Octal Cornet 2

Valverine · « **on:** 2 Aug 2004, 10:14 pm »

Greetings,

I am interested in building an octal version of Cornet 2. However I could find the schematics for octal Cornet only. Does such a thing as octal Cornet 2 exist? Had anybody modified Cornet 2 to make it octal?

Thanks!

GRD · « **Reply #1 on:** 3 Aug 2004, 12:40 am »

If you search the site, there will be some information on the Octal changes to the Cornet 2. Below is a link to the resistor values. The CCS resistor values are also noted in other messages.

Good luck.

Grant

http://www.audiocircle.com/index.php?topic=4328

hagtech · « **Reply #2 on:** 3 Aug 2004, 05:55 am »

Maybe you could try a hybrid? To me, the 6SL7 just doesn't provide enough gain. You could use the 12AX7s for the gains stages and then a 6SN7 for the output buffer - best of both worlds. Then you only need modify the current sink resistor values and the voltage dropping resistors in the power supply filters.

Use the info from the Cornet octal and you'll get good results. Might need to tweak a few resistor values, but with the front end gain stages intact, the EQ will be just fine.

jh

flocchini · « **Reply #3 on:** 5 Aug 2004, 05:00 pm »

I am putting a hybrid together

Per a previous thread I have changed R220 and R221 to 1.2k; R218 to 510 and R2223 to 1.5.

I just getting to the point where I will be wiring the 8 pin tube socket for the 9 pin that is on the board for the 12AU7

Best

Bob

GRD · « **Reply #4 on:** 5 Aug 2004, 05:43 pm »

Thanks for the update. I am considering doing the same and would be interested in your findings.

flocchini · « **Reply #5 on:** 13 Aug 2004, 10:11 pm »

Status Report

I have wired everything up for the 12AX7 - 6SN7 - Bendix 6108 rectifier system

I used 1.2k at R220 and R221
I used 510 at R218
I used 1.5 ohms at R223

Heater voltage is 5.7 V
Plate voltages are 133V
B+ at test point is 330V. This might explain why my other voltages are low.

Nothing smokes!

I haven't put it into my system yet. That will be tonight.

flocchini · « **Reply #6 on:** 14 Aug 2004, 02:35 am »

After my first hour of listening I can say I am very happy. Smooth and detailed sound.

My AC was about 115V during the measurements I previously mentioned.

Comments/suggestions always welcome

Best

Bob

GRD · « **Reply #7 on:** 19 Aug 2004, 05:25 am »

Thanks for the update. Once you've had a chance to let the unit burn in, please let us know what you think. I noticed that the sound changes a bit during the first 50 to 100 hours - for the better.

Regards,

Grant

flocchini · « **Reply #8 on:** 19 Aug 2004, 05:22 pm »

I will post observations after burn-in

I'm trying to settle on tubes.

Currently V200 is a Mullard; V201 is a Telefunken; V203 is a Sylvania is
a VT231 and the rectifier is an Amperex GZ34. I also have a Bendix 6106 and some other 12AX7s. I think I should just let it settle.

Also I have a slight hum that I'm tracing down.

Best

Bob

flocchini · « **Reply #9 on:** 21 Aug 2004, 07:00 pm »

I changed R223 to 1.1 ohms to get the 6.2V heater voltage. I'm enjoying the hybrid as everything settles in.

More Later

Best

Bob

flocchini · « **Reply #10 on:** 25 Aug 2004, 05:08 pm »

I developed some noise in my right channel. Intermittent "swishing" especially during first 30 minutes. This occurred after I had been doing some tube rolling. I'm guessing it is in my 9 pin to 8 pin conversion for the 6SN7. Any suggestions how how to keep that socket from flexing would be greatly appreciated.

After I get this solved I'll rectify my slight hum problem whick I believe is because I have the unit in a wood frame. No hum with previous phono amp which is in metal box.

System: Empire turntable, RS Labs arm, Denon DLS1, YA audio step up, Cornet2, Borbely balanced linestage, Marchand electronic crossover, AKSA amps and home brew (PHLs and Raven) speakers with 96dB efficiency.

Best and thanks.

Bob

flocchini · « **Reply #11 on:** 7 Sep 2004, 05:33 pm »

I have lived with the Cornet 2 Octal for about a month now having played my favorite LPs with the unit. I highly recommend the hybrid approach. The soundstage and space around instruments is incredible. I have listened to a number of vocals and find the Cornet2 to be excellent with both male and female vocals.

I still have a bit of hum? but that could be do to my 96dB speakers.

I'm also thinking of experimenting with a Transfomer Volume Control.

