[BUILD] FET/500 Official Support Thread

[Echo North]

Hey Mike (or anyone that can offer advice),

I bought a pair of FET500 rev D kits, first one works great, second one not so well.

I've checked and rechecked the solder points, and I've gone through the BOM and verified that each resistor is correct. I've verified that each polarised cap is facing the right way, and that all diodes are facing the right way.

My problematic 1176 is making 'starved voltage' sounds and requires unreal amounts of input gain to register any signal at the output (there don't seem to be any issues with the input registering signal). However, at the output it's making clipping and farting noises.

Here are two videos I made detailing the symptoms. The first video shows the output gain problems, and the second video shows the noise my unit makes.

Apologies for my New Zealand accent!!

Thanks, Alex Harmer.

https://www.youtube.com/watch?v=o9RC4MRNCqg

https://www.youtube.com/watch?v=DqILqkZGpfQ

If you (carefully) remove the Q1 FET does that give you more gain?

Mike

 

[zarndyhoff]

If you (carefully) remove the Q1 FET does that give you more gain?

Mike

Hi Mike,

...no, issue is unchanged. I measured voltage and the values were the same. And it was making the same sounds.

 

[Echo North]

If you (carefully) remove the Q1 FET does that give you more gain?

Mike

Hi Mike,

...no, issue is unchanged. I measured voltage and the values were the same. And it was making the same sounds.

You've got something in the gain sections.

http://mnats.net/files/FET-D500.pdf

se the parts in the schematic in the top 1/3. Something up there. Check R values, cap polarity, reflow joints.

 

[Stonecutter67]

Ok, not sure I'm posting in the right place but... I just completed 2 builds of FET 500 Rev D's.( I am not a complete novice. I have built a Lola and 8 other preamps from another company but I'm certainly not an expert.)  I put the first unit in my rack and set up the 0 db(.775v) 1K signal on the input. Measuring the output to begin the calibration process, the maximum reading I can get for the Q bias is 2.64v.  Any advise on where I should start looking for errors in my build?

 

[Echo North]

Ok, not sure I'm posting in the right place but... I just completed 2 builds of FET 500 Rev D's.( I am not a complete novice. I have built a Lola and 8 other preamps from another company but I'm certainly not an expert.)  I put the first unit in my rack and set up the 0 db(.775v) 1K signal on the input. Measuring the output to begin the calibration process, the maximum reading I can get for the Q bias is 2.64v.  Any advise on where I should start looking for errors in my build?

Are you sure you have the bias all the way out.  Does rotating the bias change the output level?

 

[Stonecutter67]

No. So I went over both builds to check solder joints. I found a couple un-soldered leads and fixed that. I put both units in the rack (separately), sent the signal and the first one measured around the same 2.5 v and no adjustment made any difference. I walked away for a bit (frustrated) and when I came back it the meeter was displaying around 22 v! Again adjustments made no change. I took that one out and put the other one in and it read around 6.5 v.  Adjustments made tiny changes but never more than 6.7 v.
I've done something wrong... and apparently twice... (which would make a good blues song) LOL!

 

[Echo North]

No. So I went over both builds to check solder joints. I found a couple un-soldered leads and fixed that. I put both units in the rack (separately), sent the signal and the first one measured around the same 2.5 v and no adjustment made any difference. I walked away for a bit (frustrated) and when I came back it the meeter was displaying around 22 v! Again adjustments made no change. I took that one out and put the other one in and it read around 6.5 v.  Adjustments made tiny changes but never more than 6.7 v.
I've done something wrong... and apparently twice... (which would make a good blues song) LOL!

The 22V thing was probably some oscillation.

Sounds like you have the same stuffing error in both.  You could send 1 in for repair. We'll fix it and tell you what you did wrong and then you could check the other on yourself.

 

[zarndyhoff]

Issue now resolved, thanks Mike.

Resistor was marked as a 1.8 meg, actually measuring 180k, in a spot meant for a 180 ohm. 

All sorted now, both calibrated and sounding awesome. Keep an eye out for sound examples - no one else seems to have them so I'm going to make some for the greater good. These things rock!

