beppe61 said:
Hi bg
The system I use is based around lossless audio and bit-perfect playback via a PC with an RME Fireface audio interface, That's pretty much all the front end consists of,. From there it goes on to the amps and out through a pair of ATC SCM7 speakers that are usually used as surrounds. Unfortunately I can't test with my mains as they are 3-way actives and I don't have enough of the AKSA's or SKA's to achieve this. What I hope to do is to pick the best of the DIY designs I've listened to and buy more to complete the amp lineup.
ATC SCM7
FYI
These speakers are down about 2db @ 100Hz and -6db @ 60Hz.
Hard to conclude about bass response with such speakers.
Also they are only 84db sensitive. They can take quite a bit of power.
In my view over 100W would be the minimum for speakers of this sensitivity. 55W may not be enough for them to do their thing.
However, if listening levels are kept moderate, I expect they will reveal much about differences in amps.
cheers
FYI
These speakers are down about 2db @ 100Hz and -6db @ 60Hz.
Hard to conclude about bass response with such speakers.
Also they are only 84db sensitive. They can take quite a bit of power.
In my view over 100W would be the minimum for speakers of this sensitivity. 55W may not be enough for them to do their thing.
However, if listening levels are kept moderate, I expect they will reveal much about differences in amps.
cheers
Re: ATC SCM7
That was my concern too. They're nice speakers but do present some challanges for amplifiers. And yes they can easily soak up 55w.
The bass that these speaker's output, whilst somewhat rolled off in the lower couple of octaves, is very revealing. The in room response is also flat down to 60hz in 1/2 space/close to the rear wall. The -6dB point is 45hz. So whilst these aren't the last word in extension they make up for it with tight and tuneful bass.
Of course the ultimate test would be with my Perceive design.
hifryer said:
That was my concern too. They're nice speakers but do present some challanges for amplifiers. And yes they can easily soak up 55w.
The bass that these speaker's output, whilst somewhat rolled off in the lower couple of octaves, is very revealing. The in room response is also flat down to 60hz in 1/2 space/close to the rear wall. The -6dB point is 45hz. So whilst these aren't the last word in extension they make up for it with tight and tuneful bass.
Of course the ultimate test would be with my Perceive design.
Hi Greg
Just a few questions
1. It looks like the amp has differential input stage with a complementary output stage. Is that correct?
2. Do the input stage bipolar's need to be matched?
3. Do the output stage mosfet's need to be matched?
4. Complementary output stages are noted for having excellent local feedback, which provides for low distortion, but, are not noted for handling difficult loads, such as <4 ohm loads. How is the GB300D in this area?
5. It would also appear that no special classA biasing circuit is required. Is that correct?
6. I know the design is simple, and as a result is low cost and excellent value, but, the power supply needed appears to be smaller than others with the same power rating. Is that correct?
7. So for the GB300D, what is the smallest size transformer that you would recommend?
thanks
Just a few questions
1. It looks like the amp has differential input stage with a complementary output stage. Is that correct?
2. Do the input stage bipolar's need to be matched?
3. Do the output stage mosfet's need to be matched?
4. Complementary output stages are noted for having excellent local feedback, which provides for low distortion, but, are not noted for handling difficult loads, such as <4 ohm loads. How is the GB300D in this area?
5. It would also appear that no special classA biasing circuit is required. Is that correct?
6. I know the design is simple, and as a result is low cost and excellent value, but, the power supply needed appears to be smaller than others with the same power rating. Is that correct?
7. So for the GB300D, what is the smallest size transformer that you would recommend?
thanks
lineup said:
... , he will not be able to comment in this topic.
But I am sure he will read anything posted here.
By the way, he is a member at another Forum, DIYHIFI.org:
Greg's Simple Killer Amp Q&A , How good?
.
KLe
What I know,
Greg (amplifierguru) will not reply in this thread.
But you can find him at another diy forum.
Regards
ShinOBIWAN said:
Thanks a lot Sir for your extremely kind and interesting reply.
1) I read great things about the RME Fireface. Exceptional sound quality indeed. Congratulations!
2) I can see you have a really great system. Also ATC speakers are of extremely high quality.
3) Your main rig is very high quality and much more complex than mine.
By the way I would be very interested in hearing how this SKA behaves driving a full range speaker.
Its sound quality could vary with the difficulty of the load.
Thank you very much again.
