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crazy bill the eel killer  
#1 Posted : Sunday, April 28, 2013 12:33:18 PM(UTC)
crazy bill the eel killer

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Hello Brian and Russ,

Hope you enjoyed your vacation.

this one's got me really interested, as I'm now playing w/ MM cartridges, so the ability place the phonostage close to the turntable is important ( keep capacitance down w/ short as possible interconnects ). So I've got two questions.

First, I haven't got a clue how to figure this out from the spec sheets of the opamps used.
Any idea what the input capacitance of the stage is ?
Also, what is the current draw as I'd like to try a battery PS.

I don't have the time to read the DIY thread and come up empty. But if the answers are in there, just let me know and I'll find them.

Thanks, Crazy Bill
crazy bill the eel killer  
#2 Posted : Tuesday, April 30, 2013 9:56:59 AM(UTC)
crazy bill the eel killer

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OK, just got through the thread and am studying the schematic ( ain't tubes, so I'm guessing at a lot of stuff ).

Am I correct in assuming that the input cap. spec would be primarily determined by C3 & C4 ?

And that the cartridge sees the summation of the two caps, i.e., a total of 11pf ?

Thanks in advance for any help.

Cheers, Crazy Bill d'oh!

P.S. I haven't got a clue how to figure the output impedance of the stage from the schematic. Anybody care to throw a number out there ? Or give a quick tutorial on how to do it ?

Russ White  
#3 Posted : Wednesday, May 1, 2013 3:32:03 PM(UTC)
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Yes C3 and C4 are the input caps. Often they are omitted. The cartridge would see it roughly as you describe. Basically as two caps in series, but with a midpoint to GND. :)

Output impedance is dominated by R16/17 which are usually 21R, but can be tweaked as desired.

Cheers!
Russ
Russ White  
#4 Posted : Wednesday, May 1, 2013 7:00:29 PM(UTC)
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Oh forgot to answer the question on current draw.

It should not be too bad. I am guessing something like 50-70ma with 12-15V rails.
crazy bill the eel killer  
#5 Posted : Wednesday, May 1, 2013 8:27:39 PM(UTC)
crazy bill the eel killer

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Thanks Russ.

As soon as schools out I'm going to have to build this thing. I'll place the order in as few weeks.

then it'll go head to head with my Sonic Frontiers Phono 1. Should be a very interesting shootout.

I'm assuming the Placid BP I ordered for my Ventus build will do nicely to compare the two PS options.


Cheers, Crazy Bill
Russ White  
#6 Posted : Wednesday, May 1, 2013 11:37:13 PM(UTC)
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Yes, placid BP will work nicely here. :)
pelliott321  
#7 Posted : Wednesday, May 22, 2013 5:10:54 PM(UTC)
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I am trying to be patient while waiting for my Retro (maybe it will be in my mail box when I get home)
anyway
what is advantage/disadvantage of leaving or taking out C3/C4
I have a moving coil off a SUT set at 100 ohm load

Also tweaking the two resistors on the output. What range can I go. 2o ohms is pretty low, but lower the better, right?
My Preamp has the usual 47k input impedance
Russ White  
#8 Posted : Wednesday, May 22, 2013 9:19:18 PM(UTC)
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I would try leaving those caps off to begin with.

The output resistor selection will depend on you cables and load. For a capacitive load or cables i would use 21R If you cables are not very capacitive then I would just install jumpers.

Cheers!
Russ
pelliott321  
#9 Posted : Wednesday, May 22, 2013 11:50:33 PM(UTC)
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Thanks for the info
crazy bill the eel killer  
#10 Posted : Friday, May 9, 2014 12:57:40 AM(UTC)
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Hey Russ,

I'm back and ready to go at this thing. Just ordered the Hi-Z full kit. Checked my Fidelity Research FR66s tonearm and my grounds are isolated, so I'm good to go.

While I've got a Placid BP in house that I bought for my still as yet unbuilt Ventus, I want to start w/ a battery supply and go from there. However, I've never done anything like that, so I'm only guessing at what I'm doing, but here goes.

If an alkaline D-cell is rated for, lets say 10,000 mah, will that mean I should expect, based upon your low end estimate of 50 ma for current draw, an estimated 200 hours or so of run time from the battery bank ?

So I don't blow anything up, am I assuming correctly that if I series 20 alkaline D-cells, and reference the node between the 10th and 11th cell to ground, I'll have my +- 15V supply. ( I'm obviously no whizbang at this stuff. )

And last for now ( and this is open for anyone ), I know I'm going to have to change my phono cable. The FR66s came w/ silver coax, ( rca's and din ) but I'm sure that's no good for balanced, as I would think I would need a high quality twin coax cable to wire balanced. Anybody have any ideas about a raw cable that I could use to construct a new balanced phono cable. I'm presently going to use this kit w/ an Audio Technica AT150MLX, so I want to keep the cable capacitance as low as possible.

Alternatively, I also have 60 ft of 29 gauge 5 nines silver in house that I could construct my own cable from. I'm a little concerned about the standard twisted pair ( no pun intended ) shielded cable being too high in capacitance for MM cartridges. Anybody have any thoughts on a low capacitance shielded cable design that I could construct myself.

As always, thanks in advance for any help,

Cheers, Crazy Bill Think
Brian Donegan  
#11 Posted : Friday, May 9, 2014 7:51:28 PM(UTC)
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Alkaline cells have a very high output impedance, and will yield less-then-good performance. LiPO batteries are what most people use for this type of thing, as the output impedance is much lower.
crazy bill the eel killer  
#12 Posted : Wednesday, June 11, 2014 3:05:27 PM(UTC)
crazy bill the eel killer

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Hello Brian,

I had done some studying on battery ps, and was aware that performance was not optimal, but I was looking for the easy way out ( throw away and replace the batteries ) instead of recharging. But you talked me out of it.

Now I've got to decide between NiMH and LiPO batteries. I know the LiPO's would offer the ultimate performance, but I may settle on the NiMH for various reasons. Which begs a couple of questions.

You spec 12-15v bipolar supply. Are there any sonic or performance advantages to keeping that supply as close as possible to the 15v. Also, can I exceed that 15v rating a bit. If I go the LiPO route w/ 5 in series for each rail, I'll be @ 16v/rail. I don't know anything about SS circuits, except that I've read that they don't overload gracefully like tubes do, but that they fail catastrophically when exceeding their ratings.

I'd like to not smell any smoke Pray

As always, thanks for any help.

Crazy Bill

LeonvB  
#13 Posted : Wednesday, June 11, 2014 4:58:33 PM(UTC)
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A fully charged Lipo is 4.2V times 5 makes 21V. Even the nominal voltage of 3.7V makes 18.5V using a 5-pack. And also with LiFePO (3.3V nominal/3.7V max.) 5 cells is on the high side.
crazy bill the eel killer  
#14 Posted : Wednesday, June 11, 2014 5:40:36 PM(UTC)
crazy bill the eel killer

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Thanks Levon.
I reckon I'll keep that 4 in series, but I'm having a hard time finding an appropriate holder for them. I guess I could always DIY one.
thanks again for your help.
NoellEagan  
#15 Posted : Wednesday, October 25, 2017 5:04:17 PM(UTC)
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Hi...i am a new user here. As per my knowledge the output resistor selection will depend on you cables and load. For a capacitive load or cables i would use 21R If you cables are not very capacitive then I would just install jumpers.

one-stop pcb

Edited by user Sunday, March 13, 2022 8:42:15 PM(UTC)  | Reason: Not specified

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