Hi All
First post to this forum. It will be kind of long.
I have some problems with my Thule IA100 amplifier, that I’ve had since 15 years ago but it is probably around 20 yearsold.
Problem description:
When warm (after approx 30 minutes) I get intermittent loud pops in the speakers and the protection relay clicked, then the amplifier resets itself and continued playing as before.
I opened up the amp and figured that I would go ahead and change all electrolytic capacitors since that seem to be the weak point of these amplifiers.
I managed to get hold of the servicemanual and schematics for the amp but the manual is for board revision EM 1071rev 7 while my amp have EM 1071 rev 9.
The main change between revisions seem to be that the 10uF 16V SMD electrolytic caps have been replaced with tiny ceramic ones.
Apart from C14 and C15 which are SMD Tantalum caps by the looks of things (orange SMD caps). Also C56 is replaced bya 2.2uF 35V Tantalum SMD cap (might be some earlier repair bfore i bought it).
After replacing all electrolytics(replaced the SMD ones with regular ones) including the main filter caps (4x10000uF Nichinon), hooked the amp up to some dummy load resistors and gave it a go.
After reading up on these amps on this forum i also added heatsinks to the regulators (Lm137 and LM 337), the underside of the board shows a slight brown tint underneath these so I guess that these do indeed run hot.
Unfortunately, the problem persists whenthe amp gets up to temp.
It seems like this amplifier really runs hot, at full power the Pcb gets up to around 50°C and the heatsinks and output transistor reach close to 70°C. The regulators and the relay are getting close to 80° when the amp is pushed to higher power.
I measured the DC idle current on thespeaker outputs to around 4mV on both speaker outputs but when hot I havesudden spikes up to a couple of volts (when the relay clicks).
Next I will try to measure the output voltage from the voltage regulators (should be 7.5V and see if that is what is spiking when hot).
Any ideas what may cause the problems I’m having?
Faulty protection relay?
Suspect Tantaliumcapacitors? (the orange ones seem to bein the protection circuit, I also have pops in the speakers when going to standby after use).
The 2.2uF35V is quite suspect since it seems out of place and is part of the voltage regulating circuit.
Adding some pictures of the inside of the amp aswell as the schematics and pictures of the suspect components.
Best regards
Henrik
First post to this forum. It will be kind of long.
I have some problems with my Thule IA100 amplifier, that I’ve had since 15 years ago but it is probably around 20 yearsold.
Problem description:
When warm (after approx 30 minutes) I get intermittent loud pops in the speakers and the protection relay clicked, then the amplifier resets itself and continued playing as before.
I opened up the amp and figured that I would go ahead and change all electrolytic capacitors since that seem to be the weak point of these amplifiers.
I managed to get hold of the servicemanual and schematics for the amp but the manual is for board revision EM 1071rev 7 while my amp have EM 1071 rev 9.
The main change between revisions seem to be that the 10uF 16V SMD electrolytic caps have been replaced with tiny ceramic ones.
Apart from C14 and C15 which are SMD Tantalum caps by the looks of things (orange SMD caps). Also C56 is replaced bya 2.2uF 35V Tantalum SMD cap (might be some earlier repair bfore i bought it).
After replacing all electrolytics(replaced the SMD ones with regular ones) including the main filter caps (4x10000uF Nichinon), hooked the amp up to some dummy load resistors and gave it a go.
After reading up on these amps on this forum i also added heatsinks to the regulators (Lm137 and LM 337), the underside of the board shows a slight brown tint underneath these so I guess that these do indeed run hot.
Unfortunately, the problem persists whenthe amp gets up to temp.
It seems like this amplifier really runs hot, at full power the Pcb gets up to around 50°C and the heatsinks and output transistor reach close to 70°C. The regulators and the relay are getting close to 80° when the amp is pushed to higher power.
I measured the DC idle current on thespeaker outputs to around 4mV on both speaker outputs but when hot I havesudden spikes up to a couple of volts (when the relay clicks).
Next I will try to measure the output voltage from the voltage regulators (should be 7.5V and see if that is what is spiking when hot).
Any ideas what may cause the problems I’m having?
Faulty protection relay?
Suspect Tantaliumcapacitors? (the orange ones seem to bein the protection circuit, I also have pops in the speakers when going to standby after use).
The 2.2uF35V is quite suspect since it seems out of place and is part of the voltage regulating circuit.
Adding some pictures of the inside of the amp aswell as the schematics and pictures of the suspect components.
