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Post by lark on May 19, 2011 6:07:55 GMT
For the source I'll be using it's actually not very loud, I think I need to increase the gain a little - how do I do this?
Edit: Looking at the assembly instructions that come with the kit it suggests replacing R1 & R4 with a 7.5K and R2 & R5 with 1.2K and C1 & C2 with 100pF
With Alex's mods we don't install C1 or C2 so I'll ignore that change. Are the instructions still valid with Alex's mods?
Cheers.
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Deleted
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Post by Deleted on May 19, 2011 6:26:32 GMT
For the source I'll be using it's actually not very loud, I think I need to increase the gain a little - how do I do this? Edit: Looking at the assembly instructions that come with the kit it suggests replacing R1 & R4 with a 7.5K and R2 & R5 with 1.2K and C1 & C2 with 100pF With Alex's mods we don't install C1 or C2 so I'll ignore that change. Are the instructions still valid with Alex's mods? Cheers. lark If you only need a modest increase in gain, change R1 and R4 from 1K to 2.2K. This will increase gain from 2 x to 3.2x . Going much higher will degrade performance a little. Dynamics will improve when the JLH is fitted and "burned in." Alex
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Post by lark on May 19, 2011 6:31:01 GMT
Thanks Alex, What about R2 & R5 - if I change R1 & R4 do I need to change R2 and R5? If so, what is the relationship between them so I can try different values. PS. I have the JLH fitted and burning in Cheers.
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Deleted
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Post by Deleted on May 19, 2011 6:46:51 GMT
lark There is no need to change those for a modest increase in gain. It may be wise to strap out the optional R3 and R6. Why not just try that simple change first, and see if you actually need more gain than 3.2X ? (1K +2.2K/1K) Alex
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Post by lark on May 19, 2011 6:55:03 GMT
I've got some 2K7's here, will they be ok (3.7X) without changing others?
Edit: I put the 2k7's in but for quiet recordings max volume still isn't very loud - is 4K7's going to reduce SQ much? Would I need to up R2 & R5?
Cheers.
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Post by lark on May 19, 2011 7:49:42 GMT
Sorry for so many questions... But so much to learn I'm using this: cgi.ebay.com.au/ws/eBayISAPI.dll?ViewItem&item=150602136524It can take 11 to 22V AC or 15 to 32V DC which means I could take the supply from: 1) Ac from the 15VAC 30VA supply 2) 15V DC from the output of the SC powersupply 3) 15V DC from the output of the JLH My initial assumption would be to use the 15VAC from the toroid - less stress on the regulated path? Cheers.
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Deleted
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Post by Deleted on May 19, 2011 8:06:40 GMT
Sorry for so many questions... But so much to learn I'm using this: cgi.ebay.com.au/ws/eBayISAPI.dll?ViewItem&item=150602136524It can take 11 to 22V AC or 15 to 32V DC which means I could take the supply from: 1) Ac from the 15VAC 30VA supply 2) 15V DC from the output of the SC powersupply 3) 15V DC from the output of the JLH My initial assumption would be to use the 15VAC from the toroid - less stress on the regulated path? Cheers. lark I have one of those too, but haven't used it yet. I would be inclined to feed it +15V from the PSU PCB, and reduce the value of the 12V regs input capacitor from 1,000uF to 100uF 25V Alex
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mrarroyo
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Our man in Miami!
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Post by mrarroyo on Jul 2, 2011 14:19:49 GMT
A very helpful and friendly member sent me four (4) 4,700 uF 10 Volt Suntan caps as a gift. THANKS.
Yesterday (July 1, 2011) I was able to install them on the amp that Alex built. The unit has about 18 hours of burn-in and sounds very nice. The four larger capacity caps (originally they were 2,200 uF) are intended to improve the bass. Thanks again.
