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First DIY-Alpeh Ono Prototype
First DIY-Alpeh Ono Prototype
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Old 19th April 2003, 11:22 AM   #1
TheMyxin is offline TheMyxin  Germany
diyAudio Member
 
Join Date: Jan 2003
Location: Munich
Smile First DIY-Alpeh Ono Prototype

fter 4 hour debugging yesterday(there was a contact-problem between Q3 and Q6 due to resoldering the Q3) my
Aleph Ono Prototyp now works well. The sound on my Rega Planar 3/2000 with
Elys (MM) is really detailed and IMHO the
rhythmic drives sounds very well (i have
heard Supertramp "brother where you bound and Bryan Ferrys "Boys and girls".
Ok some technical datas:

First i am using a torridal Transformer from
Thel-Audio Germany with nominal 120 VA.
I get on the PCB without any loads +/-
33,7 V after regulation and filtering and
42,6 V at the Relais-Outputs.

Due to the matching of the 4 2SK170 at the MC-Preamp-Stage i get over the Source-Resistors (R45 to R48) the following voltages:

R45Left = 90,3 mV; R45Right=94,8 mV
R46Left= 91,4 mV ; R46Right= 94,3 mV
R47Left= 89,6 mV; R47Right=93,7 mV
R48Left=90,1 mV; R48Right=97,6mV
Really nice values due to the carfully
matchings :-))

Other interressting Voltages
On R67 i got on the Left side 1,061 V and on the right 1,066V
On R53Left=1,064V and right 1,062V
On R65Left= 613mV and right 632mV
On R64Left=915 mV and right the same
value.
On R57Left 5,94V and Right 5,90V
The Justage on the Poti R25P is a little bit difficult. I have noticed at the first
10 Min or so a slight drift to higher voltages (+ 10mV) so i decided to trim
it at 350 mV after 30 Min. I have also noticed that the MOSFET Q7,Q9,Q18,Q19 and especially the 9110D become hot (subjective i would say 50 C ??). I think to put some adittionally small IC-heatsinks on the
MosFETs. I know from PQuadrat that normaly the MOSFET dont need heatsinks on the Aleph Ono but this would for me more safe and i hope that
the above voltage-drift on R28 and R27
would be more stable ?
Important for me is that on one Channel
the voltage over R27 is nearly (+/- 1-2 mV) the same as over R28 measured at the same time.

For cases i have found a nice reseller
on www.19zoll.com for german user.
I think to order a case with 2HE from this reseller. The sells now also on end-
users through there online shop. But the
2HE-Cases are available at KW 25/2003.
When its finished in this case i will post
some photos.
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Old 4th May 2003, 01:22 PM   #2
toshiba is offline toshiba  Germany
diyAudio Member
 
Join Date: Apr 2003
Location: Meersburg
Hi Myxin,

i'am waiting for Peter's PCB's to build my own Ono. In advance,
I have done many psice simulations about the circuit and found something wrong in your measurements.

Matching the 2SK170 for same IDSS one thing, but getting the right working point another. Anyway, your matching is really good!

Question : Did you match teh FETs with or without source resistor ?

My oppinion is, that any 2SK170 in the mc-preamp has to work at about 2mA idle current (sum = 8mA).

If you use 22 Ohm source resistors, your measurement tells me, that one FET works at about 4 mA idle current. ( sum = 16mA)

I thing it is too much for the cascode (Q14) while the gain select jumper for R66 isn't installed. At sum of 16 mA idle current, normaly about 16 Volt should drop across R66+R40.
Result : Uc of Q14 = 14Volt. Otherwise the cascode is biased with Ub = 15 Volt. Theoreticly Ucb of Q14 is negativ !?!?

I don't thing that Nelson Pass is going to design amplifiers which can achieve conditions like that one !

toshiba
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Old 5th May 2003, 06:30 AM   #3
TheMyxin is offline TheMyxin  Germany
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Join Date: Jan 2003
Location: Munich
Default RE: First Aleph Ono Prototype

[QUOTE]Originally posted by toshiba
[B]Hi Myxin,

i'am waiting for Peter's PCB's to build my own Ono. In advance,
I have done many psice simulations about the circuit and found something wrong in your measurements.