Best regards
Henrik
Attachments
When i measure the voltages from the voltage regulators i get the following values:
Reg 1 LM317:
Vout to ground 7.2V
Reg 2 LM337
Vout to ground -50V !!
Seems like reg 1 is doing its work but reg 2 seems to deliver the rail voltage of 50V.
Seems like i found a likely culprit to my problems.
will order some replacement regulators and swap them out.
Hopefully this will solve my issues
Reg 1 LM317:
Vout to ground 7.2V
Reg 2 LM337
Vout to ground -50V !!
Seems like reg 1 is doing its work but reg 2 seems to deliver the rail voltage of 50V.
Seems like i found a likely culprit to my problems.
will order some replacement regulators and swap them out.
Hopefully this will solve my issues
Just a thought while im waiting for parts
The regulators are now beeing fed 50v thru a 680 ohm 3w resistor. (see the power regulation circuit in first post)
I think that this results in an unnecessary high input voltage for the regulators (LM317 and LM337). im thinking of replacinging the resistors with 1.2 kohm resistors to bring down the input voltage and hopefully less strain on the regulators.
Any thoughts on this?
Should i also as a safe guard, change the caps in the regulation circuit (3 ceramic 10uF 16V and one tantalium 2.2uF 16V) to 4 ceramic 50V counterparts?
I also think i will replace the relay and the tantalium caps in the protection circuit because i think that these parts have also had a hard life.
The regulators are now beeing fed 50v thru a 680 ohm 3w resistor. (see the power regulation circuit in first post)
I think that this results in an unnecessary high input voltage for the regulators (LM317 and LM337). im thinking of replacinging the resistors with 1.2 kohm resistors to bring down the input voltage and hopefully less strain on the regulators.
Any thoughts on this?
Should i also as a safe guard, change the caps in the regulation circuit (3 ceramic 10uF 16V and one tantalium 2.2uF 16V) to 4 ceramic 50V counterparts?
I also think i will replace the relay and the tantalium caps in the protection circuit because i think that these parts have also had a hard life.
I had one too and wrote about it here I think. There is a big diff in the current to the reg's depending on standby or on. In standby the input voltage will be on the limit of the reg's specs, and at least in the early amps the caps will see serious over voltage. The caps will be fried from the heat from the regulators and over voltage, the regulators will start to oscillate and destroy the amp.. Really nice design! 
However, a nice sounding amp IMO. I measured distortion on mine, and all I could see was low 2nd & 3rd harmonics.
If you use higher resistance on the resistors the voltage drop could be too high when it's on. Maybe Zeners would be an option. Or zener+resistor. Maybe your regulators are oscillating, or maybe they are broken because of those voltages you see. I'm amazed the amp is working at all!
Remember to check the voltage setting resistors for the reg's too (R137/47 etc)
I added a separate small PS to feed the regulators. There is a lot of room for it next to the main transformer.
However, a nice sounding amp IMO. I measured distortion on mine, and all I could see was low 2nd & 3rd harmonics.
If you use higher resistance on the resistors the voltage drop could be too high when it's on. Maybe Zeners would be an option. Or zener+resistor. Maybe your regulators are oscillating, or maybe they are broken because of those voltages you see. I'm amazed the amp is working at all!
Remember to check the voltage setting resistors for the reg's too (R137/47 etc)
I added a separate small PS to feed the regulators. There is a lot of room for it next to the main transformer.
Last edited:
I've got some parts now and will start seeing if i can repair this amp.
There seems to be some more changes between my amp (rev.9) and the schematics (rev.8).
The resistors on the inputs for the regulators are not 680ohm as in the scematic but 470 ohms, these doesnt look resoldered so i guess that they have been that way since factory. I guess this would make the regulators run even hotter, right?
I've found another thread here on diy forum that have some suggested improvements for the regulation circuits. there was this document by user tiefbasseubertr
What happen to thule audio? post#79
last page show some modifications including zeners and transistors, i guess this is a more elgant solution than simply increase the resistance.
@rallyfinnen, your solution sounds really elegant!! can you share some more information on how you did it? what type of PS you used? etc.
Did you add a power supply for +- 7.5 V and feed the pre amp directly bypassing reg 1 and 2 completely or did you use the additional PS as input voltage for the regulators at say +- 15v or so?
There seems to be some more changes between my amp (rev.9) and the schematics (rev.8).
The resistors on the inputs for the regulators are not 680ohm as in the scematic but 470 ohms, these doesnt look resoldered so i guess that they have been that way since factory. I guess this would make the regulators run even hotter, right?
