Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Headphone Systems Everything to do with Headphones

Cheap as Chips OPA1688 Low-THD Muscle Amp
Cheap as Chips OPA1688 Low-THD Muscle Amp
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 2nd September 2019, 06:02 AM   #231
Buzzy is offline Buzzy  Singapore
diyAudio Member
 
Join Date: Apr 2007
What does the 2.2k resistor, R4 in schematic in post #1 do ? Is it some kind biasing for the opamp ?
  Reply With Quote
Old 2nd September 2019, 06:11 AM   #232
abraxalito is offline abraxalito  United Kingdom
diyAudio Member
 
abraxalito's Avatar
 
Join Date: Sep 2007
Location: Hangzhou - Marco Polo's 'most beautiful city'. 700yrs is a long time though...
I'm not sure, it could be an attempt to keep the impedances at the opamp inputs more or less the same. But then it shouldn't be 2k2 rather the parallel combination of 2k2 and 6k8 which is ~1k6.
__________________
I know you think you understand what you thought I said but I'm not sure you realize that what you heard is not what I meant - Alan Greenspan
  Reply With Quote
Old 3rd September 2019, 11:58 AM   #233
xrk971 is offline xrk971  United States
Got Foam?
diyAudio Member
 
xrk971's Avatar
 
Join Date: Oct 2012
Location: Metro DC area
Cheap as Chips OPA1688 Low-THD Muscle Amp
Abraxalito is correct. Make it 1k6 if you want best impedance matching. 2k2 value lets you increase gain by using larger feedback resistor.

Not shown in schematic (but as built) is a 220pF cap from the input to GND for RFI filter for combo 2k2 and 220pF for about 300kHz low pass.
__________________
XRKaudio https://www.etsy.com/shop/XRKAudio

Last edited by xrk971; 3rd September 2019 at 12:01 PM.
  Reply With Quote
Old 14th September 2019, 05:10 AM   #234
xrk971 is offline xrk971  United States
Got Foam?
diyAudio Member
 
xrk971's Avatar
 
Join Date: Oct 2012
Location: Metro DC area
Cheap as Chips OPA1688 Low-THD Muscle Amp
Testing out the 8x OPA1622 amp with an eBay dual TPS7A low noise regulator board set for +/-18.5v and an eBay +/-24v DC-DC step up. All powered from 12v Pb-acid gel cell. Source is 2ppm 1kHz Akitika oscillator, and sound card is Focusrite 2i4. Signal out of amp is adjusted to be 1.0Vpp into 51ohm dummy load. Setup is not the cleanest, so picking up some very low level -120dB 60Hz. But overall, the amp with this PSU shows a -130dB noise floor and 5.7ppm THD with dominatn H2 and about -12dB less H3 and nothing else.

Cheap as Chips OPA1688 Low-THD Muscle Amp-muscle-amp-tps7a-ldo-24v-dc-dc-1-0vpp-51ohms-44k-jpg

Cheap as Chips OPA1688 Low-THD Muscle Amp-muscle-amp-tps7a-ldo-24v-dc-dc-1-0vpp-51ohms-44k-test-setup-jpg
__________________
XRKaudio https://www.etsy.com/shop/XRKAudio
  Reply With Quote
Old 20th October 2019, 08:28 AM   #235
jfetter is offline jfetter  Costa Rica
diyAudio Member
 
jfetter's Avatar
 
Join Date: Jun 2012
Location: na
Cheap as Chips OPA1688 Low-THD Muscle Amp
Very awesome...!
  Reply With Quote
Old 20th October 2019, 09:01 AM   #236
jfetter is offline jfetter  Costa Rica
diyAudio Member
 
jfetter's Avatar
 
Join Date: Jun 2012
Location: na
Cheap as Chips OPA1688 Low-THD Muscle Amp
Quote:
Originally Posted by tomchr View Post
In a composite amplifier, you need to simulate all loops. Both any inner loops and the outer/global loop. All loops need to be stable. Finding a good point to break the loop for the stability analysis can be tricky, especially if you have multiple loops.

Tom
Tom, you are of course correct on the loop simulation but I don't have enough mortal time remaining to invest on tweaking the cad models.

So I use the 'trial and error' method combined with hunches, guesses and some nice test equipment.

Bruce

-
  Reply With Quote
Old 21st October 2019, 05:00 PM   #237
xrk971 is offline xrk971  United States
Got Foam?
diyAudio Member
 
xrk971's Avatar
 
Join Date: Oct 2012
Location: Metro DC area
Cheap as Chips OPA1688 Low-THD Muscle Amp
I’m working with Jhofland on a new Muscle Amp Lite with only 4x OPA1622 for outputs but a much improved front end topology using OPA1656’s. Will have provision for balanced input sources and even BT option. Power will be via a custom DC-DC converter with linear regulators. Looking forward to comparing it with the correct 8x rig.
__________________
XRKaudio https://www.etsy.com/shop/XRKAudio
  Reply With Quote

Reply


Cheap as Chips OPA1688 Low-THD Muscle AmpHide 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

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
New Audio Op Amp - OPA1688 johnc124 Vendor's Bazaar 56 2nd November 2017 09:38 PM
P-P with some muscle bigjppop Tubes / Valves 43 18th October 2009 08:22 PM
Cheap DAC chips harryeng Swap Meet 1 16th September 2007 08:13 PM
cheap lm3886TF chips? jeffshort2000 Chip Amps 3 8th January 2007 08:38 PM
Help Cheap as chips speaker project DAVOhorn Full Range 2 5th November 2005 03:35 PM


New To Site? Need Help?

All times are GMT. The time now is 12:14 AM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2019 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 14.29%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2019 DragonByte Technologies Ltd.
Copyright ©1999-2019 diyAudio
Wiki