TR-1010 receiver restoration

Tandberg TR-1010 with a faulty channel (actually it is like an onion of problems, as I peeled away one fault I found another, very interesting..).

About Tandberg TR-1010

TR-1010 is the same as Tandbergistas favourite model TR-1000 with additional AM radio.

TR-1000 and TR-1010 is a sophisticated design: dual power supplies for the power amp (one massive transformer but two separate windings, two rectifiers and filter capacitors). A fine, regulated power supply for the pre amp, naturally with its own transformer winding. All discrete components. It also has a built in RIAA phono stage of very high quality. The whole unit is built like a tank, around a clever aluminium frame.

It is a capacitor coupled design, which means it has a capacitor after the power amplifier. This also means it has a power rail that swings from 0 to full rail voltage (+64V in this case). The output then sits in the middle of this voltage, 30V in the TR-1010. The other type of amplifier design, which is the standard today, is the Direct Coupled, where the output swings between a positive and a negative voltage and the output sits in between at 0 Volts. This eliminates the need for the capacitor at the output, but is risky in case something goes wrong in the power amp, so Direct Coupled designs often have a protective relay that sense if there is DC at the speaker output and in this case disconnects the speakers to protect them. You hear these amplifiers ‘click’ at startup, as long as everything is fine.
But the TR-1010 thus has no relay and no ‘click’ at startup.

I paid 639 SEK (about 53 Euro) for this unit in decent cosmetic condition. If it was working it would have been worth considerably more. Sold by the son of the owner who had passed away. The seller had tested it and said Right channel was silent. It had been in storage for a long time.

Restoration of Tandberg TR-1010 begins

Initial check

Inspected it visually on the inside and checked fuses. Then did a simple test, with headphones (headphones = the speaker outputs but with large resistors in series) and radio, the only thing that was heard on R channel was hum, volume independent, not a trace of radio. L channel though sounded good, with good reception. I didn’t bother trying some other source/input, because of the hum (on all inputs) I was pretty sure that there was a problem in the amp, either pre or power amp. My guess was the power amp.

Starting to locate problems

Measured midpoint voltage, the voltage on the output capacitor. It should be 30V, but it is 64V!
What can cause this? Lets see if we can rule out the power amp. Removed the signal cable from the pre amp, because it is possible that a leaky capacitor fed the PA (Power Amp) DC. Not likely, I then realized, because there is a 47uF cap on the last stage on the pre amp and a 22uF cap on the input of the PA, then they must both be leaky. But lets see what the PA does on its own. Problem persists.
So something in the PA makes it go up to full rail voltage. I had to take out the PA board.

I first suspected Q701, because voltage on its emitter, which is supposed to be 20V, was 0V.
While I suspected a transistor, the fault was actually a very leaky capacitor – C705. This is the first time I have encountered a capacitor that makes an amplifier behave like this.
Also replaced the other capacitors, they were not measuring up to spec, for example C704 measured 300uF but was supposed to be 220uF. A little out of range is ok, but this was 36% out of spec, a sign that the capacitor is not what it used to be. ESR (cap internal resistance) was a little high too (I use a Peak Atlas capacitor tester).

C705 is DC blocking for feedback. Q701 does what today is implemented as a differential amplifier. It compares input with output. When C705 shorted Q701 emitter to ground, the upper output transistors went up to full rail voltage.

I wrote a mini-article about “recapping”, should you replace capacitors or not, on the page Tandbergista Talks, which is a collection of small articles. Scroll down for to “Should you do a total recap or just replace bad components?“

The plan with this TR-1010 was to keep it as original as possible, which means only replacing what is faulty. This was not to be at all..
But at this stage, the first layer of the onion, considering the state of the Frako caps in Right channel, it seemed probably a good idea to replace them in the other channel too.

The big capacitor cans, 4 of them, for power supply filtering and outputs, seem to be ok and I plan to keep them. The brand is “Micro”, haven’t inspected them closer yet, only measured. There is close to zero DC leakage on the speaker outputs.