I've found another thread here on diy forum that have some suggested improvements for the regulation circuits. there was this document by user tiefbasseubertr
What happen to thule audio? post#79
last page show some modifications including zeners and transistors, i guess this is a more elgant solution than simply increase the resistance.
@rallyfinnen, your solution sounds really elegant!! can you share some more information on how you did it? what type of PS you used? etc.
Did you add a power supply for +- 7.5 V and feed the pre amp directly bypassing reg 1 and 2 completely or did you use the additional PS as input voltage for the regulators at say +- 15v or so?
I used a small transformer from kjell&company, I think it was 12VAC, soldered together my own rectifier/caps on a proto board, and fed that to the regulators. I placed the extra PS next to the main transformer. Just removed the resistors and soldered in the supply leads in the holes and added a ground wire from my new PS to the regulators ground ref. I wanted to keep the regulators to take care of the ripple. Twisted the wires and kept them away from small signal part of the amp.
I actually increased the capacitance a bit in the main caps when I replaced them (looked like they put in smaller ones in the pdf?).
Another point: The washer on the transformer was touching the lid on my amp, making the case a 'shorted turn', which was not so good.
I also added extra cooling holes to get some cool air to the PCB where it was running hot. I even drilled some holes in the PCB's for the airflow too and added small heat sinks on the regulators. The original design has bad airflow IMO, airflow was just on the main heat sink. I guess you can see the hot spots on the PCB color in your amp?
I bought the amp from a friend, and after all the upgrades, he wanted to buy it back at a much higher price
I actually increased the capacitance a bit in the main caps when I replaced them (looked like they put in smaller ones in the pdf?).
Another point: The washer on the transformer was touching the lid on my amp, making the case a 'shorted turn', which was not so good.
I also added extra cooling holes to get some cool air to the PCB where it was running hot. I even drilled some holes in the PCB's for the airflow too and added small heat sinks on the regulators. The original design has bad airflow IMO, airflow was just on the main heat sink. I guess you can see the hot spots on the PCB color in your amp?
I bought the amp from a friend, and after all the upgrades, he wanted to buy it back at a much higher price
Thank you for that explanation definately sounds like that is the way to go.
I've replaced both regulators and caps 40, 41, 55 with ceramic 10uF 50v ones and C56 with a 10uF 50v Tantalum (apparently LM337 does not like low ESR caps on the output).
I've experimented with the resistors before the regulators increasing from 470 to 1.2kOhm. This resulted in the input voltage dropping to low and i could not maintain +-7.5V out.
I then tried 600 ohms resistors but this resulted in input voltages around 30V which to me seems unnescessary high. I unfortunately did not measure the Vin before replacing both regs and all capacitors around them to 50V (instead of original 16v) so i do not know what the original Vin would have been with 470 ohm resistors (should have been around 36V).
So i think the next step will be that i will go ahead and copy your solution with a separate power supply to the regulators.
However i think that i might have found a possible problem with the relay.
The original fault was that the relay started to disconnect after about an hour of playing music, a fault that was still present during the initial testing after recapping. The relay gets pretty hot after a while (around 75°C)
The relay is a Schrack RT424024 which is indicated for 24v coil voltage.
But when i measure it has 40V across the coil. Clearly this can not be good.......
But i am having trouble understanding the circuit for the relay with two 1k resistors in paralell and a diode. How is this bring down the supply voltage (50V) to 24V for the coil??
All components measure ok (resistors and diode).
(See schematic of protection circuit in first post)
I can not believe that it is designed this way with 40v coil voltage (almost twice what is indicated in the specs) so perhaps something else is wrong.
This amp is a little like a pandoras box, everything seem to be designed to operate at max specification (or above).
I thought old B&O amps were tricky but this is something else....
But i must say that i really enjoy the sound from this amp when it works......
I've replaced both regulators and caps 40, 41, 55 with ceramic 10uF 50v ones and C56 with a 10uF 50v Tantalum (apparently LM337 does not like low ESR caps on the output).
I've experimented with the resistors before the regulators increasing from 470 to 1.2kOhm. This resulted in the input voltage dropping to low and i could not maintain +-7.5V out.
I then tried 600 ohms resistors but this resulted in input voltages around 30V which to me seems unnescessary high. I unfortunately did not measure the Vin before replacing both regs and all capacitors around them to 50V (instead of original 16v) so i do not know what the original Vin would have been with 470 ohm resistors (should have been around 36V).
