[dBel84]

in case any of you have not yet seen the "ALL in One" - not a headphone amp but pretty sweet ..dB

 

[Coreyk78]

Quote:

Originally Posted by dBel84 /img/forum/go_quote.gif in case any of you have not yet seen the "ALL in One" - not a headphone amp but pretty sweet ..dB

oh man, that's really cool, I can hear my wallet crying...

 

[BoilermakerFan]

It seems pretty cool. All it needs now is Diamond Buffers and a headphone jack and it will look a lot like a MHM...

I'm still catching up on his blog posts since Dec. 2008 to present. That ortho thread moves faster than I can keep up now too!

 

[Coreyk78]

well, it seems strange, but I'm very happy. I seperated the PSU and Aikido grounds, and reinstalled the resistors for the solid state output section, and it all works! The B+ voltage dropped to 168v with the solid state section connected also, which is where I had expected it to be.

I think I cooked my potentiometer with all the resoldering though, because I have a buzz and a channel imbalance in the left channel that wasn't there with the pot bypassed, so I need a new one of those, and I'm still waiting for the choke I ordered for the Aikido to come, the one for my Simple SE is too big to even be able to mount it inside the case anywhere, hehe. Sound on the not-buzzy right channel is just awesome though, I'm excited about this project again now! It isn't just an expensive pile of fail anymore

 

[looser101]

Great. Good to hear.

 

[digger945]

Good news.
I can't wait 'till you get it fixed, if it's like mine it's really fun to listen to your music.
Maybe you can rob a pot off something to get it patched up and be listening while your waiting for parts.
I think you will be pleasantly surprised and satisfied with the SQ.

 

[Coreyk78]

Well I kept messing with it for a while last night, I have a pot on order, so I bypassed the one I have now and used my Zero Dac's preamp section for volume control. I have a persistent hum that stay at a constant level regardless of volume setting from the Zero, or whether there is a source connected or not. Music plays over the top of it and I can drown it out, but it's still there in the background and between tracks. I'll need to finish diagnosing that once I get the new pot and I know that part of the chain is OK. I think the hum must be power supply related, hopefully once I get the proper choke and the RC filter added it will help.

Also right now listening to headphones straight off the solid state HP output the hum is the same, but I get a nasty shutoff pop, any way to cure that?

Also I was playing around with my Grayhill selector switch and there seems to be some sound "bleeding" through on the other 5 positions if I have only 1 source connected, althought the bleeding sound is very quiet I'm wondering if this is normal?

 

[looser101]

Some power grounding info here.

Suggested signal path connection diagrams in the Beta22 wiring and ground section is a good start.

Bleeding signal - are your signal wires twisted? Can you post a picture that includes everything (grounds, signal, etc)?

 

[Coreyk78]

I had already built up a ground loop breaker like the one on your first link last night, but I only had the power supply ground connected to that, since I currently have the Aikido pcb grounded through the center mounting hole with the gnd jumper on the board.

My signal wires are all twisted pairs for L and R + from the RCA jacks to the selector switch, bundled together with zip ties. The out wires from the switch are the only ones not twisted because I just temped it to the inputs on the aikido board. I'm wondering if the selector switch needs to be isolated from the chassis somehow, I'm going to check it to see if the body of the switch is conductive.

I do notice that the hum changes a lot when I touch them, and thats just touching the insulation, not the bare wire. I'm a little concerned that maybe the input wiring is too close to the mosfet heatsinks, I can post a picture when I get home to show what I mean.

The RCA grounds are tied together with a seperate 18ga solid copper wire running through the ground tabs, all the left jacks on one, right on the other, with a single wire from each of those solid copper wires to L and R input gnd.

I'm still a bit suspicous of my heater supply, since I don't have anything connected to the ref pad yet, I don't know if the heaters could induce hum or not.

 

[Coreyk78]

Oh and one other thing about my PS, I ordered the parts before I saw the other schematic on your site Renato, so I didn't have any part values for a high voltage supply so i took the values from Broskies schematic in the 24V Aikido manual that suggested 1000uF caps on either side of the choke. Would my caps being 10x larger have any negative effects?

 

[digger945]

I was looking at your pic Corey and I wonder if those two transformers being so close to one another could have something to do with the hum.
Are you still getting a hum with the source disconnected?
Are your input RCA's and HP jack isolated from the chassis?
I don't think the PS caps would make a difference, I have seen some of JB's schematics very similar to yours that have 2200uF caps in the same positions.

 

[Coreyk78]

I was wondering a little about the transformers, but I was trying to keep them as far as possible from the board, I may try turning the filament transformer 180* to see if it changes anything. I've also read of connecting the CT to ground if its not being used?

The hum is still there without a source.
All RCA's are isolated from the chassis, the HP jack I believe is not though, that's one thing I was going to look at today when I get home.

 

[digger945]

I don't think I would connect the CT to ground. Maybe you could take the transformer loose from the chassis and move it around some and see if it effects anything. I did this one time witha CKK amp and it made a huge difference. This would at least let you know that it is or isn't one or the other transformers.
My thinking originally was that maybe one transformer might be interfering with the other, magnetically speaking. They do look to be pretty close.

 

[Coreyk78]

Yeah the plastic bobbin on the filament transformer is only a few mm from the toroid. The toroid is a medical grade one though, so it has a screen ground tap that I connected to the chassis star gnd so hopefully that will work in my favor a bit.

I am wondering where I'm going to have room to mount the choke though. I was thinking I could cut away some of the perfboard and mount it right next to the PS near the front of the case.
Option 2 would be mounting it horizontally to the rear panel above the transformers since I have a 5" tall case, don't know if that would add to a magnetic interference problem If I do have one, but I experimented placing the big choke I'm using directly on top of the other 2 and didn't hear any change in the hum.

Maybe I should order one of those internal divider panels from par-metal to use as an EMI shield between the PS section and the board, or just make my own panel from some flat sheet from the hardware store.

 

[Coreyk78]

Every time it feels like I'm close to making this thing work some problems just keep coming up.

I added a 10R resistor between the rectifiers and the first C and a hammond 2.5H choke between the first and second C to the PS and added the heater gnd reference circuit. The choke cut hum dramatically but The 10R resistor had absolutely no effect on B+ voltage.

I replaced the volume pot with an alps blue 100k and that seems to be working fine. Hum is fairly minimal, if I move the wires from the pot to the inputs on the pcb around a little bit the hum changes from barely audible to unbearable. I have some different grounding ideas yet to try and see if I can eliminate it.

My main concern though is that the headphone output seems to be "clipping" badly. I don't know what other term would be appropriate to describe it. The sound cuts abruptly and I get a very nasty pop with a little pause before it pops again unless I back off the volume. It happens quite a bit earlier on the volume knob with my 48 ohm JVC cans vs. the 300 ohm Sennheisers.

It doesn't seem to happen on the line out, but I'm driving a LM3886 chipamp with fairly high gain so I can't turn it up very far before I start to go deaf anyway.

The other big issue is a very nasty turn off thump. I switched the aikido off a couple of times with headphones on my ears and I thought it ruptured my eardrums, it was actually painful. It does the same thing to the line out on shutoff, the woofers on my speakers must be moving through their full travel at shutoff, and the speaker protection relays in my amp really freak out.

I'm feeling rather frustrated again

Is there a possibility that since I'm using 10M45S for the solid state buffers that I'm running into the 50mA current limit once again on the headphone output? Or is it possible that the 180 ohm cathode resistors are running my tubes too "hot" and they are running out of breath?