the Poor Man 660 support thread

[Kingston]

Apparently a log (pot or rotary switch series) will work best with the "threshold/compress" switch as well. Someone in this thread tested it and with linear it apparently only "digs" at the audio (with modern levels) at about half or one quadrant of the pot/rotary. With log you get more even spread.

 

[elektrovolt]

thanks, I used the resistors just as the log to pot spreadsheet says, 0 to 15k ohm. so I should just use the same for the treshold ones ? sorry for being stupid

radiance, I am curious about your project, where are you having your frontpanel done ? just Schaeffer ? maybe you could help me out with this...

Jimi

 

[Kingston]

Earlier on this thread it was also discussed that 0 to 15k ohm range is pointless here, and you are only limiting your rotary switch precision with this. It goes to full attenuation, which is just not needed on compressor. You will get stupid large 6-10dB steps on the attenuator on the most important part of the gain range.

The "make up" gain stage part of the poorman has about 18dB of gain. This means that you basically want about 22dB or so of attenuation range for the rotary switch. It has been discussed in detail earlier in this thread and I strongly suggest everyone read it before soldering (or even ordering) their range of rotary switch resistors. Links to great dual attenuator gain range calculators have been posted, and these are invaluable. Even suggested values.

The same 22dB (or so) range for the threshold/compression attenuator is quite ideal as well.

[edit]

here is the good calculator I and several others have used:

http://homepages.tcp.co.uk/~nroberts/atten.html

Here's how I did mine (picked close enough resistors so that total range was 15000ohm)

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.

 

[radiance]

thanks, I used the resistors just as the log to pot spreadsheet says, 0 to 15k ohm. so I should just use the same for the treshold ones ? sorry for being stupid

radiance, I am curious about your project, where are you having your frontpanel done ? just Schaeffer ? maybe you could help me out with this...

Jimi

Jim, I'm no were near the fronpanel design stage...it will probably be schaeffer or maybe Frank Röllen
Either way, design will be done in FPD. What help do you want? Mind you, I'm living in France now... you're welcome to come over though.

 

[elektrovolt]

in France ? huh  ;D well, we are going to france this July, so maybe  ;D

I'm getting more and more confused about these attenuators, I thought that spreadsheet was the found solution but apparrently it isn't ?!

would like to know what values other people have used for the gain and treshold attenuators, and if they are happy with their choice.

as being not as a tech wonder like most people here, I'm trying !



my machine in progress:

 

[Kingston]

Just re-read the thread again if the above still didn't help. No point in posting the same thing over and over again. This has been discussed extensively.

 

[elektrovolt]

heck, I  think it is better to buy a few stereo pots for testing. I can't find any 15k pots, but 22k should be fine, I think.

still learning to DIY  8)

 

[W DeMarco]

UH OH :'(  In checking my non functional channel I removed both pcbs from the psu.  I put the left channel in place of the right and rewired to the psu.  When I powered up the unit I got a major explosive elec discharge(not me but the unit) somwhere back near the irf820.  After this happened I lost both of the high voltage rails but the trans is still working fine.  They dropped to 2 or 3 volts while the 12 and 17 volt rails were fine.  Im confused as to why this occured.  Could it have been that there was only one channel loaded?  Everything was perfect except for the problems in the left channel before I did the swap.  Im also assuming that to cure the dead voltages I will have to replace the 820 and 840 since I cant find any other damaged components?  

 

[W DeMarco]

BTW,  I found a tube supplier here in Cleveland.  Actually about 25 minutes south of Cleveland.  http://www.oldradioparts.com/      330-558-0247  He sold me 4 Tung Sol 5687 tubes for 28 bucks even.  Less than half price of tube depot.

 

[Moby]

Never try this at home 

 

[W DeMarco]

replaced 820 and 840 to no avail.  High Voltages are still dead. At this point I have 0V on both rails, then 12, 17, and 6.3 on the others. Any thoughts on what I might do to fix the problem?

 

[idylldon]

replaced 820 and 840 to no avail.  High Voltages are still dead. At this point I have 0V on both rails, then 12, 17, and 6.3 on the others. Any thoughts on what I might do to fix the problem?

You mentioned the the transformer was fine after the short, but have you checked it directly?  What do the secondaries measure at the transformer?

Remember, if you're not using insulating gaskets/washers on the 840 and 820, the heatsinks have voltage on them.  Did one of them short somehow?

Cheers,
--
Don

 

[W DeMarco]

I measured the output voltage at the input of the psu board.  They all read fine.  At work now but I recall measuring that right away fearing that I really F'd it somehow.    Now I really have come to understand the idea of of isolating your regulators. 

 

[lolo-m]

I measured the output voltage at the input of the psu board.  They all read fine.  At work now but I recall measuring that right away fearing that I really F'd it somehow.    Now I really have come to understand the idea of of isolating your regulators. 

If you have to change the IRF, put 2 IRF840 and not IRF820 + IRF840. Some poeple had problem with the 820 and the 840 handle more power/tension without any change in the result. It seam to be safer to use 2 x IRF840...
And yes, INSULATED from the heatsink. The metal part of the IRF are at +130V or +240V or so (don't remember) and the heatsink is grounded. The paint of the heatsing can do some kind of insulation (sometimes, if you're lucky) but if something is moving there's an electric contact between the two and so some sparks  :'(...

 

[emrr]

Hmm, I remember measuring the heatsinks and finding them to be ungrounded. 

 

[Moby]

Hmm, I remember measuring the heatsinks and finding them to be ungrounded.   

Yes, it's not connected to the ground plane at PCB but we are "grounded" so insulated FET's is recommended ;D

 

[emrr]

Sure; thought I was remembering correctly. 

 

[lolo-m]

Hmm, I remember measuring the heatsinks and finding them to be ungrounded. 

Yes, it's not connected to the ground plane at PCB but we are "grounded" so insulated FET's is recommended ;D

Grounded or not grounded, the FET heatsinks can touch themselves (they're really really close) and there's different voltages on them so, insulation is not only recommended but necessary... On my PM670, I measured the metal part of the IRF voltages : 340V on one and 240V on the other. If they're not insulated there's 100V between the two heatsinks  .

 

[W DeMarco]

OK this is making more sense.  Is it just the IRFs that should be insulated or the 337 and 317 as well as q1 on the audio boards?  Ive been searching mouser and digikey but for the life of me I cant find the insulators.  Anyone have a part number for these?

 

[Moby]

OK this is making more sense.  Is it just the IRFs that should be insulated or the 337 and 317 as well as q1 on the audio boards?  Ive been searching mouser and digikey but for the life of me I cant find the insulators.  Anyone have a part number for these?

No need to insulate 337/317 if they are not on the same heatsink, same with Q1. here's the link
http://www.mouser.com/Search/ProductDetail.aspx?qs=sGAEpiMZZMsQtlBhqKq43cWWDPGVV2IS