Building an ultimate low power class A amplifier – my way

Member
Joined 2014
Paid Member
Hi Gary,
You’re correct, the blue board is a ground loop breaker circuit. Tombo shared the files on this thread or the R21 ps regulator module thread, can’t remember which. Pretty straight forward grounding scheme, center GND tab on both of Prasi's psu connect to the GLB board. Chassis stud has three connections, IEC earth, transformer shield and GLB.
Amplifier Sig GND and decouple GND connect to a single gnd tab on psu board, speaker return also connects to psu gnd tab.
There is no sound whatsoever coming from the speakers when music is paused, dead quiet! ;)
 

Attachments

  • IMG_1641.jpeg
    IMG_1641.jpeg
    272 KB · Views: 126
  • Like
Reactions: 3 users
Member
Joined 2014
Paid Member
Are we ever finished with a build?? :rofl:
I'm going back in to tweak the opamp supply resistors.
Pre regulator (R21 module) voltage is 21V5, post regulator is 17V5
The R21 modules are dropping 4V and Bliss is running 1A bias current = small regulator heatsinks are running a bit too toasty ~58C for my liking. I do plan to increase bias a bit and that temp would rise higher.
Plan is to decrease the voltage drop to 2V, which means the opamp would be fed 19V5 and thats no good. So R7 and R8 need to increase to approx. 350R to drop voltage back to 17V5
Front panel drilled for switch and standby LED, ready to roll! :spin:
 

Attachments

  • IMG_1642.jpeg
    IMG_1642.jpeg
    588.4 KB · Views: 81
  • IMG_1643.jpeg
    IMG_1643.jpeg
    502.8 KB · Views: 81
Member
Joined 2014
Paid Member
Big 'ole Delta drillpress.
To make the recessed flush cut a 1.25" forstner bit works great. Drill a 3/16" pilot hole first for the forstner bit centering point. Slow and steady cutting with lots of WD40. When the cut is deep enough for the switch threaded body use a step drill bit for the 3/4" through hole.

The softstart board has indicator LED's for when AC mains are present (Standby) and when the the switch is pressed the AC flows through and the amp is then (On). The 'On' indicator is a blue ring around the pushbutton.
 
Amplifier ground, which is also a signal ground,

Amplifier signal ground is different to amplifier case ground, IMV.

is for safety reasons mandatory connected (in most cases with10R NTC, sometimes direct) to the chassis and every chassis is connected to the power earth safety wire.

If the chassis is connected to mains earth - this is 'safe practice'. In the amplifiers I build - signal ground does not touch the chassis; signal ground comes from the ground that the diode bridge(s) in the linear PS provide.
 
Member
Joined 2019
Paid Member
@tombo56 - can you point me to where your GLB gerbers/ schematic are hiding, or post them here again as I would like to get some made, thanks.
There is no need for PCB. Standard square 35A diode bridge can be used as seen here:
https://sound-au.com/earthing.htm

Check this detailed grounding guide by Bonsai (page 25 for ground lifter discussed here):
https://hifisonix.com/wp-content/uploads/2019/02/Ground-Loops.pdf

My PCB was shared by PM, but proposed use of diode bridge without PCB is perfect as well. Anyway, gerber files are attached.
 

Attachments

  • GLB.zip
    23.9 KB · Views: 62
  • Like
Reactions: 1 user
Member
Joined 2019
Paid Member
small regulator heatsinks are running a bit too toasty ~58C for my liking
Regulator heatsinks up to 90° C, are summer breeze cool.

Used MOSFET has 175° C max. silicon temperature and silicon to heatsink temperature difference is only several degrees. All electrolytic capacitors are at distance from the heatsinks.

Leave 1.5 - 2 V drop on the regulators.
 
Member
Joined 2014
Paid Member
Yep, Bliss has been performing flawlessly 8-10hrs per day for the past 2 weeks. Shortly after Bliss was in the main system I went back in to increase R7 and R8 to 347R (47R+300R), that dropped the opamp supply by 2V. Then I adjusted the R21 regulators from 17V5 to 19V5. So now the OPA828's are fed 17V5, OPS is fed 19V5 and R21 modules run a bit cooler dropping 2V instead of the original 4V.

Soundwise... This is a wonderful amplifier! Very detailed without a bit of listener fatigue and balanced sound. If you can live with the modest power output, Bliss should be on the must build list :yes:.
 

Attachments

  • IMG_1717.jpeg
    IMG_1717.jpeg
    286.8 KB · Views: 116
  • IMG_1719.jpeg
    IMG_1719.jpeg
    360.8 KB · Views: 118
  • Like
Reactions: 6 users
Member
Joined 2019
Paid Member
We have two great builds as an example how it can be done. Excellent compact build by manniraj, with very good parts arrangement, resulting with no hum despite 100 dB/1W loudspeakers, and ultimate modular build by Vunce, with great attention to every detail. With both approaches, good results are out of question.
If anyone finds single color power switches boring, here is what I use - RGB power switch:
https://www.aliexpress.com/item/329...order_list.order_list_main.150.21ef1c24lBaxtF

Using blue + green results with beautiful turquoise color. Blue + red gives pastel pink color. Playing with resistors and all three LEDs allows for any color you fancy.
 
  • Like
Reactions: 1 users