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Old 1st August 2006, 09:02 AM   #61
AndrewT is offline AndrewT  Scotland
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Hi Sono,
Quote:
The resistor 'bleeds' the signal from this point to earth.
that resistor could be before the DC blocking capacitor or after.

If before the cap, then it references the input side of the cap to ground and may be in the high k or low M range.

If after the cap then it forms the high pass filter that attenutaes the signal before entering the gain stages of the amplifier. This is likely to be mid to high k.
Quote:
4.7-6.8 ohm
where are you recommending adding this resistor?
Quote:
Cyrus 1 which has direct input from the RCA's to the blocking capacitor on the main power amps with no resistor directly in signal
are you sure? I thought Cyrus had a low pass filter before the gain stages.
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Old 2nd August 2006, 08:45 AM   #62
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Hi Andrew,

Please find an image attached showing exactly what's happening in this amp.

I've replaced a couple of the original RCAs with gold plated ones (though I'm no great fan) and taken the signal from here direct to C31, which is a 2.2uF non-polar on the original amp. I've replaced it with a 1.8uF MKT for the moment.

The signal is bleed-off through a resistor to ground near where the pot used to be.

The higher the resistor value, the more music, so resistor values of 4.7-6.8 ohm appear to give about the right volume for me

I've avoided all the input selectors and associate resistos and by having just one volume have probably taken this amp to its minimalist extremes.

I've also tried using an elma switch to allow changes in resistor value and will probably end up using something like that in the end. Values will be from 3.3 to 10 ohms in six steps.
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File Type: jpg cyrus underneath.jpg (95.3 KB, 3081 views)
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Old 2nd August 2006, 09:11 AM   #63
AndrewT is offline AndrewT  Scotland
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Hi,
I do not understand.
To compound my confusion your component values do not add up.

When was Cyrus first designed.

Look at that star ground. and marvel!
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Old 2nd August 2006, 08:58 PM   #64
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If you have a Cyrus schematic or amp lying around try to see what is actually happening.

The resistor values are correct. Can you see that the higher the resistor value the higher the volume?

Another simple way to do this is to put a low value resistor directly across the RCA. The lower the value the more signal is being dumped to earth.

I beleive Russ Andrews has used this technique in his attenuated leads.

Cheers!
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Old 3rd August 2006, 12:20 AM   #65
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Quote:
Originally posted by sonokeling
If you have a Cyrus schematic or amp lying around try to see what is actually happening.

The resistor values are correct. Can you see that the higher the resistor value the higher the volume?

Another simple way to do this is to put a low value resistor directly across the RCA. The lower the value the more signal is being dumped to earth.

I beleive Russ Andrews has used this technique in his attenuated leads.

Cheers!
Sounds like you are shorting the output (= dumping the current to ground !?!) forming an attenuator with the output impedance and a small value resistor.

Whatever floats your boat.

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Old 11th January 2007, 05:46 AM   #66
Dr. ODD is offline Dr. ODD  Germany
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Hi Peter,

any Progress ?

Does your passive line Stage also work whith your ono? (I ask that because it schould have 150 ohm output impedance, if it is not modified at this Point)

Bernhard
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Old 12th January 2007, 12:38 AM   #67
v-bro is offline v-bro  Netherlands
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Hi Peter, nice project, I've studied stepped attenuators for a while starting with a series type, than went directly to a ladder type attenuator... The laddder sounds much nicer if you'd ask me.

I chose 'dale' resistors and tested some others, but they all must've been good. I don't hear any 'quality' difference between the last- and second to last step, though the last is derectly connected... All steps have such perfect equal level and quality, I've purchased 10 resistors in each value, some values I took 20 pieces and matched them myself....(0.1% tolerance!)...

I'll look up some of the handy information I used back than...
Here's a picture of the series attenuator (my first):
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File Type: jpg attenuator1st.jpg (63.2 KB, 2541 views)
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Old 12th January 2007, 12:41 AM   #68
v-bro is offline v-bro  Netherlands
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My ladder attenuator (my second):
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File Type: jpg ladder preamp.jpg (95.6 KB, 2596 views)
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Old 12th January 2007, 12:46 AM   #69
v-bro is offline v-bro  Netherlands
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I love Elma switches, I also added built in filters with 12db/oct slopes at aprox.200 hz. This filter can be switched off.....
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File Type: jpg nicefourchannelgear.jpg (62.6 KB, 2482 views)
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Old 28th January 2007, 08:28 PM   #70
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Quote:
Originally posted by Dr. ODD
any Progress ?

Well, the work on an attenuator has been finally completed.

All credits with regards to control board, display and programing go to Veteran.

The relay board design was our combined effort, the attenuator concept was my idea, however, I was heavily inspired by Placette Audio. We have incorporated few changes though, like completely different layout, use of printed board for relays and resistors mounting and adding additonal 3 steps to lower the control range by another 12db or so.

The steps are also more uniform and the actual value of attenuation is being displayed. Mute function is also included.


Click the image to open in full size.

Click the image to open in full size.


Each channel has its own dedicated board, with SMD realys mounted on both sides:

Click the image to open in full size.
Click the image to open in full size.

For this version I decided to use nude Vishays, you need 28 resistors to complete the task. The PCB also allows the use of Caddocks, which have slightly wider footprint. I gues that type of attenuator will also work well with regular type of resistors.

Click the image to open in full size.

The resistors are mounted in two rows (series and shunt separately), the relays bypass them, depending on attenuation. I wanted to achieve the shortest signal path and it seems like it was the only elegant way to do it. This requires SMD relays though.

Click the image to open in full size.

The two Dale resistors you see here, are to provide -47db, -52db and -58 db steps (in addition to regular steps with use of Vishays)

Click the image to open in full size.

The optical encoder used to control the volume is from HP, the same as the one in ML380. The "feel" is like nothing else

Click the image to open in full size.
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