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Old 15th October 2012, 07:19 PM   #8181
Salas is offline Salas  Greece
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What brand are your BF FETS, and what type DMM you use?
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Old 15th October 2012, 07:36 PM   #8182
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The fets came from reichelt they have a Fbb42 printed... Fairchild ?... Measured 17mA idss....I am using a TENMA 72-7930
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Last edited by RCruz; 15th October 2012 at 07:41 PM.
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Old 15th October 2012, 07:43 PM   #8183
RCruz is offline RCruz  Switzerland
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Quote:
Originally Posted by Rush View Post
OK, received the caps, Mundorf 0.1 uF Silver and oil.
Took out the direct coupled JFET, added a 0.1 uF cap with 1 meg to ground on the RIAA board. Then ran to an out board DCB1 sub board and pulled power and ground from the Mezmerize B1 Buffer. I am not fretting about large caps anymore and no hum issues, sounds fantastic.
This is a must do, actually the Mezmerize B1 Buffer board could have double set of DCB1s before and after the volume as I have essentially done and it wouldn't hurt. Four JFETs are a lot cheaper than high quality, large value, coupling caps.

Thank you Salas,

Wonderful stuff!

Rush
Hi Rush

Can you post a schematic of what you have now.... very interested I am.
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Old 15th October 2012, 07:47 PM   #8184
Salas is offline Salas  Greece
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Quote:
Originally Posted by RCruz View Post
The fets came from reichelt they have a Fbb42 printed... Fairchild ?... Measured 17mA idss....I am using a TENMA 72-7930
Its 0.8% +1 count for DC mA which is decent. One 0.5% +10 count meter I got was still showing shy by 0.2mA to my best 0.15% meter for BL. So it must be IDSS and meters.
If you see a tiny f somewhere not in in part number line on your 245's face its FAIRCHILD.
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Old 15th October 2012, 08:09 PM   #8185
Rush is offline Rush  United States
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Default DCB1 added to output

Quote:
Originally Posted by RCruz View Post
Hi Rush

Can you post a schematic of what you have now.... very interested I am.
Yes, here is an earlier schematic that shows the output of the cap (0.1 uF) and 1 meg to ground (just the output is the part I used, not the RIAA from this early one) and the schematic I chopped up posted earlier. Also, the ground for the DCB1 is to the Mezmerize board.

Rush
Attached Images
File Type: jpg Salas Sept 2008 phon shc.jpg (119.7 KB, 115 views)
File Type: jpg Salas NFET RIAA DCB1.JPG (90.6 KB, 117 views)

Last edited by Rush; 15th October 2012 at 08:16 PM.
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Old 15th October 2012, 08:13 PM   #8186
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I just happen to have that very thing. Any change or diminishing ofsound, or did you get to listen, pre DCB1?
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Old 15th October 2012, 08:20 PM   #8187
Rush is offline Rush  United States
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Quote:
Originally Posted by buzzforb View Post
I just happen to have that very thing. Any change or diminishing ofsound, or did you get to listen, pre DCB1?
It is better. Better sound stage, smoother. Still trying to find time to listen more. Only have 2 hours of low level listening now.

Rush
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Old 16th October 2012, 01:06 AM   #8188
andyr is offline andyr  Australia
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Quote:
Originally Posted by Rush View Post

Yes, here is an earlier schematic that shows the output of the cap (0.1 uF) and 1 meg to ground ...

Rush
Hi Rush,

Can you tell me why you went for a 1Mohm res off the 2nd JFET Gate ... rather than, say, half that? IE. what advantage does 1Meg have here, compared to 500K?


Thanks,
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Old 16th October 2012, 01:47 AM   #8189
Rush is offline Rush  United States
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Originally Posted by andyr View Post
Hi Rush,

Can you tell me why you went for a 1Mohm res off the 2nd JFET Gate ... rather than, say, half that? IE. what advantage does 1Meg have here, compared to 500K?


Thanks,
159155
Divide your resistance then your uF into the above number and you have the 3 BD down roll off frequency. Multiply the 3 DB down frequency by 10 and that is how far the phase shift effects the frequency response.
So, 159155/1000000/.1 = 1.59 Hz x 10 = 15.9 Hz. All good, below 20 Hz
If, 159155/500000/.1 = 3.18 Hz x 10 = 31.8 Hz.

As the resistance goes down, the cap size goes up for the same roll off.

In the original circuit we had 2.2 uF and 1 meg, but I am using a DCB1 buffer with a 25k volume pot and a 220k input resistor. So an effective 22k resistance following the output cap.
The math, 159155/22000/2.2 = 3.29 Hz x 10 = 32.9 Hz phase shift
Really need to double the output cap, now that is getting pricey.

I see no advantage of using a lower resistance into a B1 buffer and I see great reasons to use the smallest cap that will do the job. The 0.1 uF coupling cap I used are $34 each, if I was looking a 4.7 uF of the same quality, would be $111 each and who knows if the bigger cap would sound as good as the smaller one, some folks would by pass the 4.7 uF with a smaller value and the cost keep going up.
I also don't have the physical space in my preamp for a larger cap anyway.

Rush
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Old 16th October 2012, 02:00 AM   #8190
andyr is offline andyr  Australia
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Quote:
Originally Posted by Rush View Post
159155
Divide your resistance then your uF into the above number and you have the 3 BD down roll off frequency. Multiply the 3 DB down frequency by 10 and that is how far the phase shift effects the frequency response.
So, 159155/1000000/.1 = 1.59 Hz x 10 = 15.9 Hz. All good, below 20 Hz
If, 159155/500000/.1 = 3.18 Hz x 10 = 31.8 Hz.

As the resistance goes down, the cap size goes up for the same roll off.

In the original circuit we had 2.2 uF and 1 meg, but I am using a DCB1 buffer with a 25k volume pot and a 220k input resistor. So an effective 22k resistance following the output cap.
The math, 159155/22000/2.2 = 3.29 Hz x 10 = 32.9 Hz phase shift
Really need to double the output cap, now that is getting pricey.

I see no advantage of using a lower resistance into a B1 buffer and I see great reasons to use the smallest cap that will do the job. The 0.1 uF coupling cap I used are $34 each, if I was looking a 4.7 uF of the same quality, would be $111 each and who knows if the bigger cap would sound as good as the smaller one, some folks would by pass the 4.7 uF with a smaller value and the cost keep going up.
I also don't have the physical space in my preamp for a larger cap anyway.

Rush
Terrific - thanks, Rush ... now I understand your choice.

What caps cost $34 for 0.1uF? I have used Relcap RTX at about $9 in this position ... I presume yours sound a lot better?


Regards,

Andy
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