leo
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Post by leo on Jan 23, 2008 0:58:04 GMT
I decided to knock this output stage to try with my diy based PCM1794 I just need to tweak the gain by altering the 330R resistors as its a bit high output. Results took me by surprise, where the hell did that bass come from!!!  Any comments on what I should try or change? sorry the schematic is a bit rough, it was quickly done  also a bit small but is the largest I can post  |
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Post by Deleted on Jan 23, 2008 1:33:24 GMT
Yes, find a way to change the O/P FET to bipolar
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leo
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Post by leo on Jan 23, 2008 1:41:20 GMT
Ok, I was waiting for somebody to mention about the j-fets  Would have liked to have tried bipolars on the input but not sure if the dacs output would like base current draw Suppose I could just stck a bipolar on the output first and maybe adjust to suit if needed |
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leo
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Post by leo on Jan 23, 2008 1:59:23 GMT
I found a couple of 2sc2240BL's so will try those, luckily I fit sockets when having a faff about, it makes changing things around so much easier
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leo
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Post by leo on Jan 23, 2008 2:18:42 GMT
Two points to Mr AK Sound has opened out and now more 3d BTW Alex that JLH really does the job here, out of interest I wired the circuit up on the outputs of the standard regulators so bypassing the JLH, massive downgrade in sound making it thin and lacking depth so the JLH's was quickly wired back in  |
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leo
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Post by leo on Jan 23, 2008 2:27:44 GMT
What about adding a Darlington on the output using pairs of 2sC2240?
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Post by Deleted on Jan 23, 2008 3:03:26 GMT
Leo
Looks like you better etch some more boards !
Sorry for the delay, but Internet connection coming and going
Alex
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leo
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Post by leo on Jan 23, 2008 3:06:01 GMT
Thats ok Alex, I'm signing off soon anyway as its late I want to play about with this thing but not sure where best to start The sound is surprisingly very good |
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leo
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Post by leo on Jan 23, 2008 3:07:11 GMT
BTW already did etch another board, this ferric chlorides really had it but I needed to have another reg
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pagan
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Post by pagan on Jan 23, 2008 6:18:51 GMT
I decided to knock this output stage to try with my diy based PCM1794 I just need to tweak the gain by altering the 330R resistors as its a bit high output. Results took me by surprise, where the hell did that bass come from!!! Any comments on what I should try or change? sorry the schematic is a bit rough, it was quickly done also a bit small but is the largest I can post I used a 2SK389 instead of the trying to match two 2SK170's And a BC516 darlington for the output. Some say the 2sk170BL output is better, dunno havn't tried it. but this was a voltage output dac. Head-Fi have a thread talking about the pcm's at present. |
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leo
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Post by leo on Jan 23, 2008 11:51:12 GMT
This works extremely good with the PCM1794, theres more detail than any op-amp I've tried in that unit.
Using a op-amp to do the differential to line out gives me 0v DC offset no DC blocking cap needed but it does not sound anywhere as good as the discrete even though theres a coupling cap.
The 2sk170's are matched as they came out of another unit that needed matched J-fets
Funny thing is trying a few different supplies this morning the JLH works the est in this circuit.
I've never been convinced with any voltage output dacs yet
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leo
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Post by leo on Jan 23, 2008 11:53:07 GMT
The transistor on the output is clearly giving the best sound here IMO
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Post by Deleted on Jan 23, 2008 12:02:07 GMT
Convinced yet ? ;D No really special bits or I.C.s, and ripe for shrinking in size ?
What transistor are you now using on the output ?
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leo
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Post by leo on Jan 23, 2008 12:20:15 GMT
With this particular output stage yes I am convinced with the JLH, I always post as honest as I can, if something does not work well to my ears I'm normally the first to let you know, I'm rather pleased now The output transistor I'm using is currently 2SC2240BL, I'm going to have a look what else I have |
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Post by Deleted on Jan 23, 2008 12:24:45 GMT
Leo I hope you aren't listening through the Kumisa 3 ?  Alex |
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leo
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Post by leo on Jan 23, 2008 12:28:31 GMT
Leo I hope you aren't listening through the Kumisa 3 ? Alex No I'm not at the moment ;D |
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Post by Deleted on Jan 23, 2008 13:35:21 GMT
Guys
If anybody is interested in WTF Leo, Allan and myself are on about, just ask. It's not a closed club ! If for example you want to know more about the JLH, including PCB layout, original article by JLH etc. , send me a PM. Leo and Allan, will,I am sure, show you how to adapt these addons to other applications for improved results. Tell us what you want to do.
Give us some fresh ideas and suggestions.
Alex
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leo
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Post by leo on Jan 23, 2008 15:16:37 GMT
Give us some fresh ideas and suggestions. Alex Yes please do! Come on gents it gets boring with just three of us |
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Post by Deleted on Jan 23, 2008 20:00:12 GMT
Leo
I tried to post this question the other day,but lost Internet access for a while.
Are R9 and R10 25 OHMS ? Is this a typo ?
If they are 25 ohms, then there would be no effect ?
Alex
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leo
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Post by leo on Jan 23, 2008 20:03:26 GMT
Leo I tried to post this question the other day,but lost Internet access for a while. Are R9 and R10 25 OHMS ? Is this a typo ? If they are 25 ohms, then there would be no effect ? Alex Alex, No typo, they are 25R, remember these are current output dacs, its simple passive I/V conversion on the differential outputs. |
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leo
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Post by leo on Jan 23, 2008 20:08:09 GMT
I tried adding some diy Darlingtons today for Q5, not sure if I like this as much as the single transistor.
I also lowered the 330R resistor on the input pair to higher the gain as it was a bit low played through the Solo but the sound wasn't as good.
I'm now thinking what else to try for around Q5, any idea's? this maybe way off but would a Sziklai work?
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Post by Deleted on Jan 23, 2008 20:15:56 GMT
Leo
I questioned the values shown only because of your base current concerns. Obviously there will be an extremely low change due to base current drawn through 25ohms, (5/8 of SFA ?)
so shouldn't be a problem.
Alex
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leo
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Post by leo on Jan 23, 2008 20:34:39 GMT
I see taa, wish someone else would build this thing |
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Post by Deleted on Jan 23, 2008 21:02:54 GMT
Leo Why ? I am sure that other people believe you when you say just how good it sounds! As usual, for most likely constructors, will be the obstacle of having to make own PCBs. Alex |
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leo
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Post by leo on Jan 23, 2008 22:05:00 GMT
Leo Why ? I am sure that other people believe you when you say just how good it sounds! As usual, for most likely constructors, will be the obstacle of having to make own PCBs. Alex I was hoping others would build it mainly so we could share idea's how to improve it I still think around Q5 can be improved |
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also a bit small but is the largest I can post
