M
Morpheus
Gjest
Her er litt bakgrunnsinformasjon om designvalg gjort underveis under utviklingen av Ember.
Over time we changed a lot of things along the way and I had to build and test some of the circuits before handing them over to Jeremy.
Most of the experiments were done on the OPA-88 amp I made a while back.
this kept us from 'finalising' the design.
Over time the following steps were made before we thought it could be called a product.
The first design was more or less a Horizon with the output stage changed to the buffer type output that is still in place. (see OPA-88 amp shown above)
Subsequently I added auto-bias.
Changed that circuit slightly in a few small iterations to make it perform better.
At this point the project Ember was more or less ready to launch we figured so hints in that direction were vented.
Next I thought it would be handy if the heater was selected automatically so a jumper was no longer needed and no errors can be made by users any more. It would also be easier to use tubes with no markings on them as the voltage didn't matter.
After that I thought it would be easier if the output R selector was simply done with 1 jumper in 3 positions instead of 2 jumpers that work intuitively 'strange' so meant a redesign.
Later I simplified and improved the auto heater select circuit
Changed the RCA output (pre-amp) voltage so it could be used better as a preamp.
Changed the output device configuration for better performance and used other devices but were hard to get so changed it back.
Added a gain select jumper as some found the gain to be on the side of too high (with a little travel on the volpot a too loud volume)
Changed the output configuration to something similar as we did on the Starlight and hoped to pump out 5W-6W on 32 Ohm this way.
a proto PCB was built.
Had some issues with the protection relay action which didn't switch as intended so made a small change.
The proto had some temperature issues and doubling the output power was not working as we wanted and were plagued by small oscillations.
This meant we fell back on the current output configuration and changed it a bit to deal with temperature issues when using normal 8-pin DIP output devices. In real life situations this worked perfectly and the temperature stayed low. On a test bench it became too hot.
I added thermal protection (which had to be tested thoroughly).
It was decided later on SMD devices were going to be used but meant these devices had to be pre-soldered.
Another change in the layout..
The layout was a constant re-arranging and optimising anyway (as it is with any design)
Indicator LED's were added and the output stage configuration was changed slightly again.
We still had some things we wanted to change but decided the amp is functioning as we wanted it too so it was finally launched.
The switch to the front was another idea that I wanted for a long time but because the DC input is at the back this meant long wires running up and down on the PCB so for optimizing power wire routing decided to keep those wires as short as possible.
Now it is up and running and performing even better than my 'proto' OPA-88 amplifier due to optimised PCB design.
We are planning to offer a linear power supply for the amplifier range (regulated 24V and 48V DC linear power supplies).
Read more: DIY Audio Heaven - Project Ember
Over time we changed a lot of things along the way and I had to build and test some of the circuits before handing them over to Jeremy.
Most of the experiments were done on the OPA-88 amp I made a while back.
this kept us from 'finalising' the design.
Over time the following steps were made before we thought it could be called a product.
The first design was more or less a Horizon with the output stage changed to the buffer type output that is still in place. (see OPA-88 amp shown above)
Subsequently I added auto-bias.
Changed that circuit slightly in a few small iterations to make it perform better.
At this point the project Ember was more or less ready to launch we figured so hints in that direction were vented.
Next I thought it would be handy if the heater was selected automatically so a jumper was no longer needed and no errors can be made by users any more. It would also be easier to use tubes with no markings on them as the voltage didn't matter.
After that I thought it would be easier if the output R selector was simply done with 1 jumper in 3 positions instead of 2 jumpers that work intuitively 'strange' so meant a redesign.
Later I simplified and improved the auto heater select circuit
Changed the RCA output (pre-amp) voltage so it could be used better as a preamp.
Changed the output device configuration for better performance and used other devices but were hard to get so changed it back.
Added a gain select jumper as some found the gain to be on the side of too high (with a little travel on the volpot a too loud volume)
Changed the output configuration to something similar as we did on the Starlight and hoped to pump out 5W-6W on 32 Ohm this way.
a proto PCB was built.
Had some issues with the protection relay action which didn't switch as intended so made a small change.
The proto had some temperature issues and doubling the output power was not working as we wanted and were plagued by small oscillations.
This meant we fell back on the current output configuration and changed it a bit to deal with temperature issues when using normal 8-pin DIP output devices. In real life situations this worked perfectly and the temperature stayed low. On a test bench it became too hot.
I added thermal protection (which had to be tested thoroughly).
It was decided later on SMD devices were going to be used but meant these devices had to be pre-soldered.
Another change in the layout..
The layout was a constant re-arranging and optimising anyway (as it is with any design)
Indicator LED's were added and the output stage configuration was changed slightly again.
We still had some things we wanted to change but decided the amp is functioning as we wanted it too so it was finally launched.
The switch to the front was another idea that I wanted for a long time but because the DC input is at the back this meant long wires running up and down on the PCB so for optimizing power wire routing decided to keep those wires as short as possible.
Now it is up and running and performing even better than my 'proto' OPA-88 amplifier due to optimised PCB design.
We are planning to offer a linear power supply for the amplifier range (regulated 24V and 48V DC linear power supplies).
Read more: DIY Audio Heaven - Project Ember