AndrewT said:
Hi Andrew,
perhaps not. But it's such a good basic design that it's interesting to see just how far it can go.
Dan
I just went a little bit further 😎
I changed the BIAS and now I have 1W in Class A, 317mA BIAS
(Good heatsink is required because it gets hot
)
I also welded 470uF under the 330uF.
Next step will be change C4 and C5 for 10uF non polar caps 😀
But now I am enjoying the sound.... better dynamics(deeper and faster bass) and better detail 😎
PS: 100nF in C4 and C5 should also improve the sound and it's less expensive that non polar caps.
I changed the BIAS and now I have 1W in Class A, 317mA BIAS
(Good heatsink is required because it gets hot
)I also welded 470uF under the 330uF.
Next step will be change C4 and C5 for 10uF non polar caps 😀
But now I am enjoying the sound.... better dynamics(deeper and faster bass) and better detail 😎
PS: 100nF in C4 and C5 should also improve the sound and it's less expensive that non polar caps.
I'm about to undertake building one of these, I have a pair of 160VA, 30V-0-30V toroids (one per channel). Now I know this is certainly within the lower limits of what is suggested but do people think I would benefit significantly from larger transformers?
chances are the amp will not be run hard (thanks to the neighbours) and I am considering beefing up the PSU smoothing caps somewhat (I have a load of suitable caps from an error on an order).
chances are the amp will not be run hard (thanks to the neighbours) and I am considering beefing up the PSU smoothing caps somewhat (I have a load of suitable caps from an error on an order).
http://www.diyhifi.org/amplifierguru/guru_001.htm
seems to me even the most experienced and demanding people are more than satisfied, and still no reports of any failure or major changes 😉
seems to me even the most experienced and demanding people are more than satisfied, and still no reports of any failure or major changes 😉
Hi any Aussies in Sydney built the amps?
I am very interested in building one if not two but would like to listen to it first.
For an exchange, you can listen to the absolute HiEnd DIY NaO speaker designed by John K and the Optimos monoblocks designed by Randy Slone.
Please send me a email if you have a GB150 or GB300 and you live in the Sydney area.
I am very interested in building one if not two but would like to listen to it first.
For an exchange, you can listen to the absolute HiEnd DIY NaO speaker designed by John K and the Optimos monoblocks designed by Randy Slone.
Please send me a email if you have a GB150 or GB300 and you live in the Sydney area.
Hi Puggie,
30Vac is a little low but since the amp module will run from the recommended 25Vac when biassed into ClassA you should have no problems.
However, the bias current in the EF stage is very dependant on supply voltage and at about +-42Vrail you may want to reduce the two emitter resistors to bring the bias back up to 7.5mA.
Your VA rating probably suits the low Vrail you are planning for 8ohm speakers but will be a bit low for 4ohm speakers. You can partially compensate for a low VA supply by increasing the smoothing caps from 2mF/Apk to 3 or 4mF/Apk of output current.
On +-40Vrails the peak output current into 8ohm is about 4.5Apk requiring +-9mF and double this into 4ohms. So a low VA transformer could require as much as +-40mF/ch.
Have you looked at the sponsored thread page in diyhifi.org ?
Ampguru responds very quickly to all technical queries.
30Vac is a little low but since the amp module will run from the recommended 25Vac when biassed into ClassA you should have no problems.
However, the bias current in the EF stage is very dependant on supply voltage and at about +-42Vrail you may want to reduce the two emitter resistors to bring the bias back up to 7.5mA.
Your VA rating probably suits the low Vrail you are planning for 8ohm speakers but will be a bit low for 4ohm speakers. You can partially compensate for a low VA supply by increasing the smoothing caps from 2mF/Apk to 3 or 4mF/Apk of output current.
On +-40Vrails the peak output current into 8ohm is about 4.5Apk requiring +-9mF and double this into 4ohms. So a low VA transformer could require as much as +-40mF/ch.
Have you looked at the sponsored thread page in diyhifi.org ?
Ampguru responds very quickly to all technical queries.
Hi HiFiNut. I am in Newcastle, and will have mine running in about 6 weeks. I would be happy to drive down to give you a listen. Let me know what you think.
🙂 Nigel
🙂 Nigel
AndrewT said:
I have emailed Greg and he thinks I should be fine with the 160VA 30-0-30 transformers, I was just looking for other peoples impressions really. My speakers will be 8Ohm (nominal) and I doubt they will be pushed very hard. The reason I asked is I also have a pair of 225VA 15-0-15V transformers but they have split 115V primaries so I could wire those in parallel to give me 30-0-30 off our 240V supply.
Puggie said:
Do that and you will double the volts per turn ratio, saturate the cores badly, and soon thereafter poof the xfmr.
That's a really bad idea.I was thinking out loud before looking into that any further, I guess I don't need to look into if that is a VIABLE idea any more, I know its really bad without the effort of doing any research 😉
Ta guys 160VA / channel it is then 🙂
Ta guys 160VA / channel it is then 🙂
Hi Puggie,
I am currently finalising my GB150D trying to retrofit into an old 80's Pioneer A400 case but I couldn't help myself writing a preliminary evaluation.
