1176 in 51x/500 format, or 51X-F76 Build Support Thread

[ramshackles]

Thanks a lot. I thought so...that comes out at ~£56 which is fairly pricey for just PCB's (IMO).

 

[taliska]

Hello folks.

(Resurrecting this thread as the boards are available again and this seems the most appropriate place).

So I've got a couple of these F76s in progress finally, and need to check some (potential) component issues. FWIW, I'm building the re-issues that ramshackles now sells, but I believe they're identical to the last ones that Igor put out (v1.4 with the exception of fewer i/o Amp choices).

I built my component list by using the ramshackle BOM doc, comparing it with Igor's original BOMs, and also using Chunger's build guide for visually checking that my choices were consistent.

Anyway, there are two carbon resistors specified in Igor's original BOM: R95 on the main board, and R46 on the attack/release board. However, in the ramshackle BOM they're both listed as metal film, and as I overlooked the difference when originally ordering, those are the ones I have.

So the question is:

Is it essential that these are carbon composition or will metal film be ok too? What differences if any, will result?

I believe the values concerned are: R95: 330R, 1/2 watt, R46 10M 1/4 watt.

Thanks for the help!

Kaz

 

[taliska]

Anyone? Anyone?

Bueller?

(I was having trouble procuring the carbon 1/4 watt 10M resistor, which is why I originally asked the above question, but today I managed to source a couple of them, so it's more or a curiosity now than anything else...for those of you based in the UK having similar issues...try www.hificollective.co.uk)

Kaz

 

[ramshackles]

there should be no problem fitting metal film resistors. May have an effect on the sound (subjective)

 

[Harpo]

Is it essential that these are carbon composition or will metal film be ok too? What differences if any, will result?

I believe the values concerned are: R95: 330R, 1/2 watt, R46 10M 1/4 watt.

High ohm value (probably anything above 1M will do) R46 in parallel to resistor network at the ratio switch is only used for bridging the switch while switching to prevent/reduce popping between switch positions. Carbon or metal film type doesn't matter.
Voltage dropping/current limiting R95 value and min.wattage needed is dependant on supply voltage (+/-16V or +/-24V) and coil resistance of your bypass relais. Again carbon or metal film type doesn't matter.

 

[taliska]

Is it essential that these are carbon composition or will metal film be ok too? What differences if any, will result?

I believe the values concerned are: R95: 330R, 1/2 watt, R46 10M 1/4 watt.

High ohm value (probably anything above 1M will do) R46 in parallel to resistor network at the ratio switch is only used for bridging the switch while switching to prevent/reduce popping between switch positions. Carbon or metal film type doesn't matter.
Voltage dropping/current limiting R95 value and min.wattage needed is dependant on supply voltage (+/-16V or +/-24V) and coil resistance of your bypass relais. Again carbon or metal film type doesn't matter.

Thanks for the detailed response Harpo! Hopefully it will be useful for other builders here too at some point, who like me notice the BOM discrepancy. As it happens I've put the carbon ones in anyway (and have metal film spares), but am unable to go any further due to a long lead time for the grayhills at digikey. Just waiting for those (due end of March) and some lundahls and should be able to finish them and post some pics! ;-)

Kaz

 

[ramshackles]

You can also get grayhill switches off audiomaintenance. I dont remember off the top of my head which ones a required for the f76, but they might be there (you can always get a switch with too many decks and take out the last deck).

 

[qmp audio]

i usually have good luck w/ greyhills from allied:

http://www.alliedelec.com/switches/rotary/?navigation=4294862273-4294965262&mkwid=swVDUtnI3&pcrid=19895068099&pkw=grayhill&pmt=p&gclid=CJTDg8aPwrwCFaZAMgodhX8AFg

 

[taliska]

You can also get grayhill switches off audiomaintenance. I dont remember off the top of my head which ones a required for the f76, but they might be there (you can always get a switch with too many decks and take out the last deck).

Funnily enough, I actually already have a number of grayhills from AML, because I just finished building a pair of EQNs. However, it's worth mentioning that the ones from AML have bushings that are too large for the front panels and brackets that frank makes.

While it's not super convenient, I don't mind the wait from digikey providing they arrive eventually! ;-)

Kaz

 

[qmp audio]

My f76's have been in service for a couple years now.  Love them and they work great,  except for 1 issue i cannot figure out the source of.

The units function as expected.  However,  after they have been on for a long time ( like 8 hours or more ) the signal is low output and crackly.    They work fine for many hours.. but then all of the sudden... low/crackle output.

