming from the LM386's and since the main volume pot is actually only doing something with the input signal to these power amplifiers this is probably something I'll have to live with? If I want true quietness on volume 0, then I'd have to have the pot attenuate after the last power amp too, right?


IMG_20170928_145116.jpg
 Description:
 Filesize:  1.08 MB
 Viewed:  139 Time(s)
This image has been reduced to fit the page. Click on it to enlarge.

IMG_20170928_145116.jpg



IMG_20170928_145126.jpg
 Description:
 Filesize:  1.26 MB
 Viewed:  127 Time(s)
This image has been reduced to fit the page. Click on it to enlarge.

IMG_20170928_145126.jpg



IMG_20170928_151130.jpg
 Description:
 Filesize:  2.31 MB
 Viewed:  131 Time(s)
This image has been reduced to fit the page. Click on it to enlarge.

IMG_20170928_151130.jpg


Back to top
View user's profile Send private message
hedefalk



Joined: Aug 29, 2017
Posts: 49
Location: Stockholm, Sweden

PostPosted: Fri Sep 29, 2017 3:05 am    Post subject: Reply with quote  Mark this post and the followings unread

I've googled a bit and tried adding a 10k resistor and a cap in series over output pin 5 and gain pin 8 or 1. Like here https://dmohankumar.wordpress.com/2015/03/15/reducing-hiss-in-lm-386-amplifier-design-note-12/#more-10895

This removes the hizz but replaces it with an even more pronounced humming. I think this method probably isn't applicable unless the gain pins are used, but the MFOS one leave them floating to use the internal 20 gain factor I think. I'll revisit the data sheet
Back to top
View user's profile Send private message
PHOBoS



Joined: Jan 14, 2010
Posts: 4106
Location: Moon Base
Audio files: 607

PostPosted: Fri Sep 29, 2017 7:54 am    Post subject: Reply with quote  Mark this post and the followings unread

Adding components between pin 1 & 8 increases the gain so yeah you're better of to leave them floating. You can indeed use it
for filtering and I don't think you would need to use the gain pins for it, but I'd have to check the internal structure of the chip.
What might help with the hum is adding a large capacitor (100uf or something like that) directly over the power pins, I am actually
a bit surprised it only uses 0.1uF in the schematic. Of course a regulated powersupply is also very important. I've had circuits that
work fine with a simple unregulated wallwart but others produce a lot of hum without any regulation. Personally I am not a big fan
of the LM386 especially not when used for an headphone amp. They are ok for adding a small speaker to a circuit or if you need to
boost a signal for processing that isn't audible.

_________________
"My perf, it's full of holes!"
http://phobos.000space.com/
SoundCloud BandCamp MixCloud Stickney Synthyards Captain Collider
Back to top
View user's profile Send private message Visit poster's website AIM Address Yahoo Messenger MSN Messenger
hedefalk



Joined: Aug 29, 2017
Posts: 49
Location: Stockholm, Sweden

PostPosted: Fri Sep 29, 2017 8:12 am    Post subject: Reply with quote  Mark this post and the followings unread

Thanks!

At this point I fell I'm stuck with this choice though since I don't think there are any pin compatible and I just want to finish this one quickly.

But out of curiosity, what power amp would you recommend to use instead of lm386? For my next amp build Smile

I'll try adding larger caps next to the IC. There are larger electrolyts on the power connection (isn't shown here)

However, the hum was just something I got when doing that feedback to the gain pins. I think I'll leave that idea aside.

I just read this once again: http://www.transkommunikation.ch/dateien/schaltungen/space_station_receiver/informationen/08_-_reducing_hiss_in_an_lm386_audio_amplifier.pdf

I don't really understand why this works only when using the gain pins because for me it gets really hummy.
Back to top
View user's profile Send private message
PHOBoS



Joined: Jan 14, 2010
Posts: 4106
Location: Moon Base
Audio files: 607

PostPosted: Fri Sep 29, 2017 11:48 am    Post subject: Reply with quote  Mark this post and the followings unread

You might not need the larger caps but I know the LM386 can sometimes be a bit picky about decoupling.
You're not really driving it very hard for headphones though (unless you want to go deaf) but it doesn't hurt to try.

Although it is not a poweramp, the NE5532 works really well.

_________________
"My perf, it's full of holes!"
http://phobos.000space.com/
SoundCloud BandCamp MixCloud Stickney Synthyards Captain Collider
Back to top
View user's profile Send private message Visit poster's website AIM Address Yahoo Messenger MSN Messenger
AlanP



Joined: Mar 11, 2014
Posts: 533
Location: New Zealand
Audio files: 32

PostPosted: Fri Sep 29, 2017 1:40 pm    Post subject: Reply with quote  Mark this post and the followings unread

Another option is the headphone driver in the Yusynth Output Module -- works very well. Mind the 1/2W resistors, though, where indicated.
Back to top
View user's profile Send private message
hedefalk



Joined: Aug 29, 2017
Posts: 49
Location: Stockholm, Sweden

PostPosted: Mon Oct 02, 2017 3:36 am    Post subject: Reply with quote  Mark this post and the followings unread

Thanks for all the tips!

I think for this module, I'm stuck with my choice and have tried all "band aid" things I've found:

1) Doing the feedback from output to gain:
1.1) If no connection between 1 and 8 and connecting the feedback cap+resistor to pin 8 I get a maxed out beep, maybe 5000Hz that almost killed my ears a few times.
1.2) Connecting to pin 1 I instead get a hum that is more pronounced than the original hizz.

2) No decoupling caps seem to make any difference at all for this hiss - it doesn't seem to be related to power flucts.

3) Modding my circuit to actually use something like a 1k + 10mF series between pin 1 and 8 I CAN connect the feedback from output to pin 8 as suggested in places like here https://dmohankumar.wordpress.com/2015/03/15/reducing-hiss-in-lm-386-amplifier-design-note-12/#more-10895

Again though, that gives me a humming that is simply worse than original hizz.

I think I'm out of options. I have only one batch of lm386-n4's that I bought from aliexpress and I'm thinking maybe they're a bit defective or something. I have tried a few. I have a few standar lm386 (lower voltage ones) on the way and I'll try those to compare but for now I'll have to live with the hizz.
Back to top
View user's profile Send private message
hedefalk



Joined: Aug 29, 2017
Posts: 49
Location: Stockholm, Sweden

PostPosted: Mon Oct 30, 2017 12:50 am    Post subject: Reply with quote  Mark this post and the followings unread

Just an update. I got a a couple of breakoutboards with LM386's in the mail the other day so wanted to compare the noise levels. I got the same noise from just powering up and connecting my earphones. Tried different PSU's too. So I've reached the conclusion (that you guys already told me Smile ) that LM386 simply isn't a good fit for an earphone amp (at least not at these supply voltages).

In loving memory, I trusted you Ray! Smile

Seems to me that one really would need to attenuate the output of these amps too if one is to use them like this. The hiss isn't related to the input levels, but a constant even if input is grounded.


IMG_20171030_074726.jpg
 Description:
 Filesize:  2.09 MB
 Viewed:  121 Time(s)
This image has been reduced to fit the page. Click on it to enlarge.

IMG_20171030_074726.jpg


Back to top
View user's profile Send private message
hedefalk



Joined: Aug 29, 2017
Posts: 49
Location: Stockholm, Sweden

PostPosted: Wed Nov 01, 2017 6:47 am    Post subject: Reply with quote  Mark this post and the followings unread

@PHOBoS,

I've breadboarded up your NE5532 schematic and it's dead quiet with grounded input! Yey! A different league than the LM386 one.

However, it dists pretty shortly if I turn up the inputs. I'm not sure about the levels it expects and what to look for here.

So Here come some noob questions:

My intention is to actually replace the headphone amp of the MFOS mixer I already built. It has a line output part which is then also fed into the headphone circuit.

Currently I'm just breadboarding and use a signal straight from an 12V oscillator and attenuate it down on the breadboard.

So it seems to start disting when input on pin5 exceeds 1.5V PP. It's still not very loud in the headphones though…? Cheap in-ear plugs. Is this to be expected?

I was wondering about the values near the output, 22 and 4.7 ohms seems very little?


IMG_20171101_143018.jpg
 Description:
 Filesize:  1.66 MB
 Viewed:  112 Time(s)
This image has been reduced to fit the page. Click on it to enlarge.

IMG_20171101_143018.jpg


Back to top
View user's profile Send private message
hedefalk



Joined: Aug 29, 2017
Posts: 49
Location: Stockholm, Sweden

PostPosted: Fri Nov 03, 2017 1:02 am    Post subject: Reply with quote  Mark this post and the followings unread

One more update:

Got the scope running and it's not actually clipping it's just very noisy. Yellow is input and blue output.

It's also a bit offset towards positive rail


IMG_20171103_085908.jpg
 Description:
 Filesize:  1.88 MB
 Viewed:  114 Time(s)
This image has been reduced to fit the page. Click on it to enlarge.

IMG_20171103_085908.jpg


Back to top
View user's profile Send private message
hedefalk



Joined: Aug 29, 2017
Posts: 49
Location: Stockholm, Sweden

PostPosted: Fri Nov 03, 2017 2:15 am    Post subject: Reply with quote  Mark this post and the followings unread

Hm, I isolated one channel now and wiggled stuff around or something and now the scope shows a pretty clean sinus curve here, but it still sounds very bad in the earphones. Don't understand…


The blue is the output straight to the earphones, it looks good even with the earphones connected but it sounds really bad.


IMG_20171103_092413.jpg
 Description:
 Filesize:  1.97 MB
 Viewed:  137 Time(s)
This image has been reduced to fit the page. Click on it to enlarge.

IMG_20171103_092413.jpg


Back to top
View user's profile Send private message
hedefalk



Joined: Aug 29, 2017
Posts: 49
Location: Stockholm, Sweden

PostPosted: Tue Mar 20, 2018 5:23 am    Post subject: Reply with quote  Mark this post and the followings unread

Just an update:

Tried this earphone output with my old Beyer Dynamic DT-100 which is at 400 ohm. Sounds waaay better and the noise is hardly audible. I would just want to state the to some probably obvious. The LM358 is waaay to noisy for low impedance earphones, but on this one it seems like a perfect match. I have tried to use these earphones in more traditional equipment before and they sound really bad there. I guess they need a lot of power and therefore also cover up a lot of weak noise.
Back to top
View user's profile Send private message
Display posts from previous:   
Post new topic   Reply to topic Moderators: dnny, Uncle Krunkus, v-un-v
Page 1 of 1 [12 Posts]
View unread posts
View new posts in the last week
Mark the topic unread :: View previous topic :: View next topic
 Forum index » DIY Hardware and Software » MusicFromOuterSpace.com designs by Ray Wilson
Jump to:  

You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
You cannot attach files in this forum
You can download files in this forum
e-m mkii

Please support our site. If you click through and buy from
our affiliate partners, we earn a small commission.


Forum with support of Syndicator RSS
Powered by phpBB © 2001, 2005 phpBB Group
Copyright © 2003 through 2009 by electro-music.com - Conditions Of Use