[Christoph]

Hello,

I assembled two TS500 and they sounded great and identical at first. Suddenly I recognized a level jump of + 2.5/3 dB on one unit, which was also confirmed by the LED Meter.
I went through the level testing routine, and the defective unit had too much level of 2.5-3V on the 1kHz and all low frequency measurements. At 10k the results were fine.

I also noticed, that with no signal at the input and Drive on max., the first 3-4 green LED show a constantly "pumping" signal, whithout anything hearable at the output.

Ich checked the test pins with a 1kHz sine at 0.4V and got the following results:

Pin 1: 1.4V (+0.25V compared to the working unit)
Pin 2: 6.1V (+1V)
Pin 3-5: 3V (+0.7V)
Pin 6: 2.8V (+0.7V)
Pin 7 5.6V (+1.4V)

I swapped ICs and LED boards between the units, I double checked the parts, resoldered and cleaned the whole board. No Success

I really appreciate any help!

Thanks!
Christoph

[JPK]

I am not sure your values are wrong.
Here are the values taken from a working unit:
Input=1kHz-0.4VAC, Both pot at 10, SPEED on 30', SAT on -, BIAS on right,
TP1 = 1.4 VAC
TP2 = 6.0 VAC
TP3.4.5 = 2.7 VAC
TP6 = 2.5 VAC
TP7 = 4.9 VAC
These value may change 10% from unit to unit because of the input potentiometer precision.
The matching must be based on the meter reading after then initial setup.

I also noticed, that with no signal at the input and Drive on max., the first 3-4 green LED show a constantly "pumping" signal, whithout anything hearable at the output.

Is this happening with the input shorted?

[Christoph]

Hello JBK,

thanks for your fast support

These value may change 10% from unit to unit because of the input potentiometer precision.
The matching must be based on the meter reading after then initial setup.

I double checked the output levels of both units. The "bad" one only has more gain in the low and mid frequencies. When matching the DRIVE levels, it sounds dull compared to the properly working unit:

conditions	reference	bad unit	good unit
1k / 0,4V	9.2V 7.4V 7.1V	10.9V 8.7V 8.1V	8.1V 6.5V 6.3V
40Hz / 0.25V	9.4V 8.5V 7.5V	11.5V 10.3V 9.1V	8.2V 7.4V 6.5V
60Hz / 0.25V	7.5V 9.3V 8.7V	9.2V 11.6V 10.6V	6.4V 8.1V 7.5V
80Hz / 0.25V	5.4V 7.9V 9.3V 6.1V	6.7V 9.8V 11.4V 8.0V	4.6V 6.8V 8.0V 5.5V
10k / 0.25V	2.5V 4.1V 5.1V 5.1V	1.4V 2.3V 2.9V 2.9V	1.3V 2.3V 2.8V 2.8V

Is this happening with the input shorted?

No. Standard balanced connection from my DA Converter. DRIVE and OUTPUT on 10. In the meantime I noticed that both units behave the same. The LEDs seem to show the level of a standard noise which I could hear when I cranked up the volume when monitoring the outputs of both units. I tried another converter and both units got even more noisy with 5-7 green LEDs flickering. Both converters by itself are dead quiet. When disconnecting the converter from the input of the units, the units are dead qiet, too. Noise level is pretty low though. Nothing to worry about in an analog envirenment. Yet still kind of strange.

Thanks again!
Christoph

[JPK]

Do you hear a change in dullness when switching the speed from 30 to 15 to 7.5 (BIAS on left)?

[Christoph]

Do you hear a change in dullness when switching the speed from 30 to 15 to 7.5 (BIAS on left)?

Yes, it gets duller on 15ips and even more dull at 7.5ips

Thanks!

[JPK]

Can you repeat the measurements with a 100Hz signal?
Adjust the drive level in order to get the same level on TP1 of both units.
Then compare TP2 ...TP7 between the units to find out the stage where the level difference begins.
This will tell you where to start searching.

[Christoph]

TP	bad unit	good unit
1	0,52V	0,52V
2	2,08V	2,08V
3	1,18V	0,97V
4	1,18V	0,97V
5	1,18V	0,97V
6	1,18V	0,97V
7	2,33V	1,94V

100Hz Input / 30ips / Saturation left / Bias right / Output max.

Thanks again!

[JPK]

Check that the tape sim coil HD1 is in the correct direction: The side marked P towards the bottom.
The issue seems to be around U2b.
Check the values and solder joints of R19...R24 and C19...C22.

[Christoph]

I checked the position of HD1, I checked all values from R19 to R24 und C19 to C22. All good.
I resoldered those resistors and caps. Still the same issue

What seems a bit strange... to get 0.52V at TP1 on both units, the DRIVE pots need to have quite different values of resistance. Measuring between the left and middle pin (front view), I get 3.1k on the good unit, whereas the bad unit has 4.0k. Between the outer pins, I get 6.7k on the good unit and 8.1k on the bad one. Is this still within the component tolerance?
I remember that one DRIVE Pot did not fit perfectly through the whole, so I had to resolder it. Maybe I damaged the Potentiometer somehow? Although it worked fine at first...

Maybe swap the DRIVE potentiometers between both units? Or anything else?

I am still sure that both units worked exactly the same in the beginning, so I don't think that I assembled anything wrong.

Thanks again! I really appreciate your fast responding

[Christoph]

It's the coil!

I swapped the coils and the good unit went bad and vice versa. Maybe something broke inside after a short time.

I will send you a request for spare parts by mail...

Thanks again

[Christoph]

Thanks for the fast shipping!

Today I received the two spare coils I ordered. With the first one I installed, this unit had about 1dB more bass than the other in all settings.
I changed the coil with the second spare part, and now the frequency response is exactly equal on both units. I am finally happy now, as I want to use them on mixbus purposes.

But, there seem to be some quality problems with the coils. I would recommend to check the production, as this is obviously a very relevant part of the TS500.

Thanks again for your help!

Christoph

[JPK]

OK, thank you for the feedback.