So i think the next step will be that i will go ahead and copy your solution with a separate power supply to the regulators.
However i think that i might have found a possible problem with the relay.
The original fault was that the relay started to disconnect after about an hour of playing music, a fault that was still present during the initial testing after recapping. The relay gets pretty hot after a while (around 75°C)
The relay is a Schrack RT424024 which is indicated for 24v coil voltage.
But when i measure it has 40V across the coil. Clearly this can not be good.......
But i am having trouble understanding the circuit for the relay with two 1k resistors in paralell and a diode. How is this bring down the supply voltage (50V) to 24V for the coil??
All components measure ok (resistors and diode).
(See schematic of protection circuit in first post)
I can not believe that it is designed this way with 40v coil voltage (almost twice what is indicated in the specs) so perhaps something else is wrong.
This amp is a little like a pandoras box, everything seem to be designed to operate at max specification (or above).
I thought old B&O amps were tricky but this is something else....
But i must say that i really enjoy the sound from this amp when it works......
Last edited:
Yes i see that now that the diode seems to be a "fly-back" diode to protect against spikes when the relay opens.
Question is if there is something wrong with this high coil voltage or if it is designed this way.
I have only managed to measure the voltage with the amplifier on and no load (have to have it partially dismantled in order to make the measurement).
Perhaps the rail voltage drop to a safer level when the amp is under load? (similar to the voltage for the regulators).
Perhaps it may also be a good idea to change out transistor Q6 if it fails when hot and therefore causes the relay to disengage.
It seems to work fine when cold, the delay between power on and the relay shutting is a couple of seconds as it should be.
@rallyfinnen (great nickname by the way ) did you power all three regulators from the external power supply or just the +- 7.5V ones?
Question is if there is something wrong with this high coil voltage or if it is designed this way.
I have only managed to measure the voltage with the amplifier on and no load (have to have it partially dismantled in order to make the measurement).
Perhaps the rail voltage drop to a safer level when the amp is under load? (similar to the voltage for the regulators).
Perhaps it may also be a good idea to change out transistor Q6 if it fails when hot and therefore causes the relay to disengage.
It seems to work fine when cold, the delay between power on and the relay shutting is a couple of seconds as it should be.
@rallyfinnen (great nickname by the way
) did you power all three regulators from the external power supply or just the +- 7.5V ones?
check out this threads:
What happen to thule audio?
Thule Audio Components - Overview
Actually it was just an emergency solution (cost effective) that could be implemented quickly (which I designed) to increase reliability. Today I wouldn't do it like that anymore.
All unwanted overheating issues just arose because - for whatever reason - no separate transformer windings were provided from the toroidal (for + 5Vdig and +/- 7V5DC).
The best solution is creating of an outdoor power supply with extra print transformers 2x9VAC and 1x6-7VAC together with the exist toroidal transformer, so as fast recovery rectifier diodes and top quality industry capacitors with screw terminals. All other approaches for me not good.
If you don't want to do without a plug connection, you should choose a strong Harting version like the one from ASR Schäfer - go to
ASR Emitter I Basic: Vollverstarker & Endstufe - Test fairaudio
09330162616RS RS PRO | RS PRO Heavy Duty Power Connector Insert, 17 contacts, 16A, Male | 171-5736 | RS Malta Online
Heavy Duty Power Connector Inserts & Modules | RS Components
What happen to thule audio?
Thule Audio Components - Overview
Actually it was just an emergency solution (cost effective) that could be implemented quickly (which I designed) to increase reliability. Today I wouldn't do it like that anymore.
All unwanted overheating issues just arose because - for whatever reason - no separate transformer windings were provided from the toroidal (for + 5Vdig and +/- 7V5DC).
The best solution is creating of an outdoor power supply with extra print transformers 2x9VAC and 1x6-7VAC together with the exist toroidal transformer, so as fast recovery rectifier diodes and top quality industry capacitors with screw terminals. All other approaches for me not good.
If you don't want to do without a plug connection, you should choose a strong Harting version like the one from ASR Schäfer - go to
ASR Emitter I Basic: Vollverstarker & Endstufe - Test fairaudio
09330162616RS RS PRO | RS PRO Heavy Duty Power Connector Insert, 17 contacts, 16A, Male | 171-5736 | RS Malta Online
Heavy Duty Power Connector Inserts & Modules | RS Components
Last edited:
Hi Again
Thank you teifbassuebertr for your explanation! You really seem to be the go to guy when it comes to these peculiar devices. I have pretty much read everything you have written here on DIY Audio about this brand of amplifiers, very interesting!
