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Another Super High End Phono Stage! No expense spared...

redjr said:
Hey guys -

If I'm going to enclose the CNC into a smallish metal/aluminum cabinet, complete with a small Rod Elliott PS (P05) using a small Toroidal x-former, do I need to provide any additional shielding of the PS, or use shielded cable to/from the RCA jacks? I figured at a minimum I would use shielded cable (couldn't hurt). What about the toroidal? Does that need to be inside another metal box? Just want to make sure I have everything and have thot through any other considerations before trying to enclose the whole thing. IOWs, I will not be using an external wall-wart or power brick.
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Because of the low levels that a phono preamp deals with, I consider shielded cable for the RCA's a requirement no matter what is done with the power supply.

Just my take on it.

Shelly_D
 
shelly_d said:
Because of the low levels that a phono preamp deals with, I consider shielded cable for the RCA's a requirement no matter what is done with the power supply.

Just my take on it.

Shelly_D
Click to expand...
I agree with you and that's been my intention all along. However, someone suggested that since the runs are so short inside a small enclosure, there's really no need for it and using a twisted pair is fine. I just thought adding the PS inside would add a dimension of EFI - however small.

This topic came up when I noticed a few builds here in this thread that only used twisted pair. That's when I asked the question a few pages back, because I thought it a bit odd too.

I have a nice roll of some super small shielded cable that I've had on hand and used with a couple other projects over the years. It nice Belden wire too.
 
ghazzer said:
. . . The only place where the L&R signals are even close enough for a crossover is inside the two ICs. With both ICs removed I have taken ohm meter readings between all he pins of both sockets.. Didn't find anything obvious, but I need to check the circuit paths to make sure that the readings are valid. If I can eliminate the PCB and the discrete components, then it must be the ICs.

.
Click to expand...

This was my reasoning for suggesting swapping the ICs. The traces do not allow one channel to get into the other channel.

My next guess would be that there is something wrong with the arm wiring. Do you have another phono setup to try?
 
hags said:
Check your cartridge pin connections as well.
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One of the early things I did was to swap in a different headshell/cart, with no change. Things continue to work OK thru the phono stage in the Sansui.

I get a lot of good suggestions like this, so thanks for thinking. My base line is that this was working a couple of times so everything else should be fine. I still get separate signals coming into the CNC. I can see these on the oscilliscope when the test record alternates the 1 KHz signal between the channels.

I think I have pretty well eliminated everything except the opamps. I'll be out of town for awhile so I am not going to order new opamps until I get back.

.
 
Has there been an updated schematic posted? I see one on page 1 and one on page 2 but neither have the RIAA parts values that are called for now.

Thanks in advance.
 
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Grainger49 said:
Has there been an updated schematic posted? I see one on page 1 and one on page 2 but neither have the RIAA parts values that are called for now.

Thanks in advance.
Click to expand...

I traced it out because I was playing with gain values as a possible preamp for a Moving Coil preamp. The RIAA values would remain the same in either case. In this drawing, the upper schematic is what I took off the circuit board, comparing it to the earlier schematics. I hope this helps you. I am NOT confident on the values of the lower schematic as a possible moving coil preamp. Use the upper diagram.
 

Attachments

Thank you.

It seems I have taken the RIAA values from the schematic in the first post. I'll see if I have enough capacitors for that configuration.

I saved your file for future use. I'm going to build a few of these.
 
Grainger49 said:
Has there been an updated schematic posted?
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Sorry, I got side tracked this afternoon. Here is a .jpg schematic that you can use if you want something you can alter. Hypnotoad has looked at it so I musta got most of it right. I still don't understand why there are 2 sets of 10 & 1uf caps to ground on B+ and B-.

I tried to make it look like the PCB so it would be easier to follow.

PM me if you need a different file format or more resolution. The original was created in PhotoShop.

attachment.php


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  • CNC Schematic.jpg
    CNC Schematic.jpg
    60.4 KB · Views: 1,787
langston said:
Could it run on AC/DC converter in lieu of batteries?
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Yes it can, you will need both a positive and negative power supply. Both should be 9 volts or more (but no more then 15 ~ 18 volts). It will work on less but the 9 volt spec provides a good bit of gain headroom. The real trick to using a power supply is keeping AC ripply out of the power feed. It adds noise.

Shelly_D
 
Ok, looking at the schematic in post #1 the RIAA RC time constants are 116.92us and 393.93us. Looking at the latest PCB the RC RIAA time constants are 119us and 86.326us.

So what is the spec??????

The reason I ask is that some of the capacitors I have looked at have been pretty expensive, $2-$3 each. Most of what I find is Polyethylene rather than Polypropylene. Well, there are metalized Polypropylene and stacked Polypropylene but not Polypropylene film.

Edit: A Google search came up with three frequencies/time constants:

3180us = 50.05 Hz

318us = 500.5 Hz

75us = 2122 Hz

None of these match with what I calculated so I'm not considering the source impedance that must be a factor.
 
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9V Battery charger

Hi,
I am running my CNC on two 9v batteries which l have to change in every 20 days(approx 36 hrs).I am thinking of using two rechargeable 9V batteries with builtin charger.Can anyone suggest me a circuit of 9V charger which can be used in CNC.I am thinking something like this:
http://cgi.ebay.com/ws/eBayISAPI.dll?VISuperSize&item=260763759722

Pic only for reference no affiliation with seller.

Regards,
Sachin
 
See the diagram in post #495 on page 33. It may help you with the overall project, but the design of your charging circuit may depend on your choice of batteries. If you get a charger with the batteries, you can just wire that in.

.
 
Hi Ghazzer,
Thanks,I read your post about charger.I am thinking of using of two 9V rechargeable batteries for its price and size.Lantern and SLA batteries are very costly in India,so they are ruled off.I don't want to use power supplies as it can add some unwanted noise.Can you suggest me a good semantic for charger,sothat I can make a small PCB which can be put inside CNC enclosure.

Regards,
Sachin
 
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Sorry, but design work is not my bag. Maybe you can e-mail the manufacturer of your batteries and ask them.

Other option is to give us a complete set of tech specs of your batteries and maybe someone will chime in. May get better results if you post it in the DIY forum.

Good luck - - -

.
 
sachu888 said:
. . . I don't want to use power supplies as it can add some unwanted noise.Can you suggest me a good semantic for charger,so that I can make a small PCB which can be put inside CNC enclosure.

Regards,
Sachin
Click to expand...

Sachin,

The AC in the CNC would introduce noise, it would best be kept outboard. You can use a four pole double throw switch, center off if you wish, to remove the outboard charger when listening.

I diagrammed a switch in this thread somewhere and I can't find it. But I can send you the schematic in a JPG privately.

Nope, it is in the LO MC PP thread:

http://www.audiokarma.org/forums/showthread.php?t=387121&page=10
 
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