Matching the 2SK170 for same IDSS one thing, but getting the right working point another. Anyway, your matching is really good!

Of course its important to get the right
working point.

Question : Did you match teh FETs with or without source resistor ?

I have used a 160 Ohm Resistor for the
Matching and used a +15Volt Voltage
Source and have measured the voltage
across the source-Resistor as described
in this Thread
http://www.diyaudio.com/forums/showt...5&pagenumber=2

I have also measured the Voltage at
least twice for each JFET and i have
wait when the voltage on the digital-
volt-meter gets constantly. Before each
measurements i have wait a little bit due
that the temperature is the same after
touching them with my finger. The
voltage difference was during 2 mV.



My oppinion is, that any 2SK170 in the mc-preamp has to work at about 2mA idle current (sum = 8mA).

If you use 22 Ohm source resistors, your measurement tells me, that one FET works at about 4 mA idle current. ( sum = 16mA)

Yes after i have finished my Ono i have measured again the voltage across the
source-resistor with 22 ohm. Its possible that the last JEFT on the right channel
is the reason for that.


Ithe cascode is biased with Ub = 15 Volt. Theoreticly Ucb of Q14 is negativ !?!?

As someone other has written the voltage is not 15 Volt from the MC-
Subregulator. I have found nearly
12,xx Volt (i dont no it exactly now but
i could measure it again) what you get
behind Q14. Than i will also measure
again the voltage across the source-
resistor.
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Old 5th May 2003, 09:01 AM   #4
toshiba is offline toshiba  Germany
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Join Date: Apr 2003
Location: Meersburg
Hi TheMyxin,

you have matched with 160 ohm source resistor, ok. But which value do you have equiped on the PCB, 160 or 22 Ohm ?

toshiba
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Old 5th May 2003, 06:15 PM   #5
TheMyxin is offline TheMyxin  Germany
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Join Date: Jan 2003
Location: Munich
Default RE: First DIY Aleph Ono Prototype

[QUOTE]Originally posted by toshiba
[B]Hi TheMyxin,

you have matched with 160 ohm source resistor, ok. But which value do you have equiped on the PCB, 160 or 22 Ohm ?

The 22 Ohm Resistors as the are in the
original Pass-Design and the second
measurement was made through this
Resistors.
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Old 6th May 2003, 07:12 AM   #6
D.Achenbach is offline D.Achenbach  Germany
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Join Date: Mar 2003
Location: Friesenhein
I have finished my Ono too. The case I used is splitted into a small compact one (from Thel ALG2055) for the preamp and a simple one for the PSU which can placed anywhere in the rack. The connection between them is a simple but relatively thick 25-wire computercable, the plugs 25pin D-type. The PSU itself has a small 1.5VA stand-by transformer which provides a voltage for a relay that switches the main transformer.

The values of the current through the MC input FET's is nearly the same. Also the problem that the supply voltage of these FET's ist very low (about 6V) if the Jumper which shorts one of the 499R resistors is not fittet. With the jumper fittet the voltage is about 12V.
I did not fit the components for the inverter because I only need a asymmetric output. So the regulator transistors in the PSU keep only handwarm.

Regards
Dieter
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Old 6th May 2003, 02:29 PM   #7
toshiba is offline toshiba  Germany
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Join Date: Apr 2003
Location: Meersburg
Hi Dieter,

nice that you has finished your Ono. Hope I receive my PCBs from Peter this week.

If it is possible, do a hearing session with MC-Input and R66 Gain-Select-Jumper not installed. I'am sure, that the amp sounds more than worse !

The same answer to you.
It dosen't matter wheter the jumper is installed or not. The Emitter-Voltage of Q14 (Drain-Voltage of the 2SK170s) has to be "constant" !!!

The idle current of any of the 2SK170 must not exceed more than 2.5mA (sum of 4 = max. 10mA). Otherwise the cascode didn't work correctly if the jumper isn't installed !!!

toshiba
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Old 6th May 2003, 07:17 PM   #8
D.Achenbach is offline D.Achenbach  Germany
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Join Date: Mar 2003
Location: Friesenhein
>The idle current of any of the 2SK170 must not exceed more than 2.5mA (sum of 4 = max. 10mA). Otherwise the cascode didn't work correctly if the jumper isn't installed !!!