I've actually made some more testing with a prototype power supply per Rallyfinnens suggestions.
I have used a cheap 12v transformer with a center tap and cobbled together a rudimentary rectifier and filter setup using a bridge rectifier and two caps that i had laying around. From this i get unregulated +16v and -16.3v for my regulators.
Now everything seems to work and the amplifier have been playing through some cheap speakers for a couple of hours.
For the more permanent solution i am thinking of replacing my simple 12v-0-12v 1000mA transformer with a small 9v toroid. the current draw that i've measured is 100mA on the + side (driving both LM337 regulators) and 33mA on the negative (for the LM337).
The question is if i should also add some snubber caps and some fuses on the
outputs of my additional power supply if something would happen to the bridge rectifier. (See scematic below).
The transformer is fused by the same fuse as the main transformer.
Any tips on improvement would be very appreciated!
On a side note the amplifier have always had a mechanical humm from the transformer, and by looking at the schematics there is an additional capacitor listed as not used (C148 in Net Filter schematic picture.)
If this cap were present wouldn't this serve as a primitive filter for the mains?
I am thinking of adding this cap and see if will have any effect.
I will also add heatsinks to the regulators and possibly the relay that i still think gets uncomfortable hot (around 65°C) probably due to the high coil voltage.
To be continued...
Thank you teifbassuebertr for your explanation! You really seem to be the go to guy when it comes to these peculiar devices. I have pretty much read everything you have written here on DIY Audio about this brand of amplifiers, very interesting!
I've actually made some more testing with a prototype power supply per Rallyfinnens suggestions.
I have used a cheap 12v transformer with a center tap and cobbled together a rudimentary rectifier and filter setup using a bridge rectifier and two caps that i had laying around. From this i get unregulated +16v and -16.3v for my regulators.
Now everything seems to work and the amplifier have been playing through some cheap speakers for a couple of hours.
For the more permanent solution i am thinking of replacing my simple 12v-0-12v 1000mA transformer with a small 9v toroid. the current draw that i've measured is 100mA on the + side (driving both LM337 regulators) and 33mA on the negative (for the LM337).
The question is if i should also add some snubber caps and some fuses on the
outputs of my additional power supply if something would happen to the bridge rectifier. (See scematic below).
The transformer is fused by the same fuse as the main transformer.
Any tips on improvement would be very appreciated!
On a side note the amplifier have always had a mechanical humm from the transformer, and by looking at the schematics there is an additional capacitor listed as not used (C148 in Net Filter schematic picture.)
If this cap were present wouldn't this serve as a primitive filter for the mains?
I am thinking of adding this cap and see if will have any effect.
I will also add heatsinks to the regulators and possibly the relay that i still think gets uncomfortable hot (around 65°C) probably due to the high coil voltage.
To be continued...
Attachments
Last edited:
I think a small fuse on the primary of the extra transformer should be enough for short circuit protection of the extra PS.
Why change the trafo? Place it far away (close to the main trafo) and any magnetic field will not be a problem. You can add a snubber on the secondary in case you have switch off ringing from the rectifier. I did it just because I could. I also did CRC filtering in the extra PS, since a little voltage drop was not an issue.
Maybe you could try different grounding from the extra PS, I connected the ground directly next to the main reg's on the PCB, but maybe connecting it to the main ground point would be an option too, not that I think it should matter..
Another thing that you could try is reverse the polarity (relative to main trafo) on the primary of the small transformer to see if it has some effect on hum.
The diodes and cap are supposed to remove small dc-components on the grid that can make the trafo hum/buzz. Not sure another cap will do much, but should not hurt either.. Check that the old cap is ok if you have hum/buzz from the transformer.
Why change the trafo? Place it far away (close to the main trafo) and any magnetic field will not be a problem. You can add a snubber on the secondary in case you have switch off ringing from the rectifier. I did it just because I could. I also did CRC filtering in the extra PS, since a little voltage drop was not an issue.
Maybe you could try different grounding from the extra PS, I connected the ground directly next to the main reg's on the PCB, but maybe connecting it to the main ground point would be an option too, not that I think it should matter..
Another thing that you could try is reverse the polarity (relative to main trafo) on the primary of the small transformer to see if it has some effect on hum.
The diodes and cap are supposed to remove small dc-components on the grid that can make the trafo hum/buzz. Not sure another cap will do much, but should not hurt either.. Check that the old cap is ok if you have hum/buzz from the transformer.
Last edited: