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Old 27th December 2007, 06:45 PM   #101
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Hi,
As you may have noticed Im also doing some mods and it appears each set of boards is slightly different. .One step at a time as is my usual method.
I am interested in your observations re uprate to 1000mfs/2200mfs ,sonically?
Also the 78L05s (78L15s) I hadnt listed this on mine.I wondered if those little regs are good enough for larger smoothing caps.?
Also I believe that all switching diodes including schottkys benefit from calculated bypass caps.Even if its only my sacd players noise senstive circuits that benefit.
Also Im a bit suprised at the comments re channel seperation.I though we had moved on from 60s thinking.
Ok there reaches a point when the specs become meaningless but it isnt 1db above a mean average unspecified rating.
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Old 29th December 2007, 07:47 AM   #102
tubenut is offline tubenut  South Africa
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I did a lot of things at once so can not comment on the specific effect of uprating the smoothing caps from 470 mfd to 1000 mfd. These are on the raw supply before the regulators so would only make their job easier, not harder. Half wave regulation, 470 mfd smoothing to supply 6 op amp sections just does not add up...
If it was not such a silly halfwave rectified PSU I would have done DC with much more smoothing outside in a bigger PSU box.
It is possible but would need a few clever moves with regard to the PSu 0 volt line etc.

The regulators are implemented in a strange way, I only noticed this once I wanted to do some volatage measurements without any ICs in place. I got 20 volts out ofd the regulators....
Turns out, they have a 900 ohms I think it was resistor from input to output on the regulators. The moment current is drawn, the voltage corresponds with the regulators. I assume this is some way to allow more current to be supplied then the 78l15 will allow?

Anyways, sound is much more solid now, deeper gutsier bass and the difference using a bigger transformer much more apparent.
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Old 30th December 2007, 08:33 PM   #103
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Hi and thanks for reply.
It seems the se version I have is only similair to yours.
Space is a limiting factor in the small box/
The effect of 12 Vishay resistors/2 schottkys/silver wire in and on power supply PLUS Reducing the length of the lead from wallwart
to rather shabby quality socket has made a big difference in tonal quality,lowered the effect of the high noise and removal glaze/splashiness of metal films.Plus A smidgeon more umph which is what missing.
I will continue to run the newer Vishays in and move to the power supply next.Plus on board caps.
My impression was that It had two identical poss+ circuits after the half bridge and no pos/neg regulaters/will let you know when I open it up again in the new year.Certainly will up them if not go for super regs.
Incidently I have only replaced one pair of the 47k resistors with the quieter vishays.(for now)I am wondering if this is counteracting the electric noise circuit which I personally dont understand?/ie does it work by feedback of resistor noise.Me having used a quiter different type.
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Old 16th January 2008, 01:00 PM   #104
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Talking upate

Well it took some time to get back after the holidays.I have still not got a circuit diagram so proceeded without. We definitely have different items.
The nifty splitting of rails remains,It is interesting.On the SE the resistor value is upped to 2.2k.
Having now replaced the 47k with a vishay the noise is down quite a bit.The 2.200 caps mayalso have helped but I am now getting a much nicer sound and I havent even touched those 5532s yet.Unless someone can I advise better im going for opa 2227s.
I guessed the 10mf was a dc blocking/couple cap and replaced them both with pre burnt in Silmecs.
Next time I open it up I will look / check the 47mfs that seem to be on the input signal.Someone earlier stated 4.7 but on this SE they seem to be 47. Circuit diagram would help?.
I will leave it to run in a bit longer but Im now convinced this could be a really really good disc unit.
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Old 28th May 2008, 07:31 PM   #105
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I am very glad I found this thread...

Any replacement suggestions for the Op-Amps in the Phonobox II unit?

I have converted mine to battery power already...

See here: http://www.diyaudio.com/forums/showt...postid=1522425

Thanx
D
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Old 28th May 2008, 08:36 PM   #106
JesseG is offline JesseG  Canada
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If the originals are standard layout 8-pin DIP dual op-amps (ala 5534) then I strongly recommend you try the National LM4562.

LM4562 - Dual High Performance, High Fidelity Audio Operational Amplifier

I have used this chip to replace 5534 and others with no other cct changes as well as in a few from-scratch projects. It is awsome and waaaaaay cheaper than the BB OPA chips.

Jess
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Old 29th May 2008, 05:44 AM   #107
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Quote:
Originally posted by JesseG
If the originals are standard layout 8-pin DIP dual op-amps (ala 5534) then I strongly recommend you try the National LM4562.

LM4562 - Dual High Performance, High Fidelity Audio Operational Amplifier

I have used this chip to replace 5534 and others with no other cct changes as well as in a few from-scratch projects. It is awsome and waaaaaay cheaper than the BB OPA chips.

Jess
Jess - you suppose I can just plonk in a set of National OA's?

D
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Old 29th May 2008, 01:37 PM   #108
lineup is offline lineup  Sweden
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Default Phono Box

Quote:
Originally posted by Upupa Epops

This preamp comes not from fa Project, but from my friend Dr. Sıkora
and I was the first, which was build it.

In original was there two NE 5534 and in servo loop TL 071.

As input cap was there foil polyester, any bipolar.
This connection is about sixteen years old and was designed ASAP cheapest.

When it was new, in many comparisions every win against all preamps in tests. Later it was published in one Czech electronic magazine and was ( and still is ) in our country very popular.
Probably from this magazine it was stealed by fa Project and later reduciert to the form, which show Dimitri.

This amp is very simple, but have very good sound and noise parameters thanks to " active damping " ( very low current noise ).

Dr. Sıkora is not fool - to this time he develope many better preamps
- in this time he's working for fa Clearaudio.

-

Thanks for info & story of circuit, Upupa

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Old 29th May 2008, 04:32 PM   #109
JesseG is offline JesseG  Canada
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Quote:
Jess - you suppose I can just plonk in a set of National OA's
Yep! if you compare the specs of the 5534 and the LM4562 you will find that the operating limits are wider for the National chip than any of it's predecessors.

Actually, you can have a lot ot fun OA rolling (just like the tube guys do ). carefully unsolder the original chip, clean up the pads on the board and solder in a good quality 8-pin chip socket. Then, you can try a variety of chips very easily and decide which one works best for you.

Cheers
Jess
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Old 29th May 2008, 04:42 PM   #110
JesseG is offline JesseG  Canada
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BTW guys...

I just noticed this up aways.

Quote:
The effect of 12 Vishay resistors/2 schottkys/silver wire in and on power supply PLUS Reducing the length of the lead from wallwart
If you get noticeable improvement by shortening the length of the PS lead as stated, then you will get even more improvement by passing the wall-wart lead in one loop through a ferrite doughnut. Your could use a split ferrite choke as well, but would need a much larger size to get the wire to pass through twice.
See the bottom of this page:

Ferrite Chokes

Have fun!
Jess
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