Cornet3 Prototype

roger15ohm · « **Reply #40 on:** 21 Dec 2009, 01:27 pm »

Hai guys,

finally firm on my choice and bought it.

With some input I made a bit of changes in resistors. One step further, all signal to Takman 1/2 watts (30cent more each compare to PRP). 1/2 watts not only save cost but can fit into the board better then the 1w, 13mm long. The rest PRP. All metal film. I really hope this will end up a killer.

I also purchase Multicap pptmf for the RIAA (both 0.001 and 0.0047). Silver mica don't have that value. Any recommendation on this?

Bernie,

Takman don't serve 910r too. So I'd bought PRP 910r 1/2w and some 1k8 1w for parrarel. Partsconnexion is not a bad place to shop.

Call it a day for my Cornet2 resistors....

Best regards.

Bernie · « **Reply #41 on:** 21 Dec 2009, 04:21 pm »

roger 150hm, Multicap is a good choice. The Partsconnexion is a great company to aquire high quality parts, and are great to work with as well. I have been dealing with them for many, many years. Good luck on your build, and keep us informed on your progress.

Bernie.

tubesforever · « **Reply #42 on:** 22 Dec 2009, 07:55 am »

For those looking into the right resistors to buy for your C2 or C3 project consider the following.

There is a reason why the 2 watt Kiwami carbon comp resistors sound so good. They see no stress at all within the Cornet 2 or Cornet 3 circuit and play very cleanly. You find these in the 30k dollars Boulder phono preamp. Enough said.

I would not use any 1/2 watt resistors on the board unless you are prepared for some sonic nasties. I use .6 watt Vishay nudes in the direct signal pathway only. Even then I fried one of the Vishays while hot swapping a tube.

The Kiwami 2 watt resistors would have coasted through the event unscathed.

More importantly resistors exhibit less noise if operating on the low end of their operating range. Why not let the resistors coast through their chores and play silently.

I would not recommend 1/2 watt resistors to any C2 or C3 kit builder unless they know exactly what to listen for and never plan to do hot swap tube rolling.

This is one area where exceeding the spec will provide better sonics in most cases.

roger15ohm · « **Reply #43 on:** 24 Dec 2009, 06:51 am »

Tubes,

Thanks for the advice. I just have to set budget vs performance. Sad to say USD currency is not cheap to us. Otherwise I will be happy to go either equal, or better voltage handling. Well that case i have to be extra careful when rolling tubes. Anyway I have not start to collect x7 and u7.

R200, R201 1/4watt-Takman

R204,205,207,208,212, 213,214, 219, 222 1/2watt-Takman

R101,102 2watt-Kiwame

The rest 1 watt-Prp.

Any advice?

Partsconnexion have not give me the finally invoice-plus delivery. I think is due to holidays. So i have ampel of times to get things correct.

Best regards,

Wan.

hagtech · « **Reply #44 on:** 25 Dec 2009, 01:04 am »

Dug open my old notes for variable EQ. The reference phono I've been working on for so many years (it keeps changing) had finally narrowed the EQ thing down to three positions (same as the Zanden folk). All of the microgroove can fit nicely into these categories, only the 78's get out of range.

In the Cornet, C2, or C3, the second set of EQ is done using a 1nF capacitor. This is what needs to change. I re-did the calculations and came up with the three values needed:

1) Two 680pF in parallel : Columbia/NAB
2) One 1000pF : RIAA
3) One 680pF : ffrr/EMI

The problem is switching into position will cause a huge "tic" or "thump" in the output. I thought of maybe keeping the unused positions charged up with a 1M bleeder, but this would only screw up EQ in the bass region.

I'll look at possibly switching in/out resistors instead.

jh

tubesforever · « **Reply #45 on:** 25 Dec 2009, 02:59 am »

Excellent news Jim!

Isn't it a shame you could not simply advise folks to turn down the volume before changing the RIAA?

Its a crazy world we live in where designers have to build to the least common denominator!

Thanks for addressing the RIAA or better stated the eq requirements of LP playback.

Merry Christmas, Happy Holidays and Here's to a brighter more prosperous new year!

analog97 · « **Reply #46 on:** 26 Dec 2009, 03:54 am »

Put me down for a Cornet3 pre-order. This time around I have decided on an a far better build. I will try the $2-3 resistors and maybe some teflon bypass caps. I just love my Cornet2, but I also enjoy the process of building and look forward to my 11th Hagerman project. Get your pre-orders in gents and maybe we can provide some support for this project. Happy Holidays all!!

Bill Epstein · « **Reply #47 on:** 26 Dec 2009, 10:18 am »

Quote

The problem is switching into position will cause a huge "tic" or "thump" in the output.

Maybe this is an ignorant question, but what about a MUTE or STANDBY switch?

hagtech · « **Reply #48 on:** 27 Dec 2009, 04:03 am »

Quote

Isn't it a shame you could not simply advise folks to turn down the volume before changing the RIAA?

The thump gets sent down the cable to a linestage, which might overload the input prior to volume control. The comment on adding a mute switch is more appropriate.

So I took a look at it. If I add a knob for EQ, maybe I should add one for gain or loading? Lots of people have asked for a volume knob, so I found a way to add it in. And fortunately, if turned down eliminates any pop from an EQ change. It does, however, add another critical signal cap to the path (but only when not at full volume).

