the Poor Man 660 support thread

[elektrovolt]

well, after measuring every single resistor three times, R8 seems to be the troublemaker.
it measures around 150K instead of 47 ohm, making 120 V out of 245 V, does that sound reasonable ? I will be getting a new one at radio twenthe tomorrow.

thanks for your advice !

another thing, before the PSU died, compression worked, but I couldn't get the attack pot working. pot seems ok, tried both boards, it sounded like it was fixed at the slowest setting, no matter what I did.

 

[ChuckD]

Hello

what does it mean when a Transformer hums? My UTC's  (A-43 and A-15) are all humming and vibrating when the power is on in my circuit. It's a *******ized Poor-man meets Fairchild monster type thing.

I hooked all the ground shields to ground and was wondering if that could make these audio path guys hum?
Or is it due to improper loading or something else perhaps?

Thanks in Advance!

-Chuck

 

[elektrovolt]

replaced the faulty resistor, all psu voltages are ok now. also, just as Moby suggested, bypassing R1 on the heater board solved the low heater voltage problem.

still have another problem, when turning the attack pot to the right, it seems to compress just less than setting the pot to the left. all settings here give me a very slow release, as the meter shows. OR, the meter buffering is a little weird.

EDIT: after some testing, suddenly the meter dropped and sound level dropped, plus a lot of distortion. the 136 and 245 V lines give only 20 and 40 V ! measured without the compressor board connected, the voltages seem to be fine. connected it again, powered up, voltages went up, then down again after a few seconds !

this is just crap  :'( :'(

 

[ChuckD]

What kind of gain, from input to output , of the gain amp is this unit supposed to provide?
Mine is attenuating with the side chain completely disconnected and just the gain amp. I checked the 15K and it reads 0-15 as desired.
I set the bias up correctly.
I get what looks like plenty of gain at R5  but then the 10K:600 steps it down to below what went in...

Any ideas?

Chuck

 

[Kingston]

It should have 18dB of gain. Attenuators wired wrong? mistake with transformer hook up? double check all connections?

 

[radiance]

EDIT: after some testing, suddenly the meter dropped and sound level dropped, plus a lot of distortion. the 136 and 245 V lines give only 20 and 40 V ! measured without the compressor board connected, the voltages seem to be fine. connected it again, powered up, voltages went up, then down again after a few seconds !

this is just crap  :'( :'(

You have something on those boards that draws a lot of current making the PSU choke... Maybe the short you had earlier damaged something on one or both of your boards or maybe even a (audio) transformer.
Did you try connecting only 1 board to the PSU?

 

[elektrovolt]

Yes, I connected only one board, the other one has a few broken copper traces, so I cannot test it.

I will measure the transformers again, could it be a conducting capacitor maybe ?

 

[radiance]

Check the resistors near the place where you had a short....might be a faulty one there as well...

 

[bernbrue]

Yes, I connected only one board, the other one has a few broken copper traces, so I cannot test it.

I will measure the transformers again, could it be a conducting capacitor maybe ?

Hi,
if your PSU voltages are alright with audio board disconnected, it is likely that one of your audioboards has a short. Keep in mind, that all audio transformers have to be connected, before you power up the unit. If not, the 330R (R10) resistor will burn, thats for shure. Check the broken copper traces before you fire it up. The power transformer is very solid, I don´t think that the mistake is there, Good luck!
regards
Bernd

 

[elektrovolt]

hm, still having troubles, but I don't have time to test thoroughly as I am moving to another home at the moment... will try somewhere this week again.

 

[mpc3000limited]

Has anyone else had issue with the Edcor Power x-former? Tested my output legs everything was on EXCEPT the 250v is reading 285V! Called Edcor and they said it shouldn't be 285 but my meter isn't lying! Gotta send it back but check the legs before hooking up to the PSU pcb! I don't think the psu would be regulating that much over voltage...

 

[veermaster]

I´m not sure if I got it right but do you measure the output voltage of your power tx without anything connected?
Then it is normal to have higher voltage than speced. After connecting it to a load it will fall to the speced voltage.

 

[mpc3000limited]

That is correct without a load. I thought the output would be closer to 250v before regulation. It blew Q3.... but then i checked and i had Q1 & Q3 switched stupidly! Still don't want  top buy more transistors. I forget how to simulate a load so i need to do some searching.

 

[Soeren_DK]

How to make the attenuator switch?

I can't figure this out. I have an Elma 2x24 switch for the GAIN and one for the THRESHOLD. I have read the thread almost through but couldn't find the exact answer for my question.
I have downloaded the Excel sheet from Volker http://www.silentarts.de/DIY/PM660/LogPotToSwitch.xls and looked at it for a long time without understand it totally.

