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Re: Rotel RT-1084 Help Needed

daschwa79
 

Adding an update and some pictures.  I took out the tuner module(broke some things along the way) and removed the shields.

The tuner board has a top and bottom, pictures are attached and labeled as such.  The coils are on the top.

After I put it back together I tweaked some coils and eventually got it to where my preferred station would come in quickly in HD.  The coil on the lower left of the board seemed to increase volume of the analog singal.  The coil on the upper right (Red circle) seemd to effect ability to lock in HD reception.  All stations still show one bar in Analog mode.  This was a very unscientific process (obviously without test equipment)

I'm pretty certain this thing is seriously out of alignment or has a bad part somewhere, or both.   Without a service manual not sure of a way forward but as my preferred station is working could use this as an HD tuner for a spare room.

My hopeful side thinks this thing could still be salvaged.  Any further ideas from the experts appreciated.

Dave



locked Re: Measuring and matching 10.7 MHz ceramic filters

Radu Bogdan Dicher
 

After recalibrating - which I'm about to redo, as I'm not 100% sure of all steps - I'm getting this out of a 150kHz filter (JA). I trust I need to recalibrate or maybe the device is subpar?... I'm invariably getting about 5dB lower readings on the left/lower side of the response plot. I'm definitely willing to persist quite a lot, but I'd really love to figure out where the deficiency is...
Radu. 
image.png


On Wed, May 6, 2020 at 8:12 PM newaag via groups.io <newaag=yahoo.com@groups.io> wrote:
Here is a wider frequency scan showing, for comparison, the response of both the previous Murata 280 (red) and Murata 150 (black). Note, these are better examples of almost perfect looking filters. They don't all look this good, for frequency or shape. As one can see, the group delay gets very noisy outside the filter passband. 
Bob


locked Re: Measuring and matching 10.7 MHz ceramic filters

newaag
 

Here is a wider frequency scan showing, for comparison, the response of both the previous Murata 280 (red) and Murata 150 (black). Note, these are better examples of almost perfect looking filters. They don't all look this good, for frequency or shape. As one can see, the group delay gets very noisy outside the filter passband. 
Bob


Re: Need help with Mitsubishi DA-F20

newaag
 
Edited

I wanted to update this topic with more information. Here's a quick recap of the problem. The tuner, a DA-F20, did not play in stereo, and reception was poor.
A quick alignment showed the both detector zero adjustments were way off. The narrow detector on this unit is used to enable both muting, and also stereo reception. If that detector is not at zero, stereo will not engage, regardless of any other settings (muting off, etc). So this was a quick fix.
But there was more wrong - the reception sensitivity was poor, and distortion measured high.
It turned out the crystal oscillator was off specification, (as per previous messages), tuning the IF to 10.67 instead of 10.70. It appears the previous tech who worked on this unit also saw this, and tried to correct it, but installed the wrong ceramic filter set in narrow (4 filters). They were marked, in handwriting, 10.72 on each filter, so they were obviously tested and sorted before installation. But the correction went the wrong way - 10.67 filters should have been used.  
It was likely an easy mistake to make, though. I frequently do a very low RF signal test, in IF narrow. Then tune the RF signal generator slightly above and below the station frequency (say 98.10 MHz), to see if noise goes lower and sensitivity improves slightly off frequency. It is a good test for crystal oscillator based tuners. 
For this tuner, initially the sensitivity improved, with lower noise, with the stereo generator tuned about 30 kHz above the actual target station - in this example, it was best at 98.13 MHz. 
This could give one the impression that the IF filters need to be moved "up" in frequency from 10.70. In fact, if the actual IF is measured, it would be where the oscillator told it to be, at 10.67. This is due to frequency inversion, as noted in previous messages. But...
The "fix" may not be using new narrow filters selected for 10.67 MHz. Because one needs to measure the other IF (wide) IF path, and see where it is "centered". In this case it was measured, and found to be correct, at 10.70 MHz. When going to all this trouble, you want the IF path centers to "match" each other, AND also match the oscillator. And in this tuner, the wide LC filter is a closed box and non-adjustable. So the wide IF drives which filters you select for narrow, and where you adjust the crystal oscillator.
Long story short - a new 10.000 MHz crystal was installed, and the 20 pf cap was selected so it ran exactly on frequency. Then 4 new narrow filters were fitted, all selected for 10.700 MHz. 
Then the tuner was completely re-aligned - this is a MUST after moving the IF frequency (from 10.67 to 10.70) and fitting new filters.
These changes completely transformed the tuner - it now is both sensitive, selective, and tests very low for distortion in both wide and narrow, with excellent stereo separation (over 50 dB in both wide and narrow).
That is basically the end of the story. I will document the alignment "how to" specifics elsewhere at a later time. The service manual could be a lot better for this unit.
Bob


