DIN input (European) on jvc RC-series-can the resistor be replaced by a trimmer?

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H3NK3L

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Maybe a stupid, but so far I haven't found any trustworthy answers...

Late 70s and 80 boomboxes here in Europe usually ime with a 5 pin DIN in/out (rec/pb, depending on the pins being used), no Line in our AUX or RCA for that matter.

The only brand I am aware of that uses a resistor on the DIN in (left and right) is JVC...leading to : normal volume on radio and tap hut... Low level on DIN.

I followed the technical manuals, schematics,.. And noticed din directly goes to amp pcb

Hence my question before blowing the amp... Can I put in a trimmer / variable resistor instead of the installed 1/4 watt resistor without taking too much chances of blowing the amp?

As far as I, with my limited knowledge, can see it... All the resistor does is take take the input level down before it goes to the amp... And this works fine when you plug in din to din... But when you plug in RCA to din (Bluetooth adaptor for instance)... You get about half volume, in my opinion due to these resistors beingmade for lower signals and perhaps being over calculated to avoid damage.

PS : by accident I once soldered a normal line level to the wrong side of the resistor and it behaves like when you put a line leven into PHONO input, distorts and such... With "normal" volume.

Hence my question : if I replace those resistors with variable ones (taking care toeqsure them before and putting them to near zero before attaching them), what risks do I take.
 

floyd

Boomus Fidelis
I'm no expert but I think the safest way to do this is externally because it might have too much resistance internally and you take a chance of blowing out the preamp.
Externally the signal is attenuated before it makes it into the boombox the other way might affect the circuitry or like I said even blow out the preamps.
 
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H3NK3L

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you
Hi All. H3NK3L.I have read your post and feel that it could be very related to my problem.Could you please read my post? Thanks
AIWA TPR-990 .Phono/Line-in problem | Stereo2Go forums
"Resistors R311 and R312 show strange values.R311 -92.8, R312 -60.4 "
Hello Floyd I read your post,

Never had an Aiwa myself, but from the (quiet) sound of it we seem to have the same issue : low level on DIN (IN).
I saw you schematics - I looked at the wiring diagram (the pcb and the components and where they go on mine) .
So far I only had this issue on JVC m70 / JVC RC-555 / JVC M60 / JVC M80 and some other jvc rc-series.
Fysically on the PCB they all have resistors (1M value) between input pins. 1 Resisor per channel soldered direcdtly from where the input pins go to the circuit that then goes to the amp pcb.
The "odd" thing on your aiwa seems : you have an input type selector you can set to PONO or Line In - so it would seem logical you get a higher input level (and output level) when set to line in (and plugging in a line out to it)
.
My solution on the JVCs was to concider the DIN in as phono input. Let me explain : when I plug DIN one side /RCA other side into it : it has low level output (low volume / quiet) - so i used a reverse RCAA on it and put that between, in my case, a bluetooth recevier and the rca input and miraculously...i got "normal" volume" But again these JVC's do not have the input type selector (PHONO/line in)...

On a few Crowns, philips (magnavox/radiola), panasonic, sharp I never had this issue - the only difference between the jvcs and the others i have and had is the presence of those 2 resistors (eacht time they were 1 mega ohm) - some of them had a selector switch like yours to choose between PHONO or Line In , and that worked fine on them (usually radio had slighter higher volume then tape / din , but decent level)d

I got this JVC RC-555L very cheap so for now I replaced the original resistors of 1M by 500k resistors...that does seem to get the volume that is output a bit higher (not totally as radio and tape). Without resistors its just like using the mic input with a line in level . I ll see what happens when i leave it on for a day or so (if the amp chip gets warm or anything starts smoking). If it turns out to be working fine I ll replace the resistors with variable ones so I can set it as I want .

These Din-circuits are odd birds, especially the REC?PB ones that have an entire circuitery for IN as well as OUT.
Theoretically yours has a circuit for processing PHONO and a circuit for Line level so it should work fine, perhaps in issue with the input type selector switch on yours ?
 

