XTRProf
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Pssst ! Got any spare capacitors ?
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Post by XTRProf on Jul 7, 2010 12:00:00 GMT
Alright, then a V1, V2 or V3 will be ok. Any other commerial ones will do as well. Just a reference point as this SCHA can drive 8 ohms and above which is very good for such a cheapo. Most HA can't do that in a stable way except for the newer HA. Btw, how many watts can this SCHA pump out? Chong The basic SC HA is only an average, good value for money, performer. All the mods lift it way above that, and some say it is then better than the GS SRG2.However, it then can't readily drive 8 ohm headphones unless the Zobel network is retained. I will email you more info. Alex Thanks for the info thru email. I assume what is written at Jaycar is correct here: Stereo Headphone Distribution Amplifier Enables you to drive up to two stereo headphones from any line level (1volt peak to peak) input. The circuit features a facility to drive headphones with impedances from about 8-600 ohms. The Jaycar kit comes with all specified board components and quality fibreglass tinned PCB. Power Supply to Suit: KC5418 PC board size: 134 x 103mm
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Post by Deleted on Jul 7, 2010 12:05:39 GMT
Chong Yes, the info is correct. You will also need the KC5418 PSU or your own +-15V PSU, a 15-0-15VAC 20 or 30VA toroidal transformer,case, and potentiometer/Attenuator etc. for the basic version. Alex
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Post by Deleted on Jul 7, 2010 18:11:01 GMT
Alright, then a V1, V2 or V3 I have both of these. My MF V2 has all the DIY mods I know (but not Done-by-Mike) with a Little Pinkie. My AK mods SCHA has all the mods stated in the tweaks thread. To me the the most obvious difference (and only that, I could not say one is favourable over the other at all times) is that the V2 has a more full bodied ("A little south of neutral") presentation, without losing detail and nuances, making it a good late night listen, when my ears seem more sensitive to HF energy. Whereas the AK-SCHA has a more forthright ("A little north of neutral") which endows it with wonderful pace. There are other little differences but the above stands out to my ears.
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Post by Deleted on Jul 7, 2010 23:13:27 GMT
Chris Have you compared them both using 24/96 or 24/192 material ? This is becoming more important these days , mainly due to the ever growing catalogues from HD Tracks especially. ( (owned by the Chesky brothers) Alex
P.S. Did you upgrade the SC HA's JLH to 2 x 4,700uF per rail?
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Post by punkjr on Jul 8, 2010 9:42:08 GMT
I have my scha coupled to a CA DAC Magic, and volume control is from the Rotel RSP-1068 running in bypass mode. My main source is a Rotel RDV-1060 runnig 24bit 192khz material. I could not be happier, and at the risk of overdoing it (I have thanked him many times), I am amazed at the generousity of Alex, both with his knowledge and time. I feel as though I have the perfect system for my tastes now, and old music has taken on a new lease of life.
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Post by Deleted on Jul 8, 2010 12:13:28 GMT
Tom Which 24/192 DVD-As do you have ? The majority of DVD-A players don't do justice to DVD-A or SACD, and you can get far better byripping DVD-A to your PC HDD. Alex
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XTRProf
Fully Modded
Pssst ! Got any spare capacitors ?
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Post by XTRProf on Jul 8, 2010 12:44:01 GMT
Alright, then a V1, V2 or V3 I have both of these. My MF V2 has all the DIY mods I know (but not Done-by-Mike) with a Little Pinkie. My AK mods SCHA has all the mods stated in the tweaks thread. To me the the most obvious difference (and only that, I could not say one is favourable over the other at all times) is that the V2 has a more full bodied ("A little south of neutral") presentation, without losing detail and nuances, making it a good late night listen, when my ears seem more sensitive to HF energy. Whereas the AK-SCHA has a more forthright ("A little north of neutral") which endows it with wonderful pace. There are other little differences but the above stands out to my ears. Hmm, seems that you are really impressed with it. Ok, the typical tube versus SS sound. Obviously, SS should have a better pace because of the better control thru a better damping factor due to the lower output impedance. This SCHA can take 8 ohms HP, man! Almost as good a spec as the MF V8. Now I'm impressed and itchy backside because of the low price. Chris, you've got a PM.