The current through the FET's (BL-Type) is about 4mA, which is realy too high. Maybe for this circuit with the 22R Resistors BL-type ist the wrong type, GR types has a lower current and should be OK here.
I think I will order some of the GR and check out what happens.

Does anybody know which type is used in the original Aleph ONO?

The other way is to increase the restistor from 22R to 100R to get a current of 2mA (checked it out with a spare FET in the test circuit).

Regards
Dieter
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Old 7th May 2003, 08:22 AM   #9
hsort is offline hsort
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Join Date: Feb 2002
Location: europ,germany
Hi toshiba,
you are right,that for the input stage the iddle current must be lower than 16 mA , when the jumper across r 66 isn ' t installed.then the cascode doesn ' t work properly.
i am still wondering that in the circuit the Voltage at the Drain is about 15 V with or without the jumper.Perhaps you have to increase the rail to higher numbers , or to decrease the iddle current to proper value.

what Pspice Version do you have with simulation for the 2 SK 170 ?
__________________
hsort
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Old 7th May 2003, 10:14 PM   #10
toshiba is offline toshiba  Germany
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Join Date: Apr 2003
Location: Meersburg
Hi hsort,
Hi LSV-Dieter, nice to meet you here!


Don't look at possible literal mistakes in the schematics of the Ono! Look at the circuit and try to understand it.

If the output-voltage of the MC-sub-regulator is really 26 Volt,
the cascode Q14 will be biased at it's base with about 13V.
So the Drain voltage can't be 15V !

Another (possible) mistake is "SHORT for -4db". Halving the gain-resistors (R66+R40) of the first stage normally gives -6dB. (Ok, I don't look at the following load-resistance)
And if you take a look here and see what Nelson Pass prints on his boards : "Remove for high gain + 3dB"
What is true ???

hsort, why to increase the rail, only why there is mark "15 VOLTS". I think 26 Volt is more than enough to get the amp work.

Yes, to decrease the idle current by increasing Rs is one way.
But what's about the gain (30dB) and those one, whose output of the MC-System is equal or less than 100uV. Good input value to the MM is about 10 mV.

You can calculate the gain in a simply way :

4 * (R66 + R40) / (RS + 1/gm)

"RS" is value of the source resistor (22) and "gm" the transconductance of the FETs (with assumption that all FETs have the same gm). Look at the datasheet of the 2SK170. Typical value of gm is 22mS. With R66 shorted, you get about 30 dB.

Sorry I lost the way !

Why are Pass amps so expensive and the circuits so simple ?
I think one of the most reason is the costs of matching.
Dieter know this too. Or isn't it ???
And this would be one way (perhaps Nelson Pass's way) to solve the R66-Jumper problem. But an expensive way. Which DIY'er buys hundrets of FETs to match out 8 ?
It's easier to calculate the 30dB gain with new values for RS and R40 following for high gm (>22mS), low drain current (< 2,5 mA/per FET) and a good operating point which should not drop under 15V at the collector of the cascode Q14.

For those which want to match their FETs and use the original values :

The 2SK170s should be matched to a good value of gm ( > 22mS), by matching the FETs to same IDss with very low gate pitch-off voltage "Vp".
In other words : try to match the FETs with 22 Ohm source resistor to max. 2,5mA drain current and look for gm >22mS.

Because gm is also a function of IDss and Vp, theoretical all IDss classification types ( GR, BL, V ) can be used. I thing it's better to use BL or V types, which have principal higher IDss values.
With a lower pitch-off voltage, you can achieve lower drain currents by using the same value of RS.
For those who understand the theorie, the drain curve in the tranconductance figure of the datasheet plunge down more from IDss before it rounds up than with higher Vp-values (square law form of the drain curve).

All others which had build their Ono and want to use the MC-Input and have measured that the sum of drain current through all Input-FETs (Q10-Q13) is greater than 10mA : Install the jumper over R66. The MC-Preamp will function. The only disadvantage is, that the amp produces more current noise.



@hsort

I use Orcad 9.2.2. which includes Pspice. The 2SK170 is part of the japan JFET library. But i've build own models with different IDss values.

@Dieter
Gibts bei dir au Prozentle ?


toshiba
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