Hi!
My old Marantz amp (PM750) is slowly dying, so i need to change it. I could repair it, but it's quite complicated and it uses very strange audio cables (anyone know what they are? they go from inputs to preamp).
A friend kindly offered me his Quad405-2 layout with some mods. I must say i never heard real 405, except brother's which was built with very bad material and mods are probably not well done.
Can someone please comment the sound of 405-2? Is it high quality amp and can be compared to "better" amps?
What i need is nice neutral amp that can drive my passive KRK ST8 (120Wmax) studio monitors. At some occasions i will use tube preamp with it, to smooth the sound a bit (this monitors sound a bit harsh).
In short words; do you suggest making it for my needs if i get lots of material for free and some help from very experienced friend (he built at least 20 Quads)?
Btw, is it possible to replace input op amp with discrete version? How much gain does it need? I have some very nice sounding DOAs.
Miha
My old Marantz amp (PM750) is slowly dying, so i need to change it. I could repair it, but it's quite complicated and it uses very strange audio cables (anyone know what they are? they go from inputs to preamp).
A friend kindly offered me his Quad405-2 layout with some mods. I must say i never heard real 405, except brother's which was built with very bad material and mods are probably not well done.
Can someone please comment the sound of 405-2? Is it high quality amp and can be compared to "better" amps?
What i need is nice neutral amp that can drive my passive KRK ST8 (120Wmax) studio monitors. At some occasions i will use tube preamp with it, to smooth the sound a bit (this monitors sound a bit harsh).
In short words; do you suggest making it for my needs if i get lots of material for free and some help from very experienced friend (he built at least 20 Quads)?
Btw, is it possible to replace input op amp with discrete version? How much gain does it need? I have some very nice sounding DOAs.
Miha
QUAD 405-2 reborn
...Hi, Miha
My first Quad 405 was built in 1981 , I remember , voltage rail only 24 V with 2N3055 transistors . Not long time ago I start to make a new improoved (reborn ) Quad 405 . Here you can find some pictures http://i27.tinypic.com/71h6oh.jpg voltage rail +/-60V and another variant http://i27.tinypic.com/11m40pg.jpg and this one with lateral mosfet http://i26.tinypic.com/1smhrk.jpg finally , the case http://i28.tinypic.com/wr19nt.jpg . 🙂 . The sound is clear , warm and ...... IC cannot be substitute by discrete componnents , u can use LME 49710 . Regards alex mm .🙂
Sorry for my poor english 🙁
...Hi, Miha
My first Quad 405 was built in 1981 , I remember , voltage rail only 24 V with 2N3055 transistors . Not long time ago I start to make a new improoved (reborn ) Quad 405 . Here you can find some pictures http://i27.tinypic.com/71h6oh.jpg voltage rail +/-60V and another variant http://i27.tinypic.com/11m40pg.jpg and this one with lateral mosfet http://i26.tinypic.com/1smhrk.jpg finally , the case http://i28.tinypic.com/wr19nt.jpg . 🙂 . The sound is clear , warm and ...... IC cannot be substitute by discrete componnents , u can use LME 49710 . Regards alex mm .🙂
Sorry for my poor english 🙁
Hi Alex!
Nice amp! Congratulations. I think i'm going to build one myself(now waiting for the parts.😉 ).
How warm are you driving it? I mean your heatsinks are not very big how do they handle the heat?
By the way, where did you buy the LM and the power transistors?
Nice amp! Congratulations. I think i'm going to build one myself(now waiting for the parts.😉 ).
How warm are you driving it? I mean your heatsinks are not very big how do they handle the heat?
By the way, where did you buy the LM and the power transistors?
Hi,
I'm quite sure it's possible to change op amp with non-inverting discrete version. Anyone have experiences with this kind of mod?
I have some experiences with Leach amp, can someone please comment how it sounds compared to Quad? Are they close in sound?
I must say i don't have good experiences with brother's Quad405II. Highs are a bit muddy and "sweet". Lows are not good either, they are somehow exagerated, boomy at around 50 to 80Hz. But amp is built with bad material,so i guess this is the reason for problems i mentioned.
Any more thoughts about sound of this amp when is well built?
Miha
I'm quite sure it's possible to change op amp with non-inverting discrete version. Anyone have experiences with this kind of mod?
I have some experiences with Leach amp, can someone please comment how it sounds compared to Quad? Are they close in sound?
I must say i don't have good experiences with brother's Quad405II. Highs are a bit muddy and "sweet". Lows are not good either, they are somehow exagerated, boomy at around 50 to 80Hz. But amp is built with bad material,so i guess this is the reason for problems i mentioned.