Restoration continues – Step 2

A project like this isn’t done in one go. Sometimes life comes and interferes with a restoration.
4 months later, let’s continue where we ended last time..

After removing the left PA (Power Amp) board as well, cleaning with a small vacuum cleaner.

The plan is to recap also the Left channel Power Amp, just in case. Right was in such a bad state that who knows how long Left will work.

Before recapping, cleaning the inputs and outputs. Also cleaned the speaker connector screws.

The other (Left) channel Power Amp

Left channel Power Amp, which someone has worked on before.

Why do we restore vintage hifi?

I sometimes think, “why do I do this”? Not only restorations, which really is hard work, but also document it on a blog? Because it is fun, challenging and I learn a lot. And it is satisfying. I guess there is also a not so small part sentimentalism, to keep vintage hifi going and at the same time a dissatisfaction with various things in the world today, so much of what is produced today is crap.
This blog, I suppose, was created for self-satisfaction, a way to document and “relive” my projects. Since then it has actually become quite popular.

If you have read other of my posts, you know that I am just an amateur, not a pro. With dedication though, I managed to revive quite a number of Tandberg receivers. This is the eight year since I started trying to repair my own hifi.
If you are thinking of getting into restoring vintage audio, buy a simple model and try on. Tandberg TR-1010 is not a good model to start with, it is quite complex. I would recommend a Japanese unit, but not a monster receiver. Or if you are a fellow Tandbergista, perhaps a TR-200 or Sölvsuper 11. These are easy to work on.

Sometimes you find tracks of earlier technicians. Like the non-standard screw above.
This unit is in good cosmetic condition but have had some work done on it.

The unique Tandberg construction and a few tips about Tandberg chassis screws

Tandberg receivers are built in a clever way with aluminium frames. The text below is from a forum thread at Audiokarma.

Tandberg started out making portable radios for the Norwegian armed forces back in the 1930’s, IIRC. They held onto that aluminum frame concept for another what, 70+ years? Nice to never have to worry about rust either, but you do want to be careful with removing and reinstalling the sheet metal screws into that softer metal. Take the time to rotate backwards until you feel the original grooves start to engage, then rotate forwards and don’t over-torque when you tighten them. Don’t use electric or other powered drivers on them either, surefire way to ream out the holes and in some cases that means you’ve made the chassis grounds mechanically (and electrically) unreliable. (by JDurbin)
https://audiokarma.org/forums/index.php?threads/tandberg-receiver-info.817780/page-3

Signal tracing, a faulty Mono L/Mono R/Stereo switch

Reinstalling both Power Amps and testing the TR-1010 unfortunately still produced no sound in Right channel. How disappointing, or not, because signal tracing is fun, lets see what’s wrong.
It took a lot of work to figure this out, because the behaviour was so weird. I traced it to the Mono L, Mono R, Stereo switch set. Right channel didn’t pass. It would have been nice to have two signal generators, to inject different signals.

Anyway, I could not think of anything else than a mechanical problem. Had to remove the front. The switch set was sprayed with an oil-containing (lightly lubricating, which I seldom use here) electronic cleaner. Then DeOxit and resolder. Suddenly we had signal coming thru it! I have never experienced a switch so dirty that not a single electron goes through it, and then starts working normally after the clean-and-resolder trick.

Cleaning

While I had the front off, it is a good idea to do a good clean.

I tried my new ultrasonic cleaner on the knobs.

One metal spring inside a knob was lost, so I had to make it myself.

The flippable panel is regreased. I have noticed that the original grease seems to have a tendency to dissolve the black paint on the bottom. I remove the old grease carefully. Not sure what causes it, before I thought it was my cleaning process, but for this unit I used only soap and water, so I think it must the old grease.

Testing (some more trouble)

To be able to test it with speakers and a good source I needed to remove the Sölvsuper 11 currently connected in my setup. This was another interesting restoration, which will get its own post some day.