Kind regards,
beppe
Here's my thoughts on the SKA after spending a several hours listening to it in the comfort of my own home. I was going to wait a little longer but in all honesty I don't think I need 100's of hours of exposure before I can offer an opinion, I've listened to many of my favourites from my collection and I'm familiar with how these sound so I can get a good feel for an amplifier or any equipment from listening to these.
First off I'd like to say a big thanks to Greg for offering a superb amplifier at a rather cheap price for a kit set, especially when you consider that the sound is amongst the best I've ever heard from a solidstate design. I had my modules constructed and tested by Greg since it was so cheap anyway it made sense to do it that way but from looking at the instructions and the PCB's its an easy amp to build anyhow - even simplier than my AKSA 55N+ looking at things. Greg had clearly took care with the building and his soldering is certainly better than my own, extremely neat and tidy, even down to how the resistors were meticulously lined up, I know its not important to the sound but it does highlight a care and attention to detail that's rare. He even included a postcard from Australia to remind me of just how cold it is here in the UK at this time year - nice touch The packaging was good and there was a bag of sillica gel for moisure absorbtion, again attention to detail is great and can only inspire similar confidence in the overall design and sound of the amplifier itself.
I'd thought I'd pretty much got all the bits needed to get the SKA's going on their arrival but sadly I forgot one thing - the heatsinks. I really wanted to get them going and Greg helpfully suggested that I use my AKSA heatsink along with a piece of wood and spring clamps to temporarily mount them. I did this and whilst its rather crude looking it works fine and I got to hear the amps. Unfortunately this means that the 55N+'s are out of action so no direct comparison's. If I get chance in the future I may do write up on an AB compare between the SKA and AKSA but I'm not sure its needed.
After setting bias and dc offset according to Gregs instructions I let the amps play in the background whilst I went about surfing the web, watching TV and left them running today whilst at work. The aim being to run them in a little before taking a more serious listen. Even so the character of this amp or rather the extreme lack of it was apparent without sitting down in the sweet spot and giving 100% of your attention to the sound.
Anyway I decided to start out with some of the really good quality recordings I have and the first was the Andreas Vollenweider' "Vox" album. There's some great acoustic peices here that mix synthesized with natural. The SKA really is a top notch amp to the extent that its actually hard to fault, at least for me anyway, perhaps I haven't heard enough excellent amps? Eitherway I seriously doubt anybody would rate this amp as less than very good and consider the price that Greg is asking... he could ask double and I'd still have payed it.
Another important thing to mention is that the SKA's I have use only base components, so no fancy blackgates or other expensive electrolytics, no silver mica's, no 0.01% resistors etc. so in other words there's actually room for improvement however small it could be. But its interesting to see that design does so well in standard guise, I guess Greg' anal approach to design looks more toward layout and topology than diminishing returns offered from the esoteric components route. But if anyone want to hotrod one of these its entirely possible.
I've come in to some flak from a particular member about the wording I use in my reviews, in fact I think their exact words were 'a review without weasel words' I think you know who you are But I don't see how just saying an amp sound very good is constructive to anyone and beside I enjoy writting about something I really like. So sod you and I'm sticking to my weasel words! 
The biggest thing for me about this amp is its sharp but extremely smooth character. A contradiction? Not at all, its got top draw detail but it always seems to presented with a nice natural edge. Greg cites this design as low distortion (~0.008%) but to my ears it isn't like some of the other low distortion designs, its not bright and over hyped but its feels just as detailed with a really appealing softer edge that makes listening very easy. More refined overall I'd say is the best way of putting it and especially in the upper frequencies.
Soundstaging is amongst the best I've heard from a solidstate designs and really only seems to be limited by the recording and the rest of your equipment. I'm feeding it with some great quality DAC's and bit perfect playback so this gives the SKA one of the best signals it can hope for. The SKA doesn't flatter rubbish recordings and they still sound rough but not to the extent that you couldn't enjoy them its just that in comparison to the better/best recording you don't get the awesome realism and that really involving nature.
What it does do with the right recording is completely fool you into thinking that your actually listening to the real thing. It does a great job of creating spaces and sizes, it seems to be able to relate the whole picture with proper proportions without blowing things up or bringing details to the fore that perhaps should be so obvious. Like I said the best word for this is natural, its often used word and there's varying degree's of it but here it really does feel right.