Any more thoughts about sound of this amp when is well built?
Miha
Hi,
I've never been too thrilled with the sound of the Quad 405. Sonically I think (I know !) you can do much better. The whole reason for the current dumping philosophy was to enable a "slow" pair of outputs to be used with no adjustment for quiescent current. From a technical view it was a truly radical new way of thinking. If you want to build one you must stick to the original concept and design. The component values are crucial for it to perform as it does.
Regards Karl
I've never been too thrilled with the sound of the Quad 405. Sonically I think (I know !) you can do much better. The whole reason for the current dumping philosophy was to enable a "slow" pair of outputs to be used with no adjustment for quiescent current. From a technical view it was a truly radical new way of thinking. If you want to build one you must stick to the original concept and design. The component values are crucial for it to perform as it does.
Regards Karl
rotation said:
It's a little harsh to say the the Quad 405 were built with 'bad material'. It was pretty much state of the art when it was released.
My first was a low serial number, about 1066 I think, and like a lot of Quad stuff, it did sound warm and 'flat', the Quad sound.
My later 2 both sounded a lot more lively. All benefitted from change of I/O connectors.
There are pages and pages of mods for these amps including upgrading the op-amp.
good luck
Andy
Hi,
it was not original Quad, sorry, i should say it. A friend built it for my brother with what he had at hand.
Can you compare it to modern amps?
Miha
it was not original Quad, sorry, i should say it. A friend built it for my brother with what he had at hand.
Can you compare it to modern amps?
Miha
Based on the schematics I've seen the whole discrete opamp version has been done, Quad called them the 606, 707 and 909.
There is still an op-amp in the circuit, but it's role is that of a normal DC servo.
Stuart
There is still an op-amp in the circuit, but it's role is that of a normal DC servo.
Stuart
Hello Alex mm,
Just been having a closer look at your handiwork -- very nice job indeed. The "one with a lateral" got my attention (Think you know why 🙂) Did you use the lateral for the Class A output section ? What did you use for the dumpers ? and how true to the original design is it.
Regards Karl
Just been having a closer look at your handiwork -- very nice job indeed. The "one with a lateral" got my attention (Think you know why 🙂) Did you use the lateral for the Class A output section ? What did you use for the dumpers ? and how true to the original design is it.
Regards Karl
Lateral mosfet Quad .....
Hi , Mooly
Sorry, for delay , but I'm bussy at my job . So, let's see first schematic http://i32.tinypic.com/f0opom.jpg and then one of the PCB 's http://i32.tinypic.com/24gnnud.jpg , the rest should be clear 😀 .Regards alex mm .
Hi , Mooly
Sorry, for delay , but I'm bussy at my job . So, let's see first schematic http://i32.tinypic.com/f0opom.jpg and then one of the PCB 's http://i32.tinypic.com/24gnnud.jpg , the rest should be clear 😀 .Regards alex mm .
Thanks for posting them Alex -- will have a closer look. Just done something silly, clicked on "unsubscribe from all threads" accidently.
Thanks
Thanks
Very nice. It's pretty true to the original concept. See you changed the Op-Amp configuration to non inverting.
How would you rate it ultimately for sound quality ? Asking a lot of questions now --- just interested 🙂 . See the laterals have a 220 ohm between the gates, do they run at zero quiescent current with no signal ( as in nearly at the point of conduction but not quite).
One thing always puzzled me a bit with this design. The original "concept" used a low value resistor in the "bridge" network but this was replaced by a coil in production on the grounds of power loss in that low value resistor. This required the replacing of one of the other bridge components by a small capacitor--- the 120pf, to maintain the AC balance as it were.
I always wondered what really happened with a reactive load like a speaker, rather than a resistive test load and whether the error signal ever got caught out. The amp as a whole never claimed to run at zero quiescent current -- only the dumpers -- so how much of a problem was the power loss if a resistor had been kept.
I really admire the design, I just have these nagging doubts so tell us all. HOW DOES IT SOUND 😀 😀, and what have you compared it to. I do like your PCB's, I am getting the itch again 🙂
How would you rate it ultimately for sound quality ? Asking a lot of questions now --- just interested 🙂 . See the laterals have a 220 ohm between the gates, do they run at zero quiescent current with no signal ( as in nearly at the point of conduction but not quite).
One thing always puzzled me a bit with this design. The original "concept" used a low value resistor in the "bridge" network but this was replaced by a coil in production on the grounds of power loss in that low value resistor. This required the replacing of one of the other bridge components by a small capacitor--- the 120pf, to maintain the AC balance as it were.
