Thank you for your explanation
The article I have read about K75 and teflon bypass is this one. There is an article, that one, about K72 and TF1. There are both in Valtek shop (yes it was the shop I was speaking of), but K72 are 0,01uf, maybe to big...
TF1 are available in 1200pf and 850pf. Does a smaller value cap work in higher frequencies or it takes effect in all the spectrum (but less perceptible than a bigger bypass cap) ? I mean... do the 2200pf and 850pf work in the same range of frequencies ?
Maybe I prefer to try with 850pf if its effect is lighter or concerns higher frequencies than 2200pf... but after all the difference between this values is so small...
I am sorry for my english
Marco
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Your english is fine.Thank you for your explanation
The article I have read about K75 and teflon bypass is this one. There is an article, that one, about K72 and TF1. There are both in Valtek shop (yes it was the shop I was speaking of), but K72 are 0,01uf, maybe to big...
TF1 are available in 1200pf and 850pf. Does a smaller value cap work in higher frequencies or it takes effect in all the spectrum (but less perceptible than a bigger bypass cap) ? I mean... do the 2200pf and 850pf work in the same range of frequencies ?
Maybe I prefer to try with 850pf if its effect is lighter or concerns higher frequencies than 2200pf... but after all the difference between this values is so small...
I am sorry for my english
My Italian is zero.This is only my opinion about bypass cap value. I don't know if it is technically correct.
The small cap value is good because the internal resonance frequency goes up as the cap gets smaller. Adding a small bypass keeps the cap in it's operation zone and lets the higher frequencies pass through clearly. Above a certain value, a smaller value cap doesn't help anymore regarding resonance because the resonance is above any audio frequency. My guess is that even 0.01 uF is high enough for resonance.
The other factor in bypass cap value is how the main cap and bypass cap mix together in sound. A bigger bypass cap seems to make it's sound stronger and sometimes it doesn't make a smooth combination with the main cap. For example, with the K75, I started with a 0.022 uF bypass cap an the bypass cap made the high frequency sound too strong for the main cap. Next, I tried 3000 pF and I thought that was much better, but still a little bit strong in my opinion. Then I tried 1000 pF and found it to be the best value for me with the 1 uF K75. The difference between the 3000 and 1000 pF was small, but you can hear it.
I suspect that either the 1200 pF or the 850 pF would be almost the same as the 1000 pF. Pick either one and you will be OK.
One word of caution. Some of the older FT-1 teflon caps have lost value as they get older. I have found that about 1 of 10 are out of spec in the smaller value caps. This is not a big problem. You can email valtek and he will refund your money for the number of bad caps that you find. But you probably should order a few extra, just to make sure.
Of course, my system will be different than your system, so your choice may be different. I hope you enjoy trying a few different choices and deciding what works best for you. Isn't DIY fun?
Jac
Thank you again for share your experience about these cap ! Yes it's fun, it's just a question of time and money!
Maybe I will have some problems to fit K75 in the board, I have seen some photos and they are about 5cm long... so I don't know yet if it's better to try to put them under the board or in the upper face. Every way, If it's impossible to fit them correctly, I will use these cap for the crossover of my speakers, because I have a 1uf cap in series to tweeter.
Bye !
In my case, I put the bypass cap directly between in normal C13 terminals on the board. The bigger, low frequency cap hangs off the board a little. This was something that Andrew suggested and I think it is a good one. The bypass cap carries the high frequency, so it is good to put it as close to the ground plane as possible for minimum inductance. The low frequency cap is not as important to minimize inductance because it mainly carries lower frequency.
Outside of the board, as atupi suggests is also OK, but I might want to keep the wire from the audio ground close to the high frequency cap for the same reason.
Jac
I had very good experience with K75 bypassed with teflon FT1 0.019uF also from Valtek .
K71-4 seemed a bit dry for me also
This is a great example of different system, different choices. I respect atupi's experience with 0.019 uF. That would have been too strong for my system, but every person and every system is different.
If I remember correctly, Jon L used 2200 pF FT-1 for bypassing, but he also used larger ERO polypropylene. The best thing is to buy a few cheap bypass caps and try them.
