Reactcore
1000+ Head-Fier
See also the making of my Choral housed Mscaler and optical dual data link Here
And placing Dave's original PSU in external box Here
Edit: important notice at this post end!
Hi all,
Welcome to yet another modification of my Chord Dave.
This time its about making a add-on to its power feed to the amplifier section.
I'm not writing a introduction about the Dave DAC as that has been well covered in its own thread Here .
Dave is one of the most transparent and revealing DAC/pre Amps on the market available.
Since its output signal is processed and noiseshaped in the digital domain it could be equipped with a very simple analog output stage made out of discrete components. One key benefit is that this maximizes transparency due to the absence of analog filtering. Many, including myself, have noted that any external headphone amplifier in the chain degrades its transparency and its better to use its internal one.
But reviewers and other owners of a Dave have pointed out that its headphone driving capabillity is staying behind of when using some of the best external amplifiers connected to the line outs, especially when using harder to drive headphones.
So why would this be? its not the output voltage which at 6v should be more than enough to drive the toughest loads.
But many have questioned its switchmode power supply (SMPS).
During last years there have come different solutions for upgrading Dave's internal power supply by an external one.
But i didnt found much wrong with the sound coming out of Dave using my (quite easy to drive) Senns HD800's.
Until i got my ears on a Farad stack of Linear supplies hooked up to a Dave and i could A-B listen to it next to my stock unit.
What i heard supprised me alot.. i heard more pronounced mid-bass notes as well on my speakers as on my headphones.
Hm why would this be, in my reasoning its not so much about RF rejection since the SMPS should be taking good care of that as it is natively equipped with extending noise filtering cause of their own switching activity.
A transformer is not isolating a supply from net noise and so filters must still be applied for a LPS.
In my theory it had to be the Farad's heavy buffering by the use of capacitors with low Equivalent Series Resistance (ESR)
Ok so what does this do?
Imagine a voltage of 10v is supplied to a amplifier which is amplifying a sound signal.
Cause of this the amp draws a varying current out of the supply depending on the load it drives.
The power supply must keep its voltage steady but is showing a tiny variation of milivolts cause of the fact they exhibit internal resistances creating their voltage.
By nature PSU's are equipped with capacitors to smooth out the output voltage (ripple) which is either created by 10khz+ pulses (SMPS) or a double rectified sinus of 50 or 60Hz (LPS)
SMPS vs LPS ripple
These capacitors also help to keep the total voltage steady when current is drawed from it.
But they have internal resistance in series with its 'energy container' over which their loaded voltage is devided.
ESR principle
Lower ESR means less voltage loss to keep the capacitor's charge on its leads steady.
Ok so due of lower ESR it can help to reduce voltage modulation cause by current drawn.
Bigger capacitors have a lower ESR compared to smaller ones, a capacitor's charge 'container' size is as many know put in farads.
Imo the importance is to get as low as possible ESR. This because the'container' wont get time to discharge as the frequency of the audio signal modulation is simply to high.. so a super high capacity (in F) is not most important but a internal resistor reacts directly by dropping the capacitor's voltage alowing the PSU voltage to drop.
Ok now i could create a external PSU loaded with capacitors in parallel to lower the combined ESR but then resistance is added again by the cabling, connectors and Daves PCB tracks before the power reaches Dave's internal regulator.
No i rather not allow a modulated voltage to keep existing over these internals, i want to add my buffercaps where its needed most: as near as possible to the amp.
So i measured inside Dave and located the two LM307/317 regulators which make +and- 12v out of the PSU supplied +and- 15v.
Under a schematic of where i intended to place my capacitors, in red the added part
Ofcourse many big sized (in farad F) capacitors wouldnt fit inside Dave so i went searching for smaller ones but as small as possible ESR i can find with at least 15v operating voltage.
I found newly released types with ultra low ESR made by TDK which are normally used in the electric automotive industry where theyre used to supply high currents for car motor regulators.