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Post by Dickybottle on Jul 8, 2010 15:56:38 GMT
Hi Alex, Could I ask a couple of questions please? I am in the process of building the SCHA but progress is slow due to finance issues... The PSU regulator is built and tested OK and the main HA board is complete except for the Toshiba O/P transistors. I am awaiting JLH pcb's and have yet to order parts for it. My questions are mainly about the JLH - When the JLH is installed, how do I know it's working (please don't say "because it sounds better") - Is it possible to test it's operation. Also, the latest JLH upgrade seems to be to increase the value of C4 to 2 x 4700 uF - Why is this? And how is SQ affected?
I have been thinking about a suitable case to house the completed amp, again when finances allow, will the entire kit fit in a Hammond 1455T2201 - 220mm x 165mm x 56mm?
Can I please also confirm the LME49720HA pinout - Looking onto the top of the can, pin 8 is indicated by the tag, and the pins number down to 1 clockwise?
Many thanks - Ken
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Post by Deleted on Jul 9, 2010 0:04:04 GMT
Ken Re the JLH : Assuming a +-15V supply,important Voltage readings are approx. 1.8V at the BC639/BC640 base . Measure at 120K resistor. Approx.11V at the Collectors of the BC550C/BC560C - measure at the 2K7 resistors. and 6.7V at the emitters of the BC550C/BC560C - Measure at the 2k2 resistor. All readings are with respect to Earth. (0 Volts) The photo posted by XTRProf was of Miguel's unit before it had a few more mods. The case used is shown at the attached link. You should be able to work out the required dimensions from the photo and the dimensions of the case at the link. www.altronics.com.au/index.asp?area=item&id=H0476The use of 2 x 4,700uF per rail in the JLH gives a small improvement right across the board. The LM4562HA pinout is correct. Don't forget that the case is connected to the -VE supply rail ! Alex
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Post by punkjr on Jul 9, 2010 7:03:23 GMT
Hi Alex, my DVD-A player is the Rotel RDV-1060, which is a very good mid-fi player. I don't have 192khz capable with my DAC Magic, so i stick with the player when i can. I only have a few disc's, but I will getting some over the coming months. Everytime I walk into JB Hifi and ask for a DVD-A, I get the funniest blank looks on the kids faces, so it the internet is really the only option.
I have Frank Sinatra Live at the Sands with Count Basie (my favourite), Ratpack live at the Villa Venice, some Andre Ruiaeui in Vienna, and Wagner Overtures.
BTW, I've never figured out how to rip a dvd-a to my pc. i'd love to back up discs, as my sinatra at sands is a little scratches.
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Post by Deleted on Jul 9, 2010 7:26:42 GMT
Tom Carly Simon-No Secrets is 24/192 and VERY good. Fleetwood Mac -Rumours 24/96 is also quite good., There may be a few Diana Krall DVD-As still around. DVD-As are now very hard to find worldwide. I use the program DVD Audio Explorer for ripping them to the P.C. Alex www.videohelp.com/tools/DVD-Audio_Explorer
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Post by punkjr on Jul 9, 2010 8:09:35 GMT
oh thanks Alex, i'm looking into as we speak.
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Post by Dickybottle on Jul 9, 2010 8:46:43 GMT
OK, many thanks Alex.
BTW, do you have a link to the original John Linsley Hood design(s)? I am very interested in the development of this circuit - Sad I know...
Also BTW, I have installed the LME49720HA - Am I safe to power up the amplifier without the output transistors fitted, just to check the circuit operation?