I always wondered what really happened with a reactive load like a speaker, rather than a resistive test load and whether the error signal ever got caught out. The amp as a whole never claimed to run at zero quiescent current -- only the dumpers -- so how much of a problem was the power loss if a resistor had been kept.
I really admire the design, I just have these nagging doubts so tell us all. HOW DOES IT SOUND 😀 😀, and what have you compared it to. I do like your PCB's, I am getting the itch again 🙂
I am looking for upgrading my two 25 year old Quad 405-2. I will try something simular to the Keith Snook "405-Mod-3". I do not think any Quad power amp is as transparent as say a Rotel RB-1080. All the Quad power amp are a bit "veiled" but they are not in any way sounding aggressive. A touch of "tube" sound perhaps?
Karl,
The project is presented here.
The boards are projected by Alex mm.
The sound of QUASAR (QUAD405 mosfet version) have nothing to do with his father. 😉
The sound is fast, with excellent macro and micro dynamics, fluid - like very best class A amplifiers.
Amplifier is able to handle very complex passages with easiness.
Soudstage is deep and each instrument can be easily located in space.
Amplifier sound is not compressed at all. 3D is also over many expensive amplifiers.
The transparency is breathtaking.
Bass is deep, round and very detailed.
No listening fatigue even many hours.
I'll place this amplifier in the range of 4000-6000 euros.
The amplifier was, so far, directly compared with Unison Research Sinfonia, Naim NAP250, Symphonic Line RG10 and Sugden A21SE, in different systems.
Speakers used in these tests: Triangle Antal EX, ProAc 140, Spendor S5E, Jm Lab Electra.
Cables: Audioquest Cobra, Kimber, Chord
Sources: Naim 5x, marantz56 NOS supertuned, Sugden CD21SE
My system is:
source - Marantz CD56 supertuned
interconnect - Audioquest Cobra
amplifier - QUASAR
speakers - Triangle Antal EX biwired with NAIM cables.
Regards,
Tibi
The project is presented here.
The boards are projected by Alex mm.
The sound of QUASAR (QUAD405 mosfet version) have nothing to do with his father. 😉
The sound is fast, with excellent macro and micro dynamics, fluid - like very best class A amplifiers.
Amplifier is able to handle very complex passages with easiness.
Soudstage is deep and each instrument can be easily located in space.
Amplifier sound is not compressed at all. 3D is also over many expensive amplifiers.
The transparency is breathtaking.
Bass is deep, round and very detailed.
No listening fatigue even many hours.
I'll place this amplifier in the range of 4000-6000 euros.
The amplifier was, so far, directly compared with Unison Research Sinfonia, Naim NAP250, Symphonic Line RG10 and Sugden A21SE, in different systems.
Speakers used in these tests: Triangle Antal EX, ProAc 140, Spendor S5E, Jm Lab Electra.
Cables: Audioquest Cobra, Kimber, Chord
Sources: Naim 5x, marantz56 NOS supertuned, Sugden CD21SE
My system is:
source - Marantz CD56 supertuned
interconnect - Audioquest Cobra
amplifier - QUASAR
speakers - Triangle Antal EX biwired with NAIM cables.
Regards,
Tibi
Hello Tvicol,
Thanks ever so much for that, I will have a good read through it all.
ALL the comments you describe --- I know EXACTLY what you mean --- this is what I feel I achieved with my MOSFET amp. Once you have experienced this, and this may sound a bit unkind, but it makes other offerings seem well lets just say "very average" You have obviously experienced this.
I too used the new Sugden A21SE as a kind of benchmark, it's a very good piece of kit, but musically I feel I have bettered it.
The PCBs by Alex look very good I must say.
My system --- unchanged for years because I am so pleased with it,
MOSFET amp --- in these forums 😉 Just wish someone with a top flight system would build it 🙂
Micromega Stage 2, sensibly tweaked.
Pure DRX701
Good old Sony Minidisc !!
B&W 703's -- Wonderful.
Edit, just looking at your pictures. They are a real credit to you.
Thanks ever so much for that, I will have a good read through it all.
ALL the comments you describe --- I know EXACTLY what you mean --- this is what I feel I achieved with my MOSFET amp. Once you have experienced this, and this may sound a bit unkind, but it makes other offerings seem well lets just say "very average" You have obviously experienced this.
I too used the new Sugden A21SE as a kind of benchmark, it's a very good piece of kit, but musically I feel I have bettered it.
The PCBs by Alex look very good I must say.
