robertkd
Been here a while! 
Electronics Engineer from sunny Queensland
Posts: 111
|
Post by robertkd on Mar 13, 2009 13:13:21 GMT
The bipolar input capacitors should be replaced by higher quality film type capacitors. The Wima 4.7uF MKS2-XL capacitors are a good choice , as they have 5mm lead spacing. Polypropylene capacitors will give slightly better results again, but are physically awkward to implement because of their bulk. (See Reply#8) What is the minimum capacitance allowable for the input caps, I have a couple of 2.2uF polypropylenes to hand, would these be OK here until I can get something else? well for all practical intents they will be fine, in a standard build the 2.2uF will give you very acceptable low end, I am currently running 3uF PP's and really can't tell the difference between this an the 2uF PP's (2*1uF) I was previously running, in any case I am sure you will find the improvement in SQ over the bipolar caps to be well worthwhile. Robert |
|
|
|
Post by rossman on Mar 13, 2009 13:22:47 GMT
Thanks Robert, I will see if I can get them in some time over the afternoon.  |
|
robertkd
Been here a while!
Electronics Engineer from sunny Queensland
Posts: 111
|
Post by robertkd on Mar 13, 2009 13:34:33 GMT
Thanks Robert, I will see if I can get them in some time over the afternoon. no worries, do let us know your findings here, I "like" bass but for me anything below 30Hz needs to come from a sub woofer  Robert |
|
|
|
Post by rossman on Mar 13, 2009 16:31:58 GMT
Well I would say that bass quality has improved but with no increase in quantity. For me the main improvements are in queter background and increased detail. PRaT and soundsatge also seem improved so I think it is a very worthwhile improvement even after the short listen that I have had so far.
|
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on Mar 13, 2009 23:21:10 GMT
rossman
Recent thinking is to have a much larger value capacitor at the input, than that dictated by the -3db rolloff point as so often used previously.The idea is to minimise the source impedance as seen by the input stage, which when coming from a CD/DVD player is only a few fundred ohms.
SandyK
|
|
|
|
Post by rossman on Mar 14, 2009 10:16:51 GMT
rossman Recent thinking is to have a much larger value capacitor at the input, than that dictated by the -3db rolloff point as so often used previously.The idea is to minimise the source impedance as seen by the input stage, which when coming from a CD/DVD player is only a few fundred ohms. SandyK Alex, the first part about the larger capacitor made sense then the rest went totally over my head. I am happy with the improvement gained for now but would like to take it even further at some point. At least I feel that my build is now ready for the arrival of the Audio GD evaluation OPAs. Can you give me an idea of what value I should be looking for the input caps? I've just bought a book to try and learn more about electronics so I might have more understanding of the more technical aspects in the future. Thanks. Paul |
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on Mar 14, 2009 10:24:05 GMT
paul
I would leave it at 2.2uF to 4.7uF . The SQ of polypropylene capacitors would more than likely outweigh the advantages of having electros more than 10 x the value. As you have already found, the polyropylenes sound cleaner. Have you tried the LM4562HA yet ? Below are comments from jeffc about this chip.
I think he likes it ? ;D
Alex
Re: LM4562HA Group Buy
« Reply #65 Yesterday at 11:37am »
--------------------------------------------------------------------------------
OK .... 24h on the dial and the LM4562HA is moving into serious Zen-ness territory in my DAC . Hard to believe it has the same innards as the plastic opamp, awesome detail and realism in spades.
You guys still waiting on one are in for a real treat, its one damn opamp.
cheers.. jeffc
|
|
robertkd
Been here a while!
Electronics Engineer from sunny Queensland
Posts: 111
|
Post by robertkd on Mar 14, 2009 10:35:11 GMT
Paul Agreed 2.2uF to 4.7uF will be fine, I have also been listening to the OPA SUN in a "stock" SCHA build and I'm liking it however I need to set up a level control with RCA's so I can use the DAC analogue output to compare as I don't really think my iPod is doing it justice  all good Robert |
|
|
|
Post by rossman on Mar 14, 2009 11:43:35 GMT
paul I would leave it at 2.2uF to 4.7uF . The SQ of polypropylene capacitors would more than likely outweigh the advantages of having electros more than 10 x the value. As you have already found, the polyropylenes sound cleaner. Have you tried the LM4562HA yet ? Below are comments from jeffc about this chip. I think he likes it ? ;D Alex Re: LM4562HA Group Buy « Reply #65 Yesterday at 11:37am » -------------------------------------------------------------------------------- OK .... 24h on the dial and the LM4562HA is moving into serious Zen-ness territory in my DAC . Hard to believe it has the same innards as the plastic opamp, awesome detail and realism in spades. You guys still waiting on one are in for a real treat, its one damn opamp. cheers.. jeffc Thanks Alex & Robert. I haven't tried the LM4562HA yet, I am waiting to see what the Audio GDs are like first before I make a decision wether to try the metal version. |
|
|
|
Post by jphoward on Mar 14, 2009 23:42:34 GMT
I've just completed the basic SCHA kit from Jaycar (my first ever electronics project!) and am very happy with the result.  I'm now going to try to build a 2nd one - this time with sandyk's enhancements as shown in post #2 of this thread. I've already ordered the replacement opamp, which should arrive, tomorrow. I do have some questions which I'm hoping some of you knowledgeable folks can help with... - I don't understand what to do with the 'JLH ripple eater'. Where do I get a PCB from (I'm in Melbourne)? What parts do I need? Where does the circuit fit - between the PSU output and the amp input?