- How should the resistors be mounted on the Elma switch? (two decks, etc..)
- What is the talk about dB (-4dB to +18dB)

Sorry if I have missed the answer for this question...
Cheers
Soren

 

[radiance]

- How should the resistors be mounted on the Elma switch? (two decks, etc..)

Each deck has 24 pins. On top you'll see the numbers of the pins. In the excel sheet you'll see for example "from pin 1 to pin 2  closest E24 resistor = 180.
This means: solder a 180R resistor from pin 1 to pin 2.

All this is the same for each deck

- What is the talk about dB (-4dB to +18dB)

If you use the excel sheet to from your link you'll end up with a rotary from which a part of the range is not very useful. If you've read the whole thread you probably have seen an alternative version of the excel sheet that gives your switches a better range....

Here a lot of info on  rotary switches.

http://www.goldpt.com/diy.html

 

[Soeren_DK]

Thanks for the link and info radiance. I found the numbers on top of the switch. They are really small..

Step 1, Attenuation = 22 dB, Rx = 13809 ohms, Ry = 1191 ohms, Resistor = 1191 ohms.
Step 2, Attenuation = 20 dB, Rx = 13500 ohms, Ry = 1500 ohms, Resistor = 309 ohms.
Step 3, Attenuation = 19 dB, Rx = 13317 ohms, Ry = 1683 ohms, Resistor = 183 ohms.
Step 4, Attenuation = 18 dB, Rx = 13112 ohms, Ry = 1888 ohms, Resistor = 205 ohms.
Step 5, Attenuation = 17 dB, Rx = 12881 ohms, Ry = 2119 ohms, Resistor = 231 ohms.
Step 6, Attenuation = 16 dB, Rx = 12623 ohms, Ry = 2377 ohms, Resistor = 258 ohms.
Step 7, Attenuation = 15 dB, Rx = 12333 ohms, Ry = 2667 ohms, Resistor = 290 ohms.
Step 8, Attenuation = 14 dB, Rx = 12007 ohms, Ry = 2993 ohms, Resistor = 326 ohms.
Step 9, Attenuation = 13 dB, Rx = 11642 ohms, Ry = 3358 ohms, Resistor = 365 ohms.
Step 10, Attenuation = 12 dB, Rx = 11232 ohms, Ry = 3768 ohms, Resistor = 410 ohms.
Step 11, Attenuation = 11 dB, Rx = 10772 ohms, Ry = 4228 ohms, Resistor = 460 ohms.
Step 12, Attenuation = 10 dB, Rx = 10257 ohms, Ry = 4743 ohms, Resistor = 515 ohms.
Step 13, Attenuation = 9 dB, Rx = 9678 ohms, Ry = 5322 ohms,  Resistor = 579 ohms.
Step 14, Attenuation = 8 dB, Rx = 9028 ohms, Ry = 5972 ohms,  Resistor = 650 ohms.
Step 15, Attenuation = 7 dB, Rx = 8300 ohms, Ry = 6700 ohms,  Resistor = 728 ohms.
Step 16, Attenuation = 6 dB, Rx = 7482 ohms, Ry = 7518 ohms,  Resistor = 818 ohms.
Step 17, Attenuation = 5 dB, Rx = 6565 ohms, Ry = 8435 ohms,  Resistor = 917 ohms.
Step 18, Attenuation = 4 dB, Rx = 5536 ohms, Ry = 9464 ohms,  Resistor = 1029 ohms.
Step 19, Attenuation = 3 dB, Rx = 4381 ohms, Ry = 10619 ohms, Resistor = 1155 ohms.
Step 20, Attenuation = 2 dB, Rx = 3085 ohms, Ry = 11915 ohms, Resistor = 1296 ohms.
Step 21, Attenuation = 1 dB, Rx = 1631 ohms, Ry = 13369 ohms, Resistor = 1454 ohms.
Step 22, Attenuation = 0 dB, Rx = 0 ohms, Ry = 15000 ohms, Resistor = 1631 ohms.

I have looked at the tabel from Kingston. I can't figure this out.
- Does he use a "22step" switch for this or do I miss something?
- Should the resistor between pin 1 and 2 be 1191 ohms and 309 ohms from pin 2 to 3?


I made this from the link Kingston mentioned cause I thought that this would be correct for a 24steps.

