No, I built the modules as per the instructions I received before the mod was released.
I thought I'd burn it in and have a good listen before doing the mod. The way it's constructed, I can drop down the front heatsink 90 deg to access both sides of the PCB so it should be simple.
Looking forward to it. Greg is making up a volume pot with active buffer for me to run the CD player direct and still have a low impedance drive to the GB150. He has PCBs for these. I should have it in a couple of days.
I thought I'd burn it in and have a good listen before doing the mod. The way it's constructed, I can drop down the front heatsink 90 deg to access both sides of the PCB so it should be simple.
Looking forward to it. Greg is making up a volume pot with active buffer for me to run the CD player direct and still have a low impedance drive to the GB150. He has PCBs for these. I should have it in a couple of days.
Hi HiFiddleHiFiddle said:
Sounds good. Keep us posted on your thoughts/impressions and progress
In the meantime the active buffer sounds interesting. I use a passive volume control, so, I must send him email and ask him about them
What benefits are you expecting (or Greg has informed you off) by using the active buffer
rgds
Greg gave me a pic of the PCB. It's small enough to fit into many amplifiers, not mine though. You should contact him -
http://members.dodo.com.au/~gregball/guru_001.htm
http://members.dodo.com.au/~gregball/guru_001.htm
Attachments
One of Greg's SKA transplants is now for sale on eBay -
http://search.ebay.com.au/Metaxas-power-amplifier_W0QQfromZR41
http://search.ebay.com.au/Metaxas-power-amplifier_W0QQfromZR41
Hi HiFiddleHiFiddle said:One of Greg's SKA transplants is now for sale on eBay -
http://search.ebay.com.au/Metaxas-power-amplifier_W0QQfromZR41
Do you know why it is being sold. You see Greg quite regularly, did he mention anything
rgds
SKA mods overview
Hi,
I've ordered 8 x GB150D kits to go with my Orion speakers. I've seen a couple of mods mentioned, but with little discussion of sonic differences or improvements. I am not so keen to experiment with 8 channels at a time, so I am wondering, is there an overview somewhere of SKA mods and their supposed or experienced effect?
Thanks.
Hi,
I've ordered 8 x GB150D kits to go with my Orion speakers. I've seen a couple of mods mentioned, but with little discussion of sonic differences or improvements. I am not so keen to experiment with 8 channels at a time, so I am wondering, is there an overview somewhere of SKA mods and their supposed or experienced effect?
Thanks.
Hi,
before you do the mods, check your boards match the instructions.
The PCB layout requires some components and top to bottom wire links to be soldered to both sides of the PCB.
On my pair, 13 of the double soldered connections were not done on each board. One missing link under D2 required it's removal and replacement.
They are clearly shown as Grey dots on the layout.
Soon after my cases arrive I should be able to review the mod effects.
before you do the mods, check your boards match the instructions.
The PCB layout requires some components and top to bottom wire links to be soldered to both sides of the PCB.
On my pair, 13 of the double soldered connections were not done on each board. One missing link under D2 required it's removal and replacement.
They are clearly shown as Grey dots on the layout.
Soon after my cases arrive I should be able to review the mod effects.
Hi,
couldn't wait for my cases.
Jury rigged my first GB150. No mains safety earth, there's nothing to connect to.
300VA, 35Vac +35Vac (from 230Vac but used 240Vac).=103Vdc
+-2*15mF63V smoothing = 60mF total.
Dual 25A bridge rectifiers.
100r+47nF pes snubbers across each leg of the bridges. Just a guess.
100nF cer across the ~~ of the bridges.
Both cap and Zener modifications incorporated into the LTP CCS.
10uF63V electro, 36K, 18K & 20V5 Zener. not 27k+27k+15V.
0.6C/W sink.
On first power up (using light bulb) the voltages rose nicely and output offset was 7mVdc, with the input co-ax shorted. Didn't need to tweak the presets. Output bias low at 280 to 400mV (28 to 40mA) and seems to vary oddly but both halves always identical.
Now plugged direct into mains, output offset =9mVdc
But unusually, the output Vac measures 0.0mVac on my multimeter. All my previous efforts read at least something on the lowest scale. Seems as though the PS artefacts are completely eliminated in the volt amp stage!
If the zero DMM reading means less than 0.05mVac (half LSB) then hum and low frequency noise are about -120db below maximum output. That's an excellent result. I have never achieved this before.