I went for the Axial types to have shorter leads in my Dave:
I picked the ones that still fit which are the 1700uF ones, but i place 2 in parallel for each voltage.
They cost as little as €6,50 each.
Enough theory.. lets get my Dave.
First i start by making a 2.5mm massive copper leadwire and bow this in shape so i can lineup the capacitors.
Then i soldered the capitors, two with the plus side and two with the negative side on it.
I bowed the other side's leads already in a way it can be installed fitting on the regulators.
Now putting them into Dave.
The ground lead i soldered directly on the headphone socket's ground, this minimises ground currents flowing through Dave's PCB which probably lower groundplane noise further.
All can be placed without needing to take the PCB out.
The +15v lead i soldered directly on the regulator's input pin.
Also this picture shows the ground lead on the headphone socket.
On the negative regulator it is done the same.
But here the input is on the middle pin which is short combined with its baseplate.
With carefully alighning it can be soldered quite sturdy.
A big help to let solder attach well and not to short the regulator's pins is the use of separate flux.
I used this one:
After soldering it in, i just heated the ground lead again to take the tention off the other leads.
If all is done right it can be measured the voltages on the capacitors:
So now im ready to listen to my 'Supercharged' amplifier inside my Dave.
And boy this thing got muscles now! i'm in my second day listening and am asthonished by the authority this brings, specially on higher volumes it holds grip on my headphone's drivers giving stronger and better defined bass notes without losing anything of Dave's famous transparency. Its a real joy to listen to all my recordings once again.
I hope you all enjoyed reading my long dragging post.. and.. happy modding
This guy dives in his music collection now..
Important Edit:
Soldering the ground lead on the headphone socket's ground pin caused the contact for the relay not to close and preamp mode was not activated when pulling the headphone jack.
This because it bowes the thick lead too much.
So place the ground lead on the bolt island aside it.
First make a circle on the end.
The bolt island is also PSU ground
Place the lead under the bolt.
I also soldered it on the island
Now the headphone socket can freely switch the pre/hp relay.
And placing Dave's original PSU in external box Here
Edit: important notice at this post end!
Hi all,
Welcome to yet another modification of my Chord Dave.
This time its about making a add-on to its power feed to the amplifier section.
I'm not writing a introduction about the Dave DAC as that has been well covered in its own thread Here .
Dave is one of the most transparent and revealing DAC/pre Amps on the market available.
Since its output signal is processed and noiseshaped in the digital domain it could be equipped with a very simple analog output stage made out of discrete components. One key benefit is that this maximizes transparency due to the absence of analog filtering. Many, including myself, have noted that any external headphone amplifier in the chain degrades its transparency and its better to use its internal one.
But reviewers and other owners of a Dave have pointed out that its headphone driving capabillity is staying behind of when using some of the best external amplifiers connected to the line outs, especially when using harder to drive headphones.
So why would this be? its not the output voltage which at 6v should be more than enough to drive the toughest loads.
But many have questioned its switchmode power supply (SMPS).
During last years there have come different solutions for upgrading Dave's internal power supply by an external one.
But i didnt found much wrong with the sound coming out of Dave using my (quite easy to drive) Senns HD800's.
Until i got my ears on a Farad stack of Linear supplies hooked up to a Dave and i could A-B listen to it next to my stock unit.
What i heard supprised me alot.. i heard more pronounced mid-bass notes as well on my speakers as on my headphones.
Hm why would this be, in my reasoning its not so much about RF rejection since the SMPS should be taking good care of that as it is natively equipped with extending noise filtering cause of their own switching activity.
A transformer is not isolating a supply from net noise and so filters must still be applied for a LPS.
In my theory it had to be the Farad's heavy buffering by the use of capacitors with low Equivalent Series Resistance (ESR)
Ok so what does this do?
Imagine a voltage of 10v is supplied to a amplifier which is amplifying a sound signal.
Cause of this the amp draws a varying current out of the supply depending on the load it drives.