If you (carefully) remove the Q1 FET does that give you more gain?

Mike

Hi Mike,

...no, issue is unchanged. I measured voltage and the values were the same. And it was making the same sounds.

You've got something in the gain sections.

http://mnats.net/files/FET-D500.pdf

se the parts in the schematic in the top 1/3. Something up there. Check R values, cap polarity, reflow joints.

 

[Stonecutter67]

No. So I went over both builds to check solder joints. I found a couple un-soldered leads and fixed that. I put both units in the rack (separately), sent the signal and the first one measured around the same 2.5 v and no adjustment made any difference. I walked away for a bit (frustrated) and when I came back it the meeter was displaying around 22 v! Again adjustments made no change. I took that one out and put the other one in and it read around 6.5 v.  Adjustments made tiny changes but never more than 6.7 v.
I've done something wrong... and apparently twice... (which would make a good blues song) LOL!

The 22V thing was probably some oscillation.

Sounds like you have the same stuffing error in both.  You could send 1 in for repair. We'll fix it and tell you what you did wrong and then you could check the other on yourself.

Update:
I went over both builds again, checked every resistor, cap and diode orientation, etc. and didn't find anything out of place. The only thing I hadn't done was center all the trimmers. So I did that and tried again. The first one I was only able to get 5v on the q-bias but I went ahead with the calibration anyway and was successful! Seems to be working great. The second one I'm still having problems with. I put it in and immediately get 22v on q-bias. Adjusting the trimmer makes no change. I'm not opposed to sending it in for repair but it seems like this should be something obvious. Any thoughts?

 

[Echo North]

Has to be some kind of oscillation.  Make sure you don't have some mix up like a  470, 47K, 470K resistor swap.

Outside of that, it's hard to say...look for short...re-flow suspect joints.

Mike

 

[Stonecutter67]

Has to be some kind of oscillation.  Make sure you don't have some mix up like a  470, 47K, 470K resistor swap.

Outside of that, it's hard to say...look for short...re-flow suspect joints.

Mike

Well... I'm gonna have to throw my hands up and surrender.  I went through the build again, found nothing wrong, re-flowed the joints, put it back together and when i tried to do the Q-bias I only got 2.5 volts. ( the other one I only got 4.5 volts... but I was able to finish the calibration.) I tried to finish with the 2.5v, but I couldn't get to the next step because I was unable to get 4.88v from the output. I think I'd better "cut my losses" and send it in for repair.

 

[Sinkia]

Hey Mike I have finish my rev A from your, this units is awesome !

Thanks for your calibration video ! appears to be way more easier from the mnats version..

Can I ask you why you start with the Qbias, when Mnat's start with meters?

I was having trouble when I started with meters, but then with your video, everything went smooth !

Here, I have a question for you !

I'm about to order an other analog fet/500 rev A to make a couple. do you think you could send me with my new order a stereo matched FETs and a link cable?

Like thant I can change the fet from the first one I bought and have a real "couple"v

Best !

 

[Echo North]

Has to be some kind of oscillation.  Make sure you don't have some mix up like a  470, 47K, 470K resistor swap.

Outside of that, it's hard to say...look for short...re-flow suspect joints.

Mike

Well... I'm gonna have to throw my hands up and surrender.  I went through the build again, found nothing wrong, re-flowed the joints, put it back together and when i tried to do the Q-bias I only got 2.5 volts. ( the other one I only got 4.5 volts... but I was able to finish the calibration.) I tried to finish with the 2.5v, but I couldn't get to the next step because I was unable to get 4.88v from the output. I think I'd better "cut my losses" and send it in for repair.

Sorry I don't know what the voltages convert to dbu off the top of my head.  In bypass mode for a 1K 0dbu signal and the in/out centered you should have about 16dbu on the output with the rev D (19dbu with the A).

Looking at the math the 4.5VAC (about 16dBu) one seems to be working fine.

Mike

http://www.sengpielaudio.com/calculator-volt.htm

 

[Echo North]

Can I ask you why you start with the Qbias, when Mnat's start with meters?

