The Dynaco Tube Audio Forum

Would you like to react to this message? Create an account in a few clicks or log in to continue.

The Dynaco Tube Audio Forum

Dedicated to the restoration and preservation of all original Dynaco tube audio equipment - Customer support for Tubes4hifi VTA tube amp and preamp kits and all Dynakitparts.com products

Home Gallery Latest images Search
Search Query
Display results as : Posts Topics
Advanced Search
Register Log in

You are not connected. Please login or register

+2

Roy Mottram

Skydogcable

6 posters

Go to page : 1, 2

PH16XW NoiseFloor/Hum

Skydogcable: Posts : 28
Join date : 2018-12-04

Post n°1

PH16XW NoiseFloor/Hum

by Skydogcable Fri Jan 04, 2019 3:09 pm

Hey. I have recently built a PH16XW. It's an exposed tube wood case version of the PH16. I am experiencing a mostly hum noise floor that is noticeable at idle from the listening position. It sounds like a ground issue to me but I feel like I have all of the needed jumps to ground. I'm hoping that someone out there can help me narrow it down and also decide if I should swap out the R23 resistor. The following is a list of ground connections and test numbers.

GROUND Connections :
-Between the psu and the main board.
-Between the psu and the IEC ground.
-A jumper on the PSU board.
-A small jumper on the main board.
-A jumper from the bottom plate to IEC ground.
-The purple wire from the transformer.
-A jumper from the phono input ground post to IEC ground.

Voltages
-D3=18.5vdc
-H+/-=12.7
-B+1=175
-B+2=166
-Line voltage Rock solid 120V

The manual says to change out the R23 resistor if the D3 voltage is below 20Vdc. Per Roy swapping this for a 210K would up that by 10vdc but lower the B+ by about 5% to around 166. This would put the B+ below spec. What should I do? Is there a way to bump up the D3 and keep the B+ in spec? Thanks in advance for any help!

PH16XW NoiseFloor/Hum Ph1610

PH16XW NoiseFloor/Hum Image410

PH16XW NoiseFloor/Hum Image310

PH16XW NoiseFloor/Hum Image112

Peter W.: Posts : 1351
Join date : 2016-08-07
Location : Melrose Park, PA

Post n°2

Re: PH16XW NoiseFloor/Hum

by Peter W. Fri Jan 04, 2019 3:29 pm

I am operating on the assumption that the PH16 and its brethren are dedicated phono preamps, and that you do not have the MC Step-up transformer option.

A few things to try, irrespective of anything else and as a way to eliminate the obvious:

1. With shorting jacks on the inputs, do you still have the hum?
2. With shorting jacks on the inputs, and the volume at 50%, what voltage (AC or DC), if any, are you getting from the outputs?
3. Is the hum 60 hz or 120 hz (assuming you are in the US) or 50/100 if in Europe?
4. Does every ground go to the same point?
5. Is the Chassis Ground the same as the Audio Board Ground?
6. I see DIP switches. Have you exercised them lately (with the amp turned off, of course)?

Now, on the advice side:

DO NOT connect your TT ground to the ground lug on the pre-amp. That is an open invitation to hum loops. Try connecting it to either headshell of the patch-cords coming from the TT. In bygone days, the likes of AR, Revox, and often Thorens and Dual would supply their TTs with this done in the factory - typically to the left headshell. Then, people started preferring esoteric cables, so all but AR stopped doing this.

Let us know what you discover. You might try the ground wire trick first. You can friction-fit it for now, and if it works, do a proper soldering job.

Last edited by Peter W. on Fri Jan 04, 2019 3:30 pm; edited 1 time in total (Reason for editing : I may be from the Philly area, but, Yo, I am not from south Philly.)

Skydogcable: Posts : 28
Join date : 2018-12-04

Post n°3

Re: PH16XW NoiseFloor/Hum

by Skydogcable Fri Jan 04, 2019 3:39 pm

My PH16 does have a SUT installed. Sorry for not mentioning that detail. I will make some measurements this evening. If I floated the ground post from the top plate and connected it to signal ground I'm assuming that would accomplish what you recommend in a clean way. The questions that I can answer now are below.

3. Is the hum 60 hz or 120 hz (assuming you are in the US) or 50/100 if in Europe? 60 hz

4. Does every ground go to the same point? Eventually yes. signal ground is isolated from chassis but the main board ground is jumped to the PSU board and that is connected to IEC ground. I get continuity between input ground and the IEC plug ground post.