Even though the Pioneer amp was only 50W I used its trafo (32V output) & heatsink as the EI trafo looked big & beefy ("Meaty Beaty Big & Bouncy" - name the band - don't cheat & use Google) & the heatsink was a honeycomb construction about 4"W X 3"H X 6"L. I used 14,700uF on each rail - 4,700uF of some good caps (Evox Industrial Long Life PEH200) & 10,000uF of various other brand caps (ELNA & Nichicon).
Anyway, after some hiccups which Greg helped me out of (his service is second to none & response to problems patient & fast - Number of emails & replies to date ~ 70) I got the amp working. I can attest to the robustness of the amp as I made some dumb mis-wiring mistake with the thermal sensing transistors & when I connected up one board it burnt out the 10R 1W Rs connected accross the fuse holder. No damage was done to any part of the circuit.
When I corrected this problem & fired it up after setting bias & offset I heard a fascinating sound I had not heard before. Fluid & liquid sound from a CD walkman. All my amps to date have been more hiFi'ish (including the Pioneer which was rated in the press) although I have never had any so called high-end amps. All the superlatives have already been posted but a relaxing & effortless sound sums it up for me. Being the obvious cheapskate that I am I also appreciate the entry level pricing for these sonics.
However, my trafo was underpowered - it was heating up & heatsinks are marginally capable (they are hot to touch but bearable). So, I changed to two 160VA toroid trafos (25V output) & adjusted some settings to retain bias range for this low a voltage. Sound is improved mostly in the area of channel seperation.
I will be applying other changes to maximise the amp's operation at these low voltages. I haven't implemented the zener mod yet either but look forward to squeezing the last bit of performance from this excellent design.
I have to say I respect Greg for his ability to analyse amplifier design & find a new & innovative perspective on the accepted traditional configuration. This is an example of genuine creativity at work, not just tinkering around the edges with part selection & tuning. I look forward to his future designs as I'm sure his innovation is not yet finished.
John
I am currently finalising my GB150D trying to retrofit into an old 80's Pioneer A400 case but I couldn't help myself writing a preliminary evaluation.
Even though the Pioneer amp was only 50W I used its trafo (32V output) & heatsink as the EI trafo looked big & beefy ("Meaty Beaty Big & Bouncy" - name the band - don't cheat & use Google) & the heatsink was a honeycomb construction about 4"W X 3"H X 6"L. I used 14,700uF on each rail - 4,700uF of some good caps (Evox Industrial Long Life PEH200) & 10,000uF of various other brand caps (ELNA & Nichicon).
Anyway, after some hiccups which Greg helped me out of (his service is second to none & response to problems patient & fast - Number of emails & replies to date ~ 70) I got the amp working. I can attest to the robustness of the amp as I made some dumb mis-wiring mistake with the thermal sensing transistors & when I connected up one board it burnt out the 10R 1W Rs connected accross the fuse holder. No damage was done to any part of the circuit.
When I corrected this problem & fired it up after setting bias & offset I heard a fascinating sound I had not heard before. Fluid & liquid sound from a CD walkman. All my amps to date have been more hiFi'ish (including the Pioneer which was rated in the press) although I have never had any so called high-end amps. All the superlatives have already been posted but a relaxing & effortless sound sums it up for me. Being the obvious cheapskate that I am I also appreciate the entry level pricing for these sonics.
However, my trafo was underpowered - it was heating up & heatsinks are marginally capable (they are hot to touch but bearable). So, I changed to two 160VA toroid trafos (25V output) & adjusted some settings to retain bias range for this low a voltage. Sound is improved mostly in the area of channel seperation.
I will be applying other changes to maximise the amp's operation at these low voltages. I haven't implemented the zener mod yet either but look forward to squeezing the last bit of performance from this excellent design.
I have to say I respect Greg for his ability to analyse amplifier design & find a new & innovative perspective on the accepted traditional configuration. This is an example of genuine creativity at work, not just tinkering around the edges with part selection & tuning. I look forward to his future designs as I'm sure his innovation is not yet finished.
John
I agree its a great introduction as an A/B amp for the diy beginner.
I recently sold mine to a local who is need of an amp upgrade. At the moment I have too many amps and not enough space or time.
It will be interesting to see what the Guru comes up with next.
macka
I recently sold mine to a local who is need of an amp upgrade. At the moment I have too many amps and not enough space or time.
It will be interesting to see what the Guru comes up with next.
macka
The SKA amps were designed by Greg as DIY platform, allowing for AC or DC coupling, Class AB or Class A in a novel completely symmetrical design - at very reasonable cost.
I am continually amazed at the sheer quality from my little GB150D dual supply unit which seems to outperform almost everything - so reasonably and so simple to build.
I am continually amazed at the sheer quality from my little GB150D dual supply unit which seems to outperform almost everything - so reasonably and so simple to build.
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