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Old 6th December 2007, 12:54 PM   #11
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Quote:
Originally posted by spzzzzkt
good to hear. just thought that point six in post two indicated that the 1.6V LED was a unicorn when mouser, digikey, rs-components et al do stock a LED that should be close to that figure.

I've had a set of Ralph Stens' (X)Ono boards since early january this year and have been thinking about finally pulling the finger out and building them up. Still need to pick up the psu board, but if i wait til the 26th I can order on the 12 month anniversary of ordering the channel boards

Still checking out parts sources - at this stage I think I'll go for Vishay VSH-J bulk foils for the RIAA resistors and PRPs for the rest.

I used PRP as well, but you'll have to suppliment with another line as PRP is not extensive enough. I used some Holco as well. If the proper RIAA values aren't available in Vishay bulk foils, they definitely are in Roederstein Resista, which Michael Percy carries.
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Old 6th December 2007, 09:25 PM   #12
m2003br is offline m2003br  Brazil
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Default Donīt care about leds

Hi all,

To me is incredible, how many is discussed about one simple led.
Papa Nelson (or Wayne Colburn?) stated in the service manual: "R53 and R67 at 1 volt after the base emitter drops. This reading across these two resistors is important for this stage to work properly."
This only means that is necessary 2,1 mA and 6,7 mA in the CCS's.
The simple way to obtain this target values is by tweaking the values of R67 and R53, wathever the led used.
Conventional red led give 1.9V with 4mA (R5=6k8), wich calls for about 570R for R67 and 180R for R53
If the final goal is to obtain a aleph ONO clone with identical sound to originals, electrolictics C1, C41, C 12, 21, 22, 29 and all film caps have to be identical to the originals.
And, if necessary any fine adjust in Vled, tweak the value of R5 give some results. the led is happy in the range of 1 to 15 mA. I have measured 1.83V with 1 mA and 2.0V with 10 mA.
Some "crystal" red leds with medium efficiency exibits exactly 1.7V @ 4mA.


Hope this help.

Marcos
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Old 6th December 2007, 09:41 PM   #13
m2003br is offline m2003br  Brazil
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Dear Wayne,

I've read your posts after posted the above, you is the right track.
Actually, the lower the current, the more is thermal stability, cause lower heating in the junction. And do not forget the fact R5+Led receive voltage from a stabilized power supply, wich means near constant current for the led.

Cheers,

Marcos
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Old 6th December 2007, 10:13 PM   #14
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Quote:
Originally posted by luvdunhill

I used PRP as well, but you'll have to suppliment with another line as PRP is not extensive enough. I used some Holco as well. If the proper RIAA values aren't available in Vishay bulk foils, they definitely are in Roederstein Resista, which Michael Percy carries.
I had been looking at using beyschlag/vishay/phillips mrs25 resistor which are the Audio Note entry level and available from a local surplus barn at a reasonable price. However, some posts to diyaudio and availability of correct values have convinced me to try out the Holco/PRP combination you suggest. According to MP's catalog he should carry the VSH-J in all the required values for the RIAA resistors.
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Old 8th February 2008, 03:55 PM   #15
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OK heres the latest.

I have boards and I've stuffed all the components.

When I fired them up, they seemed to be pretty good - but not
100% yet. After turning on, making adjustments as appropriate
I decided to go for the "Hail Mary" by connecting to stereo,
given the outputs had no bad DC offset voltages. I didn't have
a scope at home so all I could measure was voltages. Yes I
was as careful as I could be with my setup - starting out at the
lowest volume position (after all the mutes were lifted).

When connecting to MC source input, both channels seem to
work pretty good, except gain is far too low. Turning up preamp
volume to full gives clear sound with at least decent frequency
response, but as I said, it was nowhere near 76 dB gain.
I had a Pearl in there before and if the Pearl is around +40 dB's,
I'd say right now my Onos are in the +30 dB range or so.

So clearly I have to get a scope in there with a signal generator
and I'll start down that road this weekend a bit.

For now though most seems well, I can adjust the R28 to 0.350V
easily, and I see about 1.11V across the R36's and 1.10V across
the R40's. So the main part of the amp is at least nominal in
terms of the current sources and the active components being
sane. I do have to adjust the resistors above though to get
the voltages down from the 1.1V range to the 1.0V range.

For now I have a question I hope someone can help me with.

When I have the shorting plug NOT shorting out R66 (the -4dB plug).
I see these voltages on Q14:
E = 3.6V
C = 3.3V
B = 4.1V

and the voltages across R45 - R48 are between 110 and 180
mV (ie not very well matched)

When the shorting plug IS shorting R66,
I see these voltages on Q14:
E = 12.2V
C = 16.7V
B = 12.8V

and the voltages across the R45 - R48 are all very close, at
93 mV, say +/- 1 mV.

I bought 65 2SK170's, and I have fairly well matched quads so
the currents thru the R45 - R48 should all be close, which they
are when the emitter of Q14 is at 12V.

