I have a Hohner Pianet e-piano (same as Pianet T but active, with built in tremolo, chorus effect and dedicated amp) in which I've done a full recap except for the two C1,C2 filter caps as I'll source them tomorrow. I've also replaced the ESM532 output IC3 (almost unobtainable) with a TDA1111 (equivalent - hard to get too but locally scored) as the R30 (47R) was slightly burned (replaced that too indeed) and i was getting almost no signal at all in that channel. Problem solved, but i still face a weird robotic/oscillation(?) noise in that channel just 2 sec. after turning the thing off (issue was there from beginning). Like an ic or smthng is near death kind of.
Shot a quick vid so you can hear by yourself.
https://we.tl/t-1BBALB9xPs
What do you think smthng like this could come from?
CD4011, 4558 ...?
I'm also getting pop when turning on and off. Any thoughts on this too?
(https://i.postimg.cc/ZCyzK7V8/M-Scheme.jpg) (https://postimg.cc/ZCyzK7V8)
Is the noise on one or both power amp channels? That would be something to look at.
My initial guess is it is some sort of power amp motor-boating when the main power rail drops to either 10V or 15V; 3 seconds of idle load through 2x4700uF.
When I look at the power amp schematic then look at the datasheet I can't help but notice that the datasheets use 100ohm for R30 and R39 and don't have diodes D1 or D2. Is that the cause? No idea, it's only a difference. The diode + resistor may help or hinder either reliability or performance.
It would be best to check the noise isn't present on pin 1 or pin 7 of IC 4 before going forward. If it's in the preamp circuits then that's a whole different ball-game. IC1 doesn't have a 100nF cap across pins 2 and 3 so maybe regulator is oscillating - I have doubts it's that but it's another crack in the design.
QuoteIs the noise on one or both power amp channels? That would be something to look at.
As i mentioned above, it's on the one channel only, the one that i replaced the ESM532, R30 and D2. But was there from beginning.
QuoteWhen I look at the power amp schematic then look at the datasheet I can't help but notice that the datasheets use 100ohm for R30 and R39 and don't have diodes D1 or D2. Is that the cause?
Where do you see that? R30 is 47ohm in the scheme and on my board too. Diodes exist too. What do you mean by datasheet?
Did you see my video Rob?
QuoteAs i mentioned above, it's on the one channel only, the one that i replaced the ESM532, R30 and D2. But was there from beginning.
OK, got it. if the noise is coming from the IC3 channel, notice the preamp of that channel is different to the other channel. The noise could be coming from anywhere along the preamp IC8, IC5, IC4, or the power amp IC3.
QuoteWhere do you see that? R30 is 47ohm in the scheme and on my board too. Diodes exist too. What do you mean by datasheet?
I dug up the ESM532 datasheets and the TDA1111 datasheets. I didn't keep the links. I have seen diodes in that type of circuit before however there's a small chance the diodes could cause a problem on those devices.
It's probably worth checking the preamp signals first.
QuoteDid you see my video Rob?
Yes. I've heard plenty of commercial equipment do stuff like that at turn off. Usually the noise was there since new.
QuoteQuote
Did you see my video Rob?
Yes. I've heard plenty of commercial equipment do stuff like that at turn off. Usually the noise was there since new.
So it could be there since new.
About pop switching on/off noise do you think the fragile CD4011 could have smthng to do with it?
Look, i have in my shelves all of the ics used in this circuit (well except for ESM/TDA1111s). Do you think it is wise to desolder them all (pre's&CD), install appropriate dip sockets(making my life easier for the future) and replace/leave/use accordingly? Or i could damage those "valuable" RC4558s and RCA CD while desoldering in the case of leaving the old component(when this isn't the culprit)? :icon_biggrin:
(https://i.postimg.cc/KkdgXp09/IMG-20221208-070516.jpg) (https://postimg.cc/KkdgXp09)
QuoteSo it could be there since new.
I wouldn't be surprised at all.
In fact I just realized the .jpg schematic has an extra 4016 IC9. To me it looks like the circuit had a problem (in the PDF schematic) and they added IC9 to disconnect the preamp from the power amp to hide the noise. I'll admit I haven't check all signals but it sure looks like a fix.
That's being the case I'm suspecting the preamp more now.
The fact you only have the issue on the IC3 channel means the noise is likely to originate from that chain of preamp ICs I mentioned.
I would just listen to the outputs of those points and see if you can workout at what point the noise starts in the audio chain.
QuoteAbout pop switching on/off noise do you think the fragile CD4011 could have smthng to do with it?
I've got my doubts but we can't assume anything.
QuoteLook, i have in my shelves all of the ics used in this circuit (well except for ESM/TDA1111s). Do you think it is wise to desolder them all (pre's&CD), install appropriate dip sockets(making my life easier for the future) and replace/leave/use accordingly? Or i could damage those "valuable" RC4558s and RCA CD while desoldering in the case of leaving the old component(when this isn't the culprit)? :icon_biggrin:
I would leave it as is. Find where the problem is first. If you have an oscilloscope the shape of the waveform can be used to deduce what's causing it.
Hmm, that fix looks more like a muting during power ON rather than power OFF.
I agree with Rob that the 4016 switches do look like an attempt to prevent this sort of thing. Disconnect the power amp from the preceding stages to save your ears and speakers.
It's a bit tangled to work out, but I'd get the oscilloscope on the 4016 switch control pins (pins 6 and 12) and see if you can see anything happening there.
I also agree with Rob that testing the output of the various amp stages going through to see where the noise first appears is a good idea. It'd be nice to know how far back it starts, and that might give us a clue.
OK, seems there are two schematics out there :icon_rolleyes:
1. https://www.clavinet.com/shema_PIANET_M.pdf
2.https://www.musiker-board.de/threads/hohner-pianet-m-an-verstaerker-angeschlossen-nun-stumm.654929/
Post #9
(https://i.postimg.cc/RJ51ctgq/Pianet-M-Schaltplan.png) (https://postimg.cc/RJ51ctgq)
Mine is mixed but mostly the first one.
On my board there is no CD4016. Only CD4011.
(https://i.postimg.cc/21Wf8RPY/IMG-20221209-012234.jpg) (https://postimg.cc/21Wf8RPY)
Just replaced the C1,C2 filter caps and the noise is gone. Well you can still slightly hear a tiny pop like but certainly not that loud constant faded robotic noise of the video i uploaded.
So filter recap seems it did the job.
(https://i.postimg.cc/34zPv03f/IMG-20221209-050921.jpg) (https://postimg.cc/34zPv03f)
Now one last thing that was there from the beginning too and never gone (maybe it's a bit normal like they say in all those e piano forums, but heh i think no any hum/noise is acceptable, right?), is a 50/60Hz hum i get from both channels. It's there with all pots down - not so loud though and that could be normal - but what it's not normal for sure is that it gets increased then as you turn up the Bass Pot P1, so this hum is related to P1 bass pot. Unfortunately no scope yet.
Any thoughts?
I have an Eminar Bass amp that will get a tone that starts high and reduces in frequency quickly a few seconds after turning it off. It's always done it. I once had somebody trip over the power cable, pull it out of the power socket, and bend down and plug it back in without losing any volume. I just assumed the nice big power supply caps, and a toroid transformer with a heap of magnetic field can probably hold some charge for a bit, and the tone is what happens when they finally discharge.
I'm not surprised you get hum with the volume turned down. The only volume control I see is a gain control in the preamp. Any hum present in the circuit is given free rein and boosting the bass is sure to increase it. There is a 7.5v reference supply filter C13, a 15v filter C3 and power amp 30v filters C27 and C37. Probably change those caps at a minimum.
While you're at it, you might as well replace electro caps at the power amps. As you know these amps failed sometime previously.
QuoteThere is a 7.5v reference supply filter C13, a 15v filter C3 and power amp 30v filters C27 and C37. Probably change those caps at a minimum.
While you're at it, you might as well replace electro caps at the power amps. As you know these amps failed sometime previously.
Have replaced every electro except for the blue radials which I'll do today.
(https://i.postimg.cc/tYxWz75X/IMG-20221106-081627.jpg) (https://postimg.cc/tYxWz75X)
(https://i.postimg.cc/YGPL6wLG/IMG-20221209-050921.jpg) (https://postimg.cc/YGPL6wLG)
Don't judge, i just replaced them with NOS electros. I know i know. It's my first time doing this. Scored a big bag full of NOS components for almost nothing (10bucks) from an old small shop's clearance stock, including about 200 electros, 250 film foil caps (mustards, fish's, styros, PIOs etc), 100 germaniums (ac122/132s mostly), other interesting Lockfit/TO105 transistors i need for my old organ/keys repairs, old ceramic caps and military USSR and Beyschlag resistors. The only bad thing (if you can call bad such a deal) is the lack of the common values. I just took whatever had been left there, so 1K,10K,100K resistors were gone. Same for film caps, 22 and 100nF.
(https://i.postimg.cc/nMm2THpG/IMG-20221122-202331.jpg) (https://postimg.cc/nMm2THpG)
(https://i.postimg.cc/877mJDKv/IMG-20221201-211706.jpg) (https://postimg.cc/877mJDKv)
(https://i.postimg.cc/9rFp2yyJ/IMG-20221201-212506.jpg) (https://postimg.cc/9rFp2yyJ)
(https://i.postimg.cc/XGbfz5VK/IMG-20221202-020623.jpg) (https://postimg.cc/XGbfz5VK)
(https://i.postimg.cc/HrF4bKRh/IMG-20221202-072901.jpg) (https://postimg.cc/HrF4bKRh)
(https://i.postimg.cc/4KtvPPTN/IMG-20221202-123252.jpg) (https://postimg.cc/4KtvPPTN)
(https://i.postimg.cc/HVZtkj2H/IMG-20221207-005121.jpg) (https://postimg.cc/HVZtkj2H)
(https://i.postimg.cc/62frJQ3k/IMG-20221207-011655.jpg) (https://postimg.cc/62frJQ3k)
(https://i.postimg.cc/G8yFMQwm/IMG-20221210-090907.jpg) (https://postimg.cc/G8yFMQwm)
So it's the first time I'm using nos electros. Tested for capac. & leakage, used wisely and accordingly. It's for my own gear anyway, time will tell.
