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HPS 6.1
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Old 6th September 2019, 07:43 PM   #31
syn08 is offline syn08  Canada
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Quote:
Originally Posted by rrrremus View Post
Hello,
you are correct, i do mean the low frequency fluctuations, im sorry for creating a confusion. Are these eliminated now?

Regarding the heat, do you think that mounting the bottom of the PCB close to the chassis with a thermal transfer compound would pose a problem?

What is the current consumption of the HPS6.1? Would i be able to use the power supply used for HPS5.1? I have 750mA per secondary available and about 32V on the filtering caps, can the on-board regulators handle the voltage drop across them as well as power dissipation?

Thanks
Not completely, they are unavoidable in single ended high gain (around 86dB at LF) amplifiers. These fluctuations are of thermal origin and would be largely avoided by lowering the input stage current (hence the power dissipation), like in HPS 6.2 (comes with some noise penalty, though).

Any cooling method is acceptable and would help with the fluctuations, assuming you isolate the board from the chassis.

HPS 6.1 takes some 140mA worst case, with the gain relay activated, otherwise about 120mA, this is from the positive power supply, per channel. The negative power supply current is very low. The 5.1 power supply is more than enough for HPS 6.1. Make sure you minimize the voltage drop across the LDO voltage regulators, they don't need more than 0.5V to be in spec and you don't want them to run uselessly hot. Either adjust the output voltage, or use bleeder resistors on the unregulated power inputs.

Once again, if you are not sure you can solder the LDO DFN packages (it is not trivial, requires hot air soldering tools and good skills) use the version with LM317/LM337 regulators (Gerbers and schematics in the same thread), without any performance penalty, those will also be much more tolerant to power dissipation.

Last edited by syn08; 6th September 2019 at 07:52 PM.
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Old 15th September 2019, 01:09 PM   #32
pipbogdan is offline pipbogdan  Romania
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Hi Ovidiu.

Am I missing something? I checked your schematics and:
1. Both in HPS6.1 and in 6.2 the feedback resistor dividers for TPS7A4701 and TPS7A33 seem to be designed for a very low output voltage. You would get +-18V only if R504 would be 20k instead of 200k and R501 16.5k instead of 165k. Am I right?
2. Looking at HPS6.1 it seems the bipolars in the cascodes are not properly polarized (Q209 to Q216): 1N4735 drives the base voltage to ~6.2V, while the collector voltage is ~25% of VCCL (4.5V based on R222 of 1Meg and R228 of 330k). The bipolars are saturated and can't work. Maybe some component values are not right?

Last edited by pipbogdan; 15th September 2019 at 01:27 PM.
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Old 16th September 2019, 12:11 PM   #33
fasterbyelan is offline fasterbyelan  United Kingdom
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HPS 6.1
Has anyone got HPS6.1 running in Spice (LT preferably)?
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Old 16th September 2019, 05:11 PM   #34
syn08 is offline syn08  Canada
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Quote:
Originally Posted by pipbogdan View Post
Hi Ovidiu.

Am I missing something? I checked your schematics and:
1. Both in HPS6.1 and in 6.2 the feedback resistor dividers for TPS7A4701 and TPS7A33 seem to be designed for a very low output voltage. You would get +-18V only if R504 would be 20k instead of 200k and R501 16.5k instead of 165k. Am I right?
2. Looking at HPS6.1 it seems the bipolars in the cascodes are not properly polarized (Q209 to Q216): 1N4735 drives the base voltage to ~6.2V, while the collector voltage is ~25% of VCCL (4.5V based on R222 of 1Meg and R228 of 330k). The bipolars are saturated and can't work. Maybe some component values are not right?
1. Values are wrong, R402=R403=R502=R503=240k, R404=R504=20k, R401=R501=16.5k See below the comment about the board photo.

2. You are again correct, values on the schematic are wrong. R222=R322=2Meg R228=R328=1Meg so the voltage should be ~6V.

The Zener diodes D201, D301 are any 3.3V in SOD-323 case.

I apologize for these issues, the root cause is that in Orcad it is impossible (or very difficult) to use the same schematic for simulation and board layout. Once you decide for the topology, you assign the devices footprints and start routing the board; in parallel you can calculate and then run simulations to optimize the device values. This makes the schematics to diverge. I should have updated the board schematics in #1 with the right values.

As a rule, when something looks wrong, check the board photo (that's why I posted large board photos in #1 and the following). I can guarantee those values are correct, since those are fully working boards.

P.S. I see I can edit #1, I will try to update the schematic archive as soon as I have the time to make the corrections and double check them.

Last edited by syn08; 16th September 2019 at 05:24 PM.
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Old 16th September 2019, 06:24 PM   #35
pipbogdan is offline pipbogdan  Romania
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Thanks for the update of the HPS 6.1 component values!

Which is the current set point for the input stage in case I plan to run HPS 6.2 at +-18V?
C216 & C316 from HPS 6.2 are indeed 1u / 50V film type? From the picture they look like Panasonic ECP-U1C105MA5. Any film @50V would be quite large for the footprint.
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Old 16th September 2019, 07:51 PM   #36
syn08 is offline syn08  Canada
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Quote:
Originally Posted by pipbogdan View Post
Thanks for the update of the HPS 6.1 component values!

Which is the current set point for the input stage in case I plan to run HPS 6.2 at +-18V?
C216 & C316 from HPS 6.2 are indeed 1u / 50V film type? From the picture they look like Panasonic ECP-U1C105MA5. Any film @50V would be quite large for the footprint.
Please check again, C216 & C316 are ceramic 0.1uF decoupling on the schematic. The two 1uF caps are both ceramic, X7R, 1206
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Old 16th September 2019, 08:38 PM   #37
pipbogdan is offline pipbogdan  Romania
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Quote:
Originally Posted by syn08 View Post
Please check again, C216 & C316 are ceramic 0.1uF decoupling on the schematic. The two 1uF caps are both ceramic, X7R, 1206
I mean the one in the picture. This is film type or am I wrong? A ceramic in this place is strongly not recommended.
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Old 17th September 2019, 02:17 AM   #38
syn08 is offline syn08  Canada
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Quote:
Originally Posted by pipbogdan View Post
I mean the one in the picture. This is film type or am I wrong? A ceramic in this place is strongly not recommended.
Sorry I was looking at HPS 6.1. Yes, the cap is film 1206 in size DigiKey 338-4076-1-ND or equivalent. Any value between 0.1u and 1u is good enough in that position.

JFETs are running at about 1mA each, total 8mA.

Last edited by syn08; 17th September 2019 at 02:22 AM.
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Old 17th September 2019, 06:16 PM   #39
syn08 is offline syn08  Canada
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Not sure why the forum software is not letting me to edit the attachments, nevertheless find attached the updated schematics for HPS6.1. Keep checking against the board photo in #1 when in doubt.

One last (hopefully) correction: Zener diodes for the cascode are 3.3V in SOD323, for example DigiKey MM3Z3V3BCT-ND or equivalent.
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File Type: zip HPS61.zip (625.7 KB, 92 views)

Last edited by syn08; 17th September 2019 at 06:32 PM.
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Old 4th October 2019, 09:46 AM   #40
fasterbyelan is offline fasterbyelan  United Kingdom
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HPS 6.1
Does anyone have the LTSpice models for the 2 Ic's used in the head amp (OPA2132 and LME49610)?

Thank you,
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