- If I don't install the ripple eater, can I still use all the other tweaks - or are some/all of them dependant on using the ripple eater?
- For a complete novice like me, what are the simplest and most effective modifications I should start with?
|
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on Mar 15, 2009 0:04:51 GMT
jphoward
"spirit" (Phil) up in Queensland, may be able to help with the JLH PCB shortly.Send spirit a P.M. The JLH is simply connected between the Power Supply PCB and the main PCB. All of the other modifications will work without the JLH PCB, but the JLH PCB markedly improves the low end "punch" as well as leaving low level detail clear of residual noise, which makes it cleaner sounding,and also improves channel separation. There are other ways to accomplish fairly similar results, but they entail making a series of modifications to the main PCB. The simplest and most worthwhile modifications appear to be upgrading the opamp from the original OPA2134, and replacing the output BD139/BD140 transistors with Toshiba 2SA1930/2SC5171. These devices will be available from RS Components at good price, but there will most likely be a delay in arrival due to them being on back order.
W.E.S. in Sydney may have them in stock, but expect higher prices than RS.The list of components for the JLH should be posted somewhere already, but I will email you a copy.
Alex
|
|
|
|
Post by jphoward on Mar 15, 2009 0:50:30 GMT
Many thanks Alex - that's exactly what I needed to know. I'll get in touch with Spirit regarding the PCB.
Does anyone have a suitable CAD file (or similar) I could use to print on a laser printer? If so - I should be able to etch a board myself, right... or send it off to a PCB prototyping service? (I've done neither of these things before - but this sounds like a good opportunity to learn!)
|
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on Mar 15, 2009 1:02:05 GMT
Many thanks Alex - that's exactly what I needed to know. I'll get in touch with Spirit regarding the PCB. Does anyone have a suitable CAD file (or similar) I could use to print on a laser printer? If so - I should be able to etch a board myself, right... or send it off to a PCB prototyping service? (I've done neither of these things before - but this sounds like a good opportunity to learn!) jphoward Unfortunately, most PCB makers require something like Gerber files,which have embedded drilling information. I will email you a copy of Dave Mitchell's artwork so that you can try etching your own. Alex P.S. The middle group of the PCB artwork is the non current limited version which we use for this project. Also, missing from the components list is a 3 pin terminal block with 5.08mm pin spacing. e.g. Jaycar CAT. NO. HM3173 RRP $1.55 3 WAY PCB MOUNT SCREW TERMINAL - 5MM PITCH Ideal for those situations where wires leave a PCB. Just solder the terminal strip to the PCB and connect wires. 2 way (HM- 3172) and 3 way (HM- 3173)...more... QTY 1+ $1.55 |
|
|
|
Post by jphoward on Mar 15, 2009 5:27:33 GMT
Well I heard back from Spirit - sounds like he's only days away from having boards ready, so I won't try to create my own just yet...
I'm thinking of creating a little wiki page or blog post or some such describing how to built this unit, plus the tweaks, aimed at complete n00bs (like me). Is it OK if I include the images of the tweaked layouts/schematics, ripple eater parts list, etc, on that page? I've found this a really great first project - I've learnt a lot about electronics building techniques, and a walk-thru of build would probably help others interested in starting on this hobby.
|
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on Mar 15, 2009 6:47:53 GMT
Jeremy
Perhaps not a good idea, as we are already possibly infringeing Silicon Chip's copyright by even posting modified diagrams and modified schematics. You may have noticed that I haven't posted a copy of the original schematic as published,or the unedited original layout diagram, for this reason. This is also why I have only ever offered additional information such as colour pages from the magazine via email to those who had purchased the kits,except for a couple of small sections. I only did this because some of the black and white photocopy pages supplied may have been hard to follow.
What I did post was on the assumption that the vast majority of constructors would be purchasing the kits from Jaycar and Altronics, where the photocopies were approved by Silicon Chip magazine.
Also, the original article for the JLH PSU add-on was copyrighted by Electronics Today International, and although the project has been substantially modified , may still be subject to copyright restrictions too.