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Post by Deleted on Nov 6, 2012 11:29:04 GMT
Device selection. Further small gains may be obtained by careful selection of higher gain versions of the BC547 and BC557. More technical members may wish to investigate the use of the B and C versions of the BC547 and BC557, or appropiate members of the same family of devices, including the BC548,BC549,BC558,BC559, BC550B,C and BC560B,C. It is best to use devices with gain (HFE) not much more than 600, and try to use different polarity devices with reasonably close HFE in each channel,as well as the other channel. i.e. The 2 x BC547 (etc.) should if possible, have a similar gain,and also similar to the 2 x BC557 (etc.) Hey guys, This is one thing I have left out from my order of parts. Which transistors did most people settle with? Or will the standard BC547 and BC557 suffice?
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Deleted
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Post by Deleted on Nov 6, 2012 11:47:06 GMT
Vince Unless you have a transistor tester and a quantity to select from, I would order BC547B and BC557B which have a higher minimum HFE. Alex
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Post by Deleted on Nov 6, 2012 12:19:13 GMT
Hey Alex
Upon your recommendation I did end up buying a DMM with a HFE tester. I'll look into it after I've done all other mods.
Cheers, Vince
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Post by Deleted on Nov 20, 2012 12:31:23 GMT
Has anyone actually gone to the trouble of building/using a preamplifier for the SCHA and reverting the 2k resistors to their original value as stated in the instructions?
I was thinking of building a preamplifier, preferably tube to make a hybrid set up.
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Deleted
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Post by Deleted on Nov 20, 2012 20:35:01 GMT
Vince The modified version of the SC HA works well as a preamplifier. The gain can be increased a little if need be, by changing R1 and R4 to 2.2K. I simply would not recommend going there with the hybrid route. I would leave hybrid to people like Musical Fidelity who knew what they were doing, and lasted more than just through a short warranty period like most present ebay offerings. Alex
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Post by Deleted on Nov 20, 2012 21:49:51 GMT
Cheers Alex. Your advice probably has saved me a lot of trouble.
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Post by bluerob on Mar 15, 2013 5:27:07 GMT
Hi chaps Jaycar kit is on its way and in the mean time I'm gathering the bits and pieces for the suggested mods but I´m having a hard time getting my paws on some of the 2SA1930/2SC5171 suggested. The idea is to find some replacements or even upgrades (maybe a more recent model) and has to be available locally, I´m kind of reluctant to order them to the US (shipping cost) and a Ebay is flooded with counterfeits or so I hear.
What other alternatives are out there? Maybe some more recent models? Upgrades?
Thanks.
Rob.
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Deleted
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Post by Deleted on Mar 15, 2013 5:52:07 GMT
Hi chaps Jaycar kit is on its way and in the mean time I'm gathering the bits and pieces for the suggested mods but I´m having a hard time getting my paws on some of the 2SA1930/2SC5171 suggested. The idea is to find some replacements or even upgrades (maybe a more recent model) and has to be available locally, I´m kind of reluctant to order them to the US (shipping cost) and a Ebay is flooded with counterfeits or so I hear. What other alternatives are out there? Maybe some more recent models? Upgrades? Thanks. Rob. They can be obtained within6 working days from RS Australia, and probably other RS branches.
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Post by bluerob on Mar 21, 2013 8:54:30 GMT
LOL when I said locally I meant somewhere near ( I´m in Mexico) Australia is a bit far away...just, well in the other side of the globe I found them stocked at Mouser, and as you can imagine I ended up buying a gazillion more components, you know its just like entering a new candy store LOL In the meanwhile I´m building the enclosures, one for the amp itself and other for the transformer and PSU, I´ll upload some pics of the progress later on. Cheers
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Post by videoguy on Aug 23, 2014 17:56:30 GMT
It seems I am often late to the game. I held a headphone meet here in Central Fla. & demoed the SCHA; all comments were positive. This week i've been thinking of increasing the voltage from +- 15vdc to +- 20vdc. Tweaked the power supply up to 20vdc & installed an LME49860NA, in place of the AD823. The new I.C. & raising the voltage immediately resulted in better resolution & more punch in dynamics. Interested to see if it wil improve much more after the opamp is burnt in awhile.