Unfortunately it still did not work, at least on Tape 1. I know that the amp worked though, so I suspected the inputs and when touching the cable now in the Tape 1 input = obvious case of bad contact. This is a common thing on all vintage receivers. Easy to fix.

While the back cover is off, I cleaned the RCA connectors.
I have heard that this is pure silver connectors. Won’t swear on it, but I think it is.
That is why they are black on the surface. But silver oxide, from what I have heard, conducts, so fret not about them looking dirty or oxidized, no need to do some hysterical or abrasive polishing. Copper oxide is different. I just used a little DeOxit and gentle swabs, after which I washed with a little bit of IPA spray. I know these inputs work well even if they look black. Tandberg did not skimp on anything, they used top class parts.

Tandbergistas from all over the world

If you live outside Scandinavia and you have a TR10xx, you know that you have a very special piece of hifi gear? Here in Scandinavia the brand is well known and treasured. We have access to quite a lot of Tandberg information, but maybe not so outside Scandinavia. This is why I write in English. I am happy to see that this blog reaches around the globe
I sense that Tandberg is specially popular in Poland, the UK, Germany, Australia and the US. It is great also to see a few Tandberg videos from Japan and Korea on Youtube.

It works, first impression

Now it seemed to work. I am thinking what to do next. Shall I leave it as it? Honestly it does not sound as good as my TR-1000 Magnum Opus. But that project was something extraordinary, a cost-does-not-matter restoration. This project was about just making it work.
It sounds milder, softer, a little subdued. TR-1000 Magnum Opus is clearer and has more space/air though, it is kind of holographic like a tube amp.
This TR-1010 has been in storage, maybe for as long as 30 years (not sure) and needs some time to wake up. Plus the new capacitors. And I haven’t even cleaned the switches (except Mono/Stereo). Or it could be that some capacitors in the pre amp are not fresh and would benefit from replacement. I will think about it and for now keep on listening to it for a while.

Another interesting thing is that I prefer the TR-1010 without Loudness. I normally always use Loudness. The TR-10xx Loudness has sometimes a tendency to be a bit too much, depending on the rest of your setup, and the music. On this TR-1010 I just listen and enjoy it with Loudness off.
(Later, this would change, just a proof of how sound can change during a restoration..)

The vintage style power plug – “it does not fit into contemporary wall sockets”

What to do with power plugs that have no ground, but are big and does not fit into todays grounded outlets? Replace the plug is an option. But I would rather not do that on this unit (though I confess I have done that earlier). I have DIY’ed adapters. But with several receivers in use, it would be nice to have a power strip for vintage plugs. So I built one.

This power strip was a flea market find. Swedish made and vintage. Proper metal inside that cleaned up well. Simple but clever construction, heavy plastic. Much better quality than most of the crap they sell today. This was made to be able to be repaired, todays units you can’t even open. It is a joy to work on such well made things.
Some may have opinions about grounded plugs this and that, but I don’t care. This means we can run several vintage hifi gear at the same time without having to replace plugs.

Easiest is to buy a female non-grounded socket. You can find them anywhere even today. Then build your own adapter with a grounded plug in the other end, like a single-variant of the above.

TR-1010 Restoration continues – Step 3

Much later. It is now late 2024. This project was done over the course of a year.

As often is the case, more problems revealed themselves. Intermittent problems are the worst. Left channel disappeared at times. I traced it to the balance pot. Tried DeOxit and resoldering. It worked, for a while.

There was also noise in Right channel on startup. I suspected the silent-start-circuit. A small circuit in between the power amp sections in the schematics, below. I replaced the capacitor, to no avail. The problem was actually that I had forgot to attach the blue wire on point 444, from the power amp to the silent-start-circuit. An unforgivable error that could have shorted something when the cable hanged lose under the power amp board, but luckily it didn’t.