Cheers - Ken
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Post by Deleted on Jul 9, 2010 9:48:50 GMT
Ken Personally, I would try any new project like that with a cheap opamp initially, even when you have the output devices fitted too.Why not try it initially with the opamp supplied with the kit ? This also gives you some idea of the performance improvement. I have sent you an email with details as requested. Alex
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Post by Dickybottle on Jul 9, 2010 11:38:16 GMT
Ken Personally, I would try any new project like that with a cheap opamp initially, even when you have the output devices fitted too.Why not try it initially with the opamp supplied with the kit ? This also gives you some idea of the performance improvement. I have sent you an email with details as requested. Alex OK, many thanks for the JLH info Alex - It's just what I wanted. Damn, I should have thought of fitting the supplied opamp first, the 49720HA was quite difficult to fit, so I am a bit reluctant to remove it again. Without the O/P devices I won't be able to assess the SQ, so I'll warm up the old 'scope and do a few response checks. Cheers - Ken
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Post by Deleted on Jul 9, 2010 12:03:56 GMT
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Post by Dickybottle on Jul 9, 2010 12:42:42 GMT
Thanks Alex - They are a good reference. I assume they are taken on the headphone output, I am looking on the opamp out (pins 1 & 7).
I will try and post some screen shots when I have time to get the camera rigged up, but things are looking good to me - Certainly nothing wrong with the square wave response within the audio band. And this is with the stock PSU only!
I am getting a warm feeling about this amp - I can't wait to get the remaining bits to complete it.
Cheers - Ken
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Post by Deleted on Jul 9, 2010 12:52:12 GMT
Ken Don't forget that if you have no more than a couple of DC mV from your sources, that you can bypass the input capacitors for a further SQ improvement over even 4.7uF polyprops. Alex
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Post by Dickybottle on Jul 10, 2010 9:55:02 GMT
OK, here are a few 'scope screen shots looking at the LME49720HA output. The input caps are 6.8uF poly film and are IN circuit. Signal is generated using a Thandar TG210 - 1V p-p. Top trace is input signal, lower trace is output. 10Hz100Hz1KHz10KHz100KHzThey all look pretty good to me - Just a little ringing at 100KHz, but not an issue. Please feel free to comment. Cheers - Ken
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Post by Deleted on Jul 10, 2010 10:15:11 GMT
Ken What value were you using for feedback capacitors C1 and C2 (if any) ? Alex
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Post by Dickybottle on Jul 10, 2010 11:30:08 GMT
Ken What value were you using for feedback capacitors C1 and C2 (if any) ? Alex C1 & C2 not fitted as per your mod. Ken
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Post by Dickybottle on Jul 23, 2010 14:10:50 GMT
I now have the SCHA complete - Toshiba output transistors fitted and all seems to be working fine. Nothing getting hot, and all voltages good - Output offset <2mV.
I have no pot fitted yet, so I am using the volco on my SB Classic. Even using the phono out from the Squeezebox, I must say the sound quality from the SCHA is pretty damn good into both my K701's and HD600's.
Still waiting for the JLH PCB's from Jon, so I can't wait to build them, but the amp sounds so good as it is, I can't imagine how it can be improved.
Is it worth fitting one of the Valab attenuators off Ebay which aren't much more expensive than the Alps RK27's?
Cheers - Ken
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Will
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Post by Will on Jul 23, 2010 17:06:58 GMT
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Post by Dickybottle on Jul 23, 2010 18:16:55 GMT
Hi Will, Some nice looking builds there, thanks. However, I had an idea to fit my SCHA and associated bits in a Hammond 1455T2202 case, but with the new JLH design, it's looking like it will be a pretty tight fit. The attenuator needs a lot of clearance. I think it will (just) go, but I haven't got the JLH boards yet - I just hope there is enough height to stack them.
Then there's the rear panel ... IEC, fuse, switch, input phono's ...
Ken
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Will
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Post by Will on Jul 23, 2010 18:28:33 GMT
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