Re: TU-X1 - MODIFIED BY JOSEPH CHOW OF AUDIO HORIZONS [ME TOO!]

sedond
 

well, it's been a lot of years since i've used joseph chow's services, and i had very good results.  15 years ago, he converted a japan-spec acuphase t109 for me, and upgraded it as well.  the work was very good.  a couple years later, i had him convert a japan-spec sansui tu-x1 for me, he also upgraded it.  again, i was pleased with the work.  in fact, a couple years later, when i started hearing audible crackling noises in the audio output, i sent it back to him, and he replaced aging caps that were causing the noise.  i was only out the shipping costs to get it back to him.  no, i did not have him go through the entire tuner, replacing everything the 1st time around - i can only imagine what it would cost to do that to a tuner like the tu-x1.

perhaps his efforts have diminished more recently?  i would suggest reaching out to him directly with any issues you may have had.  in my experience, he always tried to make things right.

ymmv,

doug s.

On Tue, May 5, 2020 at 12:42 PM, Mark Hubbard wrote:
Unfortunately, I too have had negative experiences with Mr. Chow's work. A few years ago he sold me a modified Music Hall mmf-25 CD player, supposedly having upgraded parts and enabling it to be used as a digital transport with an external DAC as well as a stand-alone CD player. As a CD player, it worked for a while and then lost output to the right channel. I took off the cover and noticed a small component that he added had become unsoldered at one end. A local repair shop was recently able to resolder the joint for me at a cost of $50, but when I try to use the mmf-25 as a transport, it doesn't work at all. Add to that the difficulty I had getting the unit in the first place (requiring threatening him with a bad review on Audiogon before he finally shipped it to me), and I too cannot recommend his "upgrades." I'm only out about $400 altogether, and the CD player works as such, but I would not buy equipment or services from him again. Your mileage may vary.


locked Re: Measuring and matching 10.7 MHz ceramic filters

newaag
 

For comparison, here is the same filter. Blue plot is the standard response. The black lower plot shows the effect of adding a 180 pf C to the output (instead of 10 pf).
Insertion loss goes way up (response goes down)
Bob


locked Re: Measuring and matching 10.7 MHz ceramic filters

newaag
 

This is a standard Murata 280 kHz filter swept with 404 points (4 segments). The total span is 600 kHz, centered at 10.7 MHz. Group delay is below. 
I did a right click and adjusted the group delay Y axis amplitude min and max settings. This is helpful to compare different types of filters, which is difficult using the default "autoscale"
Also - there are two plots shown. The first one is in blue, it was taken first, then used "set current as reference". I then removed the 10 pf cap, and did another sweep. 
The darker black line shows the effect of removing the Murata recommended 10pf cap on the output. The group delay actually looks flatter. The response curve shifts slightly to the left when 10pf is removed. 


locked Re: Measuring and matching 10.7 MHz ceramic filters

newaag
 

This is a screen shot from nanosaver showing how to setup a band centered at 10.7 MHz - that you can recall later.
Note is is accessed from Display Settings" > "Manage Bands"


Re: TU-X1 - MODIFIED BY JOSEPH CHOW OF AUDIO HORIZONS [ME TOO!]

