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Old 18th March 2020, 02:43 PM   #501
BigE is offline BigE  Canada
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Perhaps lifting the shield grounds from the case on the input side, but keeping them connected is correct? I'll make a drawing.

Last edited by BigE; 18th March 2020 at 02:50 PM.
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Old 21st March 2020, 03:24 AM   #502
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KOR952 WROTE below( I've tried it never better....., it's great for my Benz wood HO )


If there is more gain needed (+ 15dB), for instance when a Denon DL-103 is used, it is possible to change the second stage as follows.

R2 = R3 = 1k8
R4 = R6 = 1M
R5 = 100k
C2 = 3.3nF
C3 maybe the same (10uF) but may be changed to a 4.7uF

The gain of the first stage is R1 / cart. imp. x loss factor (due to the parallel RIAA cap)

For a DL-103 this will be 1620 / 40 x 0.9 = 36.45 x

The gain of the second stage is R5 / R3

For the original this will be 33k / 3.3k = 10 x

For the modified 15dB + version this will be 100k / 1.8k = 55.55 x

Output of a DL-103 with the original components = 0.3mV x 36.45 x 10 = 109 mV

Output of a DL-103 with changed components = 0.3mV x 36.45 x 55.55 = 607 mV

Difference in output is 14.9 dB

If you want less gain change R2 and R3 to a higher value, for instance 2.2k instead of 1.8k gives -1.74dB (0.818x) less gain.

RIAA filtering will not change while the values of caps and resistors are switched.


My 2 cents,

Ronald.

Last edited by BigE; 21st March 2020 at 03:27 AM.
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Old 13th May 2020, 12:33 AM   #503
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I wanted to revert to stock, and now the power supply is not working.

It showed +18.3 and -17.4 rails, I put in new opamps, it jumped around 0-10v, I turned it off, resoldered U1,Q2 Q1, Q2, and turned on again. Back to an unregulated 18 and 17 volts.

It seems the regulators have failed. The op amps were opez27.... I guess they are dead now too?

Any help getting this going again would be *greatly* appreciated, as this is my only phono section.
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Old 13th May 2020, 01:32 AM   #504
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stable now. its all about poor measuring skill

15.2 and -15.4

Last edited by BigE; 13th May 2020 at 01:54 AM.
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Old 13th May 2020, 05:11 AM   #505
Temaad is offline Temaad  Australia
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Default Will it suit a Accuphase AC-2

Hi, Have been looking for a MC phono amp that can work with my Accurphase AC-2, see specs

Output voltage: 0.18mV

Frequency response: 20 Hz to 60 kHz

Channel separation: 30dB

Channel balance: 0.5dB

Internal impedance: 4 ohms

Load impedance: higher than 50 ohms

Will this unit be OK, need at least 75dB of gain.

Cheers
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Old 13th May 2020, 10:42 PM   #506
Temaad is offline Temaad  Australia
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Also, I suppose I should ask, P
eter do you still have some boards.

Regards
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Old 19th May 2020, 05:14 PM   #507
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I've been taking my stupid changes out of the phono section. Never again will I doubt the skills of the designer. Rookie egotistical mistake. I apologize for that.

I've learned enough to know I don't know very much at all. The power supplies are back to original and have reasonable voltages. One last change is to remove is the added 15 dB gain from a post earlier in this thread....

Can someone tell me please..... how can a circuit with a shunt regulated supply and no ground connection hum? Is this a floating circuit? If this is a floating circuit, a ground loop breaker, (two diodes back to back with resistor and capacitor between the power supply zero volt line and the earth ground), should not be needed. Is that correct?

Also, should the ground lug for the TT be isolated from the chassis and connected to earth ground or should the ground lug be attached directly to the chassis which is already connected to earth?

I see about 3 mV of noise on the output with a scope attached.

Last edited by BigE; 19th May 2020 at 05:27 PM.
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Old 20th May 2020, 12:44 PM   #508
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Looks like this is headed to the bin
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Old 23rd May 2020, 09:59 PM   #509
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fixed!

There are quite a few vias under parts. If you like to remove/replace a lot, you run the risk of damaging these vias. You then need to be creative.
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Old 23rd May 2020, 10:26 PM   #510
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If you are going to build this, my recommendation is to match R2 and R3, the resistors between the Op amps.

Also, I believe that the sonics are related strongly to the quality of the caps. I tried a few, and in the 0.1 uF position, to my ear, Vcap is stellar

.
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