Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Steve Blackdog on October 21, 2020, 12:33:50 pm
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Hi Folks
I have been a fan of this forum for ages, but this is my first post. I hope someone can help me with this query.
I am building a new FX loop /back end to my Blackstar HT60 Soloist from the schematic up. I have two queries about SMD equivalents that I might actually be able to solder!
1)
At the fx input and return jacks there are a bunch of EMF suppression filter inductors. The specification is for SMDs :-
1000r @100mhz .2A 0402 ferrite bead, such as this:
https://uk.farnell.com/murata/blm15hg102sn1d/ferrite-bead-1-1ohm-250ma-0402/dp/1515788?CMP=KNC-GUK-GEN-KWL-MAN-L5Pages-New-Structure-Test47UK-31Aug2020-MURATA&mckv=_dc%7Cpcrid%7C462466328125%7C&gclid=Cj0KCQjwuL_8BRCXARIsAGiC51C65Fg1_bSY_CGsDMOliQs0i3xLPmH0XJhJz29nGVKmvoZw10hlJ0kaApjtEALw_wcB
I am trying to find the equivalent AXIAL ferrite that I will be able to solder without the need for an eye transplant. Any suggestions?
2)
I am also looking to replace BAV99 high speed diodes with pairs of 1N4148 diodes wired in series anode-cathode/anode-cathode
(https://pinout.net/element_browse.php?conid=1523)
Does that sound right?
Any help very gratefully received.
Cheers
Steve
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> pairs of 1N4148 diodes wired in series anode-cathode/anode-cathode.... Does that sound right?
No. That won't break-down until 60V either way. Far above inst/line levels, far below wall voltages. What do you really want to do?
The fancy inductor is probably for EMI testing. Betcha the cost of a few 1k resistors that a a few 1k resistors will be good enough for most uses.
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Thanks for that.
Here’s the relevant section of the schematic. The inductors are at the jack sockets on the right hand side. I think they are there to get rid of the ‘noise’ from the switches on the switched jack sockets. So they are not really working as a resistor, more that the ferrite bead will filter out unwanted signal interference.
The BAV99 I want to find an alternative for is in the speaker out circuit at the bottom left.
Any other thoughts?
Cheers
Steve
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What do you really want to do?
are you "copying" the FX to your amp, or fixing an existing one?
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Hi Shooter
Don’t ask me why, but I am building the amp. I have the front pcb, but the rear pcb is out of production. I am skipping the emulator circuit, but building the rest of it.
I can get the parts as SMDs, but prefer to go through the hole.
Does that make sense?
Cheers
Steve
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so the parts your sourcing are for your "version" of the out of production?
IF the parts in ? are for a board using SMD's, use SMD's.
get a good mag-glass, 26ga silver wire, 30ga solder, flux,...............It's doable but not fun
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> 1N4148 diodes wired in series
I misunderstood. Yes, 1N4148 do the same thing only bigger.
The chokes, I would just do jumpers. That's cool for 99% of external jacks ever made. Yes, some internal or external HF crap could get in or out, and you don't want to build a million of them and *then* discover interference, but in DIY it seems awful paranoid.
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> 1N4148 diodes wired in series
I misunderstood. Yes, 1N4148 do the same thing only bigger.
The chokes, I would just do jumpers. That's cool for 99% of external jacks ever made. Yes, some internal or external HF crap could get in or out, and you don't want to build a million of them and *then* discover interference, but in DIY it seems awful paranoid.
Ok, so Blackstar designed the product with ferrites in an abundance of caution. That makes sense. I have found similar ferrites in solid state schematics, such as Line 6, which presumably are there for the same reason.
I did think, “well Jim Marshall didn’t think they were necessary”...
I am starting with no rear board at all, so all of this will be through the hole or wired point to point.
I bought the front pcb cheap (£30) NOS. It was cheap because a couple of the pcb mounted pots had been snapped off. I have taken all the pcb pots off and the pcb valve seats (ECC83s and EL34s). I am making my own chassis so it will end up as a head amp, rather than the original HT 60 combo.
The worst thing that might happen is that the main IC turns out to be faulty. Blackstar told me that they are “made of unobtainium”. If that is the case, I will strip out all of the bells and whistles and use what’s left to make a more traditional pure tube amp.
I am figuring this will keep me entertained in the long winter nights during the next Covid-19 lockdown :icon_biggrin:
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so the parts your sourcing are for your "version" of the out of production?
IF the parts in ? are for a board using SMD's, use SMD's.
get a good mag-glass, 26ga silver wire, 30ga solder, flux,...............It's doable but not fun
Good advice. I was wondering if I could make SMD tabs with self adhesive copper foil, tin the foil, drop the SMD in place and give it a quick touch of the iron.
If I go the SMD route I will need to buy hundreds of them. If I drop any, there’s no way I will ever find them - they make an ant’s finger-nail look big :laugh:
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The fancy inductor is probably for EMI testing. ...
Ok, so Blackstar designed the product with ferrites in an abundance of caution.
Not just "caution" but because regulatory approvals to sell into certain markets (like the EU) require testing to prove the device doesn't spew high frequency interference that will mess up the operation of other items. Especially since this amp has a clock-circuit for a digital microprocessor or 2.
Consider the ferries like complying with Building Code. Just like the metal cages around tubes in many modern amps to keep you from touching them.