Author Topic: Everything works but high frequencies are getting lost somewhere

October 17, 2021, 11:02:09 PM
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rianwithaneye

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Hello! I recently built two TS500 kits and one of them works flawlessly, while the other passes a very, very dark signal. The meter is accurate, the levels match the other unit that works well, and the bypass works and passes a clean signal. 

When I fist powered the unit up it oscillated like crazy and I discovered I had installed U5 backwards. I ordered a replacement part from Mouser and replaced the chip, and while the oscillation problem is gone it now passes a signal that sounds aggressively low-passed.

I've double-checked all the solder joints and re-flowed any joints that looked suspicious. The problem persists.

Ring any bells? Thanks for your time!

October 18, 2021, 09:25:10 AM
Reply #1

JPK

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Try replacing U3 as well.
With a cable wire connected to a monitoring input, "listen" to the sound on TP1, TP2, TP3, TP4, TP5, TP6 and compare to the corresponding position on the working TS500.
The test point where the sounds differ will tell you where is the issue.
JPK

November 03, 2021, 12:09:48 PM
Reply #2

rianwithaneye

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Thank you so much for your reply! I replaced U3 and the sound was still dark, so I took some measurements as you suggested.

I only have one 500 series power extender, so here's what I did:

- I sent a 1k sine wave to the input and adjusted the level of the send until it measured 1VAC
- I put one test probe on the 0V test point and then measured the reading at each of the other test points.

The values were as follows, the values from the working unit are on the left and the malfunctioning unit is on the right.

TP1: 0.576 -- 0.594
TP2: 2.547 -- 2.623
TP3: 0.910 -- 1.075
TP4: 0.910 -- 1.075
TP5: 0.909 -- 0.484
TP6: 0.830 -- 0.442
TP7: 1.662 -- 0.883

Test points 1-4 look fine, but 5-7 are a bit off.

Does that shed any light on how I should proceed? Thanks again for your help on this.

November 04, 2021, 06:31:54 PM
Reply #3

JPK

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Check component value, direction and solder joints on:
R33, R34, C35 to C38, U10, U6.
Try removing U6 and listen if it makes a change.
JPK

May 15, 2022, 01:30:58 AM
Reply #4

Dolbah

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Check component value, direction and solder joints on:
R33, R34, C35 to C38, U10, U6.
Try removing U6 and listen if it makes a change.
Sorry for bumping this old post, but I seem to have the same issue.


  • I have gone over all joints.
  • Replaced U3
  • Checked R33,R35 and C35, C38 + Replaced U10.
  • Removed U6 = Same result, no audible change in sound.
Left picturer is a Pink Noise without TS500, the right is the same Pink Noise with TS500 set at:
- 30"
- Tape Sat at middle
- Bias/EQ to the right


I listened to the TPs and it starts after TP5

Honestly, i thought this was normal until i started checking out sound demos online with nice clear Highs, and then i saw this post. 



« Last Edit: May 15, 2022, 07:52:03 PM by Dolbah »

May 15, 2022, 09:19:42 PM
Reply #5

Dolbah

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Check component value, direction and solder joints on:
R33, R34, C35 to C38, U10, U6.
Try removing U6 and listen if it makes a change.
Sorry for bumping this old post, but I seem to have the same issue.


  • I have gone over all joints.
  • Replaced U3
  • Checked R33,R35 and C35, C38 + Replaced U10.
  • Removed U6 = Same result, no audible change in sound.
Left picturer is a Pink Noise without TS500, the right is the same Pink Noise with TS500 set at:
- 30"
- Tape Sat at middle
- Bias/EQ to the right


I listened to the TPs and it starts after TP5

Honestly, i thought this was normal until i started checking out sound demos online with nice clear Highs, and then i saw this post. 



UPDATE:

I've located the point on the PCB. The change on high frequencies occurs after R35, when i listen to R35. it sounds nice and clear but on R36 and Pin 1 on U11, the highs have been pulled down. The same on C39, C40 and C41.
 
I've changed U11 with several other OPA2134 frm other SS gear i have, same results. Is it supposed to be like this? I dont get the impression from listening to any demos.

