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Post by Deleted on Mar 10, 2009 2:57:38 GMT
Dave
You can also probably blame me for part of Leo's less than enthusistic review of the Dou Dou. Leo was using a couple of my ClassA power amp modules into headphones for comparison.
Alex
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FritzS
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Post by FritzS on Mar 10, 2009 5:59:21 GMT
Will The selected and matched devices perform very well indeed,and the MPSA18 are only a few cents each if you buy a couple of hundred from Jameco. Friedrich obtained his LS devices from the Austrian distributor, but they won't export them. (That is assuming they still have stocks.) Alex P.S. Anybody wanting a copy of the schematic should PM Leo or myself. I think that for the moment, it would best be restricted to RG members only. This I have in my stock + price that I pay'd for: 2 pcs LSK389A-TO71 € 6,70/pcs 2 pcs LSK170A-TO92 € 0,77/pcs 2 pcs IT124A-TO71 € 5,80/pcs 4 pcs LS313A-TO71 € 4,95/pcs 4 pcs LS352A-TO71 € 4,95/pcs The price did not include VAT (20%) and shipping. Leo if you want to test some I can help you  |
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Post by leo on Mar 10, 2009 21:18:35 GMT
Those DACT2's are seriously pricey aren't they ... the Rolex of attenuators. Probably be running smooth long after our el-cheapo metal film one's have give up the ghost.  How close does the LM'd SCHA come to this class A in SQ? Yes , the DACT's look nice, I just hope they are not ladder types I've now got the metal can LM4562 in the SCHA which has improved the sound quality a fair bit. In all honesty I still prefer the classA, the classA has serious depth which to me the SCHA cannot match when using the highly modified Buffalo dac. It all just sounds more realistic to my so called golden ears |
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Post by Deleted on Mar 10, 2009 22:03:23 GMT
Those DACT2's are seriously pricey aren't they ... the Rolex of attenuators. Probably be running smooth long after our el-cheapo metal film one's have give up the ghost. How close does the LM'd SCHA come to this class A in SQ? Yes , the DACT's look nice, I just hope they are not ladder types I've now got the metal can LM4562 in the SCHA which has improved the sound quality a fair bit. In all honesty I still prefer the classA, the classA has serious depth which to me the SCHA cannot match when using the highly modified Buffalo dac. It all just sounds more realistic to my so called golden ears Leo It may be that as the SCHA gets further improved, that we will need to use it a a preamp for closer evaluation, as headphones just can't give the depth of image/ 3D sensation that you can get with good speakers. With the metal can LM4562HA onboard, the SC HA will make a fine preamp if input selection is added. It already sounded pretty good as a preamp with the normal LM4562 when I tried it. Alex |
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leo
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Post by leo on Mar 10, 2009 22:35:26 GMT
Yes , the DACT's look nice, I just hope they are not ladder types I've now got the metal can LM4562 in the SCHA which has improved the sound quality a fair bit. In all honesty I still prefer the classA, the classA has serious depth which to me the SCHA cannot match when using the highly modified Buffalo dac. It all just sounds more realistic to my so called golden ears Leo It may be that as the SCHA gets further improved, that we will need to use it a a preamp for closer evaluation, as headphones just can't give the depth of image/ 3D sensation that you can get with good speakers. With the metal can LM4562HA onboard, the SC HA will make a fine preamp if input selection is added. It already sounded pretty good as a preamp with the normal LM4562 when I tried it. Alex I use HD250 linears for evaluating, these cans are seriously brutal at showing up problems, I do understand why 90% of people hate the 250's, they sound god awful if your not careful I have to wait until the weekend before trying as a pre-amp, main reason is by the time I get home during the week its not really convenient when I want to have a proper good listen through the main system ;D |
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Will
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Post by Will on Mar 11, 2009 16:31:48 GMT
Yes , the DACT's look nice, I just hope they are not ladder types Can I ask why you would not like them to be ladder type attenuators? |
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leo
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Post by leo on Mar 11, 2009 23:47:33 GMT
Yes , the DACT's look nice, I just hope they are not ladder types Can I ask why you would not like them to be ladder type attenuators? My mistake, I mean't series types not ladder |
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Post by Deleted on Mar 12, 2009 0:49:11 GMT
The CT2 Audio Volume Controls are high quality stepped 24-position attenuators. Designed for maximum sonic quality, accuracy and reliability. This makes them equally suited for audiophile and professional applications.