About hum, I'm talking about the hum i get as i turn up the Bass pot P1 in scheme.
Quotebut what it's not normal for sure is that it gets increased then as you turn up the Bass Pot P1, so this hum is related to P1 bass pot.
Any thoughts?
With the volume control right at the start of the amp board, you may never get rid of the hum. It would ideally have a stereo volume control at the inputs to the power amps then the preamp circuit hum & noise can be turned to zero at the same time as any signal. The only noise left then is from the power amps and their supply.
NOS electro caps might well be below their best now, but if you can leave it powered up for a good while they can reform to a degree and hum may, if you're lucky, reduce.
QuoteNOS electro caps might well be below their best now, but if you can leave it powered up for a good while they can reform to a degree and hum may, if you're lucky, reduce.
I know, thanks for the advice Jim.
QuoteWith the volume control right at the start of the amp board, you may never get rid of the hum.
So as it is now there are no many things left to do i guess. Like playing with different opamps (ic5/6)/replacing 2458DC with 4558.. Or a culprit component in between and before the P1 pot ..
Considering that the bass control happens soon after the input gain stage, I think it's likely that hum is present on the opamp Vref supply that comes from the 10k resistor divider off the 15v supply. Try adding capacitance across the Vref cap to see if it improves things. Remember, opamps have good supply noise rejection so the most important place for ripple reduction is the opamp reference supply.
The Volume pot ideally goes to zero ohm at minimum. Try to measure this. Not all pots manage to zero and it's as a variable resistor that this is most troublesome. Then any hum from the pickups will still get some amplification.
I seem to remember reading that Pianets couldn't be used sat atop a Hammond without terrible interference being picked up while the Clavinets were fine in that placement, so I expect there is some hum coming in at the preamp and it might not be directly amplifier power supply related.
I found a clear schematic with no 4016 here...
https://www.clavinet.com/shema_PIANET_M.pdf
And the Vref divider values are 15k with a 47uF filter cap. That ought to be pretty good at removing power hum.
Quote from: anotherjim on December 10, 2022, 08:30:05 AMI found a clear schematic with no 4016 here...
https://www.clavinet.com/shema_PIANET_M.pdf
And the Vref divider values are 15k with a 47uF filter cap. That ought to be pretty good at removing power hum
You mean with 4011, right?
The 47uF vref filter cap you're talking about is the C13 right? If so, instrad of 47uF it's a 100uF on my board. So i guess that ought to be really good.
Yeap i was also reading about Pianet placing right now. No room left, it sits just above a Philicorda and a Farfisa Compact :icon_lol: maybe it could bd only from this. Without input signal (pickups disconnected from amp) there's no Bass pot hum.
So maybe it has also to do with the pickups too.
QuoteWithout input signal (pickups disconnected from amp) there's no Bass pot hum
That pretty much proves the hum is from the pickups.
I've never seen the inside of a Pianet. Most keyboards with wooden bodies had a sheet of foil stuck to the inside bottom face under the keyboard frame to screen it. I don't even know how the pickups are arranged and if they are supposed to have any humbucking arrangements.
Yeap they used to do this
https://youtu.be/84rIQC2Ot18
But as stated here (auto Google Translate) it has more to do with the static than hum.
http://forum.anafrog.com/phpBB/viewtopic.php?t=6060
That "static" noise seems like guitar string noise, usually reduced (but not completely) by grounding the strings via the bridge to the jack screen. The cure shown for the Pianet is a similar thing. That does nothing for hum pickup though, it isn't really screening anything.
It's the actual disposition of the pickup system and wiring I'm interested in knowing about. I'm not finding much about it.
I found this image...
(http://www.vintageaudioberlin.de/vabgalerien_2/tasteninstrumente_elektronisch/Hohner_Pianet_T/images/d.jpg)
This seems to be a basic direct output model with a line-matching transformer and the reeds are removed.
You can see the coils and a bus connection strip PCB below. I would expect the coil polarities alternate by the connection order so some hum cancellation occurs - like a Precision Bass split-coil only more so. If it doesn't alternate polarity, they missed a trick! However, with 61 keys, there's one odd coil and spread over a wide area, I think the cancellation cannot be perfect.
When I was looking at this the other day I found some schematics showing one half of the coils connected in opposite phase to the other half of the coils for humbucking purposes along the lines of Jim's post.
[link fix:
http://www.vintageaudioberlin.de/vabgalerien_2/tasteninstrumente_elektronisch/Hohner_Pianet_T/]
I assumed the banks were far apart so the cancelling is limited. For example, if the magnetic field from the unit's *mains* transformer was a problem it would inject more hum into the end close to the transformer and less into the ones far away and the hum wouldn't cancel. The Fender Rhodes units were better. They connect banks of three in parallel then wired pairs of banks of three as a humbucker. That means the humbucking is in the same physical region and works much better. (FWIW, I'm not a keyboard guy at all but I have looked at the Fender Rhodes design in the past.)
All the above assumes the hum is getting in because the pickups are picking up stray AC magnetic fields.
QuoteYeap they used to do this
https://youtu.be/84rIQC2Ot18
But as stated here (auto Google Translate) it has more to do with the static than hum.
http://forum.anafrog.com/phpBB/viewtopic.php?t=6060
This scheme is preventing hum and noise getting into the wires themselves. Another type of interference. This is capacitively coupled and because of that it sounds buzzy.
Yet another cause, which is very possible on a keyboard is noise in the grounds. Maybe you should check all the ground wires, ground screws etc on any wires between the pickups and the wires that go to the transformer board.
Often old equipment would make ground connections to the chassis at a place close to where the connections were made. This often resulted in multiple ground points. When you have multiple ground points you can get hum problems. Sometimes you can get away with it but if one of the ground connections goes bad you can get hum.
The way the pickups are wired on those Hohner units seem to have the potential for this type of problem. If we changed the wiring a bit I suspect it could be improved somewhat. The input to the circuit uses a transformer but it doesn't take advantage of the transformer to the fullest extent - it just wires the one side to ground and wires the pickups to ground. You could rejig the wiring to be sort of differential with respect to the "center" of the pickups.
The last points I'm just mentioning in passing as it's going to be more work than most people are willing to spend on it. I'm also assuming there's a problem in this area. Maybe if the grounds are all OK the hum is low enough.
In short there's three ways hum can get in. It takes some effort to workout what type you are dealing with. Then you have to find a solution.
EDIT: Texted this before you guys posted in the second page.
Telepathy kind of ;D
**** My model is the Pianet M. (Not T)
All the thing till the amp is the same to the Pianet T. A Pianet M is a T connected to an amp with speakers via an RCA cinch.
So if you want to know about M's electro mechanics, housing, keys, sticky pads, reeds, pickups etc. just search about T and you have the M too.
http://hohner-pianet.com/hohner_pianet/pianet_T.html
https://youtu.be/ypTZHK5UVck
https://go.skimresources.com/?id=24063X829826&isjs=1&jv=15.3.0-stackpath&sref=https%3A%2F%2Fen.audiofanzine.com%2Felectric-piano%2Fhohner%2FPianet-M%2Fmedias%2Fother%2F%23id%3A480265&url=https%3A%2F%2Fmedias.audiofanzine.com%2Ffiles%2Fhohner-pianet-m-notice-technique-480265.pdf&xs=1&xtz=-120&xuuid=845260264d123ceeb1fbe8937147ee22&xjsf=other_click__contextmenu%20%5B-1%5D
Pups are wired in series (in both T and M).
Up to this point they are both the same.
(https://i.postimg.cc/YGRdKQRw/Hohner-Pianet-4g.jpg) (https://postimg.cc/YGRdKQRw)
(https://i.postimg.cc/V0NDY5Z0/IMG-20221103-025542.jpg) (https://postimg.cc/V0NDY5Z0)
(https://i.postimg.cc/LqzyDcZ5/Screenshot-2022-11-03-09-58-46-179-cn-wps-xiaomi-abroad-lite.jpg) (https://postimg.cc/LqzyDcZ5)
Then, for T, the pickups output (hot/gnd) signal cable goes to an output transformer and then to the out jack and that's it (passive circuitry).
(https://i.postimg.cc/t1K15gxQ/IMG-20221212-032329.jpg) (https://postimg.cc/t1K15gxQ)
(https://i.postimg.cc/SXTGgmxy/ooxdg3v32tacj84ruhcr.jpg) (https://postimg.cc/SXTGgmxy)
(https://i.postimg.cc/cK4m7vZ9/oxzdabi396hxuzrgbvht.jpg) (https://postimg.cc/cK4m7vZ9)
(https://i.postimg.cc/ftVfF1VY/pianet-t-18-645x0-is.jpg) (https://postimg.cc/ftVfF1VY)
For the M, the pickups cable (green with RCA cinch) goes into a female amp mounted RCA socket (no matching trafo) and from there straight into the input of the amp C9 10uF input cap.
(https://i.postimg.cc/687HF7F8/IMG-20221103-020538.jpg) (https://postimg.cc/687HF7F8)
(https://i.postimg.cc/4mx2b25b/IMG-20221212-020315.jpg) (https://postimg.cc/4mx2b25b)
My pleasure Jim (hope it's not boring for you though), me too didn't have any clue at all untill i got the instrument in my hands. I then started to complete the puzzle.
Actually I'm waiting for the T's equivalent replacement transformer, Calrad 45-703 (as suggested by Hohner itself). It can be sourced only in US, i have my ex co-producer there, so he bought and will import in EU for me in a few days.
Doing this, i will mod the M into a T when i want to amp it and be able to return back to M playing through speakers / trrmolo chorus fx and its cheapo amp when i want to.
***** UPDATE: when i disconnect amp and plug the pickups (green rca cable) into a common phono preamp i get no hum at all. Ultra clean signal.
Thanks for the reply Rob, note that my model is the Pianet M. Read my post above.
So no passive, no output transformer. Mine is an active instrument, the pickups go straight into the amp's input (no trafo in between) via the green RCA cinch cable.