Tonality was perhaps covered in the last bit but just to be sure; its just plain natural Go play the piano (if you have one) or another musical instrument and then go listen to something similar on the SKA. It sounds very nearly as real. Few amps I've heard do this. If only it had an ounce more detail it would be heaven but then again my speakers are most likely the weak link though that's about to sorted out in a big way.
Imaging is drool worthy. I'm sure some folks can relate to what I'm about to write; have you ever heard those systems that have the kind of imaging that suspend disbelief? Well the SKA is nearly as good and again my speakers and room are probably the weak link so I expect improvments in the future. When playback is going on you hear very precise locations of certain sound or voices. You even get a good sense of depth with it being apparent that things are further away than other sounds. Another big deal is the amps great way with folly effect. I listened to many tracks and a few had me thinking that I could hear reflections off walls behind me but what I was actually hearing was the acoustic space of the recording, its a amazing effect to hear and always puts a smile on my face.
Bass again is better than I'm used to with the AKSA. Tight, smooth and rhythmic. I think that bass performance of many amps is one the biggest let downs and that a well conrtolled bass lift the entire performance on a notch. Room problems could be blamed but I do use DRC so that isn't a big problem for me.
Overall I'd have to say that this is the best DIY design I've come across yet and just happens to be the cheapest too. Its very hard to fault and I really do think that any real improvements above and beyond what performance is offered by the SKA isn't to be had from better amp design but from considerations of room and better loudspeakers.
I've been shopping around for amplifiers to complete my reference 3-way actives and in the SKA's I've found that. Things can only get better!
First off I'd like to say a big thanks to Greg for offering a superb amplifier at a rather cheap price for a kit set, especially when you consider that the sound is amongst the best I've ever heard from a solidstate design. I had my modules constructed and tested by Greg since it was so cheap anyway it made sense to do it that way but from looking at the instructions and the PCB's its an easy amp to build anyhow - even simplier than my AKSA 55N+ looking at things. Greg had clearly took care with the building and his soldering is certainly better than my own, extremely neat and tidy, even down to how the resistors were meticulously lined up, I know its not important to the sound but it does highlight a care and attention to detail that's rare. He even included a postcard from Australia to remind me of just how cold it is here in the UK at this time year - nice touch
The packaging was good and there was a bag of sillica gel for moisure absorbtion, again attention to detail is great and can only inspire similar confidence in the overall design and sound of the amplifier itself.I'd thought I'd pretty much got all the bits needed to get the SKA's going on their arrival but sadly I forgot one thing - the heatsinks. I really wanted to get them going and Greg helpfully suggested that I use my AKSA heatsink along with a piece of wood and spring clamps to temporarily mount them. I did this and whilst its rather crude looking it works fine and I got to hear the amps. Unfortunately this means that the 55N+'s are out of action so no direct comparison's. If I get chance in the future I may do write up on an AB compare between the SKA and AKSA but I'm not sure its needed.
After setting bias and dc offset according to Gregs instructions I let the amps play in the background whilst I went about surfing the web, watching TV and left them running today whilst at work. The aim being to run them in a little before taking a more serious listen. Even so the character of this amp or rather the extreme lack of it was apparent without sitting down in the sweet spot and giving 100% of your attention to the sound.
Anyway I decided to start out with some of the really good quality recordings I have and the first was the Andreas Vollenweider' "Vox" album. There's some great acoustic peices here that mix synthesized with natural. The SKA really is a top notch amp to the extent that its actually hard to fault, at least for me anyway, perhaps I haven't heard enough excellent amps? Eitherway I seriously doubt anybody would rate this amp as less than very good and consider the price that Greg is asking... he could ask double and I'd still have payed it.
Another important thing to mention is that the SKA's I have use only base components, so no fancy blackgates or other expensive electrolytics, no silver mica's, no 0.01% resistors etc. so in other words there's actually room for improvement however small it could be. But its interesting to see that design does so well in standard guise, I guess Greg' anal approach to design looks more toward layout and topology than diminishing returns offered from the esoteric components route. But if anyone want to hotrod one of these its entirely possible.
I've come in to some flak from a particular member about the wording I use in my reviews, in fact I think their exact words were 'a review without weasel words' I think you know who you are
But I don't see how just saying an amp sound very good is constructive to anyone and beside I enjoy writting about something I really like. So sod you and I'm sticking to my weasel words! The biggest thing for me about this amp is its sharp but extremely smooth character. A contradiction? Not at all, its got top draw detail but it always seems to presented with a nice natural edge. Greg cites this design as low distortion (~0.008%) but to my ears it isn't like some of the other low distortion designs, its not bright and over hyped but its feels just as detailed with a really appealing softer edge that makes listening very easy. More refined overall I'd say is the best way of putting it and especially in the upper frequencies.