Megablast_73

Member (SA)
Hi.Thank you for your reply.However, there is indeed something ****ed up in mine.I have seen on Youtube that these Aiwa TPR-990 can play correctly through line -in.I am consulting this topic with others...maybe we can find the fault
 

H3NK3L

Member (SA)
Hi.Thank you for your reply.However, there is indeed something ****ed up in mine.I have seen on Youtube that these Aiwa TPR-990 can play correctly through line -in.I am consulting this topic with others...maybe we can find the fault
Fors starters, both resistors should (if i follow schematic logic) be the same value.... 30 pct difference is a lot - are their color-codes the same (the colored bands on them) ? and what does service manuel say for value for those resistors ?
 

H3NK3L

Member (SA)
I'm no expert but I think the safest way to do this is externally because it might have too much resistance internally and you take a chance of blowing out the preamp.
Externally the signal is attenuated before it makes it into the boombox the other way might affect the circuitry or like I said even blow out the preamps.
I figured that much, thanks for confirming :)
Although...DIN goes directly to amp it seems (Through some circuitry, but not using preamp circuit) - odd
Going from 1M to 500k resistors makes a slight audible difference but the difference between radio/tape/phono and DIN remains "vintage", so I put in a pair of new 1M ohms . Also there is no "switch" on the DIN connector on the boombox itsself - noticed some have this copper-platy thingy and some dont, on a crown and a panasonic the little copper plate seemed to serve asa a contactor / detector for plugged in or nothing plugged in on DIN , I presume to cut/mute sound from tape/radio when on DIN ... since the ones I came accros with this little contactor did NOT have an input selector switch for DIN and the ones that didnt have this little contacter thing did have a dedicated position for DIN on the input selector switch.

They remain odd things these DINs...or rather the dedicated circuitry that was engineered behind it.
 

Megablast_73

Member (SA)
Fors starters, both resistors should (if i follow schematic logic) be the same value.... 30 pct difference is a lot - are their color-codes the same (the colored bands on them) ? and what does service manuel say for value for those resistors ?
I measured these resistors without desoldering.They should have 470k.Some mistake in measurements
 

H3NK3L

Member (SA)
I measured these resistors without desoldering.They should have 470k.Some mistake in measurements
Measuring is a whole science lol

Personally... If it isn't the selector (phono/line) switch, if there doesn't seem to be an circuitry issue and if you used the correct input pins... I would try to use PHONO (that works, right?) as line in, using a reversi RIAA to bring down the line level to PHONO level. Those reverse RIAAA can either made by oneself or bought as kit or finished product, as pcb with or without a box for it. That's what I do (but that's me and may not be what you want to do) on European boomboxes with din and PHONO only. Has one other side-advantage : often they don't have an input selector switch for din, this way phono=Bluetooth for instance (of course with an on/off switch for Bluetooth so PHONO can still be used as such)
 

Megablast_73

Member (SA)
Today I'm going to bypass this Phono \Line in switch because even though it seems good I suspect it may be doing something wrong.
And as for setting the Phono switch to line-in to Phono. I don't have a turntable, but I set it to Phono with caution and the sound is very loud and indistinct, which is as it should be in this case.
 
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H3NK3L

Member (SA)
Today I'm going to bypass this Phono \Line in switch because even though it seems good I suspect it may be doing something wrong.
And as for setting the Phono switch to line-in to Phono. I don't have a turntable, but I set it to Phono with caution and the sound is very loud and indistinct, which is as it should be in this case.
when using phono for line in, I use a reverse riaa adaptor, that sets the right level for phono - so far the most easy solution i ve found for using a line input. i dont plug line in into phono directly... but much like you I found that phono (almost) always works fine - DIN is oft an issue.
 

