A Question For Jim H. Re: Slicing the Cornet 2!

amandarae · « **on:** 30 Dec 2009, 03:35 am »

Okay, wrong description to use. But please hear me out.

I am planning to separate the PSU for my Cornet 2 and use a two chassis solution using umbilical cord.

My plan is as follows:

1.) Power trafo and rectifier on one chassis( I will use choke loaded LCLC, last C is the 47uF C103) the PCB on another chassis.

2.) I will take B+, Ground, H+ (after the bridge only), and H- from the PSU chassis to the board chassis.

3.) From the umbilical chord, I will take B+ from the umbilical then connect it to one side of R107 and R220L and R220R. H+ to junction of C106 &R106. Chassis ground anything beyond the bridge for the Heater will be connected on the 2nd chassis as I found this much quieter when I implemented it on my 76 preamp.

Any comments will be much appreciated!

Happy New Year!

Abe

tubesforever · « **Reply #1 on:** 1 Jan 2010, 06:40 pm »

I didn't want to jump in before Jim posted but here are some things I have been kicking around since emailing Jim about this topic.

I got some advice from him about a two chassis Cornet 2 or 3. His comment was that we could simply take the transformer off board with a C2 or Clarinet. Run the wires in an umbilical to the standard plug ins on the pcb.

Abe think about this. I have for a couple of days now, and it seems really simple. Twist the wires for each pair of transformer leads and shield the umbilical from RFI. Basically we are just using up more wire to get from the transformer to the pcb.

You don't even need to bread board anything, and the power supply switch can be down in the transformer box also eliminating that source of emi near the signal.

I think I might build a big Mu box for the transfomer so it doesn't effect other gear around it. I could build a big case and use it to feed both my Clarinet and Cornet 2.

All the tubes and circuitry will be right there in the main case making it easier to do any tweaking.

With the C3 circuit, I think it will need to be bread boarded because the power supply chokes also need to be off board. I am hoping Jim will be willing to make a separate board for those of us who want to use this solution. If not, then point to point should work ok.

Bernie · « **Reply #2 on:** 1 Jan 2010, 07:10 pm »

Tubesforever,I know of at least one engineer who designs his preamps that way. I would like to confirm however if is proper to house the primary IEC circuit, fuse holder, and ground the transformer in the same chassis box? Also, if using a braided type shield, would you ground both ends of the shield, one at the transformer box/chassis, and the other end at the preamp chassis? Would there also be a need to run a ground from one chassis to the other?
Thanks in advance.

Bernie.

amandarae · « **Reply #3 on:** 1 Jan 2010, 08:12 pm »

Tubes,

First off, Happy New Year!

I guess what you have in mind will work. But here's my take. I try to avoid running AC on the umbilical cord as much as possible. In that way, shielding will not be necessary. You only need to have 4 wires, all carrying DC, if the PT, rectifier tube for HV, and rectifier diodes for H are all located in another chassis. The fourth wire is the GND.

Best regards,

Abe

tubesforever · « **Reply #4 on:** 2 Jan 2010, 03:13 am »

The B+ voltage is AC unless I am flunked tube amp electronics. Looking at the power supply circuit, the 360 v B+ AC voltage cuts right off the transformer's yellow/black lead and down the board.

The H+ runs through the DC conversion, and heads down the tube supply rails.

So whatever way you slice it Abe, there is going to be something in the neighborhood of 350 to 400 volts AC and 6.1 volts DC running along the umbilical.

As for shielding an umbilical I would probably use double braided shield. This needs to drain to the Power supply IEX earth ground connection. I would probably float it at the phono stage. I would probably go with a heavy conductor 14 awg copper wire from the IEC earth ground in the power supply box up to the board and out to the RCA grounding post so as to get the cleanest possible ground plane established. The main B+ power cord would be weaved with the earth ground line to cut down on emi.

The choke based power supply is something I have wanted for three years. It looks like it will be a reality now!

amandarae · « **Reply #5 on:** 2 Jan 2010, 04:22 am »

Hi tubes,

Quote

The B+ voltage is AC unless I am flunked tube amp electronics. Looking at the power supply circuit, the 360 v B+ AC voltage cuts right off the transformer's yellow/black lead and down the board

With all due respect, you got it all wrong. In my previous post...

Quote

1.) Power trafo and rectifier on one chassis( I will use choke loaded LCLC, last C is the 47uF C103) the PCB on another chassis.

As far as I know, the B+, or its nomenclature if use in amp building, is not AC. It is the voltage as a result of rectification (DC with ripple is more appropriate) and filtering of the peak to peak value from the High Voltage (HV) supply. Maybe you are referring to HV (for High Voltage lines, and measured as Peak-to-Peak.) After the rectifier, and the LCL filter, it should be almost pure DC with very small ripple if ever and is where the umbilical connection takes off. So you have B+, H+, H-, GND. B+ and H+ are both DC.

Quote

As for shielding an umbilical I would probably use double braided shield. This needs to drain to the Power supply IEX earth ground connection. I would probably float it at the phono stage........The main B+ power cord would be weaved with the earth ground line to cut down on emi.

In my opinion, this will not be necessary if all you have in the umbilical are DC voltages. Just like the Supratek umbilical cord. No issues with EMI or RF and is carrying much higher DC voltages compared to those needed for the Cornet.

Regards,

Abe

tubesforever · « **Reply #6 on:** 2 Jan 2010, 09:35 pm »

Abe sorry for the confusing messages.

How do I sort this out.

Discussion one, is how can you remote the transformer for a Clarinet or Cornet 2. Just run the apppropriate leads from the transformer to the board in an umbilical. This would send 6v AC and 360v AC through the umbilical. I would shield or even double shield the wires to keep the 60 hz in and the rf out. The wires would simply plug into the circuit board exactly like they do now.

Discussion two would be how to handle a C3 power supply off board.

I realize now reading your posts again that you are going to run both the transformer AND the B+ rectifier remotely and I agree this is best way to do this since the chokes chokes come after the rectifier conversion. This would send 6v dc and 360 v dc through the umbilical and up to the case.

That is what I plan to do on the C3 if Jim doesn't decide to do a C3 p/s board we can umbilical to the C3 board. Jim this gives you a second board to sell! Its a board we can use for Clarinets and Cornet 2's as well.

If my units were not dead silent right now, I would have remoted the P/S by now. For the next project I just think a remote P/S is how I want to fly. I am trying to keep these emi fields away from the Cinemag or Piccolo!

amandarae · « **Reply #7 on:** 2 Jan 2010, 11:42 pm »

Hey tubes,

Quote

Discussion one, is how can you remote the transformer for a Clarinet or Cornet 2. Just run the apppropriate leads from the transformer to the board in an umbilical. This would send 6v AC and 360v AC through the umbilical. I would shield or even double shield the wires to keep the 60 hz in and the rf out. The wires would simply plug into the circuit board exactly like they do now.

I guess you can do it that way if one elected not to move the rectifiers for both HV and heaters.

Quote

I realize now reading your posts again that you are going to run both the transformer AND the B+ rectifier remotely and I agree this is best way to do this since the chokes chokes come after the rectifier conversion. This would send 6v dc and 360 v dc through the umbilical and up to the case.

That is what I am planning to do. Have the PT , the rectifier, and the LCL filter on one chassis (PSU chassis) and use the last "C" to complete the LCLC chain as the 47uF(C103) already on the board. Have the heater rectified DC (just after the diode bridge, which means that the bridge will be relocated to the PSU chassis and the diodes on the main board to be discarded) on the same board and connect ouput (no#2 on the schematic) to the junction of C106 and the voltage divider(R105, R106) so as not to make any changes of relocating the other parts after that which are already on the main board.

Tubes, I was thinking of using two of these for the HV(or one 20H for a true choke input). Maybe we have to result to cap input if the B+ turns out to be too low.

http://www.alliedelec.com/search/productdetail.aspx?SKU=967-1002

What do you think?

Inductor; Filter; Ind 0.32H; Tol -20%, +50%; Cur 600mA; Leads; DCR 10 Ohms

regards,

Abe

SoundBound · « **Reply #8 on:** 3 Jan 2010, 02:46 pm »

Just wanted to add my two cents worth:

I built my Cornet 2 as a split chassis design with the separate power supply and some of the reasons I chose to locate the rectifier tube, diodes and first filter caps within the power supply chassis had to do with the construction of the umbilical cord system. By rectifying the AC and filtering it in the power supply chassis, you only have to run 3 conductors with the umbilical to the main chassis. All you end up having is +6V, +360V and ground. This means you only need 3 pin connectors and a 3 conductor cable.

Since I wanted to use larger gauge wire for the umbilical and good sized connector pins with a screw on type of connector lock, this was a big factor for me. It was much easier, and cheaper, to source good quality 3 pin connectors and heavy gauge cable. The more wires you have to run in the umbilical (as you would if you only housed the transformer) means it could be harder and more expensive to source components to make a good and reliable / safe umbilical cord system.

Just some thoughts you might want to consider.

Bernie · « **Reply #9 on:** 3 Jan 2010, 07:30 pm »

Thanks! SoundBound, if your umbilical cord worked safely for you, I will try your method. I have always had issues with what to do with the ground side of the power supply circuit when using an outboard supply.

Bernie.

Bill Epstein · « **Reply #10 on:** 3 Jan 2010, 08:22 pm »

Quote

If my units were not dead silent right now, I would have remoted the P/S by now

C'mon Tubes, anyone can build quiet, even me, but as Abe knows, to get eerie, you have to go 2 chassis.

So put down that beer and turn off the football game!

amandarae · « **Reply #11 on:** 4 Jan 2010, 01:05 am »

Quote from: SoundBound on 3 Jan 2010, 02:46 pm

Just wanted to add my two cents worth:

I built my Cornet 2 as a split chassis design with the separate power supply and some of the reasons I chose to locate the rectifier tube, diodes and first filter caps within the power supply chassis had to do with the construction of the umbilical cord system. By rectifying the AC and filtering it in the power supply chassis, you only have to run 3 conductors with the umbilical to the main chassis. All you end up having is +6V, +360V and ground. This means you only need 3 pin connectors and a 3 conductor cable.

True! I understand what you were saying.

My approach is different and, my apologies, I neglected to include C106(relocate to PSU chassis). I will ground H+ on the PSU chassis (because it is not floating) so that the large current after the rectifiers through C106 only flows to the PSU chassis star ground as well as the current from the mains rectifier through the LCL filter. Of course, the HV "0" Volt Line will be connected to the star ground as well and becomes the Ground Wire to the umbilical cord(thus the need for the 4th wire (GND) on the umbilical for the ground to the main board chassis). The last C should have minimum ripple and can be left on the main PCB board.

I have tried this on my 76 preamp with very good results regarding noise and hum. Also, with a fourth wire, I can experiment floating the filament voltage if necessary.

If you have time, you might be interested checking this out for reference purposes about grounding. I truly believe that the 0 Volt Line connection for the HV should be present on the main preamp chassis for a much better and quieter grounding scheme.

http://www.raleighaudio.com/Audio%20Component%20Grounding%20and%20Interconnection.pdf

As for the connectors, I only use these from Radioshack

Best regards,

Abe

amandarae · « **Reply #12 on:** 4 Jan 2010, 01:17 am »

Quote from: Bill Epstein on 3 Jan 2010, 08:22 pm

C'mon Tubes, anyone can build quiet, even me, but as Abe knows, to get eerie, you have to go 2 chassis.

So put down that beer and turn off the football game!

Hi Bill,

I can live by with my Cornet 2 as far as being "silent". Like you, I am using high sensitivity speakers and we know how they react to noisy components.

My problem with my Cornet 2 at present configuration is that you cannot place the unit close to my preamp or SUT's on the same rack. I have to provide ample space for it and that really annoys me a lot. It affects all the other components and produces hum. I tried encasing the power trafo with mu metal to no avail. Move it far away from the rack is not an option because I will need long IC's from the SUT, to the Cornet, and then back to the main preamp. It does not sound good with the long IC's config at all!.

So I figure, there must be a better way......

regards,

Abe

tubesforever · « **Reply #13 on:** 4 Jan 2010, 03:05 pm »

Abe,

I too have far too many transformers all within say 3 ft of my Piccolo. I have to get it in just the right alignment to keep it silent.

Off boarding the big Hammonds which are stuck right out there in the open should make for better sonics.

Bill I agree with you that "eerie" means two chassis. I absolutely agree and there is both a cool factor as well as an electronics side to "eerie". And yeah I have been watching a lot of football this week!

Abe, dcr is 10 ohms.... what is the dcr of the choke that Jim Hagerman specs out on the C3? Heck I will look it up later....

Soundbound! Your 2 chassis unit is killer! BTW since the C2 and C3 are common grounded 3 wires is all you need, but I would bring up a fourth just to weave with the 3 power lines. I would bring up the IEC earth ground so it could ground both chassis and the turntable / tonearm wire ground from the main chassis.

I would go with an independent line just to make sure there was a very clean earth ground pathway.

Weaving the power cords on the umbilical is a good way to reduce noise.

BobM · « **Reply #14 on:** 4 Jan 2010, 07:47 pm »

At some point you have to ask yourself if the additional cost to modifying the Cornet is worth it, or if you should step up and look for a "better" phono stage, like the Trumpet. Of course if you're into projects and building stuff yourself than this statement is worthless; it's the manual build that counts and that's more than half the fun.

amandarae · « **Reply #15 on:** 4 Jan 2010, 08:43 pm »

Quote from: BobM on 4 Jan 2010, 07:47 pm

At some point you have to ask yourself if the additional cost to modifying the Cornet is worth it, or if you should step up and look for a "better" phono stage, like the Trumpet. Of course if you're into projects and building stuff yourself than this statement is worthless; it's the manual build that counts and that's more than half the fun.

Hi Bob,

I had the Trumpet from July 2005 up to sometime around late 2007. I sold it. Bass is a little better because it is SS rectified, which helps when I had Martin Logans and Magnepans.

As for tweaking the PSU of the Cornet2, if the Trumpet or the Cornet 3 has a choke rectified B+, I want to try if the C2 can benefit from it also, not to mention that with the split chassis, the placement of the main unit close to other equipments can be not as critical.

Personal preference and observations only of course.

regards,

Abe

SoundBound · « **Reply #16 on:** 4 Jan 2010, 09:15 pm »

Thanks Tubes

Quote from: tubesforever on 4 Jan 2010, 03:05 pm

BTW since the C2 and C3 are common grounded 3 wires is all you need, but I would bring up a fourth just to weave with the 3 power lines. I would bring up the IEC earth ground so it could ground both chassis and the turntable / tonearm wire ground from the main chassis.

I would go with an independent line just to make sure there was a very clean earth ground pathway.

Weaving the power cords on the umbilical is a good way to reduce noise.

I understand your point about the dual ground wires. I used the same type of connector as Amandarae shows in his post above (he shows a pic of it) but I used a 3 pin version. The housing of this connector is kind of small and a 4 conductor cable (of suitable gauge and appropriate to handle voltages over 300V) would not fit well. So I used a 3 conductor cable. I did pay a lot of attention to the layout of the grounding in both the power supply and main chassis. I was careful to make a single point 'star' arrangement in both and used this single point ground system as the only points of ground contact between the two chassis.

I felt I could do without shielding the umbilical since the voltage supplies would be DC running in the cable and hoped that the filter caps in the main chassis on both B+ and H+ (C206&207 and C209-211) would help filter any AC noise that happened to be picked up in the cable.

If the connector was physically larger I would have likely used shielded cable. Anyone who has looked for reasonably priced and readily available connectors for 3 or more wires that are around 16ga in size or larger, if you find them, let me know, 'cause I am already starting to think about a Clarinet project !!

amandarae · « **Reply #17 on:** 5 Jan 2010, 05:48 am »

Quote from: SoundBound on 4 Jan 2010, 09:15 pm

Anyone who has looked for reasonably priced and readily available connectors for 3 or more wires that are around 16ga in size or larger, if you find them, let me know, 'cause I am already starting to think about a Clarinet project !!

Lockable 3-pole equipment (AC) connector with contacts for line, neutral and pre-mating safety ground.
High current capacity, rated at 20A / 250V ac
Fast and easy locking system
Extremely robust and reliable
Excellent cable retention
UL, C-UL recognized components
VDE and SEV approved

http://www.neutrik.com/fl/en/industry/210_1780630671/NAC3MPA_detail.aspx

roger15ohm · « **Reply #18 on:** 6 Jan 2010, 01:07 am »

Hai guys,

Very informative! Now, while waiting for the parts to arrive from the other corner of the world, I managed to found my ex diy thing which includes double c core trans, 1 220ufx2x450 huge carafine cap. Very wasted if i don't use it.

Should that be fine if I managed to come out with 360v for the HT? what is the range of varies for the HT?

BobM · « **Reply #19 on:** 6 Jan 2010, 02:10 pm »

Quote from: amandarae on 5 Jan 2010, 05:48 am

Lockable 3-pole equipment (AC) connector with contacts for line, neutral and pre-mating safety ground.
High current capacity, rated at 20A / 250V ac
Fast and easy locking system
Extremely robust and reliable
Excellent cable retention
UL, C-UL recognized components
VDE and SEV approved

http://www.neutrik.com/fl/en/industry/210_1780630671/NAC3MPA_detail.aspx

You actually can use a regular balanced XLR cable connector also. I believe they are rated to 200V, although the one above is probably a better choice all around, if a little more expensive.