Tube preamp huge DC thump! - Page 2 - diyAudio
Go Back   Home > Forums > Amplifiers > Tubes / Valves

Tubes / Valves All about our sweet vacuum tubes :) Threads about Musical Instrument Amps of all kinds should be in the Instruments & Amps forum

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 24th March 2004, 06:44 AM   #11
diyAudio Member
 
Andypairo's Avatar
 
Join Date: Sep 2002
Location: near Milano , Italy
Yesterday I tried replacing the "NP" caps with film types, 10 uF MKT, but things didn't change.

What else could cause this?

Remember that this problem hasn't always been there so there must be something wrong!

On the suspect list I had the el-cheapo volume pot, really small, but, apart from a bad tracking at low volumes, it doesn't show other problems...

Please help me...

Cheers

Andrea
  Reply With Quote
Old 3rd January 2014, 12:22 AM   #12
Cassiel is offline Cassiel  Libya
diyAudio Member
 
Cassiel's Avatar
 
Join Date: Sep 2004
Location: Madrid
Hi, I have this same problem. What's the cause of this? Can anybody guess? Six seconds after turn on it appears this DC 'surge' (around 1.5VDC) on my preamp outputs. It suddenly goes up and then disappears and it also happens when I turn it off. It's an Aikido preamp.

I did find out when I connected it to a chip amp with no input caps and now my speakers have departed (oh I'm not sure) to a better world. I also have a F5, can this surge kill speakers with that amp too? I'm running out of speakers.
__________________
Hobby-Horse
  Reply With Quote
Old 3rd January 2014, 12:49 AM   #13
cjkpkg is offline cjkpkg  United States
diyAudio Member
 
Join Date: Aug 2008
Location: Roswell GA
Quote:
Originally Posted by Cassiel View Post
Hi, I have this same problem. What's the cause of this? Can anybody guess? Six seconds after turn on it appears this DC 'surge' (around 1.5VDC) on my preamp outputs. It suddenly goes up and then disappears and it also happens when I turn it off. It's an Aikido preamp.

I did find out when I connected it to a chip amp with no input caps and now my speakers have departed (oh I'm not sure) to a better world. I also have a F5, can this surge kill speakers with that amp too? I'm running out of speakers.
Yes it will...

My 2 aikido amps do the same thing. Well at least one of them do...the reason I say that is that I recently changed the psu to one of them to a tube regulated circuit. I have not tested the behavior since. I have gotten in the habit of always turning on the aikido a few seconds before the power amp.

But I think a lot of it had to do with the b+ being solid state so the plates were getting hit with a good dose of DC before the heaters were fully doing their job. Even with good quality coupling caps some DC was making it to the power amp and eventually to the speakers.
  Reply With Quote
Old 3rd January 2014, 02:03 AM   #14
Cassiel is offline Cassiel  Libya
diyAudio Member
 
Cassiel's Avatar
 
Join Date: Sep 2004
Location: Madrid
Thanks for letting me know.

Quote:
I have gotten in the habit of always turning on the aikido a few seconds before the power amp.
Yeah, that solves the problem but it's still a big risk. One mistake and goodbye speakers. My dead speakers were mini monitors, computer speakers, they sounded pretty good and I'm kinda sad but when I think it could have happened to some other speakers (7.000 euros out of the window ) I feel kinda happy about my bad/good luck.

I don't know, a relay circuit maybe, I really don't want to do that though. My power supply is SS and I don't want to change that either. I can't believe this is normal behavior in the Aikido preamp.
__________________
Hobby-Horse
  Reply With Quote
Old 3rd January 2014, 02:11 AM   #15
cjkpkg is offline cjkpkg  United States
diyAudio Member
 
Join Date: Aug 2008
Location: Roswell GA
I have relay protection on a SS amp I use and the relay opens with more than 5vdc IIRC...the aikido will trip the relay on a cold start. I am running 1uF bypassed by 0.33uF Russian pio.

I will have to measure the dc sometime.
  Reply With Quote
Old 3rd January 2014, 02:38 AM   #16
Cassiel is offline Cassiel  Libya
diyAudio Member
 
Cassiel's Avatar
 
Join Date: Sep 2004
Location: Madrid
Mine is a 2uF cap. I have just checked again and with nothing connected, no inputs and outputs, it goes up to 15VDC. Whoa. Could I be getting false readings? I have used this preamp with headphones, and they're still alive. It is always after six seconds, always on time. Swiss precision.
__________________
Hobby-Horse
  Reply With Quote
Old 3rd January 2014, 09:59 AM   #17
DF96 is offline DF96  England
diyAudio Member
 
Join Date: May 2007
All circuits have switch-on and switch-off transients. The modern obsession with LF response down to earthquake-like frequencies makes things worse as the large coupling caps take a while to charge up. Many modern circuits have a lower LF point than the PSU which feeds them so they amplify any DC shifts.

Two solutions:
1. design the circuit to have a sensible LF rolloff i.e. smaller coupling caps.
2. have a reliable mute circuit.
  Reply With Quote
Old 3rd January 2014, 10:32 AM   #18
diyAudio Member
 
Join Date: Nov 2002
This thread has been around for years and people have been having the same problem when trying to use a tube linestage or preamp with a SS amplifier. When you turn on the tube line stage or preamp it has to have time to become stable and once it has THEN turn on your SS amplifier and there will be no thump. Before the tubes warm up it is normal to get some type of voltage ramp in my experience.

You have your choice...either wait before turning on your SS power amp or re-work the delay time on your SS amplifier relay circuit or the possibility of adding caps in the circuit to block the DC which is probably present upon turn on from your tube preamp/linestage.
  Reply With Quote
Old 3rd January 2014, 02:04 PM   #19
cjkpkg is offline cjkpkg  United States
diyAudio Member
 
Join Date: Aug 2008
Location: Roswell GA
I am using these on my SS amp with the Aikido and they work great - even when powered with DC.

Click the image to open in full size.
Click the image to open in full size.
  Reply With Quote
Old 3rd January 2014, 02:28 PM   #20
wicked1 is offline wicked1  United States
diyAudio Member
 
wicked1's Avatar
 
Join Date: Jan 2008
Location: Midwest
I recently hooked my aikidi pre up to a powerful amp, and notice something similar.. when I get a spike on my mains (heater turning on somewhere in the house, etc), the output of the aikido gets a large slowly alternating voltage that moves my speaker cones all the way in and out. Never noticed it on less powerful amps, but it could definitely damage my speakers w/ this amp!

I haven't started looking in to it yet.. My first guess is the ps noise injecting cap.. I'll make it a lot smaller. I'll start a new thread when I dig in, but I'm glad to hear I'm not the only one w/ odd aikido issues.
  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
need diy tube preamp (line-stage) recommendation and general tube advice Musiclover4 Tubes / Valves 16 18th May 2013 03:19 PM
FA: Eico HF-85 Tube Preamp & HFT-90 Tube Tuner joe-electro Swap Meet 0 31st May 2009 04:14 PM
switch on/off preamp thump ljk11 Everything Else 0 6th January 2009 10:48 AM
Tube Preamp Popping on Source Input Change (?) / 6DJ8 Preamp On Chip Amps MartyM Tubes / Valves 3 16th October 2008 04:52 AM
tube preamp using submini tube unclejed613 Tubes / Valves 11 19th August 2007 07:14 PM


New To Site? Need Help?

All times are GMT. The time now is 03:20 AM.


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