Mark Hubbard
 

Unfortunately, I too have had negative experiences with Mr. Chow's work. A few years ago he sold me a modified Music Hall mmf-25 CD player, supposedly having upgraded parts and enabling it to be used as a digital transport with an external DAC as well as a stand-alone CD player. As a CD player, it worked for a while and then lost output to the right channel. I took off the cover and noticed a small component that he added had become unsoldered at one end. A local repair shop was recently able to resolder the joint for me at a cost of $50, but when I try to use the mmf-25 as a transport, it doesn't work at all. Add to that the difficulty I had getting the unit in the first place (requiring threatening him with a bad review on Audiogon before he finally shipped it to me), and I too cannot recommend his "upgrades." I'm only out about $400 altogether, and the CD player works as such, but I would not buy equipment or services from him again. Your mileage may vary.


locked Re: Measuring and matching 10.7 MHz ceramic filters

newaag
 

On Mon, May 4, 2020 at 10:27 PM, Radu Bogdan Dicher wrote:
Bob, David - does this look better? Readings largely OK? More filters data would likely make it more reliable to vet the setup, but this is what I got this far.
It still looks slightly off, but better. What filter are you using? It looks like a defective filter from your displays.

Can you try another 2 or 3 filters, both 280's and 150's? You should have some of those I believe. If no change - calibrate the nanoVNA centered at 10.7 MHz, and save it. Most come with factory cal, but it may not be spot on, or was corrupted...
You can do it on the nanoVNA unit without PC and save it into the last of 5 registers. But restrict the bandwidth first to 800 kHz centered at 10.7 MHz. And do it at the end of the SMA cables. PS - use a chopstick or or stylus to tap the screen if you have big fingers like me. Wait until the selection goes green before releasing. 
The filter should look symmetric on both sides on the bottom. 
You can also cal from nanosaver, and save it there on the PC.
For a decent filter, the group delay should be mostly symmetric on both sides, with mostly equal side saddles. But not every filter is decent. 
Bob
 


locked Re: Measuring and matching 10.7 MHz ceramic filters

Radu Bogdan Dicher
 

Alright, revised setup, plus a singular reading, enclosed. Hopefully, this gets someone else a bit better advised on dos and donts with this neat thingie. 

Bob, David - does this look better? Readings largely OK? More filters data would likely make it more reliable to vet the setup, but this is what I got this far.

For shits and giggles, the 10pF is indeed a 6kV part... ;)
Radu. 


On Mon, May 4, 2020 at 8:55 PM Radu Bogdan Dicher via groups.io <vondicher=gmail.com@groups.io> wrote:
Bob,
Thank you, I actually got a couple of those from my local supplier. In an urge to support them during unprecedented times of hardship, I decided to wait 3x Amz wait times and lose an arm and a leg, but... anyway. 
I have some perf board. Did you have to enlarge the holes to fit the SMA plugs? I'm having a hard time fitting them into the holes. 

On Mon, May 4, 2020 at 8:14 PM newaag via groups.io <newaag=yahoo.com@groups.io> wrote:
Radu
I'd suggest you get some sma connectors and go right to them with the nanovna sma cables. I got mine at amazon, I think this was the one I bought for around $10. shipped for a bunch of 'em. Perfboard is fine for me.
https://www.amazon.com/Uxcell-a16011100ux0048-Female-Connector-Adapter/dp/B01DO06QYQ/ref=sr_1_2?dchild=1&keywords=sma+board+mount+right+angle&qid=1588648208&sr=8-2
 
Bob


locked Re: Measuring and matching 10.7 MHz ceramic filters

Radu Bogdan Dicher
 

Bob,
Thank you, I actually got a couple of those from my local supplier. In an urge to support them during unprecedented times of hardship, I decided to wait 3x Amz wait times and lose an arm and a leg, but... anyway. 
I have some perf board. Did you have to enlarge the holes to fit the SMA plugs? I'm having a hard time fitting them into the holes. 

On Mon, May 4, 2020 at 8:14 PM newaag via groups.io <newaag=yahoo.com@groups.io> wrote:
Radu
I'd suggest you get some sma connectors and go right to them with the nanovna sma cables. I got mine at amazon, I think this was the one I bought for around $10. shipped for a bunch of 'em. Perfboard is fine for me.
https://www.amazon.com/Uxcell-a16011100ux0048-Female-Connector-Adapter/dp/B01DO06QYQ/ref=sr_1_2?dchild=1&keywords=sma+board+mount+right+angle&qid=1588648208&sr=8-2
 
Bob


Re: Harman-Kardon F500 FM Tuner Restoration

newaag
 

On Mon, May 4, 2020 at 03:00 PM, Joseph Strickland wrote:
Do we know if more of the boards for the LM4500 will become available?

