Metropoulos Forum

Hello I've just finished my metro BB RI board and I'm confused. If anybody help me please send me PM.
Thanks for any help

Tell us more about your confusion.

Do not be embarrassed, we have ALL asked daft questions, I still do

I have the BB Ri Board and got problem with tremolo. I check the schematic and I can't find the mistakes. My tremolo only oscilate with loud buzzzz, almost no guitar sound oscilation. I chnaged tube, check the connections, change the fet -it works ok bypass wit fs.
Thanks for any help

Hi Martin, can you post a picture of the board? Perhaps we can spot something you missed. You may also want to post this in the JTM 45 forum where some more of the guys here will see it

I've drawn the line with description of tube pins and connections under the board. There is no input cable to intensity pot cause I turn off the treomolo, till it works.
TAD Kt66 tubes, metro JTM45 OT, metro BB Ri board, filter caps 32
+32uF, 16+16uF




Thanks for any help.

Hi Martin, did you ever get your tremolo sorted out?

Eamon

What do you mean?

martin g wrote:What do you mean?

Well, you said here that you ha d problem with the tremolo:

martin g wrote:I have the BB Ri Board and got problem with tremolo. I check the schematic and I can't find the mistakes. My tremolo only oscilate with loud buzzzz, almost no guitar sound oscilation. I chnaged tube, check the connections, change the fet -it works ok bypass wit fs.
Thanks for any help

I was just wondering if you ever found out what the problem was, and if so, what was it?

Eamon

No I haven't found out. I turn it off till I find the solution.

Martin, I am just putting together my BBRI PTP board and noticed something that does not agree with the circuit diagram. It has to do with the bare wire that runs from 3 resistors to the trem trim pot to the FET. If my suspicion is correct, it would explain the oscillation you hear when you engage the trem.

Now, on the layout pictures that came with my board the wiring is shown in a picture called "Bias Layout.jpg" It shows the center lug on the trim pot shorted to the lower leg of the same trim pot. I thought this quite strange so I looked the circuit diagram and there seems to be a "disagreement.

If you follow the circuit diagram the little wire should go from the 3 resistors to the lower leg of the trim pot to the lower leg of the FET. In the layout the ground wire goes from the 3 resistors to the CENTER leg of the trim pot to the LOWER leg of the trim pot. This basically shorts out half the trim pot AND leaves the FET floating with no GROUND!

If you remove the connection between the center lug of the trim pot and connect the lower leg of the trim pot to the lower leg of the FET. IMHO this should do it. Without this mod it would be impossible to get the term cuircut operating properly.

Could someone please vet this theory and see if there is problem? Am I missing something?

Hope this helps
Larry

Thanks a lot Larry.I found that difference between Bias layout and schematic. I have no connection center and lower leg of the trim pot. I'll check the fet when I get the amp. I connected the fet as the Marshall's PCB. I've just found a few schematics (datasheet) of the J174s and there are different signs of the legs. Does your tremolo work ok?

I don't know yet. I have just got the board populated. I am going to install it tonight and we'll take it from there.

Cheers.
LB

Oops, It also looks like the trem section around the trim pot is also miss wired in the pictures. For instance, the center tap on the speed pot doesn't seem to exist. It looks like the white wire from the speed pot is going to the wrong place.

I think I will follow the schematic, double and triple check against the schematic and then make some pretty pictures that I will share with you. All I ask is your love, admiration and undying gratitude.

The odd part is that I HATE the tremolo sound on this amp. Compared to power tube bias or phase inverter induced trem it is non musical to my ear. But, I am not doing anything else and I consider it a challenge at this point.

George, if you have some updated diagrams that would be good too!

BTW The pictures that Martin G posted are look like what I ended up with.

Cheers
Larry

Any luck on getting the tremelo to work on these boards?