the Poor Man 660 support thread

[[silent:arts]]

Paul, no problem - fire it up

 

[noulou]

I am having metering  problems with my poorman and I'm wondering if someone can help.

I've put in some old Honeywell vu meters which apparently have higher internal resistance than modern ones.

The parallel resistance needed for it to go to 0vu with no gain reduction is approximately 64 Ohms.

Unfortunately it is too sensitive. The Vu meter value changes when fiddling around with controls when no input signal is applied. (even the other channels controls affect it)

Is there a possible solution to this problem? Unfortunately I have already drilled holes for the mentioned meter.

Thanks,
Nikos

 

[shabtek]

noulou; maybe a trimpot R in series or an adjustable voltage divider to drop the sensitivity.

 

[Moby]

Is there a possible solution to this problem? Unfortunately I have already drilled holes for the mentioned meter.

If you can see inside meter there is for sure some resistance network or just one resistor. Try to play with that  8)

 

[noulou]

Thanks shabtek, Moby,

Unfortunately the meter is completely sealed.

I put a 10k trim in series. didn't help. I do not know where to go next really.  :-[

perhaps a buffer would help?

 

[Moby]

Thanks shabtek, Moby,

Unfortunately the meter is completely sealed.

I put a 10k trim in series. didn't help. I do not know where to go next really. 

perhaps a buffer would help?

I mentioned many times that VU is connected as DC miliampermeter in this project and it's not "just connect any VU" because ist's connected in series of supply. I doubt that buffer will help in this situation. I'm afraid that you will have to check inside the meter    Or to "rescale" zero db... BTW, I'm sure that you must "rescale" (to draw a new scale) if you want to have a real meter values 

 

[noulou]

Would it be better to stick the vu meters at the cathodes of the 6BC8s?

pin 3 of the 2n6107 via a trimpot to ground?

 

[lolo-m]

I use a vu meter in my PM670... The vu meter is connected to a 3K9 and everything is paralleled to a resistor (or pot) to have 1,27V with no compression... I didn't measure this but it is less than 1K... Tracking is quite good like this... My vu reads -9dB for 10db compression  ...

perhaps a buffer would help?

A buffer isn't easy to do, the vu is paralleled to a resistor connected to the 130V supply rail.

Would it be better to stick the vu meters at the cathodes of the 6BC8s?
pin 3 of the 2n6107 via a trimpot to ground?

No, no voltage change there... You will only see the polarisation voltage...

 

[Moby]

I use a vu meter in my PM670...

Which one? Recommended sifam?

 

[lolo-m]

I use a vu meter in my PM670...

Which one? Recommended sifam?

No, but it's an old Pekly vu meter, 3K6 internal impedance, if I remember well it's the same thing than sifam's specs. There's a build in resistor to reach the classic vu meter spec that isn't connected. In my Pekly it's a 3K9, but I'm sure a 3K6 will do fine ( maybe here is my 1 dB error  :). I did use it just because it was simple and because I was afraid to burn it. With the pot paralleled, I've got the 0 vu adjust.

 

[rrs]

Well I've finally buily my PM670.  ;D

Switched on the 240V and began testing voltages. I currently have nothing connected to the PSU.

Anyway I have identified two problems. And my DIY luck has been going so well since my first buit too.

OK when testing for +17V and -17v on the two pin connector pin 1 has +23 but trim won't adjust voltage up or down.
Pin two has no Voltage.

The connectors out next to it seem fine I am getting +23V / - 23V but of course neither trim resistor is adjusting these voltages.

All other mesurements seem fine.

Have checked for solder bridges. Any advice on where to start looking would be greatly appreciated.

 

[[silent:arts]]

OK when testing for +17V and -17v on the two pin connector pin 1 has +23 but trim won't adjust voltage up or down.
Pin two has no Voltage.

The connectors out next to it seem fine I am getting +23V / - 23V but of course neither trim resistor is adjusting these voltages

the two pin connector pin1 is +, pin two is GND - it is fine what you are measuring there.
you have only one problem: why your trimmers don't work ?

 

[lolo-m]

Any advice on where to start looking would be greatly appreciated.

Stupid questions  ;D ;D ;D :
Are the regulators mounted insulated ?
Are you sure you didn't put a LM317 instead a LM117 and so a LM117 instead a LM317 ?

This kind of things happen... I remember the last time I soldered an electrolytic the wrong way  :'( :'( :'(

 

[rrs]

Any advice on where to start looking would be greatly appreciated.

Stupid questions  ;D ;D ;D :
Are the regulators mounted insulated ?
Are you sure you didn't put a LM317 instead a LM117 and so a LM117 instead a LM317 ?

This kind of things happen... I remember the last time I soldered an electrolytic the wrong way  :'( :'( :'(

Haa Haaa no there not stupid questions when there aimed at stupid people.  ;D

But yes they are insulated and I am positive without having it in front of me they are the correct ones (Have re checked my mouser order though)



I guess my only problem is the trimmers arn't trimming. Could this only be from the trimmer being faulty or installed wrong or are there other possible factors here.
This is the trimmer I used:
http://au.mouser.com/Search/ProductDetail.aspx?R=3296Y-1-502LFvirtualkey65210000virtualkey652-3296Y-1-502LF

Multi-Turn Trimmer Potentiometers 3/8" 5Kohms Sealed Vertical Adjust

They are installed with the middle leg being in a triangular formation ie... not all 3 in a row. the trim adjusters are at the Toroidal input end.

 

[klaus2you]

rrs, regarding your trimmers; keep turning them , i had the same impression first but after LOTS of turns they finaly starts to reacts!

 

[Brolik]

yea, I learned from my seventh circles that sometimes you gotta keep turning.  He says in the build instructions 25 times counter clockwise and it will start clicking when you turn.  Then you know you're at 0

 

[rrs]

Thanks guys your right. It took a few turns just to register a change. I was worried because I have had a faulty power PSU in the past and kept turning till a resistor blew.
Anyway Voltages on PSU and main board are good.

Now for the resistor R15. As I have a stereo version I noticed earlier that 1R is an estimate.
I tried a .86R and measured 5.12V at the heater connector on PSU board. .86R measured 5.21V and .33R is measuring 5.71
I am assuming I may need to go down to .15R should this be right.

I am measuring with everything connected and from the connector on the PSU out named heater (the end one). Does this sound correct.

 

[Moby]

Now for the resistor R15. As I have a stereo version I noticed earlier that 1R is an estimate.
I tried a .86R and measured 5.12V at the heater connector on PSU board. .86R measured 5.21V and .33R is measuring 5.71
I am assuming I may need to go down to .15R should this be right.

What voltage you measure without tubes? BTW it's possible that PSU transformer is saturating .If it's not too hot go ahead  8)

 

[rrs]

I'm getting 13.5V with nothing connected to the PSU Board and a .33R resistor at R15.
With everything connected with valves in it's 5.84V at my last measurement.

No excessive heat coming from my Avil Lindberg Toroid.

 

[Moby]

Try tp measure heater current .If it's normal, than must be that TX is dropping the voltage.