A simple power off for a few seconds,  and power back on and they are like new.... at least for another 8 or so hours.

I have changed the opamps and module slots on this several times over the years,  and the same issue persists.  So i believe it is not related there.

Does anyone have any idea what could cause this issue?  A simple power off/on fixes it.

It is also a very hard issue to reproduce for testing... as i need to leave the module on overnight, at least, for the problem to happen.

Also,  it only happends to the f76's ( both of them ).  However,  no other modules are effected so i do not think it is the power supply.

Thanks for any insight.

 

[johnnyscotch]

Where are the boards available again??

 

[ramshackles]

ramshacklerecording.com

 

[taliska]

Hello all,

So I decided to go through the initial testing procedures for my first F76 as my main board is now fully populated and I thought I might as well get it out of the way while I wait for my grayhills to arrive.

Anyway, so the first test was fine...I had -9.79 vdc at the output of the regulator, so I went ahead and populated all of the ICs, installed the jumper to engage the compressor, and installed the amps too (IC output amp & albatross input amp). Forgot to connect the i/o pots, and powered up the rack.

What followed was some smoke! Specifically, the resistor below JP2 at the back of the main board fried, but I don't know whether anything else is screwed. Visually it only looks like that one resistor, but who knows...

Anyone got any ideas what I got wrong? I've included a pic which shows the problem area...

Thanks for any help,

Kaz

 

[taliska]

Here's another pic showing the exact config of the board when I was testing it...

Kaz

 

[culteousness1]

What followed was some smoke! Specifically, the resistor below JP2 at the back of the main board fried, but I don't know whether anything else is screwed. Visually it only looks like that one resistor, but who knows...

Maybe you could give us the descriptor of the fried resistor? Without having the schematics at hand,
I ASSume that this resistor is/was a 10Ω current limiting resistor on either the +16 V or -16 V rail.

Did you check for shorts after installing the ICs? Could be a IC in backwards or a faulty DOA.

Best,
Carsten

 

[taliska]

What followed was some smoke! Specifically, the resistor below JP2 at the back of the main board fried, but I don't know whether anything else is screwed. Visually it only looks like that one resistor, but who knows...

Maybe you could give us the descriptor of the fried resistor? Without having the schematics at hand,
I ASSume that this resistor is/was a 10Ω current limiting resistor on either the +16 V or -16 V rail.

Did you check for shorts after installing the ICs? Could be a IC in backwards or a faulty DOA.

Best,
Carsten

Hi Carsten,

Yeah, it was a 10R value between pin 17 (+24v) and one of the big capacitors at the back. Apologies for not being able to be more specific...can't locate that section in the schematics at the moment, so just verified that by looking at the traces on the back...

I believe all the ICs are in their correct orientation as the notches all seem to line up, (edit) the previous posted pic shows most of them best. I'll remove the DOAs and visually inspect them to check. Will need to locate some more 10Rs and replace I guess before attempting any more testing...

Kaz

 

[culteousness1]

The original Igor Docs contained a PCB overlay that might help you.
You can probe with your DMM at the fried resistor's leg and check for
a short to GND.

Remove one IC after each check to locate the faulty one.

 

[ramshackles]

before turning power on again, do some resistance checks to make sure there are no shorts/bad soldering.
Then test voltages without IC's & DOA's installed..

 

[taliska]

The original Igor Docs contained a PCB overlay that might help you.
You can probe with your DMM at the fried resistor's leg and check for
a short to GND.

Remove one IC after each check to locate the faulty one.

Thanks for pointing me back at the docs Carsten...I somehow managed to miss the power supply schematic in my panic! I've attached it for reference, but looking at it, is seems that in this design, the 24v rails are dedicated to the DOAs with everything else using the 16v rails (that's certainly what I get from looking at the schematics, but then I'm not very good at this stuff!).

I'm hoping that means that Igor's design has saved me from worrying about having fried any components except ones in the DOA path, which would be great if that's true. It would certainly make debugging it easier...

Does that seem right to you? Oh, and thanks for the help Carsten, I'm not exactly a wizard when it comes to this stuff... ;-)

Kaz

 

[taliska]

before turning power on again, do some resistance checks to make sure there are no shorts/bad soldering.
Then test voltages without IC's & DOA's installed..

Will do. Might seem like a stupid question, but I just tested the resistance on the fried resistor and it seems ok...is it a bad idea to power up without replacing it? (as I don't have a replacement handy...)

Kaz