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Deleted
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Post by Deleted on Aug 23, 2014 22:20:21 GMT
It seems I am often late to the game. I held a headphone meet here in Central Fla. & demoed the SCHA; all comments were positive. This week i've been thinking of increasing the voltage from +- 15vdc to +- 20vdc. Tweaked the power supply up to 20vdc & installed an LME49860NA, in place of the AD823. The new I.C. & raising the voltage immediately resulted in better resolution & more punch in dynamics. Interested to see if it wil improve much more after the opamp is burnt in awhile. Hi Bill It would have been interesting if Miguel had brought his along as well, as IIRC, you didn't have a JLH PSU add-on fitted at the time. My later Class A HA also benefitted from increasing the supply rails from + and - 15V to + and - 20V, just as our E.E. friend from Rockhampton said they would. What did Miguel bring along, something from RedWine with glowing thingies ?
Regards Alex
P.S. If you are using a JLH at +-20V, it may be a good idea to fit small heatsinks to the Current Limiter devices. This is more important with brand new main electros though.
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jc
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Post by jc on Aug 24, 2014 22:33:00 GMT
That's grabbed my interest! Can we really squeeze yet more out of the SCHA? So long ago now, are there any changes to main board needed for the voltage hike or do we just turn up the juice.
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Post by Deleted on Aug 24, 2014 23:11:03 GMT
That's grabbed my interest! Can we really squeeze yet more out of the SCHA? So long ago now, are there any changes to main board needed for the voltage hike or do we just turn up the juice. Hi Chris Robert Dwyer , an E.E. from Rockhampton posted some mods way back. Basically, the problem is that most opamps aren't able to work at + and - 20V, so if you use the original ones you need to supply the I.C itself with not much more than + and - 15V. Bill will no doubt post more on this subject, but in the meantime I will shortly edit this post to include photos from Bill. Bill has fitted a LME 49860 opamp which will work at + and - 20V ! Regards Alex
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jc
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Post by jc on Aug 25, 2014 11:09:40 GMT
On a quick read around it seems the LME49860 has an identical data sheet to the 4562 but with the greater voltage handling (up to 44v!) BUT that it is not a sonic match for the LME49720HA (metal can version), which many here at RG have fitted.
With all the other tweaks that have been done would it not seem more logical to go down the route of giving the LME49720HA an isolated 15v supply from the rest of the board if upping it to 20v? Although I appreciate for Bills particular build this may not be the case.
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Deleted
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Post by Deleted on Aug 25, 2014 11:33:23 GMT
On a quick read around it seems the LME49860 has an identical data sheet to the 4562 but with the greater voltage handling (up to 44v!) BUT that it is not a sonic match for the LME49720HA (metal can version), which many here at RG have fitted. With all the other tweaks that have been done would it not seem more logical to go down the route of giving the LME49720HA an isolated 15v supply from the rest of the board if upping it to 20v? Although I appreciate for Bills particular build this may not be the case. Hi Chris That's why I mentioned Robert's method. It may not be so easy though to fit 78L15 and 79L15 just for the I.C. though.
Regards Alex
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jc
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Post by jc on Aug 25, 2014 12:12:41 GMT
Yeah, I remember Roberts solution being quite a major rework, maybe that's why no one else tried it! Certainly beyond my meagre knowledge. Some kind of flying sub-board right above the IC comes to mind for the regs... I think most of Roberts links to his work are now broken.
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Post by videoguy on Aug 25, 2014 16:31:26 GMT
Hi Chris: If you decide to go this route you will need to change the 1.1k resistor in the power supply, in order to bump it up to 18vdc; with the 15volt transformer before changing the transformer for higher voltage. If you do want to go this route be sure to get the I.C. from a state side supplier. The manufacturer is now Texas Instruments. They bought National Semi. several years ago.
When I build a power supply I use a transformer that has a higher voltage by at least 10volts; that way I have room to play with the circuit, if I desire to do so. Yes you are correct the 49860 has the same specs as the 4562 & LME49720, with the exception of the voltage rating. It is hard for me to imagine any further improvement in sound quality, beyond what I am hearing. I am deaf in the right ear but the left is spot on. I will admit to being a bit tightfisted when spending money. A mutual friend of Miguel & mine from Ft. Meyers had very positive things to say; after an extended listen to the amp., through my modified AKG K340's. At the time I had an AD823 fitted & +- 15vdc operating voltage.
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