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Old 17th August 2007, 02:45 PM   #1
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Default Blameless, Dx was wrong, it is a very good amplifier


I have to apologize forum folks and Doctor Self,

I feel sorry..... really sorry, this is the third Blameless i have constructed, and seems that sounded fantastic.... i do not know what happened before...but i will discover soon and will tell you, as this interests me a lot.

The first time sounded awfull.... stérile, without dinamics, compressed...a battery portable radio.

And i made it once more when Colin re-started with that Blameless conversation.....and i was silent to publish once again that was awfull.

But this time, with the same speaker and almost the same parts (supply is different....hummm) i had a very good results.

Sounded very good, very precise, controled basses, nice and detailed non harshing trebles...nice sound stage.

I have removed the mirror and the compressive sounded disappeared and i have tweaked a little the VAS, increasing the IK resistance and reducing the capacitor to 27 picofarads..very stable it was, even without the capacitor...VAS used BC547 and BD139.

The CCS, that is substituting the colector loads into the differential had removed the emitter resistances.

This way sounded the way i like...so good that i may use Doctor Self VAS and this CCS....i have compared using resistances, and despite more compressive sonics, i perceived that details were more precise, more brigth and more focused.

So.... complicated solutions sometimes sounds fine.... Dx was wrong..... Carlos was wrong and saying sorry because his damn mouth.

Not confortable to come here to say that...but i think i have to...i must do that.

Yes, Andrew T.... complicated solutions, Doctor Self ideas can sound fine.

I could use the Blameless thread...i think i have opened that one....and others opened others about the same subject or small variation around the same theme.

Of course, moderators can join those threads if they feel this need...no problem to me.

The intention to open the new one is to show, clearly, without any doubts, that i have changed my opinion and i am saying sorry to every forum folks that have readed my test.

Sorry to you too Douglas.

regards,

Carlos
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Old 17th August 2007, 05:02 PM   #2
Giaime is offline Giaime  Italy
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Do you see it? I never mistrusted Dr. Self. I just pointed out that many of his schematics on the net are plainly wrong

(not subtle errors, but gross, it takes little amp experience to debug them).

I'm designing a D.Self inspired amp (a sort of ) now, maybe I can post the schematic to gather suggestions

So we can make this the "Oh Self Amps and Self Style Sounds So Good" thead

Btw, dear Carlos, that's very interesting about your amplifier. Well, if you read all over DIYAudio, you'll find many times that experienced amp builders get better sound with resistor loading of the input stage instead of the current mirror, and many others "improvements" (such as CCS, etc) are detrimental to the sonics (for their opinion, instead THD always increases - this confuses me, in my experience lowering THD over the whole audio band is related to good sound if properly done).

Hope the discussion will take a great start
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Old 17th August 2007, 05:10 PM   #3
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Quote:
I have removed the mirror
Hi, Carlos,

I think the current mirror load (of input differential) is one part that shouldn't be removed if you are making D.Self's "blameless". It is an important part of the whole "blameless" design concept.
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Old 17th August 2007, 06:17 PM   #4
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Default Yes.... not so important this load to the differential, i felt a little bit more

precise, more real, but sonics was not that warm i like.... i made it as a more precise, more modern unit, but was good to support that worry i have about those transistors as input differential load.

regards to you Lumanauw.

Carlos

.................................................. .................................................. ..

Yes Giaime.... you told me...i remember that


One more turn the blameless.

I hope discussions will provide us some interesting ideas, some adjustments into the blameless.

Will be good for us.

regards,

Carlos

.................................................. ..................................................

I do not intend to go feeding this thread... was more an apologise to a opening of another round of discussions...but of course, take your seat and tell whatever you want about this subject... Doctor Self is very important for us and will be a good idea to listen people talking nice things about him too... i will feel better with myself watching nice meetings talking about Self ideas...as i have bombed him a lot and it is time to correct those things.

regards,

Carlos
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Old 17th August 2007, 11:45 PM   #5
sandyK is offline sandyK  Australia
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Default .......It is a very good amplifier

Lumanauw

I agree 100% with what you are saying.
Some years ago, there was quite a bit of information about current mirrors. The general consensus at the time,was that for best results, the current mirror transistors should be matched, and with as high an HFE as possible. An HFE of around 800 was even suggested.
A friend and myself have found these suggestions enhance performance, as does minimal loading of the current mirror by the VAS stage. MPSA18 transistors are often suitable for this task, due to their high HFE, and low cost. (provided their voltage limitations and polarity are taken into consideration.)

SandyK
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Old 18th August 2007, 02:28 AM   #6
fotios is online now fotios  Greece
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Quote:
Originally posted by Giaime
you'll find many times that experienced amp builders get better sound with resistor loading of the input stage instead of the current mirror, and many others "improvements" (such as CCS, etc)
Hi Giaime
IMHO the current mirror it is usefull in practice. Because it balances the collector currents of the difference amplifier transistor pair then the offset in output becames almost zero (about 5mV usually). Thus there is no need for trimming the difference amp. transistors with the use of trimmer. As for the sound quality, if it is improved, i don't know and i am not interested. I am sure in any case that it is not aggravated by a current mirror. Well why so many noise about?
Fotios
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Old 18th August 2007, 02:56 AM   #7
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Hi, Carlos,

There's a little trick to make DSelf "blameless" sounds much better, but still a "blameless" design, not changing much of the basic concept.

DSelf himself actually mentioned this on his handbook, but didn't apply it in his "blameless" design.

The trick is to move the Cdom input point. Usually this Cdom is put between Collector of VAS to base of VAS (or B-enhancement transistor that preceeds this VAS transistor).

But to make this, you will have to cascode the input differential first.

Cdom cap has 2 legs. Keep one leg which is on the VAS collector, but move the other, originally in the VAS base, and move this capacitor leg to the input differential's collector (=emitor of cascode's).

Besides in DSelf's handbook, this method also can be read in Sackinger paper (JCX mentioned this several times).
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Old 18th August 2007, 03:12 AM   #8
sandyK is offline sandyK  Australia
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Default ....it is a very good amplifier

Carlos

Douglas Self also recommends that when the input mirror is made from discrete transistors,it needs it's own emitter degrneration for good current matching (30-60mV voltage drop will be enough ....) If degeneration is omitted, there is significant variation in HF distortion performance with different specimens of the same transistor type.

Regards
SandyK
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Old 18th August 2007, 05:03 AM   #9
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hi Carlos and Lumanauw,

I've been also on the Blameless about 3 to 4 years ago..

lack of bass was my remark,

guys, please post your improve schematics.....on this

thanks

macweb
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Old 18th August 2007, 05:08 AM   #10
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OLG is some times a problem on current mirrors,
making an amp oscillate and heat up ouput devices to death ( thermal runaway) even with lower volumes.
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