When removing the OPA, i can listen in to PIN 1 and 2, and i get a normal high freq sound, with out any loss.

May 17, 2022, 04:11:48 PM
Reply #6

JPK

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The change on high frequencies occurs after R35
This is normal because U11a does the NAB de-emphasis (low pass filter).
Maybe the corresponding initial pre-emphasis (high pass filter) made in U2a is not working. Check the value and solder joints of R7, R8, C4, C5.
JPK

May 17, 2022, 07:28:18 PM
Reply #7

Dolbah

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The change on high frequencies occurs after R35
This is normal because U11a does the NAB de-emphasis (low pass filter).
Maybe the corresponding initial pre-emphasis (high pass filter) made in U2a is not working. Check the value and solder joints of R7, R8, C4, C5.
R7 = 0,997 Ohm
R8 = 5K605 Ohm

Not sure how to read caps with my DDM without removing them, but:
C5 = 221/K1J
C4 = Wima 0.01 100-

Reflowed my joint but same results. All looks good visually. Replaced U2 just in case, no luck.


But the spectrum analyzer in my previous post shows clearly a low-pass situation going on or at least at that side of the spectrum, how would this be affected by a high-pass filter?
Do you have any frequency response charts for the unit, so i can compare?


« Last Edit: May 17, 2022, 09:29:33 PM by Dolbah »

May 18, 2022, 05:26:16 PM
Reply #8

JPK

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The frequency response also depends on the input signal level.
The more you drive it hard, the more high frequencies are attenuated, this is a normal behaviour in a tape recorder:
The high frequencies are boosted in the NAB pre-emphasis then attenuated back to normal in the de-emphasis. If, in between they are submitted to tape saturation, the de-emphasis won't be able to restore the full initial level. 
JPK

May 18, 2022, 07:04:41 PM
Reply #9

Dolbah

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I get it, but mine still doesent sound correct. I found a good way to test this by using this YT video:

TS500 demo - YT

I made a audiofile of it, and put the DRY signal from the video into my TS500 and recorded the result with identical settings:



Here is my result:
https://www.dropbox.com/s/lwvb4o8v2wqsqlz/TS500%20YT%20test.wav?dl=0

If you compare this with the wet signal from the video, you hear a clear difference.


I am listening my way through the NAB pre-emphasis stage and can hear the high pass driving the highs louder, all the way to R13 and it decreases a bit, then at R25 it decreases even more until i get to R35 and U11 again  and i'm back at the de-emphasis and everything gets pulled down to the point that i can recognize it as the level that is outputet from the module.
I have Drive at zero and saturation set to minus, and levels are on green all the time.

Any pointer in the correct direction would be appreciated
« Last Edit: May 18, 2022, 09:35:40 PM by Dolbah »

May 19, 2022, 05:25:52 PM
Reply #10

JPK

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Check solder joints and values of R19 to R24, C19 to C22, HD1 (coil).
Do you hear a brightness difference between TP3, TP4 and TP5? There shouldn't be any in 30" and bias to the right.
JPK

May 19, 2022, 05:46:41 PM
Reply #11

Dolbah

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R19 3K296
R20 180K
R21 21K99
R22 14K94
R23 9K99
R24 8K18

C19 WIMA 0.022 100-
C20 WIMA 0.01 100-
C21 WIMA 4700 100-
C22 WIMA 2200 100-


HD1 = 2043, P is downwards

30" + BIAS to the right = no change when listening to TP3 to TP5

May 19, 2022, 05:49:46 PM
Reply #12

Dolbah

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R19 3K296
R20 180K
R21 21K99
R22 14K94
R23 9K99
R24 8K18

C19 WIMA 0.022 100-
C20 WIMA 0.01 100-
C21 WIMA 4700 100-
C22 WIMA 2200 100-


HD1 = 2043, P is downwards

30" + BIAS to the right = no change when listening to TP3 to TP5
Solder joint looks good, and have been reflowed earlier (did them all)

May 19, 2022, 06:36:58 PM
Reply #13

JPK

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The values look good.
Maybe the coil? Contact us here.
JPK