I'm about to order an other analog fet/500 rev A to make a couple. do you think you could send me with my new order a stereo matched FETs and a link cable?

Like thant I can change the fet from the first one I bought and have a real "couple"v

Best !

The meter and qbias are separate calibrations so it doesn't mater which you start with as long as you start all calibration with the FET Qbias adjustment set to have the FET out of conduction.  If the qbias has the FET dumping a ton of signal to ground, the meter cal will not go well.

Sure just place an order and email up after, we'll toss in stereo FETs and a link cable.

Mike

 

[Sinkia]

Sure just place an order and email up after, we'll toss in stereo FETs and a link cable.

Mike

Awesome!

I'll let you know!

 

[nick.]

I bought a pre assembled FET 500 Rev A. I had an engineer come to my home studio to help me track some drums and he was saying that the FET 500 input seemed rather hot compared to all the compressors he has used. It does seem a little hot to me as well. My input and output never go past 12 o'clock, something they hang out at 9 o'clock. I'm going into it with a Neve 1073 LB and that pre never peaks into yellow or red territory. I don't have any of the gear MNATS has in the Youtube calibration video. Should I send it to Hairball to be serviced? Any quick ways to check if it is not calibrated correctly?

 

[Echo North]

The rev A is hotter than the other revs. 5dB which is almost double the voltage gain.

Also, the UREI pots have a very odd taper.  You just don't see tapers like that anymore.

Mike

I bought a pre assembled FET 500 Rev A. I had an engineer come to my home studio to help me track some drums and he was saying that the FET 500 input seemed rather hot compared to all the compressors he has used. It does seem a little hot to me as well. My input and output never go past 12 o'clock, something they hang out at 9 o'clock. I'm going into it with a Neve 1073 LB and that pre never peaks into yellow or red territory. I don't have any of the gear MNATS has in the Youtube calibration video. Should I send it to Hairball to be serviced? Any quick ways to check if it is not calibrated correctly?

 

[thp]

I am building 2 Rev A's simultaneously.  I am at the blue ceramic cap installation part of the build guide and am having trouble identifying which go where.

One of my kits comes with 2 blue caps that are marked 104 and the other kit comes with 2 that are marked 6R8.
Are these the same? 
The guide says that 104 = 0.1uf but there is only a space for 1 - C160.  Where does the second one go?

Each kit comes with 1 blue cap that says 100.  Where does this go?

Each kit comes with 1 blue cap that says 330.  Does this go C016?

Each kit comes with 1 blue cap that says 102.  Where does this go?


Also, we have 3 cream Kemet caps that are .15uf, yet the build guide says that Rev A only uses 2, C2 and C8.
Is this an error because there is a spot, C1, for a third one as well?


Thanks for the help!

 

[Echo North]

I am building 2 Rev A's simultaneously.  I am at the blue ceramic cap installation part of the build guide and am having trouble identifying which go where.

One of my kits comes with 2 blue caps that are marked 104 and the other kit comes with 2 that are marked 6R8.
Are these the same? 

No one is a 0.1uF and one is a 6.8pF

The guide says that 104 = 0.1uf but there is only a space for 1 - C160.  Where does the second one go?

I'm not sure how many there should be and I'm too exhausted to look right now, but are you using the build maps?  Sometimes we mess up though and there are extras or shorts.

Each kit comes with 1 blue cap that says 100.  Where does this go?

Each kit comes with 1 blue cap that says 330.  Does this go C016?

Each kit comes with 1 blue cap that says 102.  Where does this go?

10pF
33pF
.001uF

Check the build map.

Also, we have 3 cream Kemet caps that are .15uf, yet the build guide says that Rev A only uses 2, C2 and C8.
Is this an error because there is a spot, C1, for a third one as well?


Thanks for the help!

Yes should be 3 for those spots.


Mike

 

[Echo North]

REV A Main
http://library.hairballaudio.com/maps/reva500/

Meter
http://library.hairballaudio.com/maps/meter500/

Mike