Jac
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@ Atupi: k75 bypassed by FT1 works well, fine
About the way to place the K75 in the board... I still don't have FE, I have rev C with a single PCB for the right and left channels. I cannot put the K75 out of the board. I suspect that the only solution is to place the caps under the PCB well protecting them by a heat shrink sleeve, I could fix then FT1 in C13/29 terminals. Will this placement interact negatively with the circuit ?
About the way to place the K75 in the board... I still don't have FE, I have rev C with a single PCB for the right and left channels. I cannot put the K75 out of the board. I suspect that the only solution is to place the caps under the PCB well protecting them by a heat shrink sleeve, I could fix then FT1 in C13/29 terminals. Will this placement interact negatively with the circuit ?
I ordered the BOM from mouser some time ago and have been waiting for them to get some of the components which were on backorder. I checked with them yesterday and they had got some more of the components which just left the 2 WIMA 1000pF caps and the 2 KAO Speer 47K resistors. I asked them to cancel these items and send me the rest. I ordered the missing components from ebay, I found the caps ok but could not find KAO Speer resistors so I ordered some generic metal film ones which arrived today! How important are these 47K resistors in terms of sound quality and will generic ones do ok in this position?
Cheers
Davy
Cheers
Davy
If your speaking about R20 don't worry about it, it's in the DC protection circuitry.
I installed all the surface mount components today, it went ok (I think) except I noticed I had fitted R39 (470K) the opposite way around from the writing on the board. I am not aware of directional issue with resistors and it measures the same in both directions. I did try to de-solder it but as usual with these components, I failed. If I had two soldering irons I dare say I could have removed it but I don't.
I noticed a small typo on the board, not a problem for me, I worked it out quickly enough but just in case anyone else gets confused. R37 (3.3K SMD resistor) is marked as R3, the number 7 is missing from the print label.
I hope to fit all of the rest of the components tomorrow when my eyes have recovered.
I noticed a small typo on the board, not a problem for me, I worked it out quickly enough but just in case anyone else gets confused. R37 (3.3K SMD resistor) is marked as R3, the number 7 is missing from the print label.
I hope to fit all of the rest of the components tomorrow when my eyes have recovered.
Don't worry too much about it and obvioulsy it measure the same in both direction (it actually must...)
Resistor directionality is a controversial argument and I intend it as an extreme optimization.
A single reversed resistor won't change the sound of the amplifier for most people.
Proceed and only if you think there is some difference between monoblocks desolder the resistor and mount it as directed (use Chip Quick desoldering alloy).
I've looked at the PCBs I've yet to ship and the '7' is marked but, it seem, the silk screen it's not exaclty the same among boards and some have it partly erased.
In case of any doubt builders are ecouraged to post about them on this thread.
Thanks Dario, i'm really looking forward to hearing these amps now.
Do you have a wiring diagram you could post? I appear to have two separate signal and ground in positions, there's the molex connection point at the top right hand corner next to C13 and there are two round pads marked signal hot and signal ground on the middle right hand side above C15. Are they only there to bypass C13 if wanted?
I take it PGND gets connected to the main safety star earth point?
I just want to be absolutely certain of the connections before I power up the boards.
Cheers
Davy
Do you have a wiring diagram you could post? I appear to have two separate signal and ground in positions, there's the molex connection point at the top right hand corner next to C13 and there are two round pads marked signal hot and signal ground on the middle right hand side above C15. Are they only there to bypass C13 if wanted?
I take it PGND gets connected to the main safety star earth point?
I just want to be absolutely certain of the connections before I power up the boards.
Cheers
Davy
The molex connector is the standard signal input when C13 is mounted on board
Those additional pads were added on 1.05 boards to help people who use outboard capacitors.
Use whatever pair is more comfortable for your specific build and/or needs.
Well, no and also yes...
The amp works (and sounds) well with PGND connected to the star ground or not.
BTW for best results (soundwise) PGND should be left disconnected as in the My_Evo Rev A, it's present on board as a commodity.
This also means that the build should try to follow as much as possible double insulation guidelines.
PGND is not a problem, just follow the tutorial
