When and where to ground

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dave slagle
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Re: When and where to ground

Post by dave slagle »

that depends on the preamp design and ultimately the signal levels involved. The 6H30 has a mu of 15 so call it a gain of 3.75 after the stepdown. Feed it with 2V in and you net a meax of 7.5V out which is fine for the autoformers. Feed it with 4V and you might start to run into low frequency overload if you hit the autoformer with 30V.

The answer becomes try it at both places and see.

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Re: When and where to ground

Post by 2Bexperienced »

I just read through the instructions from the old TVC and it said to have the TVCs on the input side so that's what Ill do. I had assumed it was on the output side and was questioning why my switch seemed to be wired for the input. It makes sense now. Thanks
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Re: When and where to ground

Post by 2Bexperienced »

I was going through some old emails from John and Dave and I saw where they had changed some of the resistors on the input side to allow for the TVC. Is the AVC of similiar resistance that a swap between the two is possible without modification?
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Re: When and where to ground

Post by dave slagle »

they should be interchangeable the autoformer just has a single ground wire and the TVC has two (primary and secondary) which are connected together.


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Re: When and where to ground

Post by 2Bexperienced »

Dave, I got the autoformers hooked up last night and the passive side sounds great with plenty of gain, but the active side is nothing but a loud AC hum no signal at all, so I obviously did something wrong. I'll have to figure that out.
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Re: When and where to ground

Post by 2Bexperienced »

DD power supply.jpg
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Dave, I looked at my switch wiring and that seems to be correct. All I'm left with is that somehow AC current is affecting the signal. There were five yellow wires running from the main board to the output board. Per your instructions I removed the Negative leads for both the right and left channel and left the positive leads for each channel. I left the fifth wire labeled shield in place, It seems attach to the common. I have a star ground which is attached to the earth ground of my AC plug. I have also tied the REF of the input to this ground as well as the Chassis ground coming off the common of the power supply. Also it seems strange to me that you would have me disconnect the negative leads to the output board that seems to leave the large capacitors with a connection on only one end. I have included the schematic of the power supply here.
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Re: When and where to ground

Post by dave slagle »

did you also reference the secondary of the 1674 to ground?

It is unclear what the large cap is.... there is nothing power supply related on the output board. Only the parafeed cap and the mute circuit.
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Re: When and where to ground

Post by 2Bexperienced »

OK for clarity, I run 5 and 7 to earth. What about the point labeled chassis on the power supply. I have tied that to earth and I see that it connects to the central tap which is not supposed to be grounded. What am I supposed to do with a point that has a common ground symbol like chassis as opposed to a point that has an earth ground like pin 8 on the 1674.
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Re: When and where to ground

Post by dave slagle »

central tap???

you mean the junction of pins 1 & 3 on the 1674?

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Re: When and where to ground

Post by 2Bexperienced »

No CT on the power supply which comes off a LL1683.
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Re: When and where to ground

Post by dave slagle »

than needs to be tied to audio ground at some point.

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Re: When and where to ground

Post by 2Bexperienced »

OK, hence the title of the thread, What are all these different grounds? GRD, earth ground, signal ground, audio ground, and common. As a guy who only solders kits together its a little confusing. I realize guys may want the newbies to pay their dues but my understanding is so basic that discussions of Mu while appreciated border on territory of mystical unknowns. I'm just looking for something to solder together. I understand an earth ground but any other ground while I may nod my head at the explanation doesn't tell me where and what to solder. What is an audio ground? What does it attach to? What else attaches to it? Does the REF attach to it? Does the R and L ground, formerly L - and R- attach to it. Does the AVC GRD attach to it?
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Re: When and where to ground

Post by dave slagle »

Tha autoformers and transformer secondaries should attach to the same ground as the RCA jacks and the signal tubes which appears to be "ref" for the balanced circuit. Ultimately they will all tie together at some point and the goal is to connect them in the manner that gives the least noise.

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Re: When and where to ground

Post by 2Bexperienced »

Dave, thanks for your continuing help. In the schematic you have marked shows what was formerly L- output is now GND so my assumption is I run this to my star (earth) ground. Pin 7 I can connect to via the L- input pad on the output board. What is confusing me now is the connection between pin 5 and 8. Is this merely an additional connection or do I have to cut the trace that leads to the output you marked up as GND. On the input pad of the output board the five pads are marked L-, L+, shield, R-, R+. Do you think that shield is pin 8?
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Re: When and where to ground

Post by dave slagle »

the shield appears to be pin 8 from the diagram

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Re: When and where to ground

Post by 2Bexperienced »

So the connection from pin 5 to 8 is that additional to or instead of the connection that leads from 5 to output cause I dont see another way to make that disconnection from 5 to output other than cutting the trace
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Re: When and where to ground

Post by dave slagle »

5, 7 & 8 all can tie together and go to signal ground.
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Re: When and where to ground

Post by 2Bexperienced »

OK so don't cut the trace? You have used 2 terms signal ground and audio ground. Is one or both of these a floating ground or do they tie to earth ground.
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Re: When and where to ground

Post by 2Bexperienced »

Dave, I created a small loop on the shield pad at the input of the output board and tied pins 5 and 7 to that then tied what were the negative outputs to earth ground. I have totally eliminated the AC hum unfortunately there is no sound at all. Do I need to disconnect the pad on the power supply marked CT from the star earth ground and attach it to a new ground that attaches to the enclosure.
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Re: When and where to ground

Post by dave slagle »

Pins 5,7,8 go to ground.... I cannot use specific ground terminology since I did not design or build the circuit.

The negative outputs that were tied to pins 5 & 7 have B+ on them so shoring them to ground is not a good move. I think we may have gotten way off point here and without me being intimately familiar with the circuit, I may be adding to the confusion.

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Re: When and where to ground

Post by 2Bexperienced »

OK trying to understand why you wrote GND on the
schematic you marked up. I am starting to understand that ground is a relative term related to voltage difference, but have no idea when to utilize absolute(earth) ground or a relative (signal?/audio?) ground and if there are guidelines.
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Re: When and where to ground

Post by 2Bexperienced »

I moved the AC outlet ground from the star to the lug on the enclosure and attached the chassis point to that. I moved the negative outlets on the output board from the star ground to the ground on the rcas. Still no hum or signal. I'm thinking there may be a problem with the way the pins have been rewired. Could you take another look at that?
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Re: When and where to ground

Post by dave slagle »

At this point I think it is probably best to take the unit back to stock and make sure it operates noise free when used single ended.

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Re: When and where to ground

Post by 2Bexperienced »

OK will do. Thanks for your help.
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Re: When and where to ground

Post by 2Bexperienced »

Dave, I've been running the unit as a passive pre and there is plenty of gain even for phono. So I'm going to redo it as a fully passive. Since there is no AC chord to the unit I guess I just run my grounds to the enclosure?
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