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FREQ500 KIT Build Thread

Posted: Sat Aug 04, 2018 12:20 pm
by Joe Malone
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Build Thread is still under construction. Please ask any questions you have on this thread so we can add the detail needed.

Use FREQ500 audio path build map link below to place and tick off all parts.

FREQ500 AUDIO PATH KIT build map
http://www.jlmaudio.com/builds/maps/freq500audiomap.html

Photos of finished FREQ500 Audio path pcb.
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FREQ500 Audio path pcb can be tested by itself by fitting a jumper shunt to pin 5 & 6 in the centre of the 10 pin header.
Then fitting a second jumper to TP1 will switch the pcb from bypass to audio path which should give the same level audio output.
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Notes and Errata
5 of the 150k have been changed to 330k to balance the green led brightness better to the red led brightness.
Map shows which 5 of 150k resistors are now 330k.
Lo filter pcb need one white wire soldered under neath the pcb to link ground plane on the pcb.

Use FREQ500 filter path build map link below to place and tick off all parts that can be fitted before following the photos below.

FREQ500 FILTER build map
http://www.jlmaudio.com/builds/maps/freq500eqmap.html

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Re: FREQ500 KIT Build Thread

Posted: Sat Nov 17, 2018 12:14 pm
by Blackdawg
Hey Joe,

Noticed there is foot prints for 2520 DOA for this as well. How does that all work?

Thanks!

Re: FREQ500 KIT Build Thread

Posted: Sat Nov 17, 2018 5:24 pm
by Joe Malone
Blackdawg wrote:Hey Joe,

Noticed there is foot prints for 2520 DOA for this as well. How does that all work?

Thanks!


Yes the main audio path for the EQ is made of 4 x opamps which can be dual DIP8 running in parallel or 4 x discrete opamps with 990 or 2520 pinouts like our JLM99v.

Re: FREQ500 KIT Build Thread

Posted: Sat Nov 17, 2018 6:05 pm
by Blackdawg
Joe Malone wrote:
Blackdawg wrote:Hey Joe,

Noticed there is foot prints for 2520 DOA for this as well. How does that all work?

Thanks!


Yes the main audio path for the EQ is made of 4 x opamps which can be dual DIP8 running in parallel or 4 x discrete opamps with 990 or 2520 pinouts like our JLM99v.


Awesome!

I'm assuming this means you just don't install all the parts that are there now and just put in pins and DOA's of your choice?

Re: FREQ500 KIT Build Thread

Posted: Sun Nov 18, 2018 7:46 am
by Joe Malone
Blackdawg wrote:
Joe Malone wrote:
Blackdawg wrote:Hey Joe,

Noticed there is foot prints for 2520 DOA for this as well. How does that all work?

Thanks!


Yes the main audio path for the EQ is made of 4 x opamps which can be dual DIP8 running in parallel or 4 x discrete opamps with 990 or 2520 pinouts like our JLM99v.


Awesome!

I'm assuming this means you just don't install all the parts that are there now and just put in pins and DOA's of your choice?


The PCB is built with the same parts but instead of the DIP8 sockets the 6 x 1mm socket pins per opamp are installed. Or both DIP8 & 1mm sockets can be mounted so DIP8 opamp and discrete opamps can be swapped in and out.

Re: FREQ500 KIT Build Thread

Posted: Tue Mar 10, 2020 7:03 pm
by Claudio
Hey Joe,

This seems like a basic question, but do we have to cut away the +/- 24V pins from the connector when we don’t have a 51x rack? Or can the modules be inserted in a VPR rack just as well?

Regarding the op amps, would any 2520 DOA work, e.g. the Sound Skulptor SK99, the Red Dot, or the GAR2520? Could we also mix DIP8 op amps and 2520 DOAs on the same PCB? Or do they have to be all the same for any reason?

Why are there four op amps anyway? Does each frequency band have its own op amp? If so, would it make sense to have the cleaner IC op amps for the higher frequencies and maybe some GAR2520 for the lows and low mids for additional harmonic distortion?

Thanks a lot,
Claudio

Re: FREQ500 KIT Build Thread

Posted: Tue Mar 10, 2020 7:20 pm
by Joe Malone
Claudio wrote:Hey Joe,

This seems like a basic question, but do we have to cut away the +/- 24V pins from the connector when we don’t have a 51x rack? Or can the modules be inserted in a VPR rack just as well?

The connector is designed with short 51X pins so it should be able to plug into any 500 rack without removing them. If the 500 backplane connectors are held in by screws then they will need to be cut off as the short pins will hit the screw head. If you are going to run on 51X rack @ +/-24v then the 4 opamps on rear audio path pcb need to be +/-24v opamps and 2 regs need to be fitted to drop the voltage to +/-18v for the filter pcbs.

Regarding the op amps, would any 2520 DOA work, e.g. the Sound Skulptor SK99, the Red Dot, or the GAR2520? Could we also mix DIP8 op amps and 2520 DOAs on the same PCB? Or do they have to be all the same for any reason?

Most DOA should work on the back audio path pcb as they are all running at unity gain.

Why are there four op amps anyway? Does each frequency band have its own op amp? If so, would it make sense to have the cleaner IC op amps for the higher frequencies and maybe some GAR2520 for the lows and low mids for additional harmonic distortion?

The 1st opamp is unity balanced to unbalanced input and 2nd and 3rd opamps are unity invert stages for +/-summing of the EQ side filters back into the audio path. 3rd opamp is also +output driver and 4th opamp is -output driver. No EQ filters are inline with the audio. They all run sidechain like a compressor. Only the 4 opamps on the back edge pcb are the audio path.

Re: FREQ500 KIT Build Thread

Posted: Wed Mar 11, 2020 12:57 am
by Claudio
Thanks for your reply, Joe! I have a Trident Deca-Dent rack, so yes, the screws of the connectors would get in the way of the 51x pins. I will cut them off then.