Now dare I try listening when the contraption is sitting on an offcut of chipboard flooring?
couldn't wait for my cases.
Jury rigged my first GB150. No mains safety earth, there's nothing to connect to.
300VA, 35Vac +35Vac (from 230Vac but used 240Vac).=103Vdc
+-2*15mF63V smoothing = 60mF total.
Dual 25A bridge rectifiers.
100r+47nF pes snubbers across each leg of the bridges. Just a guess.
100nF cer across the ~~ of the bridges.
Both cap and Zener modifications incorporated into the LTP CCS.
10uF63V electro, 36K, 18K & 20V5 Zener. not 27k+27k+15V.
0.6C/W sink.
On first power up (using light bulb) the voltages rose nicely and output offset was 7mVdc, with the input co-ax shorted. Didn't need to tweak the presets. Output bias low at 280 to 400mV (28 to 40mA) and seems to vary oddly but both halves always identical.
Now plugged direct into mains, output offset =9mVdc
But unusually, the output Vac measures 0.0mVac on my multimeter. All my previous efforts read at least something on the lowest scale. Seems as though the PS artefacts are completely eliminated in the volt amp stage!
If the zero DMM reading means less than 0.05mVac (half LSB) then hum and low frequency noise are about -120db below maximum output. That's an excellent result. I have never achieved this before.
Now dare I try listening when the contraption is sitting on an offcut of chipboard flooring?
Hi Float,
seems you're right, there was no other way.
I am listening to FM radio through one GB150 just now. Plays OK. Just about as good as Cyrus Qpower with PSXr(treble) and modified SugdenP128 (mid/bass).
The big downside is lack of gain.
28times (+28.9db) with full right balance cannot match 56times (+35db) on the left channel.
I will have to change this.
This power amp is really the quietest I have ever built/assembled.
Still reads 0.0mVac on my DMM.
When mute is set on the pre-amp a small hiss and no hum is apparent - ear on the drivers.
When pre-amp is disconnected and input RCA is open a lower level of hiss is just perceptable.
When the amp has a shorting plug added, that lower level of hiss becomes imperceptible.
It appears that Ampguru's new spec sheet showing noise and hum below -100dbA rel 1W is telling the truth.
Pity my stripped down temporary assembly does not look as good as the Cyrus. (it consists of plug top-transformer-2 bridge rectifiers-4 smoothing caps-GB150-heatsink(warm)-output cable- still sitting on that chipboard.
I hope GB150 performs as well when the case is fitted around it.
seems you're right, there was no other way.
I am listening to FM radio through one GB150 just now. Plays OK. Just about as good as Cyrus Qpower with PSXr(treble) and modified SugdenP128 (mid/bass).
The big downside is lack of gain.
28times (+28.9db) with full right balance cannot match 56times (+35db) on the left channel.
I will have to change this.
This power amp is really the quietest I have ever built/assembled.
Still reads 0.0mVac on my DMM.
When mute is set on the pre-amp a small hiss and no hum is apparent - ear on the drivers.
When pre-amp is disconnected and input RCA is open a lower level of hiss is just perceptable.
When the amp has a shorting plug added, that lower level of hiss becomes imperceptible.
It appears that Ampguru's new spec sheet showing noise and hum below -100dbA rel 1W is telling the truth.
Pity my stripped down temporary assembly does not look as good as the Cyrus. (it consists of plug top-transformer-2 bridge rectifiers-4 smoothing caps-GB150-heatsink(warm)-output cable- still sitting on that chipboard.
I hope GB150 performs as well when the case is fitted around it.
Hi,
has anyone investigated changing the gain of the GB150?
Changing R3 & R23 in unison maintain input and feedback matching around the LTP.
Any thoughts on adopting 51k for these?
Gain becomes 52times (+34.3db).
Input impedance becomes 49k//1nF
Input filter becomes 260mS (a bit high) 10uF in series with 10uF.
Noise becomes?
DC offset stability becomes?
Any other consequences?
has anyone investigated changing the gain of the GB150?
Changing R3 & R23 in unison maintain input and feedback matching around the LTP.
Any thoughts on adopting 51k for these?
Gain becomes 52times (+34.3db).
Input impedance becomes 49k//1nF
Input filter becomes 260mS (a bit high) 10uF in series with 10uF.
Noise becomes?
DC offset stability becomes?
Any other consequences?
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