Step 1, Attenuation = 23 dB, Rx = 13938 ohms, Ry = 1062 ohms, Resistor = 1062 ohms.
Step 2, Attenuation = 22 dB, Rx = 13809 ohms, Ry = 1191 ohms, Resistor = 129 ohms.
Step 3, Attenuation = 21 dB, Rx = 13663 ohms, Ry = 1337 ohms, Resistor = 146 ohms.
Step 4, Attenuation = 20 dB, Rx = 13500 ohms, Ry = 1500 ohms, Resistor = 163 ohms.
Step 5, Attenuation = 19 dB, Rx = 13317 ohms, Ry = 1683 ohms, Resistor = 183 ohms.
Step 6, Attenuation = 18 dB, Rx = 13112 ohms, Ry = 1888 ohms, Resistor = 205 ohms.
Step 7, Attenuation = 17 dB, Rx = 12881 ohms, Ry = 2119 ohms, Resistor = 231 ohms.
Step 8, Attenuation = 16 dB, Rx = 12623 ohms, Ry = 2377 ohms, Resistor = 258 ohms.
Step 9, Attenuation = 15 dB, Rx = 12333 ohms, Ry = 2667 ohms, Resistor = 290 ohms.
Step 10, Attenuation = 14 dB, Rx = 12007 ohms, Ry = 2993 ohms, Resistor = 326 ohms.
Step 11, Attenuation = 13 dB, Rx = 11642 ohms, Ry = 3358 ohms, Resistor = 365 ohms.
Step 12, Attenuation = 12 dB, Rx = 11232 ohms, Ry = 3768 ohms, Resistor = 410 ohms.
Step 13, Attenuation = 11 dB, Rx = 10772 ohms, Ry = 4228 ohms, Resistor = 460 ohms.
Step 14, Attenuation = 10 dB, Rx = 10257 ohms, Ry = 4743 ohms, Resistor = 515 ohms.
Step 15, Attenuation = 9 dB, Rx = 9678 ohms, Ry = 5322 ohms, Resistor = 579 ohms.
Step 16, Attenuation = 8 dB, Rx = 9028 ohms, Ry = 5972 ohms, Resistor = 650 ohms.
Step 17, Attenuation = 7 dB, Rx = 8300 ohms, Ry = 6700 ohms, Resistor = 728 ohms.
Step 18, Attenuation = 6 dB, Rx = 7482 ohms, Ry = 7518 ohms, Resistor = 818 ohms.
Step 19, Attenuation = 5 dB, Rx = 6565 ohms, Ry = 8435 ohms, Resistor = 917 ohms.
Step 20, Attenuation = 4 dB, Rx = 5536 ohms, Ry = 9464 ohms, Resistor = 1029 ohms.
Step 21, Attenuation = 3 dB, Rx = 4381 ohms, Ry = 10619 ohms, Resistor = 1155 ohms.
Step 22, Attenuation = 2 dB, Rx = 3085 ohms, Ry = 11915 ohms, Resistor = 1296 ohms.
Step 23, Attenuation = 1 dB, Rx = 1631 ohms, Ry = 13369 ohms, Resistor = 1454 ohms.
Step 24, Attenuation = 0 dB, Rx = 0 ohms, Ry = 15000 ohms, Resistor = 1631 ohms.

Maybe if someone got the time they can shoot a close-up-picture of their Elma switch...
Cheers
Soren

 

[Kingston]

Soren,

I used a 21-step switch. Just a personal preference, no other reason for limiting the steps like that. That same exact Elma you have. Notice the little screw next to the main shaft? That's how you set the amount of steps.

Your own chart above is fine as well, no need to use mine if you don't like the way it's configured. Then all you need to do is find resistor values as close as possible to that chart. I had to get mine from several stores.

As for wiring them. Look at your schematics, and match with this:

A little logic puzzle. Start from step one with the switch. How do you make Rx = 13809 ohms (deck 1), Ry = 1191 ohms (deck2)?

 

[ChuckD]

I still am having issues with overall attenuation.

If I use only the edcors as per the the design and no mods I still see 50% signal loss from In to Out.  This is with Gain all the way up
One strange thing I noticed was when starting (warming) up the signal passes through at unity at first then once warm it slams is back down to 50%. It seems like my unit is compressing the signal maybe, but I am only looking at results with a signal generator at this point.

Does anyone have any ideas or perhaps audio signal levels I can reference at each stage to see where maybe I am losing my signal?


Thanks!
Chuck

 

[ChuckD]

Tonight I double checked all my voltages just to be sure and they all seem within reason.

Heater 6.0 V
250 V
136 V

Bias is at -2.5  and the RV6 is -4.5

The Signal passes fine and it is compressing as it should but It seems to be loading down or something.
If I remove the Side chain then I can get unity at full gain setting.
If I put it back in I get 50% input at full gain setting
Also if I take out the heater supply to channel B the the heater supply goes up to 9VDC. So I may have damaged my tubes and replaced them just in case but still no change in gain.
The Gain Atten. is 15K total and is hooked up correctly.

This is a fairly straight forward gain stage what could make it have a low output?
Is there something I am missing ?

Thanks in advance,

Chuck

 

[Hank Dussen]

Any plans for another PCB run?