Available as master volume control with 60dB attenuation range (1, 2, 4, 6, 8 decks) and as individual channel fine adjustment (CT2-10k-1/fine) with 0.5dB level change between each step (only available with 1 deck)
Their series resistor networks consist of 23 non-inductive, low noise, SMD metal film resistors.
The layout of the PC Boards and the choice of SMD resistors have reduced the signal path to a minimum length (typical five times shorter than conventional stepped attenuator designs with leaded resistors). The PCB design combined with the special resistors also account for the very low series inductance and the very low stray capacitance.
The result is a bandwidth beyond even the most demanding audiophiles’ requirements.
There has been special care taken to ensure the durability of CT2. Therefore, all contacts and PCB traces are gold plated to prevent any corrosion. As a result, the CT2s will maintain their specifications after long time of use even in hot and humid environments.
FEATURES
SCHEMATIC
Low noise, non-inductive, metal film SMD resistor network
Compact design
Entire signal path gold plated
Shorter signal path than conventional attenuators with leaded resistors
Reduced inductance and stray capacitance
Improved sonic quality
Improved accuracy - 0.05dB tracking and 0.05dB attenuation accuracy
Improved reliability
Increased bandwidth
Reduced distortion, less than 0.0001%
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Post by minivan on Mar 13, 2009 17:17:15 GMT
sorry i got a bit confused with this, is this sc class a similar to the jlh class a will posted in the 2nd post?
looking up in the altronic website for kit k5109, it said it's a 15w amp kit, so this is a low watt speaker amp but being used as a preamp?
if i want to buy one of this kit, what are the tweaks needed to be done to make it sound good?
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Post by Deleted on Mar 13, 2009 20:07:23 GMT
sorry i got a bit confused with this, is this sc class a similar to the jlh class a will posted in the 2nd post? looking up in the altronic website for kit k5109, it said it's a 15w amp kit, so this is a low watt speaker amp but being used as a preamp? if i want to buy one of this kit, what are the tweaks needed to be done to make it sound good? Minivan The PCB artwork that Will posted is of the SC15W amplifier which is also the basis of this preamp. Altronics no longer stocks this kit, although it may still appear as "stocks low." They will not be making any further kits. This means that anybody wishing to make the preamp will have to obtain their PCBs from RCS Radio in Sydney, or one of our members. A large part of the cost of the original kit was for the power output devices which aren't used in the preamp.Leo will be posting further information on the preamp as his time permits,including further listening tests in comparison with the SC HA with JLH, and LM4562HA metal can opamp. Either Leo or myself will be able to provide further information to interested members who send a PM, although we would prefer not to post them in open forum for non members to access at this point in time. Alex |
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jonclancy
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Post by jonclancy on Mar 13, 2009 21:07:35 GMT
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Post by Deleted on Mar 13, 2009 23:00:37 GMT
Jon No. The preamp is based on the 15W Class A from 1998. The layout of the later 20W Class A makes it much more awkward to implement the front end mods.The boards are also different in both channels in the later 20W design. Alex |
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Post by Deleted on Mar 13, 2009 23:47:13 GMT
Can I ask why you would not like them to be ladder type attenuators? My mistake, I mean't series types not ladder Leo favours the use of the ladder types because there are only 2 resistors in circuit at a time in each channel with this design. This gives it an improvement in signal to noise ratio, which is great if the rest of the design is able to take advantage of this small improvement.A good series attenuator, despite all the small series surface mount resistors, will still be quieter than a typical carbonised track in a potentiometer,which is actually relatively long. The attenuator will also have a much wider bandwidth than with a typical quality dual potentiometer. This translates to a potentially wider frequency response with the amplifier. The series type is also more likely to have a small audible transition between steps, and the DACT2 also has a much smoother,seamless action, and is not "clunky" between steps like most typical attenuators which are just put together on a 24 position rotary switch,which has a quite clunky mechanical action. Alex P.S. The main downside with the DACT2 is that is DAMN expensive! |
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Post by guadixman on Mar 16, 2009 14:39:26 GMT
Leo,
buy 2 x 47K naked Vishay Z foils from Texas Components and shunt the Alps with these - i'd be very surprised if you'd ever consider wasting money on anything else. They cost about $13 each and TC ship using USPS, so you don't get ripped off with UPS/FedEx.