Left and Right channels were not balanced. Right channel peaks at 10W. I measure midpoint voltage and it is too high on Right (40V, should be 30V), adjust with the trim pot. This is not how the service manual recommends adjusting midpoint voltage, but it will have to do for now (service manual tells you to connect an oscilloscope to the speaker outputs, inject a 1000 Hz signal and adjust for symmetrical clipping. I later checked and yes there is symmetrical clipping, why would you have to do it the service manual way?).

No FM stereo lamp. It just a burnt out bulb, luckily the FM circuit is ok. Replaced with NOS Philips 24V 50mA E10 lamp. It will last, maybe another 50 years, which the China made crap you buy today will not (I have had such lamps last only a couple of months).

Adjusting Quiescent current, 92mA on both channels (service manual says 100mA after 15 min). Method is like in the service manual, measuring on the power board. You have to desolder two jumpers. Actually you can measure on the power amp card directly, but it is fiddly to get the probes down there, specially on Right channel. I sometimes do this anyway to avoid having to solder on the power board, which you see in the photo below, to the upper right.

Measuring the regulated power to the pre amp and radio, I do not like what I see. There is 50Hz on it and 23V is a little low (25V normal). I end up rebuilding (recapping) the regulated power supply completely. Some caps were tired with a high internal resistance (ESR). For example, a 10uF cap measured 7 ohm, while the new Nichicon replacement measures 2,4 ohm. The big 1000uF cap is often worth replacing, it measured 20 ohm ESR. Photo below. It seems we have eliminated (lessened) 50 Hz noise on the regulated 25V supply. This is weird because there is a little rectifier in this supply and you would expect 100 Hz. Maybe it was coupled from the transformer. Sometimes I’m not quite sure what’s going on.

Ŵhile working on the regulated power supply, I accidentally broke a pin for a 25V cable. Or it was probably already bent and half broken. Resoldered it. Several other pins were bent, they are supposed to point right up. The 25V pin to the right is also bent. I did not bend them. Space is tight down here, be careful.

How about another, new problem? Keep peeling away.. White noise on left channel. It is very low and not volume dependent. I suspect a transistor in the pre amp, or a tantalum capacitor. The problem comes and goes, which does locating the source so much more difficult.

I connect headphones, this makes it easier to hear the white noise, which is like radio static. Something very mysterious happens – I hear a beep, every 5 seconds, length about 1 second. Does AM leak into a circuit, or a transistor? Did I pick up a mobile phone sending? I have no idea. It might have been the AM switch, after motioning them the noise disappears.

There is still a channel imbalance at some volume levels and it is intermittent. I suspect the volume potentiometer, it does not “feel right”. However – signal tracing shows good signal in on volume pot. Ok signal out (measuring on the viper), although it stumbles in some positions.
Measuring signal in on the power amp, there is imbalance. There must be a problem in the pre amp.

I replace all electrolytic capacitors in the pre amp, both sides. I wasn’t going to, but there is too much weirdness going on here.

Recapping the pre amp was a good decision. Most of them were ok but a couple were far out of spec.

The pre amp and selector boards are cramped, so I have this silly trick to insert capacitors. Couldn’t find my “surgery type” tweezers, those that are normally closed and you press to open (contrary to normal tweezers). Normal tweezers are a pain to use here. So I took a pen, attached the capacitor with tape, inserted, soldered and pulled out.

There is massive imbalance. And there is noise in Left channel on startup (not every time..).

There is only one thing to do, use a second oscilloscope. A while ago I bought this nice analog Philips scope. Now I can attach that to the speaker outputs and monitor if we have imbalance (because it sudden goes normal, what I call an intermittent fault), while I use the other scope to trace the signal through the pre amp.

Of course, you can use cooling spray and a hair dryer to see if you can provoke a reaction, I did (at least cooling spray), but I didn’t get any wiser. I also resoldered all joints in Left preamp. This wasn’t the problem.

I deduce that we have two problems – a problem in the Right side volume potentiometer. And something in Left channel pre amp, I suspect a transistor or tantalum cap.

What is tantalum capacitors?
Tantalum capacitors are a type of electrolytic capacitor that uses tantalum metal for the anode. These capacitors have a very high capacitance-to-size ratio. They are polarized.