5. Is the Chassis Ground the same as the Audio Board Ground? See above.

6. I see DIP switches. Have you exercised them lately (with the amp turned off, of course)? The are load switches for cartridge. I have played around a little and have not noticed any change to the noise floor.

Thanks a ton for your input!

Peter W.: Posts : 1351
Join date : 2016-08-07
Location : Melrose Park, PA

Post n°4

Re: PH16XW NoiseFloor/Hum

by Peter W. Fri Jan 04, 2019 4:04 pm

Skydogcable wrote:My PH16 does have a SUT installed. Sorry for not mentioning that detail. I will make some measurements this evening. If I floated the ground post from the top plate and connected it to signal ground I'm assuming that would accomplish what you recommend in a clean way.

Possibly, even likely, but not necessarily. That ground wire wants to be tightly 'glued' to the patch-cord, on the destination side with as little slack as possible until it reaches the headshell at the pre-amp. Even more-so when coming from an MC cartridge. Once upon a time, after-market up-graded cables for turntables came with a married ground wire option. Something like this: https://www.amazon.co.uk/Turntable-Record-Earthing-Feedback-Humming-Black/dp/B07962KP2M

The questions that I can answer now are below.

3. Is the hum 60 hz or 120 hz (assuming you are in the US) or 50/100 if in Europe? 60 hz

This leans towards (or a lawyerly 'indicates') a potential issue with the power-supply rectifier(s). 120 HZ typically indicates a problem with filter caps. Am I correct in discerning that this unit has a tube rectifier? Do you have a spare?

4. Does every ground go to the same point? Eventually yes. signal ground is isolated from chassis but the main board ground is jumped to the PSU board and that is connected to IEC ground. I get continuity between input ground and the IEC plug ground post.

"Eventually". OK - I am hoping for a "star" ground vs. a daisy-chain ground. Here is the point: A star ground puts every ground at the same potential, with nothing between any one to any other. A jumper may (not will) put everything 'north' of it at a different potential than what is 'south' of it. Continuity is not enough - the potential must be exactly the same. There are reasons for this touched on at great length in other discussions, but suffice it that a daisy-chain ground system should be avoided where possible.

5. Is the Chassis Ground the same as the Audio Board Ground? See above.

6. I see DIP switches. Have you exercised them lately (with the amp turned off, of course)? The are load switches for cartridge. I have played around a little and have not noticed any change to the noise floor.

My concern was that one of them may be not-quite-made or not-quite-unmade. Not that they were not in the correct positions.

Thanks a ton for your input!

No problem - I only hope it is actually useful. And thank you for getting back so quickly.

Skydogcable: Posts : 28
Join date : 2018-12-04

Post n°5

Re: PH16XW NoiseFloor/Hum

by Skydogcable Fri Jan 04, 2019 4:18 pm

My clear Audio Table has continuous wire from the cartridge to the RCA's at the end of the Cable. It looks much like the link on the preamp side and has no connections on the table side. It's a straight wire from the cartridge connectors to the preamp. with high end low capacitance Clear Audio wire. I'm wondering if I should break the ground jumper from the PSU to the main board and send them straight to the IEC ground to avoid the daisy chain. I can't see how it would hurt. Thanks Again.

Skydogcable: Posts : 28
Join date : 2018-12-04

Post n°6

Re: PH16XW NoiseFloor/Hum

by Skydogcable Fri Jan 04, 2019 4:20 pm

If you look at the picture that I posted the ground wire is part of the cable right where the RCA's split.

Peter W.: Posts : 1351
Join date : 2016-08-07
Location : Melrose Park, PA

Post n°7

Re: PH16XW NoiseFloor/Hum

by Peter W. Fri Jan 04, 2019 4:31 pm

Skydogcable wrote:My clear Audio Table has continuous wire from the cartridge to the RCA's at the end of the Cable. It looks much like the link on the preamp side and has no connections on the table side. It's a straight wire from the cartridge connectors to the preamp. with high end low capacitance Clear Audio wire. I'm wondering if I should break the ground jumper from the PSU to the main board and send them straight to the IEC ground to avoid the daisy chain. I can't see how it would hurt. Thanks Again.