Does anyone know what might be wrong here? Is there even
a problem? FWIW, both amps are behaving exactly the same
and the emitter of Q24 (the MC regulator output) is rock solid
at 26.1V whether or not the shorting plug is inserted. I have
gone through the circuit to see that it matches both the schematic
I printed years ago when the Pass site had these posted, and
I also checked against the schematic "Promitheus" posted
on a related thread (they are the same, except things like
extra bypass caps that don't matter).

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Old 9th February 2008, 03:16 PM   #16
m2003br is offline m2003br  Brazil
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Dear Wayne,

Your preamp appears to have the right behavior with given current values in the fets. 93mV on 22R is about 4,2mA per fet, total is about 17mA. with one resistor (R40) 499R, you have a drop of 8,43V on this, wich give about you measured in that condition. BUT, if you have 499R two times (J1 open) the total drop on this is too much to give a correct operation of the cascode. 4 solutions come in mind:
1) utilize fets with half of IDSS you actually have,
2) Raise the values of drain resistors,
3) use only two fets instead four (the rise in noise is very little), and,
4) Forget about J1, left this always closed.

don't care to much about exact voltages, about 20% tolerance is harmless for audio work, specially in those capacitor coupled circuits.

Hope this helps,

Marcos
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Old 10th February 2008, 08:38 PM   #17
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Marcos:

THanks for the info.

I did find one problem in that part of the circuit - I had captured
my schematic with C37 reversed polarity, and when I had shorted
R66, C37 became reverse-biased so it was no longer operating
like a cap. My design actually used 2x 470 uF in parallel in
place of C37 and C19, (bypassed also) so what I did is remove
both of the "C37" caps, and also one of the "C19" caps, and
I turned around the one I scavenged from the C19 position,
and I now see maybe 10.3 or 10.5 V at the emitter of Q14
when R66 is shorted. So that is fixed, and I now have bypassed
C37 and C19 both at 470 uF.

I then turned my attention to getting the MM and the INV amps
operating correctly.... and I've spent hours messing around
with hum problems. And that's where I'm at right now. It is
not fun tracking this down because you can't use test
equipment to measure for it. I have made one large stride
though and I have one more small change to my grounding to
make it identical to the way I had my Pearl grounded. Wish me
luck because I'm about at my wit's end, if this last change
doesn't work, I've run out of ideas.

Once I get past the hum, the good news is that the MM and the
INV amps both appear to be working fine as there is good music
coming out of the system (albeit the gain is far too low to be
useful) overlaid by an unacceptable amount of hum.

THen after the hum is dealt with I will again turn my attention
to the MC amps and see what else, if anything, is still wrong
in there - I would doubt it unless I've toasted some actives
when the cap was turned round the wrong way.

W.
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Old 10th February 2008, 10:30 PM   #18
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OK... good news. The one thing I was going to do turned out
to be a good fork in the road. When I get a chance I'll post a
pdf with a drawing that shows what I arrived at.

I'm going to stop now for a week or two on this and then pick
up again with the MC amp.

For now I'm going to enjoy the amp the way it is.... with the
gain on my pre turned up almost all the way since I have a
low-voltage MC cartridge (which is why I made this amp in
the first place... the Pearl doesn't have enough gain, great
little amp though it is).

Over and out for now....
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Old 10th February 2008, 10:49 PM   #19
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Wow... even better news.

This amp ROCKS.

I just put on Clapton's Unplugged, side 1. I like the music and
it is technically a very good or excellent recording. There is no
comparison between the Pearl and the Ono. The Ono has far
more separation, detail, air, and extension high and low. And
I'm taking about an amp that has been running for maybe 3
or 4 hours total right now between all the hacking I've done
since I completed it on Thursday.

Keep in mind also that I'm running a low voltage MC cartridge
into the MM input and cranking my pre up pretty much all the
way. I suspect when the MC section is fired up and the pre is
turned down a bunch it'll get even better.

Oh, and Wayne.... yes it does have a nice firm bottom. Thanks
for the great design.
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Old 15th February 2008, 06:18 AM   #20
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Default I concur with that bottom thing...

Just finnished my ono yesterday as well. i basically had the same problems with the MC frontend section and decided to use 27 ohm source resistors and only mount one 500ohm gain resistor.
I also lowered the drain voltage to 12V to create a bit more voltage margine on the cascode circuit.

Next problem was the LED reference in the MD section. The led voltage was too high resulting in a high current in both current sources. I changed the resistors to 680 and 220 ohm to get the approx currents.

Now the bias current for the output stage was way more easy to adjust and one channel came to life.

The other channel had strange noises at the output and would not give undistorted output below 20mA bias (about double the intended value) Also toutching the 2SK389 would increase the humm and RF demodulation in this channel.
I concluded that this channel was oscilating and I had to find out why.
The only very obvious occilating prevention in the MD section is the 100p cap, however it was soldered in place and had the correct value. Yet placing another 100p cap across the original made the channel dead silent. Later, after replacing the 100p cap I found that the value was incorrectly stampt and in reality it was a 10p cap.

Last point I still have to solve is the grounding. This is where I would like to have your input. How did you layout your grounding and do you also have a faint humm in your ono?

Thanks...Marcel.

PS. despite the slight humm...This amp play's very very well indeed.

Thanks Wayne!
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