I'll let you know, I may try a new supplier, should be a month or two most. The one I used was closed until things got better.
Bob


locked Re: Measuring and matching 10.7 MHz ceramic filters

newaag
 

Radu
I'd suggest you get some sma connectors and go right to them with the nanovna sma cables. I got mine at amazon, I think this was the one I bought for around $10. shipped for a bunch of 'em. Perfboard is fine for me.
https://www.amazon.com/Uxcell-a16011100ux0048-Female-Connector-Adapter/dp/B01DO06QYQ/ref=sr_1_2?dchild=1&keywords=sma+board+mount+right+angle&qid=1588648208&sr=8-2
 
Bob


locked Re: Measuring and matching 10.7 MHz ceramic filters

Radu Bogdan Dicher
 

I put this back together with 301ohm, 56.2ohm resistors and 10pF cap, and still got the misshapen curve. Tried then to tinker with the physical design of my setup - for instance, not cross the patch cables, eliminate the segments of wire, and realized this is it (or is a large part of it). The curve gets severely influenced by all these details. I think I'll have to put this together much more carefully, maybe a PCB with ground plane, all by the book. And then see what this truly shows. 

Fair warning, everyone, quickly slapping this together will not render much in terms of filters' tests. 

Thanks Bob, David, for your valuable points. 
Radu. 


On Sun, May 3, 2020 at 8:15 AM Radu Bogdan Dicher via groups.io <vondicher=gmail.com@groups.io> wrote:
David - yes, 18pF. All of the micas I have have actual, literal markings, and I don't really trust my DMM with such low values. 
I assume this may be caused by the less than ideal values of both resistors and cap. And as things go these faithful days, if you're trying to sustain your local parts supplier - it's amazing they still exist in REGULAR times, IMHO - as they operate with the slimmest staff and trimmed logistics, you get your parts much later than you'd typically expect them.
Will report later when I can reestablish the setup.
Thank you for your feedback. 
Radu. 

Virus-free. www.avg.com

On Fri, May 1, 2020 at 1:22 PM David Platt <dplatt-groups@...> wrote:
On Thu, Apr 30, 2020 at 08:13 PM, Radu Bogdan Dicher wrote:
Bob, David,
What can I say, caught red-handed. The cap is also the closest I had at hand (18pF); I really only intended to make it work generally speaking, nail the setup.
Out of curiosity, Radu, is that a measured 18 pF, or from reading the markings?  I sorta wonder whether it might be a "181" marking, which would be 180 pF.

Or, as Bob said, the perturbed shoulders might be from a less-than-ideal resistor value (looks like 270 ohms there, which is definitely on the low side), or maybe parasitic capacitance between the filter output and ground or some other signal path (those white push-in proto boards are less than ideal in that regard).


TU-X1 - MODIFIED BY JOSEPH CHOW OF AUDIO HORIZONS

dombro123
 


Hello, I am sharing information about my experience with Mr. Joseph Chow's work upgrading a Sansui TU-X1.  

I left a good review of Mr Chow's work, which I should not have done.  The workmanship and component choices were not very good to plain awful.  We learned, through extensive measurements, that the poor performance was caused by a complete lack of adjusting or aligning the tuner or MPX section. The cores were factory tight and had never been touched!  

I received the tuner back from Mr Chow about two-years ago. It sounded OK but not great.  I live in a very challenging radio-reception area.  I chalked up the poor performance to the poor reception I receive. The IEC change looked OK.  The performance seemed a bit better than when I had sent it to Mr Chow.  There were some other issues wit the unit that Mr Chow fixed, no problem. The unit was shipped with care and received with no problems, along with the bag of old parts.  

Recently, I received a Yamaha CR-1020 that is properly aligned. The Yamaha's superior performance is quite noticeable. Upon examination, I could see that the workmanship was not very good.  I decided to investigate the issue and sent the tuner to a tech in Canada.  

The tech documented numerous other examples of very poor workmanship, poor component choice and outright dangerous use of masking tape in critical power-supply areas. 

I found Mr Chow to be a really nice and honest gentlemen. I have no issue with the cost, if the work was done equal to Mr Chow's great reputation. I cannot explain the poor workmanship but believe that Mr. Chow did what he thinks is good work. Perhaps, Mr Chow is of the age that he assumes that the stupid user won't know the difference, anyhow.  