Superduper

Moderator
Staff member
Hi All. H3NK3L.I have read your post and feel that it could be very related to my problem.Could you please read my post? Thanks
AIWA TPR-990 .Phono/Line-in problem | Stereo2Go forums
"Resistors R311 and R312 show strange values.R311 -92.8, R312 -60.4 "

If you are acquiring (-) negative results from resistors, then the values are not strange at all. It means you have connected your ohmmeter to an active circuit that is passing current. First of all, you must never measure an active circuit with an ommeter or you can blow the meter. Even a boombox that is powered off can have current potential from stored capacitive charges. If in doubt, always take the resistor out of circuit when measuring. Otherwise, you can't be certain that the resistors are out of range. All sort of parallel resistance or active circuit factors could skew the reading.
 
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Megablast_73

Member (SA)
when using phono for line in, I use a reverse riaa adaptor, that sets the right level for phono - so far the most easy solution i ve found for using a line input. i dont plug line in into phono directly... but much like you I found that phono (almost) always works fine - DIN is oft an issue.
What if there were not these two 470k resistors in the Line In circuit at all? On the left and right channels?
Because I bypassed this Phono /Line-in switch and put 100k resistors because I had them.And it's almost right
 
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H3NK3L

Member (SA)
What if there were not these two 470k resistors in the Line In circuit at all? On the left and right channels?
They are there for a reason...most likely, I think ,but I m no expert, to avoid the preamp/amp getting too high an input level and burning it out. I have no idea but on some DIN circuits they seem to interconnect the R+L input and R+L output , so I guess in that circomstance they are there to "seperate" in/out ?. Anyways if the people who engineered the circuitry but in some resistors...they probably did that for a (good) reason. DIN is a standard, but like @Superduper stated in a post : they are brand/series/... boombox dependant and not all are designed for the same level input/output, which means on some boomboxes they will act like LINE IN and on others they will behave "weakly". One understands they got extinct over time like other dinosaures lol
 

H3NK3L

Member (SA)
They are there for a reason...most likely, I think ,but I m no expert, to avoid the preamp/amp getting too high an input level and burning it out. I have no idea but on some DIN circuits they seem to interconnect the R+L input and R+L output , so I guess in that circomstance they are there to "seperate" in/out ?. Anyways if the people who engineered the circuitry but in some resistors...they probably did that for a (good) reason. DIN is a standard, but like @Superduper stated in a post : they are brand/series/... boombox dependant and not all are designed for the same level input/output, which means on some boomboxes they will act like LINE IN and on others they will behave "weakly". On some they will the main input when a signal gets to them, on others you ll have to hit the REC and or play button, others yet have their designated input signal switch,...... One understands they got extinct over time like other dinosaures lol

(Currently trying to find out if I can bypass the REC bar switch to get DIN dubbing in to work without having to hit the rec button on a sharp gf-9595, or if iI d better put in a reverse RIAA and send it to PHONO input) - Panasonic RX 5120 gets the DIN input amplified when set to RADIO for instance - JVC M70 (eu version) only works with DIN when REC is pressed,..... every boombox with din seems to have its own design and way of "dealing" with DIN)
 

Megablast_73

Member (SA)
Well, yes. They are there to protect against too high input signal. But assuming that they are causing the problem, maybe, being careful with the strength of the signal received through the line in, we should remove them experimentally?
 

H3NK3L

Member (SA)
I m currently experimenting with 500k (variable resistor) .insread of 1M on a jvc RC 555... Only on left channel.. Left channel is noticeably stronger then right (but not as strong as radio /tape) . So far so good, can't notice any heating, but only been using it for 8hr + 3.5 hrs.
I think it would be wiser if
1. I knew what entrance level it expects (1 mV, 1.25mV,..?) and
2. I had an oscilloscope to verify the level it gets

But so far so good...

When I use din to din, plugging in a jvc tadedeck from the same era, when I plug in a technics tape deck from late 80s.. Volume / level is just as low as with a Bluetooth adaptor...


I don't know if my logic is solid :
1. These late 70s early 80s inputs were made on the days levels were lower than current line in if I m correct.
2. If so... Why would they put in resistors to bring down the input level?
 
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Megablast_73

Member (SA)
I m currently experimenting with 500k (variable resistor) .insread of 1M on a jvc RC 555... Only on left channel.. Left channel is noticeably stronger then right (but not as strong as radio /tape) . So far so good, can't notice any heating, but only been using it for 8hr + 3.5 hrs.
I think it would be wiser if
1. I knew what entrance level it expects (1 mV, 1.25mV,..?) and
2. I had an oscilloscope to verify the level it gets

But so far so good...

When I use din to din, plugging in a jvc tadedeck from the same era, when I plug in a technics tape deck from late 80s.. Volume / level is just as low as with a Bluetooth adaptor...


I don't know if my logic is solid :
1. These late 70s early 80s inputs were made on the days levels were lower than current line in if I m correct.
2. If so... Why would they put in resistors to bring down the input level?
I don't know anything anymore.I got tired of it.I have to think about it. But I do know one thing. I have a Hitachi TRK-8800E which plays super without any problems.It too has DIN and Phono/Line -in. And why they mount these resistors is logically trying to think now I do not know.Maybe it is because without them there would be some distortion
 
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Superduper

Moderator
Staff member
You guys keep playing with these resistors thinking that things are so simple. Resistors don't limit voltage, they limit current. They can limit voltage but they do so through a voltage divider circuit which is carefully calculated at the factory and typically involves more than 1 resistor. If you change one resistor, you've changed part of the equation. Furthermore, you've also changed the input impedance of the circuit which throws everything off because the circuit behind it (the preamp, line amp, buffer amp, etc. all expects certain voltage and current levels. For example, preamps typically use transistors that are biased and expects a tiny current. As long as the signal stays within the transistors active zone, the circuit works as intended. If the input voltage is too high, then the transistor becomes saturated and then your audio becomes crap. Plus not every circuit is the same. Each boombox has a different circuit and some may have an input voltage divider network and some simply has an input resistor which dictates input impedance. You guys are expecting older boomboxes that were designed in a different era to perform like devices today that operate with different accessories. Even if you guys change resistors and get seemingly positive results with the accessory you are attaching to it, keep in mind that you've altered the line-in characteristics and it might now no longer be a line-in jack but rather become a smartphone input jack.

BTW, @H3NK3L you must be looking at different service manuals than I am. I checked the M70 and RC-555 service manuals and the input resistor on line-in is only 27k, and the M80 is like 56k. Not sure where you are getting 1M. The only time I've seen such high resistors on inputs are on systems that utilizes opamps which has no trouble with such high impedances. It's the voltage that drives it, not current which is what resistors throttle. The only thing is that opamps weren't really utilized in classic boomboxes. They are more of a modern thing. If the version of 555 you have truly does have a 1m input resistor, I'd be interested to see a screenshot of that circuit.

Line in is a particular specification and typically requires a certain voltage to be in compliance. Todays phones and other devices do not output true line-outs. Those are generally headphone or ear bud outs, which expects low impedance, low voltage outputs. True line-outs are high(er) voltage high impedance outputs. Rather than blame and try to hack the boombox circuit itself which is probably working the way it is designed to, you probably should instead fix the issue... improving the signal from your input device by using a headphone amplifier. For example, the FIIO K5 would probably do wonders for your system and can be adjusted and tailored for almost any situation to interface whatever you have with whichever boombox you wish to hook up that day but this device is a bit pricey, around $150. Or if you don't want to spend that much money, Amazon has something like this for $25 that might work: headphone amp at amazon.

If you guys are truly interested in tinkering with the input resistors, do yourselves a favor and educate yourselves first regarding input and output impedances, their designs and why they are important, and why/how to match them. google is your friend. Imma not gonna type up a whole boatload of stuff that already exists online which you can discover for yourselves.
 