My system --- unchanged for years because I am so pleased with it,
MOSFET amp --- in these forums 😉 Just wish someone with a top flight system would build it 🙂
Micromega Stage 2, sensibly tweaked.
Pure DRX701
Good old Sony Minidisc !!
B&W 703's -- Wonderful.
Edit, just looking at your pictures. They are a real credit to you.
Hi,
That enclosure is just stunning. Made a note of the company 🙂
We seem to think alike regarding listening tests etc. I have never used a simulator, it is something I should get into though.
Can I ask-- The front end OpAmp -- apart from the obvious (the phase shift) is there any reason you used the non inverting configuration. In line level stages I tend to prefer the inverting mode, even if it means using an extra device to get back to overall non inverting of phase.
That enclosure is just stunning. Made a note of the company 🙂
We seem to think alike regarding listening tests etc. I have never used a simulator, it is something I should get into though.
Can I ask-- The front end OpAmp -- apart from the obvious (the phase shift) is there any reason you used the non inverting configuration. In line level stages I tend to prefer the inverting mode, even if it means using an extra device to get back to overall non inverting of phase.
Karl,
Yes, Sugden A21SE could be used as a reference amplifier.
You have a very nice setup !
Which cables are you using for interconnect and speakers ?
Thanks & regards,
Tibi
Yes, Sugden A21SE could be used as a reference amplifier.
You have a very nice setup !
Which cables are you using for interconnect and speakers ?
Thanks & regards,
Tibi
Mooly said:
The input stage is well presented by Keith Snook in his modifications.
The main advantage of non inverting configuration is noise reduction.
Some people will say that inverting topology will have lower distortion, but in this case the operational will not drive a very low impedance and IMHO noise is more important here, as I need to keep input impedance higher enough. Anyhow LME49710 is a stunning operational with ultra low distortion and will sound excellent in both configurations.
Regards,
Tibi
Hello Tibi,
More to read -- thank you.
Cables, nothing very exotic, for the interconnects I use some leads I got from CPC ( They are local to me) which I have shortened. At the time they were a "best buy" recommended by one of the popular mags. I do have a "Chord" phono interconnect but these are every bit as good.
Speaker leads - again from CPC - OFC Type made by Pro-Power, now these are good, and very flexible as well. Fortunately I only have a shortish run from the amp.
As you can probably see from the pic, I don't like to see cables 🙂 .
All the power for the source components is from a small box on the wall behind the amp, right next to the wall socket. The incoming mains is fed through a high current relay (I know 🙂 , they must draw all of 20 watts on together) that is switched from the amp. The signal to the box is via an opto (TOSLINK) interconnect, and the box gives a 2 minute delay when switching the amp off. Just enough time to remove a CD or finalise that Mini Disc before the power goes. There is a manual overide as well so you can record of the tuner without the amp being on if you want.
I must try some of the later OpAmps available-- when I modded the MicroMega I used OPA2604 (Used OPA604 in my amp) and AD845's. I found these very musical -- notably so.
More to read -- thank you.
Cables, nothing very exotic, for the interconnects I use some leads I got from CPC ( They are local to me) which I have shortened. At the time they were a "best buy" recommended by one of the popular mags. I do have a "Chord" phono interconnect but these are every bit as good.
Speaker leads - again from CPC - OFC Type made by Pro-Power, now these are good, and very flexible as well. Fortunately I only have a shortish run from the amp.
As you can probably see from the pic, I don't like to see cables 🙂 .
All the power for the source components is from a small box on the wall behind the amp, right next to the wall socket. The incoming mains is fed through a high current relay (I know 🙂 , they must draw all of 20 watts on together) that is switched from the amp. The signal to the box is via an opto (TOSLINK) interconnect, and the box gives a 2 minute delay when switching the amp off. Just enough time to remove a CD or finalise that Mini Disc before the power goes. There is a manual overide as well so you can record of the tuner without the amp being on if you want.
I must try some of the later OpAmps available-- when I modded the MicroMega I used OPA2604 (Used OPA604 in my amp) and AD845's. I found these very musical -- notably so.
Attachments
Quad 405 Lateral Mosfet
Nice setup, Mooly 🙂
You mean you "bettered" (tweaked) your Sugden A21SE? I still have your Mosfet Amp in target! 😉
Alex MM, very interesting! 🙂
Did you assembled the below version as well?
Nice setup, Mooly 🙂
You mean you "bettered" (tweaked) your Sugden A21SE? I still have your Mosfet Amp in target! 😉
Alex MM, very interesting! 🙂
Did you assembled the below version as well?
alex mm said:
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