OK - DANGER, WILL ROBINSON!!

http://www.robots-and-androids.com/images/xdanger-will-robinson.jpg.pagespeed.ic.kqbcz9CuIL.jpg

IF the IEC ground and the receptacle Neutral are at a different potential, whatever voltage that might be may be directed through your cartridge. Apart from the potential damage, this is how ground-loops are born in many cases, and this sort of thing gives rise to the multiple discussion on retrofitting 3-wire line-cords to 2-wire OEM designs.

That covers the 'I am wondering.... ' part.

You want all of the audio grounds to go to the same point, and as directly as possible. BUT - the TT (cartridge) ground is to eliminate feedback hum across the cartridge, and why it is to be directed to the HEADSHELL vs. an audio ground. The existing ground lug (knurled nut) IS an audio ground. Ideally, the cartridge ground should feed only into the phono pre-amp input, before any other grounds. As we are being sensitive to grammar lately - ONLY, meaning alone and singularly and INTO meaning that specific spot alone and singularly. The audio section of the phono-preamp will be grounded in its own right against system noise.

Skydogcable: Posts : 28
Join date : 2018-12-04

Post n°8

Re: PH16XW NoiseFloor/Hum

by Skydogcable Fri Jan 04, 2019 5:40 pm

I just sent ClearAudio an email asking for details on how the ground cable is terminated. I will report back once I get the details. Thanks again.

Skydogcable: Posts : 28
Join date : 2018-12-04

Post n°9

Re: PH16XW NoiseFloor/Hum

by Skydogcable Fri Jan 04, 2019 7:29 pm

From Musical Surroundings the North American ClearAudio rep.

The Satisfy tonearm is hardwired, including the ground cable which is permanently attached to the arm internally. The ground wire has no continuity with any of the signal cables, only to the metalwork of the tonearm itself.

Peter W.: Posts : 1351
Join date : 2016-08-07
Location : Melrose Park, PA

Post n°10

Re: PH16XW NoiseFloor/Hum

by Peter W. Sat Jan 05, 2019 10:44 am

Good! Now try to test taking the TT ground to a headshell.

cci1492: Posts : 331
Join date : 2016-05-09
Age : 64
Location : NJ

Post n°11

Re: PH16XW NoiseFloor/Hum

by cci1492 Sat Jan 05, 2019 5:17 pm

Skydogcable, is that a Hammond case you wrapped the amp with, or you custom make that? I love the look!

Skydogcable: Posts : 28
Join date : 2018-12-04

Post n°12

Re: PH16XW NoiseFloor/Hum

by Skydogcable Sat Jan 05, 2019 5:25 pm

It came with the kit from tubes for hifi. I’m not sure where they sourced it from. The normal ph16x has a different case but I wanted it to match my sp14. It also allowed me to use the toroidal transformer that would be in the standard closed case.

PH16XW NoiseFloor/Hum 99a44610

cci1492: Posts : 331
Join date : 2016-05-09
Age : 64
Location : NJ

Post n°13

Re: PH16XW NoiseFloor/Hum

by cci1492 Sat Jan 05, 2019 5:40 pm

If they offered one with that walnut case, the wires on the rear panel and no hum, I might buy one!

Guest: Guest

Post n°14

Re: PH16XW NoiseFloor/Hum

by Guest Sun Jan 06, 2019 1:52 am

yes, they are a Hammond chassis. I used those in the early days for my custom builds.

Skydogcable: Posts : 28
Join date : 2018-12-04

Post n°15

Re: PH16XW NoiseFloor/Hum

by Skydogcable Sun Jan 06, 2019 9:15 am

Did you experience any grounding issues or extra noise floor when using the wood case?

cci1492: Posts : 331
Join date : 2016-05-09
Age : 64
Location : NJ

Post n°16

Re: PH16XW NoiseFloor/Hum

by cci1492 Sun Jan 06, 2019 10:52 am

1. With shorting jacks on the inputs, do you still have the hum? 2. With shorting jacks on the inputs, and the volume at 50%, what voltage (AC or DC), if any, are you getting from the outputs? wrote:

PH16XW NoiseFloor/Hum Giphy

Guest: Guest

Post n°17

Re: PH16XW NoiseFloor/Hum

by Guest Sun Jan 06, 2019 12:10 pm

Skydogcable wrote:Did you experience any grounding issues or extra noise floor when using the wood case?

just sent you a 'pm'

Skydogcable: Posts : 28
Join date : 2018-12-04

Post n°18

Re: PH16XW NoiseFloor/Hum

by Skydogcable Sun Jan 06, 2019 12:17 pm

It’s less but there’s still a noise floor. I’m going to put my RTA on the output this afternoon and look at level and frequency of the noise. To my ear I have managed to minimize the 60hz hum but I’m left with something around 120hz. I’m want to document. I just ordered a replacement R23 resistor which should help since my D3 voltage is a little low. It always feels like a battle of inches when dealing with system noise. Thanks a ton for everyone’s input so far.