My electronics mentor, Stein, says: Tantalums fail notoriously because they can’t tolerate the slightest bit of mis-polarisation. Imagine an AC sine that is negatively tilted in relation to the DC offset.

I replaced all three tantalum caps in Left channel. The first 2,2uF was probably ok, but the second 2,2uF was suspect and possibly the last 47uF. Left channel startup noise disappeared after replacing them.

Why did Tandberg use tantalums here? If you know, do comment. I’ve seen some service technicians replacing them with electrolytics, but I replace like for like. I think (not sure) you can find both types in these positions on Tandberg gear. Tantalum caps seem to be quite common in Tandberg pre amps. I have heard that some studio engineers and technicians swear by their sound, like in vintage mixing consoles, that they have an “analog” character..

I measure power output. TR-1010 is supposed to deliver 35W into 8 ohms. I have a 8,2 dummy load and it delivers 34,8W. There isn’t perfect channel balance and Right channel peaks a little before Left.
I need to replace the volume pot.

Thoughts on Loudness (skip to Replacing the Volume Potentiometer unless you are a Loudness nerd)

On the TR-1000 Magnum Opus project I experimented with modifying Loudness – to see if I could have a little less Loudness effect, specially a tiny bit less bass boost. And you may ask, why not just use the bass control? Yes, that’s an idea, not sure why, it just isn’t the same thing..
This is a stupid thing to do, so don’t do it. I did it just as an experiment and to figure out how Loudness works.

I test the TR-1010 and compare to TR-1000 Magnum Opus. I need to revisit the Loudness modification on TR-1000 Magnum Opus. It was a silly thing to do, although interesting. I like the sound of the modified TR-1000, but it can be a little harsh in the top end sometimes. And now when I went back to study the original Loudness analysis, I wonder why I did that. Wouldn’t it have been better, in theory, to put a trim potentiometer after the Loudness tap, rather than the resistor to ground? (a problem is that this is probably difficult to do without modifying the PCB, which is out of the question).

The reason I wanted to take the opportunity to experiment like this is because I had to replace the volume potentiometer. I have NOS Noble pots, 25k with Loudness tap. They are smaller but will fit if I solder on longer legs. This means I could also put on an attached trim pot, an “appendix”, between the potentiometer leg and the PCB. I chose a dual pot, 2,5k. I will not need to alter anything on the board or in the circuit except this “appendix” added to the new pot..

Importantly – this is a modification which is reversible, to cut board traces or something like that is out of the question. For the TR-1000 Magnum Opus, to return it to original Loudness I just have to turn/adjust the trim pot. And the same on this TR-1010 (even easier here, just turn it fully clockwise for 0 ohm). I don’t recommend you do this. Tandberg receivers are well designed as they are.

The new volume potentiometer isn’t ideal, it has detents (click positions). If I some day find a more suitable potentiometer I can relatively easily replace it (not super easy, this took me 4 hours).

Replacing the volume potentiometer

A note on the Loudness mod

Don’t expect an amp to sound right when you are replacing capacitors or just after. It takes some time for them to sound right. I actually write a “burn in diary”, believe it or not. It is very interesting.
This is part of the TR-1010 burn in diary:

250105 4 hours after preamp recap, a bit restrained, bass does not suffer as much as midrange and treble, especially the higher treble is hesitant and not open. Maybe initially the bass was a bit swollen from the beginning, which made me want to modify the loudness circuit.
250106 5 hours
250107 13 hours – total 27 hours.
250108 15 hours – total 42 hours. The sound up to here is about the same.
250109 13 hrs – 55 hrs total.
251010 11 hrs – 67 hrs total. Now it starts to sound better, crisper treble, clearer and less veiled over the entire register, an elegant and airy sound begins to emerge. It is possible that the bass has ‘matured’, sharper edges at the same time as it has calmed down and is less prominent.
250111 2 hrs. Does not sound good, lacks something, tired and cloudy, not enough clarity, a little mushy. With TL-1520. H10 sounds better, more soulful too.
250112 3 hrs.
250113 5 hrs – total 75 hrs.
250114 3 hrs.
250115 3 hrs – total 81 hrs. Starting to open up more, not listened carefully.
..
Then it continues to about 100 hours, when it starts to sound “normal”. I have other TR-1010 and Tandberg receivers to compare with. At 120+ hours we have arrived at the right TR-1010 sound.

