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Old 25th January 2013, 01:47 PM   #11
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Quote:
Originally Posted by m2003br View Post
Dear Rolando, your problem is very simple to be solved.
The transistors Q101-103 are BC416C, wich may be substituted by BC560C.
Transistors Q107, 109, 111 are BC239C, modern equivalents are BC550C
For Q105, 113 and 115, originals are GE X32W6047 ???!!! any NPN 100V, 300mW
are good, for example, 2N5550, 2N5551 as best choices, BC639, BD139, maybe MPSA42, BF469, BF869 as secondary choices.
If this preamp are to be used as independent preamp, don't forget to put a 220 ~ 470 ohms resistor in series with the output, and at least a 4,7uF in the position of C137.
Hope it help.

Cordiales saludos from Brazil,

Marcos
Hello Marcos

Excellent! It is exactly what I needed!

It's nice to find people of a country so close and valued as Brazil
I understand that the mentioned series resistor attenuates the mV. delivering the amplifier to a level acceptable to the input sensitivity of the amplifier. Is that correct?
The amplifier to use with this preamp is a Prima Luna Dialogue Two:
Input Impedance 100 kOhm
Input Sensitivity 270 mV (for rated power at maximum volume setting)
Do not understand why I recommend replacing the capacitor C-137 of 47 uf. by 4.7 uf. .......?

Thank you very much and best regards!

Rolando
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Old 25th January 2013, 02:26 PM   #12
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Originally Posted by Kindhornman View Post
Marcos,
thank you for that information, I am sure it will come in handy.


Academia50,
Where did you find the pots and switches that you have showing in your first post. I know that a few of the switches are no longer available from McIntosh and was wondering how I was going to replace them.

Steven

Hi Steven

The switches and potentiometers (not original) I bought here in Buenos Aires for many years. The most problematic, indeed, are the input selector switches and sorting modes. At the time I did a survey of the signal path to suit the circuit Mc Intosh.
But I changed my mind. I am not going to use because the connection would be really difficult, quite likely to capture buzz, etc. And, in 30 years things have changed a lot in audio. Input for tape heads? Removed. Input Tuner? Do not listen to radio on this computer .. Currently only need a preamp with tone controls for phono MM, (I can use the new high-output MC capsules in MM) to small corrections of vinyl I own.
So the circuit again to relieve you just leave it pertains to and ecualizacón Phono RIAA.

Best regards

Rolando
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Old 26th January 2013, 12:59 AM   #13
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Quote:
Originally Posted by academia50 View Post
Do not understand why I recommend replacing the capacitor C-137 of 47 uf. by 4.7 uf. .......?



Dear Marcos

I Sorry, correction :

Circuit C:137 = .47 uf.
Your recomendation = 4.7 uf.

Because ?

Regards !

Rolando
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Old 26th January 2013, 05:26 PM   #14
m2003br is offline m2003br  Brazil
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Dear Rolando,
I suppose you want to use your preamplifier as an separated piece.
the reason for the need of more capacitance is to prevent loss of low frequencies when connected to a amplifier with low impedance input (say, 15KOhm or less). Don't forget MA6100 is a integrated amplifier, where the power amplifier is tailored to operate with this preamp in the same cabinet.
The buffer resistor I suggested in the output is for some short-circuit protection and to prevent rf oscillations when connected to the capacitance of the output cables.

Regards,
Marcos
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Old 26th January 2013, 08:22 PM   #15
m2003br is offline m2003br  Brazil
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Steven:
A good wash with isopropil alcoohol and some silicon grease in the contacts will do real miracles with old rotary and sliding switches and potentiometers, and maintain new ones as new for long time. This include rotary switches of multimeters.
If your switches are in hopeless condition, some russian multipole/multiwaffer rotary switches available in EBAY may be wired to simulate the custom switches on McIntosh.

Rolando,
For your Primaluna Tubed amplifier, the original 0,47uF is good. making a hi-pass of about
5 Hz with 220K from MA6100 output and a 100K parallel from Primaluna input.

Marcos
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Old 26th January 2013, 08:42 PM   #16
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Marcos,
Thank you for those suggestions. Now I just have to retrieve the amplifier from my friend who was supposed to have it looked at for me. I think I can do the repairs myself.

Steven
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Old 27th January 2013, 01:42 PM   #17
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Quote:
Originally Posted by m2003br View Post
.

Rolando,
For your Primaluna Tubed amplifier, the original 0,47uF is good. making a hi-pass of about
5 Hz with 220K from MA6100 output and a 100K parallel from Primaluna input.

Marcos
Dear Marcos

This is correct? (according interpret)

Very thanks !
Regards

Rolando



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Old 27th January 2013, 06:36 PM   #18
m2003br is offline m2003br  Brazil
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Hi Rolando,
220 KOhm I mentioned is the R169. What I previously suggested to you is to put a 220 Ohm (and not 220KOhm) in series with the output, exactly where you draw a 220KOhm resistor.
The 100KOhm value in my calculation is the input resistance of your Primaluna.
This manner, R169 (220KOhm) is in parallel with 100KOhm of Primaluna Input, wich make a hi-pass of about 5Hz with the original 0,47uF output capacitor in your drawing.
No need here to put a large capacitor, because the original 0.47uF is enough for your case, is what I mean.

Marcos
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Old 28th January 2013, 04:12 PM   #19
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Dear Marcos

Now I'm clear, this extra resistance in the signal path made ​​little sense, so I preferred to consult again.
Now to buy the missing components (I get a transformer for the power, 220 volts Primary, Secondary 50 + 50 Volts and 100 Amp (5 watts) and once made ​​all to produce the circuit boards!
( ecualization RIAA, tone controls and power supply )

Very thanks!!

Regards

Rolando
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Old 1st March 2013, 12:37 AM   #20
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Hello. I'm calculating the power transformer (PT) for the preamplifier.
Deputy circuit. I see that I should get DC voltages are very high (150 VDC), do not understand why ...
This value after passing through the regulator will be reduced to two voltages required, 75 VDC and 20 VDC.

I calculated a secondary 110 volts + 110 volts AC - 100 mA aprox, is that correct?

http://electricosonline.com/Privado/...ca/fuentes.htm

If Vo = ? x 1.4142 - 1 = 150 VDC

106.78 Va x 1.4142 -1 = 150.00

It would be great if someone directly measured value on your MC Intosh MA-6100 .....
thanks for your suggestions, friends

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