1

LA502T Tube Optical Compressor / Re: Some wrong parts in the kit.

« Last post by UrbanOsterman on September 24, 2026, 11:08:06 AM »

Thanks
Great Product! Works perfect now.

2

LA502T Tube Optical Compressor / Re: Some wrong parts in the kit.

« Last post by JPK on September 16, 2026, 05:20:51 PM »

I am sorry for the mistake (still a new product). We have sent the correct switches.

3

LA502T Tube Optical Compressor / Some wrong parts in the kit.

« Last post by UrbanOsterman on September 16, 2026, 04:49:52 PM »

I just received a LA502T kit and I started to build it:
But there were some wrong parts included in the kit.
The 4 switches were of the wrong type.
If you can send me the proper ones, I can send you
money for them.
I can keep the wrong types so I dont have to send them back.
Regards
Urban Osterman

 
 

4

CP5176 FET compressor / Re: SK25 output collapses and develops large negative DC offset at higher input

« Last post by steveholm on September 13, 2026, 10:35:03 PM »

LED comes on fine. 

I went ahead and ordered a new SK25 and I'll reach back out if I have more troubles after that one is built. Thank you!

5

CP5176 FET compressor / Re: SK25 output collapses and develops large negative DC offset at higher input

« Last post by JPK on September 12, 2026, 09:34:46 AM »

Does the LED lights up?
Check Q7 and Q9 with the DMM in diode mode. It is possible to test Q7 while in circuit and test half of Q9, the BC junction.
Test transistors
Generally DOA's are very difficult to troubleshoot because of the density and all the feedback paths. I would recommend to build a new one.

6

EQ573 Equaliser / Re: EQ573-II ran in my lab

« Last post by JPK on September 12, 2026, 09:11:34 AM »

Actually, this is the normal frequency response of the original 1073. About -1dB at 20kHz.
I guess that the modern reissues are modified.
You can make the frequency response flat up to 20kHz by changing the value of 2 caps:
C47 at 100pF (instead of 470pF),
C60 at 47pF (instead of 150pF).

7

CP5176 FET compressor / Re: SK25 output collapses and develops large negative DC offset at higher input

« Last post by steveholm on September 11, 2026, 07:28:37 PM »

I have also tested all the resistors, and they all match the spec. The diodes are working in the correct directions as well.

Steve

8

CP5176 FET compressor / Re: SK25 output collapses and develops large negative DC offset at higher input

« Last post by steveholm on September 09, 2026, 06:23:55 PM »

The solder joints look good for Q9 and R12.

For these measurements: 
R9 bottom: +0.12 VDC low -> -11.4 VDC high

R9 bottom means the board side of the vertical resistor. +.120VDC low is the measured DC voltage when the input voltage is at 100 mVAC. -11.4 VDC high is the DC voltage when the input voltage is at maximum input. 

All of the rest are the same: 100 mVAC input -> max input.

Steve

9

CP5176 FET compressor / Re: SK25 output collapses and develops large negative DC offset at higher input

« Last post by JPK on September 09, 2026, 04:07:17 PM »

at ~300 mVAC input it begins developing a large negative DC shift and its AC output collapses instead of continuing to increase.
It looks like the positive part of the output is not working. Check the solder joints of Q9, R12.
Can you explain your measurements:
R9 bottom: +0.12 VDC low -> -11.4 VDC high

10

EQ573 Equaliser / Re: Hi Frequiency "Hiss" when it is at pre mode

« Last post by Alex Harmer on September 09, 2026, 12:31:18 AM »

I visited the forum today to see if anyone else had had this issue.

The EQ is gorgeous. In XLR mode it is totally clean. I have operated these units successfully since early 2025 with no issues. 

Today I noticed in Pre mode that decreasing a frequency caused hiss. This happened across the highs, the mids, and the lows, but it was most noticeable with the high frequency control. 

It happened in the first 30dB of gain on the MP573. On 40dB and above, the hiss was not as bad.

I'm totally happy to just use the EQ in XLR mode, but I thought it would be worth alerting JPK.

Are you able to go in to a bit more detail about the benefits of Pre vs. XLR mode JPK?

Thanks,
Alex Harmer