To start modifying loudness before it has played >100 hours is idiotic. But, I did the modification as a study and if I was going to do it I had to do it at the same time as replacing the volume potentiometer. I thought the mod (when activated) took something away from the original sound, it did not sound right, the kind of choco fondant sound I describe under TR-1000 Magnum Opus wasn’t really there. It sounded kind of “modern”, like too clean and neutral. I want the chocolate sound.
Experimented with decreasing the loudness resistor, from 448 ohm to 136 ohm. Much better. We are almost back to normal. I will continue to experiment and compare.
In any case, I conclude that modifying the loudness circuit is futile. It is like using sugar-free and fat-free chocolate in a cake.

How does a restored TR-1010 sound?

The volume pot replacement worked. We have channel balance. The popping at startup is gone too.

I have been test running it for a couple of days.
I might change the foil on the Stereo and Loudness indicators.
Total time spent: 45-50 hours, at least.

But, we’re not finished yet.. There’s white noise on Right channel. Not too disturbing.
Channel imbalance appeared again, at times. Motioning switches, carefully spraying DeOxit.

23/2 2025.
Replaced the tantalum capacitors in Right channel (replaced them all in Left earlier). Noise in this channel disappeared. I discovered that C527/C528 were actually 10uF, while in schematics they are 2,2uF. I replaced them with 10uF tantalums. For C537/C538 I replaced the tantalums with 2,2uF Elna Silmic II electrolytics.

Lets test it

Time for a serious test listen. It’s cleaner than I expected, but still “creamy”.

“Effortless”

The combination, seen below in the blurry photo, is TR-1010 with TL-1520 speakers. The Astrud Gilberto album is a wonderful production. Though I have listened to it hundreds of times, tonight I discovered new details, like how cool the subtle bass groove on O Morro (Nao Tem Vez) is. TR-1010 and the small Tandberg speakes are a nice match – effortless, musical and rhythmic. TR-1010 isn’t a light sounding receiver, of course, far from it. But maybe that’s why it pairs so well with the gracile and lively TL-1520’s. These little speakers, I have praised them already. If only one word would describe them, maybe it would be “effortless”. Bass is snappy and quite deep considering it’s a small closed box design. There is a dry character to the treble, some say this is a trademark of paper tweeters. In some cases there can be a hint of harshness in the higher highs. Not sure if it is an album mixing thing or the gear, because this is in every sense far from a harsh setup.

Most music I listen to is pre 1970. There are exceptions, some modern music that is not over compressed and too heavily eq’ed (I often find contemporary recordings sounding too “thick”, not sure how to express it, like artificially pumped up). My favourite era of well recorded music, 60’ies and 50’ies jazz for example, like the classic Astrud album, were made for a setup like this. The Japanese album is a later production, but it’s not hard, digital or compressed. TR-1010 with TL-1520 is a setup well suited to acoustic, well produced recordings.

If you own a TR-1000 / TR-1000 – what do you pair it with? How do you think it sounds? Did it need service? Do you think my chocolate cake analogy makes sense?

A little TR-1000, 1010, 1020, 1040 and 1055 buyers guide – common problems.

TR-1040 and 1055 are a different design from TR-1000 and TR-1010), as mentioned in the beginning, but I include them here because the typical problems are similar, except that the 1040 and 1055 also has a relay that may have oxidized contacts, like all such receivers.