Also, as i say above, noticed when i disconnect amp and plug the pickups into a phono preamp i get no hum at all. So it couldn't be the pickups alone but probably a combi of common regular pickup's noise in interference with the cheaply made amp unit, its Power trafo placement, wires path etc..
Actually that green pickup's rca cable clearly touches the PT and gets attached to a cable tie adhesive mount which is stuck on filter cap's body! Is this wise?
(https://i.postimg.cc/RW5kQ5P6/IMG-20221106-081710.jpg) (https://postimg.cc/RW5kQ5P6)
***Edit: about pickups wiring, there were two submodels in T's. In the one they were wired in series (like in M too) and in the second they were wired like in the link you posted Rob
Wow so much info to process!
So far I've got this picture:
- the ground of the green wire (coax) connects to the chassis near where the
center conductor of the green wire (coax) connects to the last pickup.
- I would assume the pickup at the other end connects to ground?
So having those two separate ground points so far apart is a *potential* for noise to get into the ground.
It might be OK.
From that the green wire goes to the RCA jack, then connects to the RCA socket the amp.
On the amp side a second green wire (coax) connects to the RCA socket.
Then we get to:
QuoteActually that green pickup's rca cable clearly touches the PT and gets attached to a cable tie adhesive mount which is
stuck on filter cap's body! Is this wise?
And the coax terminates on the amp board.
So now a big oh yeah! Passing the coax past the transformer like that is just asking for problems.
We can ignore ground issues for now.
If you can re-route the wire so that it is at least 100mm away from mains wiring and the transformer it would be a very good experiment. Perhaps even a solution.
I already tried it but had no luck Rob. Well, as i get deeper into it i realise more and more things about it. Seems the M model was popular enough in France, that's why you can find many things on french forums like audiofanzine, anafrog and german musiker-board if you use auto Google Translate. In the first one, after 10 pages of reading, i see dozens of postings from guys complaining about speaker "breath air" (translated from Google), all kind of noises, clicks, pips etc. Seems to be very common for this model and no fix even after visiting pro techs (it's a forum mostly based on musicians, users of gear, not repairmen ;D)
I think one guy only was saying most of the issues were solved by replacing PT with an equivalent toroidal and anti-noise dedicated one. The bottom line told by most of their techs (from Paris to Berlin) was "leave it as is, it's just the way it was designed and it was designed with cheap in mind - Pianets were the poor man's Rhodes" and that "things were noisy back in the days" (I don't say the opposite on that lol).
But many folks have solved enough of the issues by interchanging IC's. It's said that the IC's responsible for the chorus effect are most of the times the culprits for all kind of noises and weird sounds.
And about this, only today, i realised smthng else ::)
Having turned up the Chorus pot while the tremolo pot is down you get a weird clock-y , periodically wind/waves noise. When you turn up the tremolo pot up too (so both of them are turned up) the wind noise gets away.
Wind repeatable noise only when Chorus pot is turned up alone. When tremolo pot gets in the game no wind noise.
So that it is clock-ey repeated and it's the same reminded me my old days troubleshooting on my various bbd's . Definitely related. I insist on my first thought: i believe i could see changes if i install dip sockets and play around with different IC's in there. So far, i have replaced the CD4011 and found that the tremolo effect suddenly wake up, became more present and hearable. Don't know how a 4011 can be related with a tremolo effect (I'm not expert in IC's, I'm mostly in old big transistorized and valve gear), i searched about 1' and found that can be related, but in my case changing the 4011 fixed the dead tremolo (was expecting from it to do something about the pop speaker noise, but this was mostly fixed by filter recap).
So why not try another TDA1022, 1458, 4558's?
Well, it's pretty normal for chorus effects to have some degree of noise. However, if there's circuit faults or circuit design issues these can obviously cause more problems. The design issues would have to be designed out and mods put in. It's not possible for me to workout what types of bugs you have since it can take quite a deep look at what's going on.
For the controls I would call the first knob the Chorus Depth and the second knob the Chorus Speed. The design of the circuit looks a bit weird/simple. It does have the potential to do weird stuff when the Depth is set below about 1/3. I'm not sure if this is deliberate to cut-out the Chorus effect all together when it the Depth is set to zero. I would expect not as it would kill the audio in one of the speakers. The only way to fix it would be to wire the counter-clockwise terminal of the Depth pot to a voltage divider instead of ground. If the design has potential issues then it's possible it might do weird stuff when the chorus is on as well (as the sweep can go into the bad zone). The voltage divider mod should fix that too.
As for your hum issue I have a suspicion you have a noisy ground. What happens when you pull the keyboard RCA out, does the hum also disappear from the Pianet or does it change and go buzzy? What happens if you put a short across the RCA input jack? Does that make the hum better or worse. Don't forget to set the Bass consistently to 12 O clock note the volume control positions. Advance the volume control if you can't hear hum to see if there's any hum there at all. The idea of all this is to see how much hum is from the amp part.
QuotePianets were the poor man's Rhodes"
It's a cool sound just the same, and it's kind of unique in its own right.
Did the original 4011 have an "A" suffix? The A series didn't age well, but perhaps more importantly, they were unbuffered, unlike a "modern" CD4011B part. This can make a difference in a timing circuit as the switching speed of the internal logic changed.
Thanks to the new information, the keyboard design seems to have done its best with continuous coil reversal and a single-point ground. It just needed something like a phosphor-bronze insert in the plastic key fulcrums to keep the hammer bars grounded.
No, hum & hiss wasn't considered too a big problem in the last century. The slight "chiff" from the static in the Pianet when a key is pressed and released does, I think, lend it something in the same way that the contact click and leakage of a tonewheel Hammond does.
I'll reply to Jim first as Rob's suggestions are correct but didn't find time to test, I'll be in amp's troubleshooting when find time and will be back with results. Rob, as i play the Pianet i find Bass's pot hum not to be so loud, so maybe it's a bit normal acting like that. It's just a bit louder than volume's pot hum. Yes vol pot hums too but very slightly, you really have to stick your ear to speaker to hear it and if so, certainly less than tube amps common humming. My biggest concern on amp is now the wind noise / hiss ("breath") of the IC3 / Left channel.
@ Jim, yes the original 4011 was a CD4011AE RCA 010 one, so if that counts as an A series (i think so) it may explains my case, according to your valuable input. Thanks. Now i have installed a NXP CD4011BP one.
Without having the unit in front of me it's hard to know if we are dealing with a fault or normal behaviour.
What's the value of C8 on your PCB? The schematic is unclear: looks like 830pF but that's not a standard value so is it 330pF, 820pF, or other.
If I ignore trying to read the schematic a value of C8-820pF produces a nice filter response. If the part is 330pF changing it to 820pF might reduce the noise.
Going beyond that you could tweak the filter to reduce the noise. That needs some care because you don't want to change the tone.
Quote@ Jim, yes the original 4011 was a CD4011AE RCA 010 one, so if that counts as an A series (i think so) it may explains my case, according to your valuable input. Thanks. Now i have installed a NXP CD4011BP one.
I had a quick look at CD4011A vs CD4011B and the 4011B increases the clock frequency. That could reduce the hiss *but* if that's not the intended part we are just stuffing up the chorus circuit with the side effect of less noise. The chorus circuit won't be the same. The change to CD4011B doesn't fix any weird behaviour when the Depth pot is reduce. You could also put in a CD4011B then change the part values to operate like the CD4011A but that's a redesign.
You have the eagle eye Rob, couldn't be 830p, indeed C8 is a 630p styrene on my board, although scheme calls for a weird 830p. I have some nice nos 820pF HSG (Siemens) styrenes in my shelves, BUT being 630p (and not 330/390/560p), would such a small pico capacitance increase reduce hiss in IC3 path channel even a bit? I doubt. On the other hand, I'll salvage and stock a 630p one which I don't have in my shelves 😂.
Could a 630 to 820p increase change the tone and originality of the unit on the other hand? :icon_rolleyes:
(https://i.postimg.cc/DW4YqZ5R/IMG-20221213-085212.jpg) (https://postimg.cc/DW4YqZ5R)
EDIT: I put again the original CD4011(AE) to see if the hiss could be reduced (just saying) and it indeed reduced it BUT the depth Chorus pot doesn't do anything at all. And that's why i had it removed. The old 4011 is faulty. (discolouration in its body was the first one i noticed as faulty). So it has to be changed. I could find an A series one, but definitely cannot use the old one. With that, the chorus effect doesn't work, only the tremolo (speed) works. Just to mention.
QuoteYou have the eagle eye Rob, couldn't be 830p, indeed C8 is a 630p styrene on my board, although scheme calls for a weird 830p. I have some nice nos 820pF HSG (Siemens) styrenes in my shelves, BUT being 630p (and not 330/390/560p), would such a small pico capacitance increase reduce hiss in IC3 path channel even a bit? I doubt. On the other hand, I'll salvage and stock a 630p one which I don't have in my shelves 😂.
Could a 630 to 820p increase change the tone and originality of the unit on the other hand?
630pF makes perfect sense. I'd say the 630pF is the correct value and 830pF is a typo. The response looks fine with either.
That doesn't mean you can't mod/tweak the response to see if you can remove some noise.
The filter cut-off is fairly low already, -3dB @ 3.4kHz, so we don't want to push that down
too far.
It should be obvious that adding more filtering will remove noise! However you can over do it
and start filtering the top end off the notes. The trick is to find the best balance.
If I had to take the best stab at a simple mod to try I reckon changing C8 to 1nF or 1n2 might help.
If you want you could just add a parallel cap, value around 470pF to 680pF, in parallel with the
existing 630pF. You can make changes to the other caps as well but there's good and bad ways
to go about it. You have to test these things by ear. That's were adding a parallel cap helps, you
can add it and remove it to do a quick A/B test and see if the noise drops and the notes are OK.
I hope this helps, although the different versions of the board and component values may mean some references are wrong for yours.
