Metropoulos Forum

Ok, no, u have it right. The dual cap can on the board is the V1 & V2 filters. Cheers

ivan H wrote:Ok, no, u have it right. The dual cap can on the board is the V1 & V2 filters. Cheers

Any idea about the sound posted in the youtube link?

Here is another video. Shot on my Galaxy S4.

https://www.youtube.com/watch?v=kIRroPmcZk0

Well, I redid every single ground in the amp, rewired the inputs to exactly what the metro build pdf instructions say, and removed the shielded wires from the inputs and Volume I & II. Absolutely zero change.

I also added new F&T 50/50uf cap cans where my new JJ cap cans were. No change.

Now, the Power Transformer physically vibrates and I have verified the sound is 120hz.

The 120hz buzz is greatly reduced when I touch the chassis. But it is still there no matter what. Once again, when I unplug the cord from the inputs, the 120hz buzz is almost gone. You still feel the transformer vibrating though.

I don't think I have any other choice than to try and substitute a new Power Transformer. Preferably one with a center tap. At that point, I will replace all of the diodes in case something went awry. Next pay check I will order a Classic Tone PT and swap that in and wire it up exactly as Metro directs it.

EDIT: I am also replacing all three preamp tube sockets as well. If I wired them poorly before, then at least they'll be new now and with a chance that I wired them better after replacement.

I went through and checked the continuity of every single ground in the amp. They are all good and have next to no resistance.

It is obviously very frustrating but it does sound like a ground loop.

I have heard of a similar thing happen (well similar symptoms) with a paxolin board that had become conductive due to damp, around the preamp grounds but your board looks to be of a modern type?

Stupid question but have you checked that your guitar is wired properly? Have you checked this amp with other guitars?

neikeel wrote:It is obviously very frustrating but it does sound like a ground loop.

I have heard of a similar thing happen (well similar symptoms) with a paxolin board that had become conductive due to damp, around the preamp grounds but your board looks to be of a modern type?

You know, I do have part of the old board underneath the modern board. It very well could be conductive still as it is of the Fender style that are prone to this. When my new tube sockets arrive, i will pull the board and remove the piece of old board from underneath. And then i will get the standoff's up about 3/4" from the chassis.

I have debated on abandoning the board and starting over. I didn't do the greatest job of securing the turrets.

guitarist1977 wrote:Stupid question but have you checked that your guitar is wired properly? Have you checked this amp with other guitars?

I have 12 electric guitars and I have several other amps. All my other guitars work just fine with the other amps. Not a stupid question at all!!!

Majorly overhauled the wiring in the amp yesterday. But the end result is still 120hz buzz.

Replaced all preamp tube sockets
Scrapped all of the shielded wire in the amp
Removed the pots from the chassis and tested the amp; no change
Installed new rectifier diodes
Installed DPST standby switch
Installed brand new pots for the tone controls

The amp sounds better than ever except for the 120Hz buzz that is always present and gets louder with volume knob increase and changes timbre with the tone controls.

I searched for "DC 120hz Signal" and came up with this: http://forum.metroamp.com/viewtopic.php ... 0hz+signal

But, it never found a conclusion. Some suggestions were that the ground in the cable was bad. I am going to replace it anyway and see what happens. The ground at the plug is a bit wobbly.

Short of that, the other suggestion was a failing power transformer.

The history of this specific Traynor is slightly storied. Essentially, I bought it off a guy who owns Bad Cat up in Tustin Ranch. He called me on the way up to pick up the amp and let me know that he was just testing it before I got there and it started to let out some smoke so he was going to just give it to me. He told me that he bought it for a project 15 years ago and just never got around to it. Well, I think it was a project because of the issues I am having today. The once stout iron is not so stout.

The transformers buzzed physically and the 60hz hum was always present when even in stock form when I got it repaired at old Traynor specs. Granted, it didn't have the 120hz buzz. But it always had noisy transformers.

The other anomaly that I haven't heard too much issue with is that my heaters are putting out just over 7vac. 3.51v per side. Influence or just hard on tubes?

So here is some irony for you. I believe that these Traynors have the 120hz buzz in stock form.

Listen to the whole clip of this stock version. You can hear the buzz in there no matter what. Granted, mine is louder, but it is there.

https://www.youtube.com/watch?v=Vnk-f42qVLI

I am going to try and elevate the heaters again and replace some of the preamp resistors and see if I had a noisy resistor. I will also replace the blocking capacitors in the preamp as well with the stockers. If that won't do it, I will just get a new power transformer.

I got most of the amp wired up again. I replaced the 470K mixer resistors. I rewired the power tube 1k 5 watt resistors to be out of the way a bit more. I also rewired the 5.6k grid stoppers with 600v wire instead of the 300v solid core wire I previously had.

The major work I did was rework the bias supply. The main reason I did this was to see if I could get this transformer to work correctly. I previously wired the new standby switch using a DPST switch. From there I grabbed one side of the HT VAC and sent it to the 220k resistor so I have bias going to the PT before the HT is switched on. This voltage was pulling in at 160vac before hitting that resistor. I replaced the diode with a new one just for giggles. All of the rest is the same. I am hardly getting any bias voltage on the bias tap at all.

I have a feeling that the 220K resistor is designed to be used with a 320-0-320 power transformer. And if so, the 220K is too much of a voltage divider. So I am going to replace the 220K with a 100K resistor and see where things shake out at.

The other problem that I believe is contributing to my 120hz buzz is the fact that one side of the power transformer secondary is putting out 178vac and the other side is 160vac. This is a fairly large imbalance.

I have done some reading and I understand that a PT that has a secondary that is that out of balance can create buzz that is insufferable. Combined with the fact that I am getting 7vac across the heaters, I think its time to call this PT done. The guy I got the amp from did say that the amp started smoking right before I was going to pick it up. Since it was still in the chassis, I doubt he could tell where it was smoking from. But I think the PT was the source. Bad filter cap maybe took out part of the HT secondary.

Just spitballing.

I reworked the bias circuit bouncing 160vac off one leg of the rectifier into a 220K resistor into the reverse polarity diode to the caps, etc. I am only getting millivolts of DC now. I can't seem to figure out what the heck is going on.

And I haven't put in the EL34s yet. Just trying to get the -20 to -50 VDC range before putting them in. All the other preamp tubes are in and those voltages check out just fine.

Any ideas?

EDIT: I am going to try Superlead values at the resistor before the diode.

Went back to using the separate bias tap. I don't think the full wave bridge rectifier is capable of using a leg of it to support a bias supply. Go figure.

I am not 100% sure, but I think I found the biggest problem. My cable to the wall had no continuity from the ground pin on the power plug to the ground of the cable to the chassis.

Wonderful!

EDIT: Sure enough, the only way I could get continuity is by wiggling the plug end in an awkward way and holding it at one spot which would have never been possible being plugged into the wall. I am headed to Fry's to get a new strain relief and then I can get this sucker wired up and see if my grounding issues are done.