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H3NK3L

Member (SA)
You guys keep playing with these resistors thinking that things are so simple. Resistors don't limit voltage, they limit current. They can limit voltage but they do so through a voltage divider circuit which is carefully calculated at the factory and typically involves more than 1 resistor. If you change one resistor, you've changed part of the equation. Furthermore, you've also changed the input impedance of the circuit which throws everything off because the circuit behind it (the preamp, line amp, buffer amp, etc. all expects certain voltage and current levels. For example, preamps typically use transistors that are biased and expects a tiny current. As long as the signal stays within the transistors active zone, the circuit works as intended. If the input voltage is too high, then the transistor becomes saturated and then your audio becomes crap. Plus not every circuit is the same. Each boombox has a different circuit and some may have an input voltage divider network and some simply has an input resistor which dictates input impedance. You guys are expecting older boomboxes that were designed in a different era to perform like devices today that operate with different accessories. Even if you guys change resistors and get seemingly positive results with the accessory you are attaching to it, keep in mind that you've altered the line-in characteristics and it might now no longer be a line-in jack but rather become a smartphone input jack.

BTW, @H3NK3L you must be looking at different service manuals than I am. I checked the M70 and RC-555 service manuals and the input resistor on line-in is only 27k, and the M80 is like 56k. Not sure where you are getting 1M. The only time I've seen such high resistors on inputs are on systems that utilizes opamps which has no trouble with such high impedances. It's the voltage that drives it, not current which is what resistors throttle. The only thing is that opamps weren't really utilized in classic boomboxes. They are more of a modern thing. If the version of 555 you have truly does have a 1m input resistor, I'd be interested to see a screenshot of that circuit.

Line in is a particular specification and typically requires a certain voltage to be in compliance. Todays phones and other devices do not output true line-outs. Those are generally headphone or ear bud outs, which expects low impedance, low voltage outputs. True line-outs are high(er) voltage high impedance outputs. Rather than blame and try to hack the boombox circuit itself which is probably working the way it is designed to, you probably should instead fix the issue... improving the signal from your input device by using a headphone amplifier. For example, the FIIO K5 would probably do wonders for your system and can be adjusted and tailored for almost any situation to interface whatever you have with whichever boombox you wish to hook up that day but this device is a bit pricey, around $150. Or if you don't want to spend that much money, Amazon has something like this for $25 that might work: headphone amp at amazon.

If you guys are truly interested in tinkering with the input resistors, do yourselves a favor and educate yourselves first regarding input and output impedances, their designs and why they are important, and why/how to match them. google is your friend. Imma not gonna type up a whole boatload of stuff that already exists online which you can discover for yourselves.
Thanks Super-duper, you re right (of course). Figured out as much, they did put resistors / caps etc in for a (good) reason. The 555 I ve got is a "messed with" one, specs are not as service manual says, things have been bridged, and it's particular din on this particular device seems to have a whole (I presume modified at some point during it's lifetime) part of its circuitry that from the look and smell of it (a messy component replacement, primately resistors and capacitators) was modified for PHONO. The combo resistors/ bridged /.. Seems to add up to some kind of signal deforming thing... Hence this being my "experimental" one. And those, I presume added since they seem "younger" and had their soldering all shiny contrary to the rest, resistors are 1 M (which is why I tried to mess with variable ones to go to more "usual" values, without success lol.

BTW I never expect a late 70s or early 80s device to comply with "modern" norms and standards. And defibately not on DIN which seems designed to serve different functions on different boxes But on this particular one it is extremely low. Was just wondering, and now have an answer.

Not being much of an engineer and my electronics "education" being. Vintage as well lol, I ll go with what I usually do, and seems quite safe : if it expects PHONO give it PHONO and put in a reversion RIAA.

(I don't really trust Google... And I think you may agree that a lot that's out there lacks specs and particularities and are put there guys that do not have your knowledge not experience, came across things from bypassing PHONO preamp, to directly wiring input to function selector switch to things that (even to me) seemed so odd that it s more like wizzardery and witchcraft - and while searching I did come across your din and input explanation on here)

Si tu sum it up : will not mess with inputs and their components. And got it changing 1 value on 1 component changes the entire circuit :)

And to close the subject : answer to my question : don't / don't go fiddling with resistors.
 
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