Another Amek Tac Scorpion overhaul!

[Eliani]

Typical CMRR for the 2520 differential receiver is better than 90dB, is this good or bad?

 

[critterkllr]

Would you mind posting the schematic for the Diff_Rev004? I could have swore it was posted here before. Maybe it disappeared during the server updates?

 

[critterkllr]

I wired up a Jenson JT-11P-1 input transformer to see how it sounds. I'm not 100% sure I wired it correctly. I wired both shield/can wires (black and white) straight to the same ground. I also included a 13K resistor and 620pF cap zobel network, in series between the positive and negative secondaries. There are a lot of variations in wiring from different Jenson schematics so I hope I picked the correct one.

Anyway, as it is wired, the sound difference is definitely noticeable.

I'm just using a null test along with Ozone 6's matching EQ plugin to compare what it's doing to the audio (nothing scientific!). It appears as though the channel will the the Jensen has a high frequency roll off compared to the other channel. About a .5 dB slope from 15khz to 20khz. There is a very slight change in the low end. A little rise between 20 hz and 100hz, with a dip after 20. Small decrease between 150 hz and 400 hz. As well as some changes around 1khz. Nothing large enough to tell how many dB.

Again, I only compared the modded channel to another modded channel with a Jensen input transformer.

 

[Eliani]

Would you mind posting the schematic for the Diff_Rev004? I could have swore it was posted here before. Maybe it disappeared during the server updates?

I attached to the first post in the official Help thread...
http://groupdiy.com/index.php?topic=59994.msg761490#msg761490

 

[Eliani]

I wired up a Jenson JT-11P-1 input transformer to see how it sounds. I'm not 100% sure I wired it correctly. I wired both shield/can wires (black and white) straight to the same ground. I also included a 13K resistor and 620pF cap zobel network, in series between the positive and negative secondaries. There are a lot of variations in wiring from different Jenson schematics so I hope I picked the correct one.

Anyway, as it is wired, the sound difference is definitely noticeable.

I'm just using a null test along with Ozone 6's matching EQ plugin to compare what it's doing to the audio (nothing scientific!). It appears as though the channel will the the Jensen has a high frequency roll off compared to the other channel. About a .5 dB slope from 15khz to 20khz. There is a very slight change in the low end. A little rise between 20 hz and 100hz, with a dip after 20. Small decrease between 150 hz and 400 hz. As well as some changes around 1khz. Nothing large enough to tell how many dB.

Again, I only compared the modded channel to another modded channel with a Jensen input transformer.

Did you wire the transformer in front of the Diff.Rev00x receiver? Because that would be like double balancing?!

 

[critterkllr]

I wired up a Jenson JT-11P-1 input transformer to see how it sounds. I'm not 100% sure I wired it correctly. I wired both shield/can wires (black and white) straight to the same ground. I also included a 13K resistor and 620pF cap zobel network, in series between the positive and negative secondaries. There are a lot of variations in wiring from different Jenson schematics so I hope I picked the correct one.

Anyway, as it is wired, the sound difference is definitely noticeable.

I'm just using a null test along with Ozone 6's matching EQ plugin to compare what it's doing to the audio (nothing scientific!). It appears as though the channel will the the Jensen has a high frequency roll off compared to the other channel. About a .5 dB slope from 15khz to 20khz. There is a very slight change in the low end. A little rise between 20 hz and 100hz, with a dip after 20. Small decrease between 150 hz and 400 hz. As well as some changes around 1khz. Nothing large enough to tell how many dB.

Again, I only compared the modded channel to another modded channel with a Jensen input transformer.

Did you wire the transformer in front of the Diff.Rev00x receiver? Because that would be like double balancing?!

Yes. Is there a different way I should have done it?

 

[critterkllr]

http://www.jensen-transformers.com/wp-content/uploads/2014/08/as069.pdf

This is Jensen's schematic for adding an input transformer. Jensen labels it as "JT-11P-1 improves CMRR of electronically balanced line inputs".

 

[Eliani]

http://www.jensen-transformers.com/wp-content/uploads/2014/08/as069.pdf

This is Jensen's schematic for adding an input transformer. Jensen labels it as "JT-11P-1 improves CMRR of electronically balanced line inputs".

Well, you're right!! I've never seen a balanced setup like that. but would you do so to improve CMRR or add Color?!

 

[critterkllr]

Both!

I'm not sure that I'm a fan of the HF roll off. It's a bit much and would add up. I love what it does to the midrange and low end though.

According to the schematic in that link, it should be a 20k without a cap. I'm going to try that. The Jensen is supposed to be very clean, so I was shocked to hear a difference like this.

 

[critterkllr]

I swapped the zobel with a 20k resistor. The HF roll off is much less. The difference is very subtle now.