Peter W.: Posts : 1351
Join date : 2016-08-07
Location : Melrose Park, PA

Post n°19

Re: PH16XW NoiseFloor/Hum

by Peter W. Sun Jan 06, 2019 12:26 pm

Will your VOM measure millivolts?

Peter W.: Posts : 1351
Join date : 2016-08-07
Location : Melrose Park, PA

Post n°20

Re: PH16XW NoiseFloor/Hum

by Peter W. Mon Jan 07, 2019 8:51 am

One more thing!

With shorting jacks on your power-amp, are you getting any hum? This problem may be in the amp, not the pre-amp.

Roy Mottram: Admin; Posts : 1839
Join date : 2008-11-30

Post n°21

Re: PH16XW NoiseFloor/Hum

by Roy Mottram Wed Jan 09, 2019 6:33 pm

a couple of notes here . . .
1 - remember, that with a phono pre you are amplifying the input signal by 40db for standard MM inputs, that is 100x
2 - if you are using an SUT for use with an MC input, that gives you an additional 20db gain or 10X, so now up to 1000x
3 - if you are using a wood chassis rather than a metal chassis, their is no shielding for any external influences such as EMI, RFI, etc.
4 - even if power supply noise is reduced to 10 uv (microvolts) it will be amplified by at least 40db by some circuit designs
The PH16 power supply regulates power supply noise down to less than 60db below the input, and the circuit design eliminates another 20db or so of PS noise using negative cancellation,
but almost any tube phono preamp will be noiser than a solid-state phono pre. Compare 80db S/N of a tube phono pre that is well designed, to a SS phono pre with a spec of 100db S/N.
If you are using standard design loudspeakers with an efficiency of 85-90dbw, you should be fine. If you are using high efficiency speakers of 95-100db you are asking for trouble with a tube phono pre.
5 - noise in a phono preamp is most commonly a grounding problem, there are HUNDREDs of web pages on the internet discussing this problem and solutions.
One recommended solution (assuming that the problem isn't the wiring in the phono pre) is to use an AC isolation transformer, to power the turntable and the phono pre separately from anything else.

cci1492: Posts : 331
Join date : 2016-05-09
Age : 64
Location : NJ

Post n°22

Re: PH16XW NoiseFloor/Hum

by cci1492 Wed Jan 09, 2019 8:23 pm

almost any tube phono preamp will be noisier than a solid-state phono pre. Compare 80db S/N of a tube phono pre that is well designed, to a SS phono pre with a spec of 100db S/N. wrote:

Don't shoot me, does anyone have an SS that works really well?

Peter W.: Posts : 1351
Join date : 2016-08-07
Location : Melrose Park, PA

Post n°23

Re: PH16XW NoiseFloor/Hum

by Peter W. Wed Jan 09, 2019 8:36 pm

Three, as it happens.

cci1492: Posts : 331
Join date : 2016-05-09
Age : 64
Location : NJ

Post n°24

Re: PH16XW NoiseFloor/Hum

by cci1492 Wed Jan 09, 2019 8:44 pm

Peter W. wrote:Three, as it happens.

Yeah? Spill the beans, which ones?

deepee99: Posts : 2244
Join date : 2012-05-23
Location : Wallace, Idaho

Post n°25

Re: PH16XW NoiseFloor/Hum

by deepee99 Thu Jan 10, 2019 12:15 pm

cci1492 wrote:

Peter W. wrote:Three, as it happens.

Yeah? Spill the beans, which ones?

Until Peter W. comes off with his mysterious three, I can recommend the phono pre-amp built into the old Hafler DH-101 line pre-amp, at least for 47 uF MM cartridges. I was AB'ing it with the tube phono preamp I have and was pleasantly surprised. Also, there are lots of little tweaks you can do to this and other early Hafler gear to make it run like a $2,000 preamp.

Sponsored content

Sponsored content

Post n°26

Re: PH16XW NoiseFloor/Hum

by Sponsored content

Go to page : 1, 2

Current date/time is Fri Nov 22, 2024 7:08 am