My Split Chassis Cornet II Is Born !! (pics)

SoundBound · « **on:** 28 Oct 2009, 06:11 pm »

Well, it has taken me a long time from when I first started planning, getting components and then very slowly building the chassis and then the electronics, but finally the day has arrived and it's FINISHED !!!!

I decided to build the Cornet II using a split chassis design. The power supply is separately housed from the main phono preamp. I am glad to say that all the time and care was well spent. After finishing the build last night I plugged it into the system and it ran wonderfully from the first power up. Yay. I have made component changes from the stock list and these include:

PRP Resistors (everywhere except where proper values could not be found in PRP)
Mundor Silver/Oil Coupling Caps on last stage
Russian FT-3 Teflons on the first stage coupling caps and as bypass caps on the Mundorfs
Mills Wound Resistor
Auricap on all other preamp caps

I did pre burn-in the FT-3s using the FryBaby so that the burn-in period would not be so long on the preamp. The power supply chassis was wired point to point. So here are some pics:

The power Supply and Preamp Chassis' are rather large and have a lot of space inside. I could have made them a bit smaller but don't mind the size and having space inside for caps and mods is great.

I know that the preamp chassis is rather large and empty without the power supply parts, kind of like an aircraft carrier deck!

This is an interior shot of the power supply. For shielding I applied tin foil to the interior. Seems to work fine and was easy to do. You can see part of the bottom cover where I drilled ventilation holes.

Interior of the preamp with FT-3s mounted on the side panels.

This Cornet II replaces a DIY Bugle preamp that has served me well, but was not up to the level of the other components in the system. The Cornet is being driven by a modified Thorens TD160 with SME3009 arm. It only has a Grado Blue cartridge but an Audio Technica 440 is on it's way. Tubes are:

Supply - Bendix 6106
Sovtek 12AX7LPS
RCA 5963

The sound at first impression is great. A big improvement over the Bugle in terms of space, depth and accuracy. Just wonderful to listen to and it really brings out the best (and the worst!) in albums. It is very quiet, I can only hear a small amount of hum at max volume. Can't wait to hear how it goes after a bit of burn-in.

Thanks Jim for a great project, awesome design, really fun build.
Now, let me start thinking about the Clarinet !!!!

Tone Deaf · « **Reply #1 on:** 28 Oct 2009, 09:56 pm »

Really nice work, what is the unbilical made of?

SoundBound · « **Reply #2 on:** 28 Oct 2009, 10:03 pm »

Quote from: Tone Deaf on 28 Oct 2009, 09:56 pm

Really nice work, what is the unbilical made of?

Thanks Tone. The 'umbilical' is 3 conductor, 18ga cord rated to 300V AC. I wanted to use heavier cable but it would not have fit the connector I selected.

jameshuls · « **Reply #3 on:** 30 Oct 2009, 03:45 pm »

Nice work!

tubesforever · « **Reply #4 on:** 1 Nov 2009, 07:02 am »

Shoot, I'm jealous! Envious! and Impressed!

Quilted maple, separate chassis, excellent passive parts selection and it looks professional in every way.

Way to go.

The Teflon caps and Silver in Oil caps should provide more than a bit of magic. Just wait until you have about a month on this piece. It will simply dissolve and all you will hear is pure music.

Great Job!

Jim Hagerman did an excellent job with this design. You did this project justice! Just wait until you start rolling in the tubes. At that point your smile will be permanently affixed to your face!

Cheers!

poseidonsvoice · « **Reply #5 on:** 1 Nov 2009, 09:56 am »

Quote from: SoundBound on 28 Oct 2009, 06:11 pm

Well, it has taken me a long time from when I first started planning, getting components and then very slowly building the chassis and then the electronics, but finally the day has arrived and it's FINISHED !!!!

The power supply is separately housed from the main phono preamp.

This is an interior shot of the power supply. For shielding I applied tin foil to the interior. Seems to work fine and was easy to do. You can see part of the bottom cover where I drilled ventilation holes.

SoundBound,

You have done a really excellent job here and congrats on your efforts. I would only advise one thing. You see how you've bunched up the wires coming from the bottom of the Hammond transformer (Especially the brown/white ones)? You need to clean that up, make twisted pairs of the AC wiring and snip any excess. I would definitely separate AC from DC, and anywhere they cross should be at right angles. The fruits of your labor, especially with regards to building a separately housed supply for your Cornet will be even more

.

Best of luck,

Anand.

SoundBound · « **Reply #6 on:** 1 Nov 2009, 10:10 pm »

Thanks for the tips Anand. I will be sure to double check my wiring in the power supply and do some cleanup.

After some time with the Cornet II, I am afraid that the NOS RCA 5963 is not going to make it. It is giving me midrange distortion and some other problems like thin sound and weak bass. Looks like the tube is a dud. I hope the place I bought from will exchange it. I put in a vintage GE tube I had and sound was good again.

harryf · « **Reply #7 on:** 2 Nov 2009, 09:37 pm »

What advantage did spliting up the chassis give you?

