[gosha68]

Hello everyone. I am new here, this is my first build and a first post.

Some time ago I’ve realized that if I want to get a better system – I’ll have to build it myself. So I’ve started to look around for DIY kits and found Jim’s site. I really liked his half-kit idea (so I won’t have to pay for some supplied components that I will probably replace anyway) and based on the feedback on this board I’ve decided to give it a try.  Really wanted to start with Clarinet, but boards were no longer available so I’ve ordered a Cornet2 kit (which I wanted to try anyway) and decided to build a Claricorn version – Cornet2 on PCB and p2p Clarinet’s side sharing Cornets power supply.

PCB assembly was a breeze, Clarinet’s side took a bit more time but overall actual assembly took a lot less time than I’ve expected (even though last time I’ve used a soldering iron was probably about 20 years ago). Here is my completed project:







I wish I had Hagtech logo I can put on a faceplate but I didn’t get any decals with my kit  (either decals are not a part of a kit or Jim simply ran out of them).

Anyway, I was extremely excited that there was no boom, fire or smoke when I powered it on for the first time!
Heater voltages are low, around 5.8 which I’ll adjust later, everything else measured close to what is printed on the pcb. I did get a significant hum and some higher frequency noise on the Cornet’s side and some minor, but audible hum on Clarinet’s side – I’m kind of expected it to be the other way around.  Hope I’ll figure out how to fix it – going to start with removing all bypasses to see if the poor placement/connection was an issue and will try to rewire inputs/outputs. 

One thing did puzzle me though. I do not have reverse RIAA filter so I’ve just fed sine wave through phono and line inputs and connected the scope to the Clarinet’s output. Here is what I got:



Does phono output look normal? Does not look normal to me but I have only basic knowledge and absolutely no previous experience with building audio components…

Well, even with the hum and all of the components having virtually no burn-in time on them both Cornet and Clarinet do sound great! Hope I’ll work out all the minor issues soon and be able to move on to the power amp project 

Hat’s off to Jim for his great designs and making it possible for guys like me to build and enjoy their own systems! And thank you all on this board for providing valuable and helpful information – every time during my build when I had a question I was able to find an answer on this board right away. 

[poty]

First of all great idea and neat and beautiful realisation!
I can't just now support my view (on vacation now), but I think there should be problems with some "juice" from the transformer, especially for heating.
The "phono output" looks bad for me. I don't know exactly what can cause this problem, but I'd think of low-frequency oscillation in the power supply filter. As soon as you have some other circuit consuming some energy in parallel with existing - it may be possible that the values of the existing parts in Cornet have to be changed!

[gosha68]

I asked Jim before I've started and he pointed me to this post:
http://www.audiocircle.com/index.php?topic=13978.0
So I used 372BX transformer and changed resistor values as suggested. The only difference is that I use power supply on Cornet side. It is possible that more powerful transformer placed closer to the phono stage causes some extra hum - I will experiment with shields later.

I tried to trace input signal and I can see the problem right on the first AX7 and it just amplifies further after that:



And here is how my heater voltages look like:



I really want to take care of fluctuating signal before I'll start chasing hum issues but at this point I really have no idea how to approach it. Maybe after a couple of days of staring at the schematics I'll get an idea. 

[hagtech]

The signal looks like hum on the phono output.  This is likely due to input grounding of the signals or wiring of the two boards together.  Why do you have phono out?  The phono inputs should not go through any sort of selection switch. 

I forget, but I think the original CLARICORN had the power supply transformer on the CLARINET side.  Also CORNET input was on outside of box (CORNET on left, when viewed from the front).  The problem you face is likely wiring and grounding.  A ground loop may have formed between boards - wiring of power supply returns and signal returns in different spots. 

jh

[gosha68]

Thanks! Then I'll proceed with my original hum-chasing plan - to disconnect input and output and all extras and if it will help - start adding them back one-by-one to see were the problem is. I was afraid I got some faulty component or some other issue that I would not know how to troubleshoot.

Why do I have phono out?... Originally I thought I wanted to be able to use CORNET as a standalone phono stage so I've added two more RCAs (they're right next to the board output - about an inch and a half long wires). However, now I cannot really think of any practical reason for doing that... If they prove to be a problem I'll just leave them disconnected.

Currently there are only two green ground wires (as per instructions) connecting CORNET board to a single grounding post. There is only one grounding post for both sides where all grounding wires are connected.

CORNET's input goes straight from the input RCAs to the board with a shielded twisted pair with one side of the shield connected to the RCA's shells and other to the board ground (center hole of the board input connector).
Output goes from the board to the input selector switch using same shielded twisted pair wire with one end of the shield connected to the board and the other end (at the selector switch) is floating. This wire does go next to the transformer wires and may act more as an antenna rather than a shield...

CLARINET (p2p) side has a grounding bus going from H+ filter to heaters grounds and then to the grounding post and separate grounding wires for each of the following (one per channel): B+ filters, R302/R310, volume pots, R312. All wires connected at the single grounding post.

If I had CLARINET board I would definitely go with original CLARICORN design with a power supply on CLARINET side (or more likely just build separates). But since I only had CORNET board I used it for a power supply and I switched sides to keep CORNET's H+ rectifier and filter further away from CLARINET side and inputs.

Last night I've rechecked all CORNET resistor values and found out that I did fail to replace R220 and R221 - I put in 1.8k instead of suggested 3.3k.    I do have correct values clearly marked on my scheme and I did check resistor values and matched them between channels before soldering them in and somehow I managed to order and put in the wrong ones... senior moment I guess...
On the other hand, my B+ voltages are lower than suggested (346V at 365V point and 316V at 330V point, line AC was 119V). Increasing R220/R221 resistance will drop voltages even more. I am going to get another rectifier tube to see if I'll get higher voltages but if they stay on a lower side, do I still need to increase R220/R221 resistance?

Thanks again,

[hagtech]

Don't worry about exact supply voltages.  They can vary a lot and the design still works. 

jh

[gosha68]

Well, after numerous unsuccessful attempts to fight the hum I have to admit that I've reached a dead end.
I've disconnected all inputs/outputs, reverted the Clarinet board to all "stock" components, removed all bypasses and completely separated Cornet board from Clarinet side to eliminate all possible ground loops. Pulled the grey wire from the transformer and connected it to the common ground - that did reduced hum but did not eliminated it completely. After listening to just Cornet I've decided that hum is low enough on my comfortable listening levels so I would leave it as is. I stared gradually adding back removed components and reconnected Clarinet side, taking listening tests along the way. Was not perfect, but was acceptable.
However, after final reassembly, hum returned at the levels that I cannot live with. I've spent another couple of days trying to rewire inputs/outputs and ground connections in the assembled unit but no matter what I do I cannot get rid of hum. Cannot even reduce it to the level I was reluctantly OK with...
At this point I'm sadly going to call it quits and to scrap the whole thing 
Since Clarinet boards are available once again, I'm going to order new boards and try to build separates, as I would have done in the first place if these boards were available when I started my build.