Let me know if you want some pictures of the PCB for the new EQ you're designing. The biggest difference between the Scorpion II and II is the EQ section. You may want to have some extra pads in your design to fit the scorpion II if possible.

 

[Eliani]

I swapped the zobel with a 20k resistor. The HF roll off is much less. The difference is very subtle now.

Let me know if you want some pictures of the PCB for the new EQ you're designing. The biggest difference between the Scorpion II and II is the EQ section. You may want to have some extra pads in your design to fit the scorpion II if possible.

For now I'm aiming at using the Pots to hold the PCB and wire the EQ in the circuit...

 

[critterkllr]

What do you think about sacrificing an aux to add a THAT 4301 based compressor to each channel? I'm not sure about other Scorpions, but mine has dual 10k pots for aux controls. I wouldn't mind giving up a dual pot to use for ratio and threshold.

I'm not sure if a make up gain control is necessary on a channel strip. +/-17.5v would need to be lowered to +/-15V. Since there's no psu or case involved, it could be somewhere around $25 per channel. Considering the cost of a normal compressor build, that's really enticing.

http://www.thatcorp.com/datashts/THAT_4301_Datasheet.pdf
http://www.thatcorp.com/datashts/dn107.pdf

 

[bluezplaya]

What do you think about sacrificing an aux to add a THAT 4301 based compressor to each channel? I'm not sure about other Scorpions, but mine has dual 10k pots for aux controls. I wouldn't mind giving up a dual pot to use for ratio and threshold.

I'm not sure if a make up gain control is necessary on a channel strip. +/-17.5v would need to be lowered to +/-15V. Since there's no psu or case involved, it could be somewhere around $25 per channel. Considering the cost of a normal compressor build, that's really enticing.

http://www.thatcorp.com/datashts/THAT_4301_Datasheet.pdf
http://www.thatcorp.com/datashts/dn107.pdf

Damn right! I like that idea. Adding onboard THAT comps to some channels would be awesome. I was actually going to build a 4 channel unit just to use for drums.

 

[bluezplaya]

Here is a THAT 4301 board from DIY-tubes.com that I have finished and was going to put in a standard rack. It fits very nicely with room to give at the top of the S3300 Sub channel. I typically would group drums to a stereo bus and compress it, so why not install and mount the compression in these subgroup channels, wire them in to the chain with a bypass switch, there's room to add switches for hard knee/soft knee and RMS/peak. And would have to power the boards. Could they work on the 17.5V?

 

[bluezplaya]

Pic 2

 

[bluezplaya]

Pic 3

 

[bluezplaya]

BTW, I re-read through the build thread and realized why my signal was incredibly low on the line mods. I just removed R6-8 and jumpered 6 and 7. BAM! Full signal!

 

[jensenmann]

Here is a THAT 4301 board from DIY-tubes.com that I have finished and was going to put in a standard rack. It fits very nicely with room to give at the top of the S3300 Sub channel. I typically would group drums to a stereo bus and compress it, so why not install and mount the compression in these subgroup channels, wire them in to the chain with a bypass switch, there's room to add switches for hard knee/soft knee and RMS/peak. And would have to power the boards. Could they work on the 17.5V?

I thought about something similar back then. JLM Audio´s MAC compressor was on my list to fit in there. But I never did it in the end. Fitting the VU meter in would take a lot of material from the frontpanel away hence weaken it. That was my main concern since I was planning to use the desk for livesound.

 

[bluezplaya]

I just got a hold of a couple of adapter boards to retrofit a THAT 1510 chip to the SSM2015 socket in the mic pre, and gave a thorough listen to several songs on my iPhone patched in to the line in of two channels. I compared the channels of the 1510s with the 2520 differential and they sound really good, but different from the 2520 obviously. The stock chips just weren't as smooth on the upper mids and highs, and the low mid and lows were more muddy and less pronounced. Eli, are you still thinking about doing a run of line mod boards for the THAT chips? If so, how much are you charging?

 

[Eliani]

I just got a hold of a couple of adapter boards to retrofit a THAT 1510 chip to the SSM2015 socket in the mic pre, and gave a thorough listen to several songs on my iPhone patched in to the line in of two channels. I compared the channels of the 1510s with the 2520 differential and they sound really good, but different from the 2520 obviously. The stock chips just weren't as smooth on the upper mids and highs, and the low mid and lows were more muddy and less pronounced. Eli, are you still thinking about doing a run of line mod boards for the THAT chips? If so, how much are you charging?

I'm expecting a first batch for the That.Rev001 boards to arrive next week! After a quick test I would be able to sell them for the same price as the Diff.Rev00x boards! Around $10 each... They will be a bit more complicated to build, but at a better price than the DOA differential receivers!