Soundstaging is amongst the best I've heard from a solidstate designs and really only seems to be limited by the recording and the rest of your equipment. I'm feeding it with some great quality DAC's and bit perfect playback so this gives the SKA one of the best signals it can hope for. The SKA doesn't flatter rubbish recordings and they still sound rough but not to the extent that you couldn't enjoy them its just that in comparison to the better/best recording you don't get the awesome realism and that really involving nature.
What it does do with the right recording is completely fool you into thinking that your actually listening to the real thing. It does a great job of creating spaces and sizes, it seems to be able to relate the whole picture with proper proportions without blowing things up or bringing details to the fore that perhaps should be so obvious. Like I said the best word for this is natural, its often used word and there's varying degree's of it but here it really does feel right.
Tonality was perhaps covered in the last bit but just to be sure; its just plain natural
Go play the piano (if you have one) or another musical instrument and then go listen to something similar on the SKA. It sounds very nearly as real. Few amps I've heard do this. If only it had an ounce more detail it would be heaven but then again my speakers are most likely the weak link though that's about to sorted out in a big way.Imaging is drool worthy. I'm sure some folks can relate to what I'm about to write; have you ever heard those systems that have the kind of imaging that suspend disbelief? Well the SKA is nearly as good and again my speakers and room are probably the weak link so I expect improvments in the future. When playback is going on you hear very precise locations of certain sound or voices. You even get a good sense of depth with it being apparent that things are further away than other sounds. Another big deal is the amps great way with folly effect. I listened to many tracks and a few had me thinking that I could hear reflections off walls behind me but what I was actually hearing was the acoustic space of the recording, its a amazing effect to hear and always puts a smile on my face.
Bass again is better than I'm used to with the AKSA. Tight, smooth and rhythmic. I think that bass performance of many amps is one the biggest let downs and that a well conrtolled bass lift the entire performance on a notch. Room problems could be blamed but I do use DRC so that isn't a big problem for me.
Overall I'd have to say that this is the best DIY design I've come across yet and just happens to be the cheapest too. Its very hard to fault and I really do think that any real improvements above and beyond what performance is offered by the SKA isn't to be had from better amp design but from considerations of room and better loudspeakers.
I've been shopping around for amplifiers to complete my reference 3-way actives and in the SKA's I've found that. Things can only get better!
hi hifryer,
Here's the link to Harbuch, they're just up the road from you at Hornsby. They also have custom toriods for some Silicon Chip projects. I've used them in all my amps and can't complain.
http://ourworld.compuserve.com/homepages/harbuch/harbuch.htm
regards
Here's the link to Harbuch, they're just up the road from you at Hornsby. They also have custom toriods for some Silicon Chip projects. I've used them in all my amps and can't complain.
http://ourworld.compuserve.com/homepages/harbuch/harbuch.htm
regards
Hi ShinOBIWAN,
first a splendid review. Read it with a lot of interest as I have 2 GB300 kits to be assembled as soon as I have found 2 decend toroids (or better R-core transformers, also I wonder if those will be a big improvement for these amps).
Can you tell us some more about the music you played to evaluate the amps, besides Andreas Vollenweider'.
Did you play classical music and live-recordings.
Now you heard the amps what is your opinion on the Hurbert his review in the first post of this thread.
You evaluate the amp as the best DIY amp you heard, does that imply you have heard better (commercial brand) amps ? If so which commercial amp do you regard better and in what aspects.
Thanks Henk.
first a splendid review. Read it with a lot of interest as I have 2 GB300 kits to be assembled as soon as I have found 2 decend toroids (or better R-core transformers, also I wonder if those will be a big improvement for these amps).
Can you tell us some more about the music you played to evaluate the amps, besides Andreas Vollenweider'.
Did you play classical music and live-recordings.
Now you heard the amps what is your opinion on the Hurbert his review in the first post of this thread.
You evaluate the amp as the best DIY amp you heard, does that imply you have heard better (commercial brand) amps ? If so which commercial amp do you regard better and in what aspects.
Thanks Henk.
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