The only two parts of the project that required some experimentation were the octal socket. I finally build a unit with a 8 pin socket superimposed over a 9 pin PC board unit.It's solid and I feel comfortable with exchanging tubes I also found what appears to be a test socket made by Amphenol. It is a rectangular socket with connections along the perimeter of the unit. I felt that the leads to the board might be a bit long. I also experimented with R223 to get the heater at 6.2x Volts.

Best

Bob

Galibier_Numero_Un · « **Reply #12 on:** 7 Sep 2004, 09:49 pm »

Quote from: flocchini

I have lived with the Cornet 2 Octal ... I still have a bit of hum? but that could be do to my 96dB speakers. ...

Hi,

Characteristic of all of Jim's stuff is a drop dead silence. I'd keep hunting down the hum - starting with grounding scheme (e.g. isolate RCA's from the chassis, etc.)

Cheers,

flocchini · « **Reply #13 on:** 7 Sep 2004, 11:02 pm »

I will keep tracking it down. When I installed the RCAs I know that they were isolated but things could have been bumped.

I am also wondering if placement of RCAs has anything to do with it. I built my own case. The I/O is not as in Jim's box. I have the RCAs mounted at the front of one of the long sides. The Input is wired at the R200/R201 point and the output is taken from theC208/R222 point. I am starting to wonder if those long traces help kkep the noise down. My I/O leads are about 5 inches long and are shielded twisted pair. The shield is grounded at the board for the In - at the star ground for the Out.

Thanks

Bob

Galibier_Numero_Un · « **Reply #14 on:** 8 Sep 2004, 12:20 am »

Quote from: flocchini

I will keep tracking it down. When I installed the RCAs I know that they were isolated but things could have been bumped.

I am also wondering if placement of RCAs has anything to do with it. I built my own case. The I/O is not as in Jim's box.

I have the RCAs mounted at the front of one of the long sides. The Input is wired at the R200/R201 point and the output is taken from theC208/R222 point. I am starting to wonder if those long traces help kkep the noise down. My I/O leads are about 5 inches long and ...

Jim goes through great trouble laying out his boards. We tend to think that someone as talented and experienced as he is doesn't have to work hard at building silent circuits. Unfortunately for him, this is not the case. Sometimes this leads to a layout that doesn't have the jacks in a sensible location.

The "sense" here comes from noise and not from appearance. My ex-partner built an early Coronet and moved the RCA's to a more "sensible" location. I don't have the photos around anymore, but he double shielded the short run of cable. The first shield was that of the wire. The outer shield was 3/4" diameter copper plumbing. I don't know if this was overkill, or he just got lucky, but he reports it having the typical Hagerman silence.

Here are a few links to grounding tutorials if you haven't already been here:

Kurt Strain - http://www.sonic.net/~ktstrain/Groundtutor.htm
Sakuma (direct heating) - http://www10.big.or.jp/~dh/inside/abo.html

flocchini · « **Reply #15 on:** 8 Sep 2004, 03:35 am »

Thom:

Thanks for your posts. I did check my RCAs tonight. They are indeed isolated/insulated from chassis. I hadn't thought of double shielding.

Best

Bob

flocchini · « **Reply #16 on:** 8 Sep 2004, 06:26 pm »

The project today is to wire my RCAs so that they are not star grounded at the chassis but instead they use Jim's PC ground plane. Shileding ground for input will be at the board. Shielding ground for out put will be at the RCA.

Best

Bob

flocchini · « **Reply #17 on:** 9 Sep 2004, 01:17 am »

RCAs are now wired into the PCB and the hum is GONE !!!
Thanks Thom for the two sites on grounding. THe first got me thinking about ground planes and as you stated Jim has it right. I get a bit of tube noise but I vae to turn the attenuator way up to hear anything. With music I don't hear a bit of noise.

Hybrid is highly recommended. Great sound and great project

Best

cmscott6 · « **Reply #18 on:** 25 Sep 2004, 02:22 pm »

I've been reading this post with great excitement, as I would love to try the hybrid octal cornet. Dare I ask a question as to how you mounted the octal socket and connected it to the pcb. I guess one would have to use flying leads? Does anyone have a photo?

Thanks!

Chris

flocchini · « **Reply #19 on:** 26 Sep 2004, 10:31 pm »

I used a PCB 9 pin socket and a non PCB 8 pin socket. I drilled the 9 pin so that the top ceramic could be removed. I then used best paths to "convert".
It gave a solid mount. The only downside is you have to be careful when attaching to PCB. The heat wants to un solde some of the jumpers.

This was better than my first attempt which was 8 pin with wires to PCB. Too soft and it was difficult to insert tube.

I have a picture. If you send me your email I'll send it along.

Best

Bob

flocchini@crocker.ucdavis.edu