Alex
|
|
|
|
Post by jphoward on Mar 15, 2009 11:52:38 GMT
Good point Alex - I'll contact the mags and see if I can get permission. In the meantime (assuming I find the time) I'll try to find a way to create appropriate diagrams without drawing on the origanal artwork.
|
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on Mar 15, 2009 12:02:39 GMT
Good point Alex - I'll contact the mags and see if I can get permission. In the meantime (assuming I find the time) I'll try to find a way to create appropriate diagrams without drawing on the origanal artwork. Jeremy Whatever you do, please do not mention Rock Grotto, as they may not be too happy with what has already been posted here. To make matters worse, some of it may have already been used in Head Fi ? TBH, I don't think it is a good idea to post any of this elsewhere. In fact, I would prefer that my contributions remain solely in Rock Grotto. Feel free though, to start a thread in this section of Rock Grotto aimed at "newbies", and using any of the material that I have posted. It would also be a good idea to PM Robert before you use any of his posted material. Alex P.S. I do have a couple of pages cut out of a purchased copy of ETI with the original JLH article, but the pages do not have any date on them.The article is at least 15 years old . (?) |
|
|
|
Post by jphoward on Mar 15, 2009 13:31:11 GMT
OK got it. I'll start a new 'newbies' thread here then when I have something useful to say. |
|
|
|
Post by jphoward on Mar 16, 2009 14:51:18 GMT
Can I just confirm the change to the components just before the output? Basically what we're doing is removing L1/2, the 10ohm resistor and 47nF capacitor and ground connection, and replacing the 47ohm resistor with a 68ohm resistor? Should the 68ohm resistor be 1W ? What does "adjust for headphones as required" mean - how do I do this adjustment? (My headphones as 32ohm).
|
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on Mar 16, 2009 20:31:02 GMT
Can I just confirm the change to the components just before the output? Basically what we're doing is removing L1/2, the 10ohm resistor and 47nF capacitor and ground connection, and replacing the 47ohm resistor with a 68ohm resistor? Should the 68ohm resistor be 1W ? What does "adjust for headphones as required" mean - how do I do this adjustment? (My headphones as 32ohm). That is correct. 68ohm .5W metal film resistors (e.g. Jaycar) may be used. They come in a packet of 8 for 46c Cat. no. RR0544. They have closer resistance tolerance, and will help ensure a good balance between levels in the left and right headphones. Start off with this value, as it seems to suit the majority of headphones . 56 ohms will give a slight amount of added volume and a little more at the top end. Conversely, 75 or 82 ohms will give a little less volume and a slight reduction in treble. Alex |
|
|
|
Post by jphoward on Mar 17, 2009 10:21:03 GMT
My tweaked power supply has +14.98V on one rail, and -14.80V on the other. Is it OK for the 2 rails to be different values, and for one of them to be a fair bit away from 15V?
If not, what should I should change to get them to match?
|
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on Mar 17, 2009 10:36:24 GMT
My tweaked power supply has +14.98V on one rail, and -14.80V on the other. Is it OK for the 2 rails to be different values, and for one of them to be a fair bit away from 15V? If not, what should I should change to get them to match? jphoward That won't be a problem. If you want to fiddle with the lower -VE voltage supply, and have a 10K resistor laying around, you could try soldering it across the 100 ohm resistor associated with the LM337 and see how much that increases it's voltage. Alex |
|
|
|
Post by jphoward on Mar 17, 2009 11:42:54 GMT
It looks in the diagram like the 47pF capacitor is yellow, which means 'adjust for headphones'. Can you provide some guidance on making this adjustment, please?
|
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on Mar 17, 2009 12:03:36 GMT
jphoward
The 47pf are just as printed, and not part of the modification, unless you wish to fit 47pf polystyrene types instead. There are 2 lots of 47ohm resistors in the bottom left and right corners. One of these is an additional output if required,which could also be used to feed an additional pair of RCA jacks to enable the unit to be used as a preamplifier. Both lots of resistors can be changed to 68 ohms, or one set left at 47 and the other 68 if you wish both headphone sockets to have slightly different characteristics for use with alternate headphones, or even 2 pairs at once.
Alex
|
|
|
|
Post by rossman on Mar 17, 2009 16:08:50 GMT
Can I just confirm the change to the components just before the output? Basically what we're doing is removing L1/2, the 10ohm resistor and 47nF capacitor and ground connection, and replacing the 47ohm resistor with a 68ohm resistor? Should the 68ohm resistor be 1W ? What does "adjust for headphones as required" mean - how do I do this adjustment? (My headphones as 32ohm). That is correct. 68ohm .5W metal film resistors (e.g. Jaycar) may be used. They come in a packet of 8 for 46c Cat. no. RR0544. They have closer resistance tolerance, and will help ensure a good balance between levels in the left and right headphones. Start off with this value, as it seems to suit the majority of headphones . 56 ohms will give a slight amount of added volume and a little more at the top end. Conversely, 75 or 82 ohms will give a little less volume and a slight reduction in treble. Alex Can you tell me why the resistors have been changed from carbon film to metal film and what difference this is likely to make to SQ? Thanks. Paul |
|
I'm now going to try to build a 2nd one - this time with sandyk's enhancements as shown in post #2 of this thread. I've already ordered the replacement opamp, which should arrive, tomorrow. I do have some questions which I'm hoping some of you knowledgeable folks can help with...