The TR-1000 series is well built and it seems generally people don’t have too serious problems with them. Typical problems:
1) Dirty pots and switches. The source switches and filter switches are almost guaranteed to cause problems, at least one or two of them, on a unit that has been in store for a long time. But it isn’t difficult to remedy, a little DeOxit, working the switches.
2) Cracked solder joints. Specially on the inputs in the back. I have personally not seen too many problematic joints on TR-1000 series units, except the input jacks solder points on the boards. This is typical problem for all vintage receivers.
3) Capacitors in the regulated power supply. I have seen a few of these gone bad, so I routinely replace them. But in other places, not so much a problem. Occasionally a smaller capacitor in the signal path is bad and needs replacement. The smaller caps in the power amp seems to age faster than the others, so they may be higher risk, like in the TR-1010 in this post (I do not mean the large filter caps on the output). I haven’t seen any bad power supply filter caps (power amp) or output capacitors in any of my TR-10xx’s. Not sure if this is typical, but I have heard that these are of very high quality and I don’t recommend changing them unless they are out of spec or leaky.

My experience is, and I have heard that other Tandbergistas say the same, that the TR-1000 series does not suffer from bad resistors or bad transistors. I have almost never had to replace a transistor or resistor in these. The later TR-20xx series though, I have had a few small signal transistors that caused problems and were replaced.

If you pack one for shipping or let someone else pack one that you bought – please make sure it is packed carefully! The potentiometers are fragile, packaging must be done so that there is no pressure on the knobs and that a potential shock to the parcel does not transfer to the potentiometers. See my guide to pack them for transport on the Tandbergista Talks page.

The TR-1000 series is robust and can be repaired. The construction is a little different if you’re not used to Tandberg. Not difficult, just different. The TR-1000 series models are compact, this means it is a bit cramped inside, not much empty space. But the internal connections are well marked and easy to remove. The power amp sections, as you see above, slides out the back and can be fully removed to work on.

Update – thoughts on Loudness and the troublesome filter switches on Tandberg

The Loudness modification on this TR-1010 is different from TR-1000 Magnum Opus. Normally you can’t do what I did on this TR-1010, because I put a potentiometer on the Loudness tap when I replace the volume pot. On the TR-1000 Magnum Opus I replaced the original circuit resistors (R507 below) with a trim potentiometer. But in the end I didn’t quite like the sound on the TR-1000 Magnum Opus with the increased R507 resistance, so I decided to reverse it back to original recently.
On this TR-1010 I leave the dual trim pot in circuit. If I don’t want it, I’ll just set it to zero Ohm. Now I left it at about 137 Ohm. The difference is miniscule. With a dual channel AC mV meter I experimented with frequency measurements, plotting on paper, of course because I like analog things. It showed that my LTSpice simulations were correct (at least the shape of the curves). Raising the resistance on the trim pot here, which means between the Loudness tap on the volume potentiometer and the Loudness circuit, flattens the Loudness curve. The difference at 137 Ohm is only about 1 dB at 250 Hz, for example. I leave it at that. I see no need to fiddle with Tandberg Loudness values.

The Lo Filter and Hi Filter 1 switches

On this TR-1010 dirty switches was a constant nuisance, more exactly Lo Filter and Hi Filter 1. Only these two, because they’re in series with the signal. If there’s oxidation in the switch it can cause channel imbalance. I’d say it is the most common cause of sudden channel imbalance on my Tandberg TR-10xx receivers. Usually motioning them and a little injection of DeOxit helps. On this TR-1010 the problems were persistent, specially when it was left unused for a while, I always had to motion these switches. I don’t like to modify things (which sounds contrary, considering the above), but how about bypassing these switches?

Jumpers on Lo Filter and Hi Filter 1. If for some reason you want to revert back to original and use these filters, just desolder the jumpers. I haven’t done it on any other unit and I’m not saying that it is necessary, just in case your switches are really stubborn it can be done. You could take them out and make a thorough physical clean, if you’re good at fiddling with mechanical switches, I guess that is to be preferred, but there is the risk of springs flying, plastic parts breaking and you won’t be able to put it back together.