Now the C3 has EQ and VOLUME. I took out the headamp or step-ups, because the power tranny and chokes are just too close. This stage will have to be run with 47k inputs. No knob for LOADING.

jh

jh

analog97 · « **Reply #49 on:** 27 Dec 2009, 02:26 pm »

Quote

Now the C3 has EQ and VOLUME. I took out the headamp or step-ups, because the power tranny and chokes are just too close. This stage will have to be run with 47k inputs. No knob for LOADING.

jh

This design sounds perfect. PICCOLO owners will be happy. For me, I never wanted to try to build any SUT's or the PICCOLO board into the Cornet2. That sounded like a recipe for disaster. I am assuming the C3 volume knob would act to attenuate the maximum 44db gain from the C3. So maybe the volume range would be something like 34-44db? Or would you make it 0db-44db in order to eliminate the "pop"? I always thought the RIPPER's volume control was very useful.

hagtech · « **Reply #50 on:** 27 Dec 2009, 07:43 pm »

Yes, I'd make the volume control go all the way down (which incidentally is not 0dB). It would act like a normal volume control. Or perhaps I could do a switch with 6 gain settings, allow for use of metal film resistors...

jh

analog97 · « **Reply #51 on:** 27 Dec 2009, 11:04 pm »

Quote

Or perhaps I could do a switch with 6 gain settings, allow for use of metal film resistors...

jh

My own personal preference is for a continuous gain volume knob. If that works for eliminating the "pops", that's terrific. A switch that has to click thru several gain settings to shut off the "pops" is ergonomically a lesser alternative I'd say. BUT, I don't know the trade-offs here. I am no EE designer, rather just trying to provide consumer feedback.

Bill Epstein · « **Reply #52 on:** 27 Dec 2009, 11:59 pm »

Since no one's asked...

I'm aware of the different EQ schemes but thought that the RIAA, (is that right one?), was so dominant since 1956 or so that only archivists had need of the others.

If true, why add volume controls and switches to muddy the signal? Isn't there already an Archiver product?

Further, given a choice between the above and a moving coil step-up option, I gotta have the step-up with 100-250-400-1000-47,000 selections. Why not just move to a bigger case? When I built my Cornet in the `10x17 Hammond box the Cinemags were about 4" away from the power tranny, no hum. I'm sure the chokes present an additional problem but, hey, you're Jim Hagerman!

hagtech · « **Reply #53 on:** 29 Dec 2009, 02:01 am »

Yeah, I like a pot for volume. So re-designed for EQ and VOLUME. Looked at physical layout and the placement of pots and switches leaves an open spot on front panel, so I thought about adding a LOADING switch. As this is MM only, perhaps values of 47k, 10k and 4.7k might be appropriate. I would think some of the more modern power carts like a high output dynavector MC could easily drive something other than 47k. In that sense, the loading would act as normal, with 10k dropping the HF response, make the presentation a little darker, perhaps more organic. I don't think other MM stages have this.

The DIY version can be built without these controls, for a more purist approach (like the original). I'll include them for assembled unit. Hey, from a system standpoint, adding one coupling cap and a volume pot is not such a sacrifice if it removes the need for a linestage. Perfect machine for a just phono system.

jh

hagtech · « **Reply #54 on:** 29 Dec 2009, 02:34 am »

Ok, that didn't last long. I dumped the LOADING. EQ and VOLUME kinda look like this now:

jh

Brinkman · « **Reply #55 on:** 29 Dec 2009, 03:09 am »

Maybe an allotment on the PCB for mounts at the location of the loading resistor for easy loading substitution (if space is needed). Loading experiments could be conducted with a device like the Piccolo. The "best" value for a given cartridge could then be installed in the loading position of the pre amp as part of the cartridge-swapping ritual. Or the Piccolo could be kept in the signal chain and the pre amp set at a nominal resistive loading...

gnnett · « **Reply #56 on:** 29 Dec 2009, 05:17 am »

Hi Jim

You should take a break over xmas like the rest of us, you are going too fast for me to keep up

. I fully understand your reluctance to go to a split chassis option, hence looking at MM only for C3.

However you did a great job cutting my C1 board to allow me to build a split Cornet. The C2 board did not lend itself to this so subsequent split chassis efforts have left a portion of the board un-populated, with the power supply being hardwired. With the C3 returning to the C1 layout and if I was going to start fresh, then a board that is able to be cut (in a straight line) would be key for me. I do not want to let go of my Bent SUT's, which are on very short leads and so would, in a single board C3, be too close to PS and in particular the inductors.

So my New Year's wish list for the C3 is as much flexibility as you like, but if there is a bit of spare room, a "cut line" for us hard core, hot rodding, not so pure ists.
Regards
Grant

gnnett · « **Reply #57 on:** 29 Dec 2009, 05:36 am »

PS: And if the gods were on my side, then an octal socket option on V4 and I would be in heaven.

Cheers

Grant

hagtech · « **Reply #58 on:** 6 Jan 2010, 05:40 am »

I find it's difficult to get both the octal and noval holes on the board in the same spot. The diameters are not that different and holes short together. Does anyone make an adapter? That would be handy, to convert a 12AX7 style pinout at 6.3V into a 6SN7 type.

Meanwhile, I got a prototype layout done. Was tight, as I shrunk the overall dimensions quite a bit to fit into a new box. I took your advice and drew an imaginary line between the power supply side and the preamp side, such that an easy straight line cut will do it (red line). Just three wires: ground, heater, and high voltage. Oops, I forgot to add a bleeder to the preamp side...

Input section has a little better grounding, I added both volume control and three EQ for the upper turnover (cut). Both of these can be built bypassed and not used, for a more purist C2 style unit. Of course, the two inductors are added for B+ filtering and regulation.

jh

tubesforever · « **Reply #59 on:** 6 Jan 2010, 08:37 am »

What the hell....You need to expand that board so I can fit my beloved Russian FT-3 teflon capacitors on my board....

Really nice work Jim!