The power supply must keep its voltage steady but is showing a tiny variation of milivolts cause of the fact they exhibit internal resistances creating their voltage.
By nature PSU's are equipped with capacitors to smooth out the output voltage (ripple) which is either created by 10khz+ pulses (SMPS) or a double rectified sinus of 50 or 60Hz (LPS)
SMPS vs LPS ripple
These capacitors also help to keep the total voltage steady when current is drawed from it.
But they have internal resistance in series with its 'energy container' over which their loaded voltage is devided.
ESR principle
Lower ESR means less voltage loss to keep the capacitor's charge on its leads steady.
Ok so due of lower ESR it can help to reduce voltage modulation cause by current drawn.
Bigger capacitors have a lower ESR compared to smaller ones, a capacitor's charge 'container' size is as many know put in farads.
Imo the importance is to get as low as possible ESR. This because the'container' wont get time to discharge as the frequency of the audio signal modulation is simply to high.. so a super high capacity (in F) is not most important but a internal resistor reacts directly by dropping the capacitor's voltage alowing the PSU voltage to drop.
Ok now i could create a external PSU loaded with capacitors in parallel to lower the combined ESR but then resistance is added again by the cabling, connectors and Daves PCB tracks before the power reaches Dave's internal regulator.
No i rather not allow a modulated voltage to keep existing over these internals, i want to add my buffercaps where its needed most: as near as possible to the amp.
So i measured inside Dave and located the two LM307/317 regulators which make +and- 12v out of the PSU supplied +and- 15v.
Under a schematic of where i intended to place my capacitors, in red the added part
Ofcourse many big sized (in farad F) capacitors wouldnt fit inside Dave so i went searching for smaller ones but as small as possible ESR i can find with at least 15v operating voltage.
I found newly released types with ultra low ESR made by TDK which are normally used in the electric automotive industry where theyre used to supply high currents for car motor regulators.
I went for the Axial types to have shorter leads in my Dave:
I picked the ones that still fit which are the 1700uF ones, but i place 2 in parallel for each voltage.
They cost as little as €6,50 each.
Enough theory.. lets get my Dave.
First i start by making a 2.5mm massive copper leadwire and bow this in shape so i can lineup the capacitors.
Then i soldered the capitors, two with the plus side and two with the negative side on it.
I bowed the other side's leads already in a way it can be installed fitting on the regulators.
Now putting them into Dave.
The ground lead i soldered directly on the headphone socket's ground, this minimises ground currents flowing through Dave's PCB which probably lower groundplane noise further.
All can be placed without needing to take the PCB out.
The +15v lead i soldered directly on the regulator's input pin.
Also this picture shows the ground lead on the headphone socket.
On the negative regulator it is done the same.
But here the input is on the middle pin which is short combined with its baseplate.
With carefully alighning it can be soldered quite sturdy.
A big help to let solder attach well and not to short the regulator's pins is the use of separate flux.
I used this one:
After soldering it in, i just heated the ground lead again to take the tention off the other leads.
If all is done right it can be measured the voltages on the capacitors:
So now im ready to listen to my 'Supercharged' amplifier inside my Dave.
And boy this thing got muscles now! i'm in my second day listening and am asthonished by the authority this brings, specially on higher volumes it holds grip on my headphone's drivers giving stronger and better defined bass notes without losing anything of Dave's famous transparency. Its a real joy to listen to all my recordings once again.
I hope you all enjoyed reading my long dragging post.. and.. happy modding
This guy dives in his music collection now..
Important Edit:
Soldering the ground lead on the headphone socket's ground pin caused the contact for the relay not to close and preamp mode was not activated when pulling the headphone jack.
This because it bowes the thick lead too much.
So place the ground lead on the bolt island aside it.
First make a circle on the end.
The bolt island is also PSU ground
Place the lead under the bolt.
I also soldered it on the island
Now the headphone socket can freely switch the pre/hp relay.
Last edited: