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 » Jürgen Haible designs
Triple Chorus EQ section dead.
Post new topic   Reply to topic Moderators: Scott Stites
Page 1 of 1 [3 Posts]
View unread posts
View new posts in the last week
Mark the topic unread :: View previous topic :: View next topic
Author Message
LektroiD



Joined: Aug 23, 2008
Posts: 993
Location: Scottish Borders
Audio files: 2
G2 patch files: 2

PostPosted: Mon Jan 25, 2016 6:43 am    Post subject: Triple Chorus EQ section dead.
Subject description: Random Source NoS board
Reply with quote  Mark this post and the followings unread

I managed to get my hands on a NoS Triple Chorus from Random Source stock. Built, but with a dead EQ section:

1) EQ section is completely dead (no sound whatsoever when EQ mode selected). I used a rotary switch and verified connections many times.

2) Both chorus settings work, but sound exactly the same (linear & solina). Possibly due to a faulty EQ?

3) Opamp under the Mid EQ level socket is ridiculously hot. It is not possible to leave your finger on for more than 1 second (unless wearing asbestos gloves).

I have tested voltages going to these, but appears to be negative voltages (-V), rather than +V.

I have swapped out the hot chip and replaced, the new one also gets extremely hot very fast (you can't touch it for long with your finger).

Anyone have any ideas what might be wrong? I have gone over this circuit many, many, many times, but can't see anything out of place. repeatedly checked polarity of the electrolytic capacitors.

If someone has a built one, would it be possible to check their supply voltages to the chips around the EQ section? Also put their finger on the 1458 IC (below the Mid EQ level socket), and see if it is also burning hot...

Many thanks in advance

_________________
My tunes available here
(check out the new Electro-Funk LP)
Back to top
View user's profile Send private message Visit poster's website
mc_binc



Joined: Jul 15, 2007
Posts: 1
Location: cambridge, ma

PostPosted: Sun Jan 31, 2016 8:53 pm    Post subject: Re: Triple Chorus EQ section dead.
Subject description: Random Source NoS board
Reply with quote  Mark this post and the followings unread

Have the board but haven't built it so take this for what it's worth...

JH designed this to run on -15/0V so the negative voltages may be correct.

EQ circuit is not involved in linear/solina modes under normal operations.

The voltage ref scheme (v3, v4) is... okay... if things are functioning. If not, failure in one area may perturb others via coupling in the reference points.

The Low/Mid/Hi EQ circuits are all identical, just different component values. What is shared is a gain/buffer amp which feeds the three EQ pieces. This happens to also be the Mid EQ IC. Best guess is a component or short in the vicinity of U3 but could also be U4.

With the IC making heat, the R77/10ohm resistor should be burning up. Look for heat/damage here as well.
Back to top
View user's profile Send private message
LektroiD



Joined: Aug 23, 2008
Posts: 993
Location: Scottish Borders
Audio files: 2
G2 patch files: 2

PostPosted: Mon Feb 01, 2016 12:44 am    Post subject: Reply with quote  Mark this post and the followings unread

HI, thanks for your reply. It is now fixed... Firstly the TL071 was causing the mid EQ opamp to overheat, replaced the 071 and the mid 1458, and now the EQ section working as expected.

Still no audible change between Solina and Linear though.

_________________
My tunes available here
(check out the new Electro-Funk LP)
Back to top
View user's profile Send private message Visit poster's website
Display posts from previous:   
Post new topic   Reply to topic Moderators: Scott Stites
Page 1 of 1 [3 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 » Jürgen Haible designs
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