Needless to add, I do not recommend that anyone send components to Mr Chow. I can add images of the traces and poor workmanship, if anyone is interested.  As some members said when I left a great review of Mr Chow's work, I overpaid, a lot;  like $1200.00.  It was a complete waste of time and money. I stand corrected.   I prefer to leave good reviews or none at all. In this case, I felt a need to accurately report my experience with Audio Horizons and Mr. Joseph Chow.  


Re: Post Detection Filter with buffer

Radu Bogdan Dicher
 

Bob,
Thank you for your feedback and points. I'm looking forward to further tweaking this design. 
I enclose what I'm getting from LTSpice for both circuits. This includes levels and group delay on the same plots. I also include a magnified view on the roughly 23-53kHz band. 
Radu. 


On Mon, May 4, 2020 at 4:22 PM newaag via groups.io <newaag=yahoo.com@groups.io> wrote:
here's the 19/38 notch filter simulation and board. On this design, passive de-emphasis was included in the response, hence the constant down slope. 
https://groups.io/g/FMtuners/files/LM4500%20Filter%20and%20buffer

I can likely find the notch simulation for the version without de-emphasis on my computer somewhere. 2 or 3 windows OS versions ago. 
As you can probably figure out, the higher the Q of the components used, the more narrow and deeper the notch is. But the more narrow and deeper the notch is, the harder it is to tune and get on exact frequency.
Bob


Re: Post Detection Filter with buffer

newaag
 

here's the 19/38 notch filter simulation and board. On this design, passive de-emphasis was included in the response, hence the constant down slope. 
https://groups.io/g/FMtuners/files/LM4500%20Filter%20and%20buffer

I can likely find the notch simulation for the version without de-emphasis on my computer somewhere. 2 or 3 windows OS versions ago. 
As you can probably figure out, the higher the Q of the components used, the more narrow and deeper the notch is. But the more narrow and deeper the notch is, the harder it is to tune and get on exact frequency.
Bob


Re: Harman-Kardon F500 FM Tuner Restoration

Joseph Strickland
 

I forgot to mention that I do have one of the Fisher 300 MPX signal generators to generate a good stereo FM signal that I can use to check FM stereo tuners with. Thanks to Dave Gillespie of the AudioKarma.org website and the Fisher forum there, I have the complete factory manual for calibration of the Fisher generator. I went through that process a couple of times making small improvements in its operation. Most of the issues were just some corrosion on a few tube sockets and variable controls that needed some Deoxit treatment. Now it works quite well.

Tomorrow I plan to be restuffing can electrolytics in the H-K A-500 that came with the F500 tuner.

Joe


Re: Harman-Kardon F500 FM Tuner Restoration

Joseph Strickland
 

Bob;
You are so right about these early stereo decoder circuits and their mating to the associated RF.IF/Ratio Detector or Discriminator circuitry! I still have my old H-K F-50XK kit version of basically the same FM tuner with the exception that it did not have the IF squelch circuitry and used a MPX decoder that had a 4-diode matrix instead of the 2-diode matrix of this F500 unit. I did discover that the MX600 decoder that came out later than the MX500 decoder had the exact parts that had been added by the H-K factory to the MX500 decoder. The 4-diode matrix which was in the F-50XK tuner worked better than the one in this F500 but its stereo indicator circuit (a NE2 neon lamp) was always flaky and did not fire consistently. At times the neon would oscillate and feed annoying noise into the detected stereo audio!

I finally bought one of the LM4500 boards and chip and installed it in the F-50XK and that arrangement works flawlessly and with excellent separation. I even installed a variable control to allow me to reduce separation if dealing with less than ideal signal level. Blending the two channels with that simple variable control reduces the noise level in the audio to more acceptable levels instead of using the original switch arrangement that did a fixed amount of blend.

Since the tuner does have a weak 12AX7 that is part of the feed to the MX500 circuitry, I have two of those on order. If that takes care of the distortion fine, but if not I may be looking to build up another LM4500 decoder. That decoder works so well it is silly not to use one.

Do we know if more of the boards for the LM4500 will become available?

Joe

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