SoundBound · « **Reply #8 on:** 2 Nov 2009, 11:17 pm »

Hi harryf

The main, and probably single, advantage of separating the chassis is to reduce unwanted hum from the transformer and other AC components from radiating into the preamp's amplification section. Basically it's to ensure that hum from the AC is eliminated or reduced as much as possible. I can tell you that my preamp, in separated chassis, is pretty much dead quiet. The phono preamp is probably one of the most sensitive components to hum due to the fact that it must amplify very small signals from the turntable cartridge, thus it is easy for low level hum to invade the amplifier.

flocchini · « **Reply #9 on:** 3 Nov 2009, 01:15 am »

Beautiful

harryf · « **Reply #10 on:** 3 Nov 2009, 05:04 am »

Well i must compliment you as you have put a ton of work and thought into your cornet II!
Mine in a metal hammond chassis does not hum at all.
This is why i bought from hal.
I see you lined the inside trying to reduce emf?
I was at one point going to run a custom case and do the same thing.
How do you feel about the russian teflons?I have used both those and pio's.I found the teflons gave great detail.Much better than auricaps.Although i like auricaps too.The teflons are better though.
The pio's i also enjoy for it's warmer sound.i have a few of those in my fisher stuff.Nobody here has ever run them i think.

tubesforever · « **Reply #11 on:** 3 Nov 2009, 08:19 am »

They thickened and slowed down the phono section too much. I have had the best success with these in amplifiers. For low level signals they collapsed the sound stage and made the overall sonics a lot more clouded and smokey. I went back to film caps and telfons as bypass caps.

Harry I did not check to see what equipment you run, but if you love natural tight and extended bass lines and value space around instruments and a natural timbre to instruments then you should check out a pair of 1.0 uf 1200 v Silver In Oil Mundorf caps for the final output coupling caps. They are not cheap but what they accomplish in terms of deepening and widening the sound stage is something I have yet to hear from any other cap I have evaluated.

I imagine the Audio Note silver oil caps are perhaps even tastier. I cannot afford the price of admission.

Cheers!

SoundBound · « **Reply #12 on:** 3 Nov 2009, 01:13 pm »

Thanks for all the compliments, it has been fun building this and to finally hear the results brings a tear to my eye, well, at least shivers up my spine with certain music aa

Harry, this is the first time I am using the Russian teflons, they are probably still breaking in at this point, but so far cannot complain. I agree with Tubesforever, I have the Mundorf silver oils in my main amp and used them in the Cornet as well, always loved the sound of these. They cost a bit, but compared to other caps, the price/performance ratio seems pretty good to me. Currently I am bypassing the Mundorfs with a pair of the Russian teflons, sounds ok. When it all breaks in, I might make an experiment and try disconnecting the teflons so that the Mundorfs are the only output caps and see how the sound changes.

harryf · « **Reply #13 on:** 4 Nov 2009, 05:16 am »

I always found auricaps took about 50 hours to start to sound good.
The russian teflons i have used took several hundered hours to sound good.
It was almost like one hour mone munuite someone snapped their fingers and magicaly they sounded wonderful.
Those mundorfs are way to expensive for me.
I'm sure they look great though.
I have seen russian teflons in 1 uf values.They are big but also have a low voltage rateing.I'm thinking of piggybacking them so they are good to 400v.

tubesforever · « **Reply #14 on:** 26 Nov 2009, 08:29 am »

I picked up a potential problem in the pics tonight....

If you look at the output caps you have the 1.0 Mundorfs in series with the 0.10uf Teflons.

This will generate about 0.50 uf from what I understand about series caps.

I piggy back my Teflons in a parallel wiring scheme. That gives me 1.10uf.

I wonder which actually sounds better?

How is your C2 sounding now after a couple of weeks.

SoundBound · « **Reply #15 on:** 26 Nov 2009, 02:34 pm »

Hi Tubes,
Actually the output caps are in parallel, it is difficult to see the second wire coming off the other side of the Mundorfs because I used black wire (instead of the red wire used on the other side of the cap). So I have the same 1.1 uf configuration.

The unit is sounding great, finally my vinyl excels CD in all ways. I have an RCA in the 12AU7 position now that is not as good as the GE I had in there before, I am saving the GE until after burn-in, but still sounds great. We shall see how further burn-in modifies the sound.

JayB · « **Reply #16 on:** 27 Nov 2009, 05:23 am »

Very nice indeed. I am looking for a phono preamp to build and its nice to see what can be done with this kit. I will second your opinion on the Mundorfs. I put the Silver/Gold/oil in my Paramounts and the improvement was not subtle. I wanted to use the Silvers but wasn't comfortable with their temperature rating. The question I have is why did you do the cap bypass? I understand that in parallel the total capacitance increases, but why not just get a bigger value cap? Does the voltage rating increase as well? Does it sound better?

roger15ohm · « **Reply #17 on:** 3 Dec 2009, 03:05 pm »

SoundBond,

Your completed project is perfect!! Regarding to the big chassis use for the sound stage, I did consider to cut the main board shorter if want to external the power supply. Even the new prototype C3 does have a shorter board to the C2. Anyway If i fail to think of something new, I surely will follow your split chassis. ha. Why don't you split of the filament too? Or does it have current draw problem?

SoundBound · « **Reply #18 on:** 3 Dec 2009, 05:11 pm »

Hello Roger
I also thought about shortening the board, but decided it was not worth the trouble and this leaves me the option of making it a single chassis again later if I wanted, but I don't think this will happen. The filament supply is also split with the AC rectification and first filtering stage (capacitor) in the power supply chassis. So the filament supply coming from the power supply chassis is already DC. I just decided to leave all the following signal conditioning components for the filament supply in the main chassis as it was easier to do.

roger15ohm · « **Reply #19 on:** 6 Dec 2009, 04:26 pm »

Yah I'd read one of the post that JH recommend on spliting the power.s from the board. Refering to the split out points was exactly what you are doing. According to the schematic and your picture you'd rectified in the power chassis. Sorry! I have not start my project...

What cart you match it with now? You using the Carinet too?