It might be worth checking the BBD clock pin 1 and 4 voltages. These should be square wave pulses but on DC, your meter will average at half the supply voltage at around 7.5v. Any big difference from that or between them at various speed and depth settings could give a clue. The same goes for the 4011 input pins 8 and 13. The pair of timing caps C17 and C18 need to have closely similar values to get closer to matched square wave clocks for the BBD rather than different pulses. While you're at it check R19 and R20 resistance. Diodes D4 and D5 shouldn't give much trouble but the quality of these wasn't so certain back in the 1970's so a leaky or intermittent one could happen.
The BBD clock modulation from the MC1458 pin 7 is a triangle wave that gets filtered some by R18 and C16 to make it smoother and more like a sine wave. An intended side effect will be the amplitude of the modulation automatically reduces at faster modulation speeds. R16 and R17 determine the amplitude of the triangle wave.
For the range of modulation to suit the 4011 clock generator...
C14 and R15 values determine the fastest clock speed. Too fast and the Intensity control may have no effect.
C16 and R18 determine the minium-maximum intensity available.
Without more than a DMM to test with, you can only check resistance and voltages, but if you understand what they do, you can make reasonable assumptions about the capacitors.
What a circuit analysis Jim, so much info here!
Seems i found smthng weird.
QuoteIt might be worth checking the BBD clock pin 1 and 4 voltages. These should be square wave pulses but on DC, your meter will average at half the supply voltage at around 7.5v. Any big difference from that or between them at various speed and depth settings could give a clue.
TDA1022 voltages at various speed & depth settings for Pin1 and 4 were between 7.48 - 7.54 VDC. Seems right.
BUT
QuoteThe same goes for the 4011 input pins 8 and 13.
CD4011BE
pin8 measured 15.04 VDC and pin13 7.52 VDC.
Are you sure they should be the same and at half of 15V (~7.5V)?
If so, smthng wrong must be here.
R19 and R20 measured 151K both.
Diodes seem fine too.
QuoteCD4011BE pin8 measured 15.04 VDC and pin13 7.52 VDC.
Are you sure they should be the same and at half of 15V (~7.5V)?
If so, smthng wrong must be about Pin8.
Can you try the measurement with the Depth/Intensity pot in a few different positions: min, center, full.
It's weird that pin 1 and pin 4 on the TDA1022 are OK but pin 8 on the CD4011 isn't.
Pin 8 must be doing something.
The multimeter could be loading down the circuit and stuffing something up.
Do you have a frequency meter? Perhaps on your DMM?
If the frequency on pins 1 and 4 of the TDA1022 is too low it can cause a lot of noise. It is normal for a lot of noise when the frequency is low however, maybe the problem is the fact the frequency is low!
Just triple checked. BBD pin1 and 4 are about 7.48/7.50/7.54V at min/center/full.
For the same positions for 4011 pin13 is 7.47/7.50/7.55V
and pin8 stable 15.04/15.04/15.04V. :icon_rolleyes:
QuoteIt's weird that pin 1 and pin 4 on the TDA1022 are OK but pin 8 on the CD4011 isn't.
Sure it is.
And more weird, that 4011's pin4 (connected to pin8) measures 7.52V !!
QuoteSure it is.
And more weird, that 4011's pin4 (connected to pin8) measures 7.52V !!
I have a very strong feeling pin 8 has a bad connection or a break in the PCB to pin 4. You should at least check the continuity between pin 4 and pin 8.
When you don't have the DMM connected to pin 8 the sharp edges of the signals couple from pin 4 to pin 8, just enough to trip pin 10, pin 11.
Another option is the PCB doesn't match the schematic. The basic circuit might be the same but they have used different gates in different positions. You would have to check the PCB against the schematic. If all OK go back to the pin 4 to pin 8 broken theory.
Damn i made a kid's mistake. Working on it alongside other things since many hours and was too tired. My apologies, was measuring at pin14 instead of 8 so obviously all i was getting was the Vdd 15.04V :icon_rolleyes: Pin8 is 7.48/7.50/7.52V so everything is fine there too.
I'm really sorry for the trouble Rob.
EDIT: About smthng i noticed. By chop stick tapping on IC1, IC2, IC3 's bodies (voltage regulator and power transistors) and their common heat sink i get the tap tap pops through speakers. They are microphonic.
Is this normal?
QuoteI'm really sorry for the trouble Rob.
No problem, easy to do.
It looks like it's working OK.
What we don't know is the frequencies, as mentioned a couple of posts back, it can be a problem.
In addition to that, the way the depth pot works is a bit weird. When the depth is set to full the
output of the LFO (pin 7 IC6) swing about 3.2V to 11.8V. That's more or less in a range that works
for the VCO (IC 7). However when you dial back the Depth the range of voltage moves toward 0V.
When we get to LFO voltages (pot wiper voltage) around 5V the frequency of the VCO starts to take off and at some point it seems like it could even stop oscillating (because the speed is beyond what the CD4011 can do).
I can see what they were trying to do, as you back off the depth the delay (from the TDA1022)
gets smaller and has little effect on the sound.
What position of the Depth control would you say are noisier: min, center, max, other?
Ok, to clear things up.
Hiss: There's always a slight windy hiss in the L channel (IC3) only by just powering the unit. It has certainly to do with the Chorus effect as you can "hear the wind changing as you turns the chorus pots" . It's like you hear the BBD but you don't have signal, so you hear the hiss making that effect you're controling. (Have experienced in the past smthng similar, common bbd behaviour so maybe it's normal).
Depth pot at min has no effect at all, at max you get "chorus" to maximum.
So when you have the depth pot to min you just hear the hiss.
When you turn depth pot to max you can hear the hiss "come and go" periodically/ clockey.
Then, if depth pot is up and you turn up the speed pot you just hear this hissy effect coming and going more quickly / slowly..
That's all. All this in the left channel (IC3) only, the "chorus" channel. (Makes sense).
Hum: Hum exists only if you start turning up the Bass pot. In both channels, but mostly in the Left.
Note: Have a look at the EDIT in my last post. Volt regulator and / or power output transistors are microphonic . You get really loud pops in some cases by chop stick poking. And you can microphonically listen to the tap being produced through speakers.
Also: the other day i found that during recapping i had left C27 unsoldered (really tired these days , recovering from H1N1 flu). Quickly fixed, but could something went wrong during all this time i was troubleshooting/ functioning the amp 8-12hrs/day?
EDIT: About hiss maybe it's normal. https://www.diystompboxes.com/smfforum/index.php?topic=122825.0
Just seems weird to most people in Pianet M because you have to deal with stereo here and you get the hiss in one channel only (the bbd channel ) so it makes people noticing more than in a mono stompbox
I guess I answered by myself the hiss issue, did i?
Now let's go to the hum issue, as long as I don't want to change originality by mod /LPFiltering the circuit etc. in a try to eliminate hiss. I'm already used to it, a velvet windy old hiss..
🙂
Quote from: sarakisof on December 14, 2022, 03:25:15 AM
Ok, to clear things up.
Quote
EDIT: About hiss maybe it's normal. https://www.diystompboxes.com/smfforum/index.php?topic=122825.0
Just seems weird to most people in Pianet M because you have to deal with stereo here and you get the hiss in one channel only (the bbd channel ) so it makes people noticing more than in a mono stompbox
I guess I answered by myself the hiss issue, did i?
If someone explained the behaviour of a working chorus you would pretty much say what you said. There would be some very fine points that would separate a broken circuit and a good circuit if that's the only behaviour!
Quote
I don't want to change originality by mod /LPFiltering the circuit etc. in a try to eliminate hiss. I'm already used to it, a velvet windy old hiss..
That's fair enough.
Quote
Note: Have a look at the EDIT in my last post. Volt regulator and / or power output transistors are microphonic . You get really loud pops in some cases by chop stick poking. And you can microphonically listen to the tap being produced through speakers.
You might want to try this cap. The old schematic, which seems to match you board, doesn't have it. It's very bad practice to leave that cap off. It should be mounted right on the regulator pins.
(https://i.postimg.cc/K1Bcd8qF/regulator-capacitor-difference.png) (https://postimg.cc/K1Bcd8qF)
Quote
Also: the other day i found that during recapping i had left C27 unsoldered (really tired these days , recovering from H1N1 flu). Quickly fixed, but could something went wrong during all this time i was troubleshooting/ functioning the amp 8-12hrs/day?
Well if it didn't start oscillating it was probably working OK without it. Always a good practice to have it.
Quote
Now let's go to the hum issue
You should do follow the steps I posted in reply #26. The way hum gets into this circuit can depend if the RCA input socket has a path to ground. If you just pull the plug and leave the input open you will get different behaviour regarding hum. That even goes for the green wire passing the transformer. You can get a scenario where an open RCA doesn't care about the wire being close to the transformer and the shorted input does care about the wire being close to the transformer - you can also get the reverse! When the keyboard part is plugged in it will act more like the RCA input is shorted to ground - at least at low frequencies.
I think audio engineers were glad to see the back of BBD tech for delay jobs - the horror of bringing it all back in the current vintage fad! I had a Logan string synth back in the day, wonderful sound but the volume pedal wasn't a nice optional extra - it was essential to shut the noise off hands-free when you weren't playing it.
Is there a good photo of the heatsink arrangement? Many amplifier IC's used with a single supply will have a "live" heatsink tab that must not get grounded so there may be insulation to check.
QuoteYou might want to try this cap. The old schematic, which seems to match you board, doesn't have it. It's very bad practice to leave that cap off. It should be mounted right on the regulator pins.
Already tried but didn't make any difference at all.
Shot a 20sec. video chopsticking so you can hear by yourselves.
https://we.tl/t-Rg2U7FNCwR
QuoteIs there a good photo of the heatsink arrangement?
(https://i.postimg.cc/CBF04v4q/IMG-20221215-010447.jpg) (https://postimg.cc/CBF04v4q)
(https://i.postimg.cc/YhJwP23k/IMG-20221215-010648.jpg) (https://postimg.cc/YhJwP23k)
(https://i.postimg.cc/RWKzxrst/IMG-20221215-010908.jpg) (https://postimg.cc/RWKzxrst)
(https://i.postimg.cc/7C4rxBdW/IMG-20221215-011037.jpg) (https://postimg.cc/7C4rxBdW)
I don't think is such a case, didn't see any insulation when i replaced the IC3.
QuoteAlready tried but didn't make any difference at all.
Shot a 20sec. video chopsticking so you can hear by yourselves.
https://we.tl/t-Rg2U7FNCwR
From the TDA1111data sheet the tab terminal in connected to the IC substrate/ground.
The ESM532C datasheet is less clear about where the tab connects.
The regulator tabs connect to ground/0V.
Since none of the devices are isolated then that means all the IC's metal tabs are connecting through the heatsink. Since the aluminium has an oxide coating that connection can be crappy. If banging the device upsets the ground connections is cause that noise.
There's other possibilities:
- bad solder joints on the power amplifier pins
- bad solder joints on the regulator.
- even a bad solder joint somewhere else on the PCB.
Mechanical vibrations can propagate throughout the whole structure.
Another thing which isn't a great idea is connecting the tabs together creates multiple earth connections - that's can cause hum problems. It's an inherently bad set-up. Fixing stuff like this needs some experimentation.
As far as the knocking goes I'd check for bad connections but after that you might try isolating the regulator from the heatsink. While your at is see if the hum changes.
If the PCB grounds aren't done very well sometimes you have to cut tracks and re-route grounds with wires in order to remove hum.
You might want to check if the regulator and amplifiers are wired back to ground via PCB tracks. You wouldn't want to isolate the regulator if they are picking up the regulator ground via the screw on the tab!!!
Was there ever any heatsink compound applied to the back of the ICs? I don't think it should have any in this case as it would make the heatsink ground paths uncertain.
I suppose the best thing might be to fit heatsink insulation then the grounds can only go via the PCB paths. However, I think it's pretty much impossible to insulate without losing some thermal conduction to the heatsink, but I'd expect the ICs to cope with getting a little hotter.
QuoteThere's other possibilities:
- bad solder joints on the power amplifier pins
- bad solder joints on the regulator.
- even a bad solder joint somewhere else on the PCB.
Mechanical vibrations can propagate throughout the whole structure.
It was bad cracked solder joint due to mechanical vibrations (importing - exporting the pcb) during the repair job.
Chopstick tap microphonic issue completely solved.
It's great that each all the issues being solved thanks to you guys. Really appreciate.
Now, only one left (if it can be done), is the hum issue.
Will try to record a small sample and upload here later.
Back again. After Rob's words at post #26 about my 50/60Hz hum.
(Just to refresh our minds, there's normal slight mains hum by powering the unit up, but gets worse by turning Bass pot (P1) up.
https://www.clavinet.com/shema_PIANET_M.pdf
QuoteAs for your hum issue I have a suspicion you have a noisy ground. What happens when you pull the keyboard RCA out, does the hum also disappear from the Pianet or does it change and go buzzy? What happens if you put a short across the RCA input jack? Does that make the hum better or worse. Don't forget to set the Bass consistently to 12 O clock note the volume control positions. Advance the volume control if you can't hear hum to see if there's any hum there at all. The idea of all this is to see how much hum is from the amp part. :icon_frown:
.
When i pull the keyboard RCA out (disconnect from amp) the hum disappears. This tells us it's not the amp but the pickups themselves. All those had been discussed before at post #16 and below.
QuoteWithout input signal (pickups disconnected from amp) there's no Bass pot hum.
So maybe it has also to do with the pickups.
But i couldn't find anything culprit related to the pickups.
Pickups resistance (hot signal to gnd windings)/RCA signal to gnd measured at 49ohms. Continuity test beeps but seems right. Little winding turns here, we don't except smthng bigger like guitar/bass pups, more close to spring reverb transducer coils case. Pickups are ok.
Shorting RCA input gives the same hum (maybe tiiiny bit less than the hum we're trying to solve - by A/B test shorting/unshorting signal). This happens in both cases having the RCA connected to amp or disconnecting it.
I start to believe it's one of these cases or a combination of them. (Post #10 and below)
QuoteI'm not surprised you get hum with the volume turned down. The only volume control I see is a gain control in the preamp. Any hum present in the circuit is given free rein and boosting the bass is sure to increase it. There is a 7.5v reference supply filter C13, a 15v filter C3 and power amp 30v filters C27 and C37. Probably change those caps at a minimum.
QuoteDon't judge, i just replaced them with NOS electros. I know i know. It's my first time doing this. Scored a big bag full of NOS components for almost nothing.
it's the first time I'm using nos electros. Tested for capac. & leakage, used wisely and accordingly. It's for my own gear anyway, time will tell.
QuoteWith the volume control right at the start of the amp board, you may never get rid of the hum. It would ideally have a stereo volume control at the inputs to the power amps then the preamp circuit hum & noise can be turned to zero at the same time as any signal. The only noise left then is from the power amps and their supply.
NOS electro caps might well be below their best now, but if you can leave it powered up for a good while they can reform to a degree and hum may, if you're lucky, reduce.
I don't have any expensive test gear like oscillo here, but have a trusty Uni-T UT139C multimeter μΑ, Hz and many other features, a cheapo chinese "oscilloscope"(never used, mostly used DAW PC scopes when needed), diy signal traces and old common sense troubleshooting techniques ;D
Have solved more serious issues than this in the past so far but this thing drives me crazy. Maybe, in the end of the day they are all normal, as you guys told actually above, taking as fact how this circuit is designed. I'm more and more into realising it as every demo video i watch on YT they all have in common , pops, hum and hiss, by the time they start playing the instrument. ;D
EDIT: **** Forgot to mention smthng about electros (there's a huge movement against NOS electros, i was always against that for some of them if used in certain places, anyway). So just fir the record, for the C27 and C37, power amp filters, i put four fresh Panasonic FR ones (replacing C27,C28 and C37,C38) and hum was the same (i think i already mentioned that earlier above). The only one i didn't do that (i mean to replace the nos with fresh one) is the C13. I will do that too, but i don't think it will make a difference at all.
What you have described makes 100% sense to me.
Firstly the increase of hum when you advance the bass control is perfectly normal. You are boosting bass, hum is in the bass frequencies so it gets boosted. The only thing the test tells you is the hum is getting in before the bass control. Jim mentioned that a while back.
To summarise:
- pickups alone: no hum
- amp with open RCA: no hum
- amp + pickups: hum
- amp + shorted RCA: hum
Because of the last point, the problem is hum on the ground (or Vref) on the amp board.
If you look at the circuit with the RCA open C9 and R6 are just floating. The amplifier IC5 (pin 2,3,1) sort of has no gain regardless of the volume control setting.
When the RCA is shorted to ground C9 and R6 connect to ground. Now any hum signal along the ground or Vref will get amplified. The loop of interest is the (physical) loop from IC 5 pin 3 down through Vref, along the PCB ground tracks, to where the coax ground connects to the PCB, through the coax and back, then to the point where the coax core solders to the PCB then through C9 and R6 back to IC 5 pin 2.
If there are multiple ground points it makes a mess of trying to identify a loop. And in this case power supply hum can be placed into the ground tracks themselves.
Let assume the noise is on the ground. The cause will come down to some very fine details regarding where all the ground tracks go. For example, signal grounds can be passing through tracks carrying power supply current.
Even if the tracks seem OK the multiple ground points of the power amplifier ICs and the LM7815 regulator can cause a hidden connection between the power supply and the audio grounds through the heatsink.
Some pics of the bottom top and bottom of the PCB would help spot any obvious problems with the tracks.
However a very easy test would be to isolate the LM7815 regulator from the heatsink. Without looking at PCB tracks it stands out as a possible problem area.
Quote from: Rob Strand on December 16, 2022, 10:10:42 PM
Some pics of the bottom top and bottom of the PCB would help spot any obvious problems with the tracks.
However a very easy test would be to isolate the LM7815 regulator from the heatsink. Without looking at PCB tracks it stands out as a possible problem area.
LM7815 isolated from heatsink, no change at all.
I shot some pics of bottom and top of the board. Also made a Photoshop blend mix from both so with a little effort you could see top and bottom in one pic. It's not 100% accurate as the two pics combined need to be 1:1 and same dimensions but i did my best to align them properly.
Hope it can help.
PS. Ignore the flux mess, I'll clean the bottom when full job is done.
(https://i.postimg.cc/FfR3PTm1/TOP.jpg) (https://postimg.cc/FfR3PTm1)
(https://i.postimg.cc/JtDnp9k9/BOT.jpg) (https://postimg.cc/JtDnp9k9)
(https://i.postimg.cc/2Vd2B92Z/PIANET-M-PCB-TOP-BOT.jpg) (https://postimg.cc/2Vd2B92Z)
That is interesting because it looks like the power ground has to go to the regulator 0v before is daisy chains via the power amps toward the preamp side. If you are prepared to cut a few tracks + lift links, it should be possible to change it to a star ground scheme with some added wires to a star point at the power caps negative common.
It would also be worth investigating the AC input/transformer ground arrangement to get the whole picture. This was all often done in a manner to suit economy of production, especially in the past and you wouldn't do it (or be allowed) that way now.
Yes as long as I'm into it i realise that it's simply how it was designed. AC input/trafo gnd is indeed built in an economic manner. On the other hand I'm romantic enough with this kind of old stuff, specially this one, as i know I'm one of the few people owning this unit in my area at least.
As mentioned above, i would like to do my best but in terms of not altering the originality of this piece.
For now i think I'm in a good level with it so far, maybe I'll install dip sockets for all IC's just to make my life easier in a future repair and that's it.
Rob, Jim and other people contributed here, thank you very much, without you things would be more complicated for me. Always open on learning from you guys.
One last thing only (and the very first one too, as i never managed to solve it 100%) is those pops in powering on and off the machine, even with all pots turned down. There are not so loud now (specially this robotic faded noise which has almost completely gone after having replaced C1,C2 filters), but it isn't a noiseless/popless shut on/off either. It's a small "bang/puff" when you release on/off switch, each time the same. Maybe there's an easy fix for this, like an old trick putting a safety x/y cap across mains/to gnd or smthng similar?
I'm still trying to follow where the grounds go.
When the ground enters the lower left side (as orientated in the pic) of the first power amplifier it seems to disappear. I was thinking they passed all the ground current *through* that IC. Haven't finished looking.
The other weird thing they have definitely done is created a very broken ground trace. The grounds connect to the solder tabs of the pots then continues through the pot body and then comes out on another solder tab. That continues for all the pots.
I was wondering if the pot are mounted to a metal panel or a wood panel?
If it is metal, does that metal connected through screws and metal chassis back to the aluminum heatsink?
Given what what they have done to the pots I'm suspicious they are running the ground through the amp heatsink tabs.
While I haven't identified any cause, such a connect is going to be a headache to mod.
As for the turn-on pop. There's not much you can do directly as it normally occurs because the chips lose control when the power goes off. Also, the amps have output caps so that type of amplifier tends to bang at turn-on. Some of the modern amplifier IC's had extra circuitry inside to have "bangless" power on and off - the reason they put it in there is because of this same objectionable behaviour on the old ICs! Having said that if you could disconnect the two preamps from the power amp and they band goes away then the bang could be from the preamp. You can sometimes do simple mods to fix the bang from preamps. It's going to take some form of investigation, then some of mods! You have to change something and that means cutting tracks etc. A way some stereos side stepped fixing the electronics was to have relays on the speakers which delayed connecting the speakers at power on and quickly disconnected the speakers at power off!
QuoteI was wondering if the pot are mounted to a metal panel or a wood panel?
they're mounted to a wood panel.
Tried every possible way (except for modding anyway) and it's all about how it's built Rob. Did my best eliminating any noise, I'm done and happy of how it is now.
Quote
As for the turn-on pop.....
great infos here, read and kept everything in mind but as i said above I'm not going into cutting tracks and heavy mods. I see this instrument as a piece of history in a romantic way.
Now, a very last thing I'd like to do from the beginning with it (mentioned in second page too). It's the only mod I want to do with it, even in this case I wouldn't like to open a new hole, or alter the wood case / chassis at all.
I'll explain. I want to mod it to a Pianet T (completely bypass the amp) so i can use it like a passive instrument, but being able to return to Pianet M and make use of its amp/speakers when i want to.
To do so, i had to get the Pianet T's impedance matching transformer. I sourced the appropriate equivalent replacement one (Calrad 45-703 as suggested by Hohner). It's just a mini audio 15:1 trafo 2.26K : 43 ohms wired backwards. Pickups to 43ohms primary, 2.2K sec to jack out (across a 2nF bypass cap-most people remove that) ready for external amp.
(https://i.postimg.cc/pp47g3TB/IMG-20221212-032329.jpg) (https://postimg.cc/pp47g3TB)
(https://i.postimg.cc/mhZ0MQJ7/ooxdg3v32tacj84ruhcr.jpg) (https://postimg.cc/mhZ0MQJ7)
(https://i.postimg.cc/F1PwxYX8/oxzdabi396hxuzrgbvht.jpg) (https://postimg.cc/F1PwxYX8)
(https://i.postimg.cc/ykktp7Vd/pianet-t-18-645x0-is.jpg) (https://postimg.cc/ykktp7Vd)
How could i do this simple mod without opening hole for jack out? My first idea was to just solder an extra coax/shield cable from RCA input socket to one of the two DIN outputs (canceling output for hifi speakers or headphones) which probably I'm never going to use anyway , but thought again why altering the function of the unit and who knows if someday in the future I'll need to use that headphones out?
In that case the idea was then to make a DIY cable from DIN to a box with the trafo inside and a jack out, so from that i would connect a guitar cable to external amp.
Then i realised that i could do the job from underneath (wood base of the instrument) and the trafo could be simply mounted inside there exactly like in the T (see the pic above) on the upper right corner.
Just soldering an extra coax (like and where the already green starts) wire from pickups end solder points. (see the pic)
(https://i.postimg.cc/HjRnhsQv/IMG-20221212-063058.jpg) (https://postimg.cc/HjRnhsQv)
going to the trafo.
Then there are many unused holes in the M's base (intended for T - actually the keyboard bases are the same, just in M they got veneered and T black tolexed), which i could even pass through a hardwired output guitar cable, just like they were doing in Farfisa Compact organs.
BUT, in that case (that goes for the first case too), are there any don'ts in soldering an extra cables/wires coexisting with the old green one? Any losses? I guess no, have seen many signal coax cables starting from same turret lug in every organ I've repaired.
The whole idea is to avoid opening the instrument (unscrewing) disconnecting that green M's RCA and connecting another T's RCA and vice versa every time, or using a toggle switch or whatever.
Simply, when i want T, i will just plug the hardwired cable to external amp WITHOUT powering up M. And when i want M, do what i did before turning on M, just "T's guitar cable" being unused floating around. Is this bad, to have an "extra" cable not affecting circuit, floating?
(https://i.postimg.cc/DJW67wmp/received-1557084981423681.jpg) (https://postimg.cc/DJW67wmp)
Any other recommendations and ideas welcome.
Quotethey're mounted to a wood panel.
Tried every possible way (except for modding anyway) and it's all about how it's built Rob. Did my best eliminating any noise, I'm done and happy of how it is now.
Well if it's wood then at least you don't have a whole lot of hum loops connecting back to the chassis. It really narrows things down to perhaps the fact the amp IC's are connecting to the heatsink. (Of course no guarantees that's the cause, but it's something to pursue.)
Quotei said above I'm not going into cutting tracks and heavy mods. I see this instrument as a piece of history in a romantic way.
I understand 100%. I can tell you now I've fixed all sorts of hum problems in equipment and sometimes you end-up with a lot of cut tracks, a big mess really. Neater efforts a result of using isolated connections so there less audio grounds through the chassis.
QuoteHow could i do this simple mod without opening hole for jack out?
Is the RCA connect accessible from the outside? If so just build an external box with the transformer in it then plug the RCA into that.
QuoteIs the RCA connect accessible from the outside? If so just build an external box with the transformer in it then plug the RCA into that
Nope, that's why i want to find a solution so to avoid unscrewing opening the instrument each time.
The RCA is located underneath amp cabinet. You have to unscrew about 8 screws from the narrow sides to lift up and unplug the RCA cable.
(https://i.postimg.cc/3dM0t5DT/IMG-20221223-074435.jpg) (https://postimg.cc/3dM0t5DT)
(https://i.postimg.cc/zbZ30TVk/IMG-20221223-075343.jpg) (https://postimg.cc/zbZ30TVk)
Is soldering (in the same place with the old green) like that an extra coax cable (which will go to trafo then to an output) wrong?
(https://i.postimg.cc/DJW67wmp/received-1557084981423681.jpg) (https://postimg.cc/DJW67wmp)
Have you considered a bluetooth transmitter inside the box? No need for holes and you can probably power it from the rest of the circuitry. Failing that, just an RF link. Even a baby monitor could get your signal to the outside world with no holes and they usually run from a 9 VDC 200 mA adapter and they have a selection of two frequencies to avoid jamming. And they pass all the necessary FCC certifications.
Quote from: amptramp on December 23, 2022, 07:19:32 AM
Have you considered a bluetooth transmitter inside the box? No need for holes and you can probably power it from the rest of the circuitry. Failing that, just an RF link. Even a baby monitor could get your signal to the outside world with no holes and they usually run from a 9 VDC 200 mA adapter and they have a selection of two frequencies to avoid jamming. And they pass all the necessary FCC certifications.
Thought of that for a while but soon decided it's too modernized for my taste. :icon_biggrin:
About the query i was wondering above, could soldering another extra coax cable like the one which already exists (in the same place) be wrong ? See the pic below, i have drawn the extra one coax green cable.
(https://i.postimg.cc/8FPZjndQ/received-1557084981423681.jpg) (https://postimg.cc/8FPZjndQ)
(https://i.postimg.cc/Wtwy5r94/IMG-20221223-205916.jpg) (https://postimg.cc/Wtwy5r94)
QuoteAbout the query i was wondering above, could soldering another extra coax cable like the one which already exists (in the same place) be wrong ? See the pic below, i have drawn the extra one coax green cable.
Soldering on a second wire is OK provided you don't start getting noise problems. A good coax can help but also keeping the center leads as short as possible at the solder points.
The problem with the transformer is it is permanently connected across the pickup so it will add a permanent load. The loading works the other way too. When the pickup is in use the existing electronics is loading the pickup (R6 1.5k). If you wanted to run the keyboard unpowered via the transformer output the 1.5k is feeding into unpowered electronics. You will get sound out for sure but loading something fundamental like the pickups could change the sound.
You could do a test but sometimes the changes in sound are subtle.
One way around these issues is to use a jack with switch contacts. When you insert the jack it connects the new circuit and disconnects the existing circuit. Instead of using jack switches you can use a small signal relay so when the power is off the signal is disconnects from the existing ckt and sends the signal to the transformer and added jack.
QuoteTo do so, i had to get the Pianet T's impedance matching transformer. I sourced the appropriate equivalent replacement one (Calrad 45-703 as suggested by Hohner). It's just a mini audio 15:1 trafo 2.26K : 43 ohms wired backwards. Pickups to 43ohms primary, 2.2K sec to jack out (across a 2nF bypass cap-most people remove that) ready for external amp.
The impedance values you quoted are the DC resistances of the coil.
The true impedance levels for the transformer are much higher than the DC resistance.
I'd guess somewhere around primary 43ohm * 20 = 1k ohm and secondary 2.26k*20 = 45k ohm
Here's the datasheet,
https://datasheet.octopart.com/45-775-Calrad-datasheet-37165076.pdf
45-703 Mic Input 200k ohm (DCR 2.26k), Output 1k ohm (DCR 43 ohm).
(Someone posted the real Pianet T transformer DC resistances at 38 ohm and 2.57k ohm.)
So the transformer will end-up putting 1k to 2k of loading on the pickup (very rough). Which just happens
to line-up with the R6 value.
The pickup *DC* resistance is 43 ohm, so you expect to load it with 1k to 2k. So that adds up as well.
(I'm not sure if that's the entire pickup or just one coil for a single key.)
FWIW, the purpose of the 2nF loading cap is get the maximum bandwidth out of the transformer. You often have to tune it for each specific transformer and it's not a clear-cut process.
All I'm saying here is the transformer looks like it is correct for the job but the problem is the affect on the tone of two lots of loading can only be done by experiment.
QuoteThe impedance values you quoted are the DC resistances of the coil
sure indeed.
QuoteI'm not sure if that's the entire pickup or just one coil for a single key.
it's the entire pickups.
In mine entire pickups DC resistance is 48ohms.
All you mentioned are correct, amazed at how much homework you did on this thread Rob, you've discovered almost every info i have also found searching the net, like it was your case. Really honoured.
QuoteOne way around these issues is to use a jack with switch contacts. When you insert the jack it connects the new circuit and disconnects the existing circuit.
I will do that. I'd really appreciate if you could provide a simple diagram and give ideas on how i could make the wiring inside the instrument so i can finally close the case and start playing it. Even via a simple hand sketch diagram.
So, have you decided to add a jack socket to the case?
You probably only need a socket with switching contacts, however, the switching needs to be before the output transformer so it routes there with a plug inserted or routes to the preamp with it out. If I've got that right, you can't use just any switched socket as they do not isolate both circuits from the final output connection. The only commonly available isolated ones I know * are intended to be PCB mounted - they are used in some Fender and Marshall amps.
I do have an example of a traditional metal frame 1/4" socket with an impressive array of contacts with insulated operating, it came from the headphone jack of a Farfisa organ. It would be ideal but I don't think anyone makes anything like that now *.
* I stand to be corrected!
I think Rob may have already suggested the best solution - a relay. With the preamp switched off, the contacts route to the transformer. Switched on, the relay picks and it routes to the preamp.
The lowest-tech/easy way would be to fit a switch by the extra socket to do the same thing.
Here's the idea:
(https://i.postimg.cc/QH5fKGzt/Pianet-M-with-Pianet-T-Socket-Option.png) (https://postimg.cc/QH5fKGzt)
You will need one of these sockets:
https://www.wiltronics.com.au/product/5170/6-5mm-stereo-socket-with-dpdt-switch/
(https://www.wiltronics.com.au/wp-content/uploads/products/65mm-stereo-socket-with-dpdt-switch.jpg)
To explain a a few things:
(a) The whole idea is to add a passive Pianet T connection to a Pianet M unit but without the pickups being loaded by both the transformer or the Pianet amplifier input.
(b) The Pianet amplifier ground is disconnected from the socket ground to prevent hum loops when then Pianet is plugged into the mains and the passive connection is being used.
These added requirements means we need to use a 6.5mm socket with isolated DPDT switches. These socket have been readily available for a long time.
The beefs I have with the solution are:
- The signals have to pass through contacts.
- Switching ground is a little undesirable but it meets the requirements.
- Those 6.5mm socket aren't as reliable as the conventional sockets.
(but just the same, they are used in many products.)
Thank you Rob. After Jim's idea about using switch, i was about to use a DPDT switch and just a simple jack socket. The same idea like yours, but using a simple TS socket instead of one with isolated DPDT switching (J1).
(https://i.postimg.cc/Wdgcx8wB/IMG-20221229-095312.jpg) (https://postimg.cc/Wdgcx8wB)
Two questions:
1. We want the specific J1 in order to switch ground and prevent hum loops, so i guess using a common one is denied.
I have many open stereo switched sockets in my shelves. Why these won't work?
2. In your diagram the switch is a DPDT one, correct? Or it's a relay? If it's a relay, then if i use a DPDT switch, do i definitely need the J1?
Quote1. We want the specific J1 in order to switch ground and prevent hum loops, so i guess using a common one is denied.
It's not denied but there is a chance of a hum loop if the Pianet is plugged in (on or off) and the external amplifier is also grounded. A some point these problems always show up.
Another way, perhaps even a better way around this, is to not switch the ground. What we do instead is use the transformer to do the ground isolation.
The changes would be:
- Don't switch the Pianet side ground with the contacts. The Pianet grounds always connect inside the unit.
- Break the ground connection between the primary and secondary of the transformer; currently the Pianet-T
connects the ground on both side. That's fine for the Pianet T because it doesn't connect to mains earth.
The primary (Pianet) side of the transformer connection to the Pianet ground, and the second (external) side
of the transformer connects to the socket ground.
- Optional but good for preventing RF issues. Add a 100nF cap in parallel with 100 ohm between the
socket side ground and the Pianet side ground.
See figure 2 on this page for the resistor+ capacitor idea, (in your case use 100 ohm)
https://sound-au.com/project35.htm
Treat the left side as Pianet (no sockets) and the right side as the added socket. No need for the earth switch.
Quote2. In your diagram the switch is a DPDT one, correct? Or it's a relay? If it's a relay, then if i use a DPDT switch, do i definitely need the J1?
No, that socket I linked has a DPDT contact built in. That's the advantage of those sockets.
QuoteNo, that socket I linked has a DPDT contact built in. That's the advantage of those sockets.
Cannot find those DPDT sockets here.
What if i use a DPDT switch and a mono socket next to it like that?
(https://i.postimg.cc/Wdgcx8wB/IMG-20221229-095312.jpg) (https://postimg.cc/Wdgcx8wB)
Think about how you will use the instrument.
As it's decided it can't do both modes at the same time and it must have separate outputs, how do you want it to work in practice?
If it were me, I'd want to have it set up so I could leave things plugged in and only need to switch things on or off. I'd have the M feeding a mixer, but the T's were often used like guitars with pedals and combo amps so the separate output is a good thing.
I'd go with the separate changeover switch.
It will be highly likely both feeds will route to the main safety ground, so follow Rob's suggestions with ground treatment.
(https://sound-au.com/p35-f2.gif)
The 10R//100nF network shown here really is effective. You don't need the ground lift switch shown.
What about this, simplifies switch wiring,
(https://i.postimg.cc/94LKbK5T/Pianet-M-with-Pianet-T-Socket-Option-2.png) (https://postimg.cc/94LKbK5T)
Quote from: Rob Strand on December 29, 2022, 02:57:15 PM
What about this, simplifies switch wiring,
(https://i.postimg.cc/94LKbK5T/Pianet-M-with-Pianet-T-Socket-Option-2.png) (https://postimg.cc/94LKbK5T)
Nice! It was in front of my eyes but i had my mind into complicated things and couldn't see it. Seems the best and simplest solution so far.
Going this way, we don't bother with ground switching.
The switch in this diagram is a common spdt (on off on) one, correct?
I don't have a 100nF old cap in hand (only chinese films - you know about my love in old components), but have some 82nF, 150nF tasty mustards. Can i use one of those instead (82or150nF) and should i change 10R to another value then?
QuoteThe switch in this diagram is a common spdt (on off on) one, correct?
Yes, as simple as it can get.
QuoteI don't have a 100nF old cap in hand (only chinese films - you know about my love in old components), but have some 82nF, 150nF tasty mustards. Can i use one of those instead (82or150nF) and should i change 10R to another value then?
It's not critical at all. I'd probably go for the 82nF.
The resistor isn't that critical either (10 ohm to 100 ohm). For stuff like this I'd probably use something around 47 ohm to 100 ohm and only try 10 ohm if I could hear some buzz in passive mode.
FYI, the way the switch is set up it just leaves the amp input floating. I figured a non-inverting input with 1k5 input impedance + connection with a coax is going to be fine. You could add a 1M to ground across the amp input to stop the pop when you switch from passive to active mode. Another way is to use another switch contact and short the amp input to ground - I was trying to avoid doing that.
I just finally sourced the transformer. Quick tested with alligator clips connected straight to pickups then to a jack and it works indeed. Apart from its four pin legs it has the common metal screening mount. How do i connect the two screening pin legs? To gnd alongside with other two pri. & sec. "gnd" pins, or just solder alone just for supporting?
(https://i.postimg.cc/jDCsScdx/IMG-20221231-025111.jpg) (https://postimg.cc/jDCsScdx)
QuoteYou could add a 1M to ground across the amp input to stop the pop when you switch from passive to active mode.
Like that (red colour edit)?
(https://i.postimg.cc/Mn4zMBvy/received-858029428812982.webp) (https://postimg.cc/Mn4zMBvy)
Quote
I just finally sourced the transformer. Quick tested with alligator clips connected straight to pickups then to a jack and it works indeed. Apart from its four pin legs it has the common metal screening mount. How do i connect the two screening pin legs? To gnd alongside with other two pri. & sec. "gnd" pins, or just solder alone just for supporting?
It's probably best to connect them to the external jack ground, just use a wire.
QuoteYou could add a 1M to ground across the amp input to stop the pop when you switch from passive to active mode.
Like that (red colour edit)?
Yes, that's it. It's better if it doesn't pop, more professional.
I don't think that is a "screening mount". I think it is just to hold it to the PCB. I have frequently used these by just gluing them upside-down (scrape any wax coating) to the chassis and bring wires off the leads.
QuoteI don't think that is a "screening mount". I think it is just to hold it to the PCB. I have frequently used these by just gluing them upside-down (scrape any wax coating) to the chassis and bring wires off the leads.
Technically not a screen but it does provide some screening, best not to have floating metal.
Definitely it's not a common screening can. Have seen them as output trafos in old scrap crt TV's I've salvaged in the past and those pins were just soldered alone to provide stability just hold to PCB.
QuoteIt's probably best to connect them to the external jack ground, just use a wire.
i had done so in my G9 Gyraf tube pre back in the old building days (now only repairs and mods 😂) for input & output OEP trafos (with normal screening cans) with success.
So, i won't solder those "shield" pins into ground plane, just solder alone holding to PCB and only connect one pin to jack ground via wire, correct?
EDIT: What about that 2nF bypass cap across secondaries?
Should i install it normally in the new diagram, right? (blue colour edit)
(https://i.postimg.cc/k6hHw0tz/received-1343878279764142.webp) (https://postimg.cc/k6hHw0tz)
Go ahead and ground them, if you wish.
QuoteEDIT: What about that 2nF bypass cap across secondaries?
Should i install it normally in the new diagram, right? (blue colour edit)
You can spend a lot of time testing to choose that cap. It's not uncommon for technical reasons to add a resistor in series with the cap. It also depends on the fine details of the *specific* transformer. The cap can be used to tune the high frequency performance of the transformer. However it does more than that it can help reduce parasitic resonances.
The value doesn't look unreasonable to me. You can only take the manufacturer's recommendation, 2n2 would be the closest value. If you wanted to be a little cautious you could back it off to 1n5.
Happy new year everyone. Back to base after some days off. I'm in the final procces with Rob's diagram.
Just a question. Does polarity of the mini audio transformer matters?
(https://i.postimg.cc/TLwghMst/IMG-20230104-123043.jpg) (https://postimg.cc/TLwghMst)
(https://i.postimg.cc/vxxnL7b9/received-1343878279764142.webp) (https://postimg.cc/vxxnL7b9)
I usually open out stripboard/perfboard holes to take the traffy mounting tags. Bend them over, they are eminently solderable. If the traffy can go at the edge of the board, one tag can hang over and be clenched around. If you can have a board only the width of the traffy, then both tags can be clenched on the edges. And yes, I'd connect a wire to ground.
Some small PCB mount audio transformers I've seen have a mechanical drawing showing the reference "dot" for polarity at opposite corners although, on schematics, the dots usually show at the same top end. Those with coloured wires can simply list the wires.
I can't find data for the pcb mount version you have although if you can find a photo of the wired version, those wires probably come out at the same ends of the body.
Yes, i didn't mentioned that in previous post, i already used this paper note which came up with my traffo bag
(https://i.postimg.cc/tYXDpQzJ/IMG-20230104-123043.jpg) (https://postimg.cc/tYXDpQzJ)
and compared with some 45-703's with coloured wires i found online, realised that the polarity is opposite corners order (mine doesn't came up with coloured wires, just plain legs and a "P" marking for primary side and probably at the start winding).
(https://i.postimg.cc/tYCfDVwB/45-703.jpg) (https://postimg.cc/tYCfDVwB)
(https://i.postimg.cc/nM1gv1Rs/s-l1600-1.jpg) (https://postimg.cc/nM1gv1Rs)
In a simple alligator clips test i made, the result was the same whatever polarity i wired them though.
It worked perfectly like that for example (red and white are hot/signal tips, greens are gnd sleeves , so same direction).
(https://i.postimg.cc/TK2RVwJx/IMG-20221230-114653.jpg) (https://postimg.cc/TK2RVwJx)
Do you think the polarity is critical here? If i have to wire them in opposite direction it will be difficult in a stripboard board I'm planning to use.
I'm also thinking of building it in a point to point terminal strip board.
So far, my idea is to avoid opening new holes or damaging / altering as less as possible original build.
First idea was to build Rob's diagram (board and traffo) in a board in the keyboard section (upper right, exactly like in the Pianet T) and open two holes (switch and jack) underneath wood base (holes like pickups cavities so you can have hand access to release toggle switch and in order toggle and jack wouldn't prevent instrument lying flat on table).
So the mod would be made into wooden keyboard section only, no amp cabinet upper case damage , it would be playable (rca amp disconnected) without amp only via keyboard itself, exactly just like in the T, very practical for service/troubleshooting purposes etc.. No one could notice any holes / damage until he would look underneath.
It was the perfect idea, until I realised the M has stand legs, it's a spinet instrument and that the only free space i was planning to drill those two holes, was the place where the legs and the upper amp cabinet are mounted to the keyboard. :icon_cry:
So, the idea goes to amp cabinet, especially in the power socket / outputs metal panel area.
(https://i.postimg.cc/LqSSvspv/IMG-20221231-113309.jpg) (https://postimg.cc/LqSSvspv)
"Hmm, i can see two already drilled round DIN holes, headphone and extension to hi fi speakers outputs I'm probably never going to use..."
After days of thinking, came up with this. In order altering originality as less as possible, i removed the rivets of the two outs without damaging them. They were ready to come off prone to years of usage anyway, so screws instead of rivets are always a good thing in those cases if someone wants to remove my mod and put the original DINs back in the future.
So DINs will be still there mounted inside with cable adh ties. The user can use them if open the panel only. Will never use them anyway.
(https://i.postimg.cc/w750Lxw9/IMG-20230103-024951.jpg) (https://postimg.cc/w750Lxw9)
In DINs place i will install the switch and the jack. Found some creative ways to mount them as their diameter is smaller than DINs hole. Would be better if i could find a more thick metal/aluminum even plastic plate though. Those are those thin "on off" name plates from older switches.
(https://i.postimg.cc/Btmx087L/IMG-20230105-022437.jpg) (https://postimg.cc/Btmx087L)
And the final result from the outer side will be smthng like that (with screws and maybe a blueing / darkening of the plates / or other plates will be even more beautiful). No extra screws, no any new hole opened. The unit is like before.
(https://i.postimg.cc/k6zw7Bfd/IMG-20230105-030046.jpg) (https://postimg.cc/k6zw7Bfd)
Now the big thing is about the small circuit/traffo combo. Where exactly and how? Two days thinking of many ideas but cannot decide yet. 😂
Best bet would be a double sided PCB board (Eagle and PCBway) in the back of the panel , so the switch and jack would be soldered straight to pcb , and mounted everything there. Like we do in modern stomps. Jack and switch hold the PCB itself. Of course traffo and components all soldered in that same pcb. Simple and end of story. But this would be so modernized for my tastes and Pianet's nature. Would like a fat heavy duty toggle and cannot find one with pcb legs. Pcb legs are used in those small thin toggle ones. Slide switch would be good (they were widely used in the past too, see Philicorda organs underneath so they can lie flat), but then i have to find a metal/aluminum panel with rectangular slot/notch and those switch nameplates have round hole indeed. Damn mechanical things again as always..😡
I'm thinking smthng like a p2p layout for traffo, 10ohm,100nF, 1M, 2nF or completely handwired in the air, or on a strip board. Maybe i can mount the board on the already drilled screws..
Any ideas welcome..
(https://i.postimg.cc/RJvQTyCN/IMG-20230105-030856.jpg) (https://postimg.cc/RJvQTyCN)
I don't think you need to worry about polarity in this case. If you were to use the T & M outputs together, it would be best if the phases matched, but you won't be. You can do whatever is easiest to lay out. It is, however, best practice to maintain original phase through a circuit if you can. It won't matter if the start ends are grounds.
The way Farfisa added stuff was to install an aluminium angle for the jacks and switches mounted so you had access through a cutout in the rear panel. Slide switches would be used for their low profile.
A PCB would be provided, simply screwed onto the base with plastic plain standoffs. Often, wiring pins were fitted to the board as the way they were made was to complete the mechanical assembly and then fit prepared cabling in situ.
Could something like that work in terms of good mechanical support & mounting of the little traffo? (No mount pins & PCB used).
(https://i.postimg.cc/tsbzVzcC/IMG-20221231-143152.jpg) (https://postimg.cc/tsbzVzcC)
(https://i.postimg.cc/8FPBZzD2/IMG-20230108-061518.jpg) (https://postimg.cc/8FPBZzD2)
The two eyelet boards will be then screwed onto the base with plastic plain standoffs.
The mechanical stress for any mounting needs to be transferred to body of the transformer via the mounting tabs. Hanging off the pins like that, or anything similar, is likely to fail at some point. The pins should have no mechanical stress or movement.
Quote from: Rob Strand on January 08, 2023, 02:18:38 AM
The mechanical stress for any mounting needs to be transferred to body of the transformer via the mounting tabs. Hanging off the pins like that, or anything similar, is likely to fail at some point. The pins should have no mechanical stress or movement.
I was afraid of that, i guess i have to go with a board option. The boards i have and will fit my layout i have in mind are those strip / vero boards old style with common copper. Were nice to me with everything I've built in the past but as years pass and i read more and more negatives about them people complaining about not being so robust, easily oxidizing etc. I've been suspicious of them. Nowadays, when it's about PCBs, i use to create in Eagle and send gerbers to China for manufacturing.
But in this case, I don't want to wait for so long, plus i find this
way too "modernized" for a Pianet like this. I think best bet would be an old style hand copper etched board (like they did in the T's little board I've posted in previous pages) but I was never into PCB etching solutions etc. Won't buy all those chemicals for just one tiny project like that, nor do such for the first time in a project like a valuable Pianet.
Do you think I'm overthinking it? Go with a vero spray some clear lacquer underneath / copper side and be done with it?
If you search for it, there are a few DIY etching processes using common chemicals that you might already have. The traditional brown resin-bonded paper copper-clad board is not so widely stocked, despite it still being common in consumer electronics and of course, stripboard.
Whatever you do, tarnishing is still possible. PCB lacquer can be sprayed on, essentially polyurethane varnish. You can solder through it.
After a long, nice journey I'm pleased to announce that i completed the Pianet M's mod with full success. No hum, no any noise, clean signals, mod works as it should. You just push the toggle switch up and you get Passive function (Pianet T mode), then you switch the toggle down & powering unit up and you return to its original normal function. No extra holes drilled, no components removed. Originality of the instrument kept intact. Just perfect.
(https://i.postimg.cc/62mcRGb4/IMG-20230109-065213.jpg) (https://postimg.cc/62mcRGb4)
(https://i.postimg.cc/qgs4Vkpf/IMG-20230118-042435.jpg) (https://postimg.cc/qgs4Vkpf)
(https://i.postimg.cc/1fY9Mv94/IMG-20230119-111913.jpg) (https://postimg.cc/1fY9Mv94)
I'll just add an embossing tape label reading "Passive" or "Pianet T" above the switch and I'm done.
(https://i.postimg.cc/rD8P0T6r/IMG-20230105-030046.jpg) (https://postimg.cc/rD8P0T6r)
Special thanks to Rob, Jim, PRR and everyone else contributed here. Without your valuable help it could never happen.