I'd previously used Welwyn RC55Y as shunts and in a shunt att. - not even in the same galaxy as naked bulk foils.
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Will
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Post by Will on May 7, 2009 17:42:35 GMT
Well, after Fritz pinched my set of boards  , this project stalled for me. I have enough photo-etch boards to make another set, plus a set of the offset correctors (which I've knocked up a pcb for). I also managed to talk Fritz into getting me a set of the LS devices, so that will make life a little easier. So tomorrow will see me etching a set, and finally getting round to making this amp. Time for some more solder fumes!!!  Leo, I hope yours is back in good order  |
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pagan
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Post by pagan on May 9, 2009 13:09:05 GMT
Will
If your going to etch a few pcb's for this.......
Then why don't you make provision for the offset corrector and LTP balancing?
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Will
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Post by Will on May 9, 2009 18:39:16 GMT
Hi Pagan, Boards are etched and drilled, just need to hand match components now. The artwork I used for etching is from the original article in Silicon Chip, and this along with the circuit diagram and the photos of Alex's and Leo's class A are all I have to go on. I don't have the 'luxury' of the silkscreen indicating what goes where, so I'll be referring back to photos and tracing the circuit from the schematic onto the PCB. This will make things a little more interesting on the construction front, and I'm leaving the LTP balancing modification until I've got it right. Once all is good, I may look into re-doing the PCB incorporating the thermal balancing, for other members to etch (only with Leo's and Alex's blessing). Mind you incorporating the dc offset into the main circuit is an idea... perhaps with wired links, so that you have a choice to use it or not. Mind you thats a long way off! pic of the offset board for interest. 2"x1"  |
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jonclancy
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Post by jonclancy on May 9, 2009 20:21:10 GMT
Your layout skills are awesome, matey!
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FritzS
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Post by FritzS on May 10, 2009 5:01:50 GMT
Have anyone a idea for a DC protection with a relay - but for HA use .... threshold abut +- 5 .... 10 mV This is one thing I miss David White construct one for his WNA, but I found no schema about. |
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Post by Deleted on May 10, 2009 6:10:57 GMT
Have anyone a idea for a DC protection with a relay - but for HA use .... threshold abut +- 5 .... 10 mV This is one thing I miss David White construct one for his WNA, but I found no schema about. Friedrich The best I can come up with is +-600mV threshhold. Very few would be designed for headphone amps. Alex |
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Post by robertkd on May 10, 2009 7:53:05 GMT
yes I'm thinking about that ATM  |
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leo
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Post by leo on May 10, 2009 13:44:02 GMT
Have anyone a idea for a DC protection with a relay - but for HA use .... threshold abut +- 5 .... 10 mV This is one thing I miss David White construct one for his WNA, but I found no schema about. You should at least build the amp first before worrying about DC offset |
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FritzS
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Post by FritzS on May 12, 2009 8:49:06 GMT
You should at least build the amp first before worrying about DC offset I don't mean DC offset, I mean a DC protection with a relay contact in the output line. This contact opens if more than +- 5 ... 10 mV DC are on the output line. Some power amps use this - but I don't know about commercial or DIY HA use this protection. |
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Post by Deleted on May 12, 2009 9:17:08 GMT
You should at least build the amp first before worrying about DC offset I don't mean DC offset, I mean a DC protection with a relay contact in the output line. This contact opens if more than +- 5 ... 10 mV DC are on the output line. Some power amps use this - but I don't know about commercial or DIY HA use this protection. Friedrich Commercial amplifiers are highly unlikely to protect against anything less than 600 mV. If using DC protection with 600mV sensitivity, that's only around 19mA into 32 ohm headphones without a series output resistor, and much less with a series output resistor. Alex |
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Will
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Post by Will on May 13, 2009 12:42:17 GMT
Your layout skills are awesome, matey! Why thank you, sir! I just wish I knew more about the clever bit before board layout, actually creating a circuit! It'll come. |
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, this project stalled for me.
