RMI-FC100, a single stage audio power amplifier - Page 86 - diyAudio
Go Back   Home > Forums > Amplifiers > Solid State

Solid State Talk all about solid state amplification.

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 10th July 2009, 10:49 PM   #851
Sheldon is offline Sheldon  United States
diyAudio Member
 
Join Date: Dec 2003
Location: San Diego
Right Channel:

I'm done with this baby. Listening only now. Next version will be layed out a little better, but this one is fairly compact and sounds very good.
Attached Images
File Type: png right thd.png (8.5 KB, 849 views)
  Reply With Quote
Old 10th July 2009, 11:18 PM   #852
Salas is offline Salas  Greece
diyAudio Chief Moderator
 
Salas's Avatar
 
Join Date: Oct 2002
Location: Athens-Greece
Are those field induced hum spikes on the left channel? Is there some more proximity to something than to the right channel?
I have seen in my projects that the strongest emission point with toroidals is the secondary exit points. Try to rotate if you have some slack while measuring and see if something changes. The different level and front to back distance of toroid mounting can be giving some more filed to one side in a different manner than to the other?
Attached Images
File Type: jpg fc100int.jpg (56.6 KB, 876 views)
  Reply With Quote
Old 10th July 2009, 11:36 PM   #853
Sheldon is offline Sheldon  United States
diyAudio Member
 
Join Date: Dec 2003
Location: San Diego
Quote:
Originally posted by Salas
Are those field induced hum spikes on the left channel? Is there some more proximity to something than to the right channel?
The two channels are layed out exactly the same. Just one is inverted relative to the other when assembled so that I could make the case a little narrower.

Ignore the Left/Right designation on the graph. The signal is the white trace. The green trace is just the card loop back. Left channel is the first post, right is the second. This shows noise at -90dB, but it's actually lower, as I have to limit the input to the card. As measured on the scope, it's over 105dB down.

Sheldon

Edit 3: I see that you have outlined the exits for the front end secondaries. Next time I open it up, I'll rotate the transformer some and see if anything changes.
  Reply With Quote
Old 10th July 2009, 11:43 PM   #854
Salas is offline Salas  Greece
diyAudio Chief Moderator
 
Salas's Avatar
 
Join Date: Oct 2002
Location: Athens-Greece
Aha. So its a common thing between channels. So your 0dB level isn't calibrated against 1V. What is the Voltage level of the signal spike on the graph? Of course SNR will go up with more output voltage delivery, but the noise floor level is the standard bottom. Try the rotations IMHO. If you improve it enough the amp will sound softer, deeper in 3D and more resolving. It seems adequately low, but its a gremlin. That comb extending far high is eating away resolution. Got to listen unmistakeably finer each time I have eliminated a not so obvious such problem. Its worth the chase. Beautiful aesthetics and construction BTW. Congratulations!
  Reply With Quote
Old 10th July 2009, 11:55 PM   #855
Sheldon is offline Sheldon  United States
diyAudio Member
 
Join Date: Dec 2003
Location: San Diego
Quote:
Originally posted by Salas
Aha. So its a common thing between channels. So your 0dB level isn't calibrated against 1V. What is the Voltage level of the signal spike on the graph? Of course SNR will go up with more output voltage delivery, but the noise floor level is the standard bottom. Try the rotations IMHO. If you improve it enough the amp will sound softer, deeper in 3D and more resolving. It seems adequately low, but its a gremlin. That comb extending far high is eating away resolution. Got to listen unmistakeably finer each time I have eliminated a not so obvious such problem. Its worth the chase. Beautiful aesthetics and construction BTW. Congratulations!
Signal level is about 200mV. Not sure that some of the noise isn't in my measuring system. I have a little preamp that I need to fix, then repeat the measurements.

Thanks for the compliment. I have a bad habit of trying to stuff too much into to little space. Might get away with that better with Mihai's R-cores.

Sheldon
  Reply With Quote
Old 10th July 2009, 11:58 PM   #856
Salas is offline Salas  Greece
diyAudio Chief Moderator
 
Salas's Avatar
 
Join Date: Oct 2002
Location: Athens-Greece
I have this habit too... In my KT-88 I got rid of such stuff by using copper foil around the toroid, and grounded it. It may well be your driving electronics, of course. What I do is I use a 1:10 attenuator and I run the card at 1V RMS out through it. So it picks up some SNR and then drive the amp at 1W/2.83V at 8R. At about 100mV in, they normally hit the 1W if around 30dB gain. Also the output attn brings down computer psu wideband noise that rides the card's signal in many cases. That way I avoid preamp and I am not afraid of burning the dummy by mistake on output level. If you calibrate the card with a DVM, it will follow exactly what you type in as level. Use ARTA. Its free and has a detailed calibration menu, among other excellent stuff.
  Reply With Quote
Old 11th July 2009, 12:11 AM   #857
Sheldon is offline Sheldon  United States
diyAudio Member
 
Join Date: Dec 2003
Location: San Diego
I didn't use the preamp on this test, just the card out, and attenuated the input. But I've had problems in the past with it. The pre, is just a little battery powered op amp, so I can feed it the full signal and have a nice low output impedance. Maybe I'll give ARTA a try, if I find the time to figure it out.

Sheldon
  Reply With Quote
Old 11th July 2009, 12:24 AM   #858
Salas is offline Salas  Greece
diyAudio Chief Moderator
 
Salas's Avatar
 
Join Date: Oct 2002
Location: Athens-Greece
Yes. Happy listening meantime. Great speaker you got there! Keep us posted if you nail the gremlin.
  Reply With Quote
Old 11th July 2009, 06:12 PM   #859
Sheldon is offline Sheldon  United States
diyAudio Member
 
Join Date: Dec 2003
Location: San Diego
Quote:
Originally posted by Salas
Are those field induced hum spikes on the left channel? Is there some more proximity to something than to the right channel?
Pooge and Salas. Looks like the gremlins are indeed field induced from the transformer. It's not the wiring, per se, as I can push the wires around with no change in the hum/buzz. But surprisingly small changes in transformer orientation make a big difference. So, going to have to experiment, but it appears I can get rid of this background, even in this cramped chassis.

Sheldon
  Reply With Quote
Old 11th July 2009, 06:26 PM   #860
Salas is offline Salas  Greece
diyAudio Chief Moderator
 
Salas's Avatar
 
Join Date: Oct 2002
Location: Athens-Greece
  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
Single stage amplifier Skorpio Pass Labs 33 5th January 2011 03:03 AM
RMI-FC100 MKII, single ended folded cascode VAS roender Solid State 27 9th July 2010 11:56 PM
single stage common-drain amplifier Music_Sg Solid State 4 4th July 2006 06:45 PM


New To Site? Need Help?

All times are GMT. The time now is 11:02 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