AD30TC channel 2 68k ohm resistor

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Farrerdale Records
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AD30TC channel 2 68k ohm resistor

Post by Farrerdale Records » Fri Apr 28, 2017 4:28 am

It's been a while, but I'm back on the forum and I have some questions about mods for the AD30TC

Q1 - Depending on the schematics you find, V3-A4 should have either 91K via one resistor or 94K via two resistors. Which is it? My PCB has one resistor space but had two 47K resistors in series, not sure if that was factory or from a previous mod done by a local tech. I reverted to a single 91K.

Q2 - Front panel PCB has a 68K resistor for R1, which I changed to match R2 for 91K. CH2 now seems to be noisier and more gain than previous. Shouldn't the gain and the noise go down, not up? Does it have anything to do with the location of C2?

Thanks
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Jondog
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Re: AD30TC channel 2 68k ohm resistor

Post by Jondog » Fri Apr 28, 2017 12:32 pm

The schematics I see show two 47k on the ad30tc and one 91k on the ad30 single channel. A 3k difference makes no real difference. The tone stack slope resistor change isn't going to make one channel sound like the other as each channel is voiced differently throughout the preamp. Raising the value changes the way highs and lows from the preamp are filtered through the tone stack. More signal can go to the treble caps, less to the bass and mids. I'm not sure of what you're trying to achieve by making these changes.
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Re: AD30TC channel 2 68k ohm resistor

Post by Les Paul Lover » Fri Apr 28, 2017 3:45 pm

I've seen 2 resistors in series before in AD15s.

I think it was for the 91k resistor too.

I think it comes down more to supply - 91k isn't a particularly common resistor value, and can be difficult to source at times.

However, 47k are very common, and very easy to source all of the time.
A quick internet search seems to confirm this. I couldn't find a single 91k 1/4w for sale in the UK. I'm sure I could eventually find some, but I think that is the issue really.
Ant

Current Orange Gear: RV50 MKI, R30, AD15, PPC212
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Farrerdale Records
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Re: AD30TC channel 2 68k ohm resistor

Post by Farrerdale Records » Fri Apr 28, 2017 9:08 pm

Thanks guys!

I understand the capacitors, while for the most part are the same values, just in different order in the circuit on the pre section contribute to the voicing, I underestimated the effect of changing a single resistor is in the entire design.

That being said, the reason for attempting this is that I rarely, if ever, use CH2, and I'm attempting to get the same channel voicing and use the two channels, one for humbucker, one for single coil.

Seems like lots of work.
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Jondog
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Re: AD30TC channel 2 68k ohm resistor

Post by Jondog » Fri Apr 28, 2017 9:51 pm

Farrerdale Records wrote:Thanks guys!

I understand the capacitors, while for the most part are the same values, just in different order in the circuit on the pre section contribute to the voicing, I underestimated the effect of changing a single resistor is in the entire design.

That being said, the reason for attempting this is that I rarely, if ever, use CH2, and I'm attempting to get the same channel voicing and use the two channels, one for humbucker, one for single coil.

Seems like lots of work.
To voice them the same, you're looking at changing signal bypass caps and cathode bypass caps as well.
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Re: AD30TC channel 2 68k ohm resistor

Post by fiveightandten » Sun Apr 30, 2017 2:28 pm

My AD30 has resistors twisted together in series to achieve the proper value in a number of places in the amp. There's also another somewhat questionable component where they used the wrong size cap and twisted the leads over the cap body to get it to sit on the board. These things are disappointing, to say the least, on an amp with this kind of price tag.

If you want to actually make the amp a "twin channel', you'll be changing components throughout the channel 2 pre-amp. It's not just the tone stack that is different. The coupling caps and bypass caps are also different.

It's totally doable, but not a small job, given the construction of the amp. You'll have to remove the entire main PCB, and the front PCB as well. I've always found channel 2 to be a little thin and modified channel 2 on my amp. I increased the first stage coupling cap (.0047) and changed the value of the slope resistor in the tone stack (I don't recall what I settled on here). This gave it a little more heft, which was needed, IMO.

-Nick
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Re: AD30TC channel 2 68k ohm resistor

Post by Farrerdale Records » Sun Jul 30, 2017 4:15 am

So I've been rather busy and now just getting around to my CH2 adventure, it's got me thinking, where can I actually source these value caps, particularly the 4n7?

400V are hard to find, most sites are offering 500V which should be fine, but I can't find the 4n7 or even 2n2. There is a large wholesaler by the office I'll check out on Monday.

That being said, lots of times people put in different brand of caps. If I guy was going to recap in general, are there any recommendations for source, brand, or material?
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Re: AD30TC channel 2 68k ohm resistor

Post by fiveightandten » Sun Jul 30, 2017 10:09 am

Mouser.com will have everything you need. Measure the lead spacing for anything you want to replace and get something that fits. I'd recommend WIMA caps.
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Re: AD30TC channel 2 68k ohm resistor

Post by Farrerdale Records » Mon Aug 14, 2017 4:11 am

So this weekend I had a couple cracks at updating the caps, all seems good, some patience was required but it looks good.

I haven't started it up yet, was doing some other basic checks and I found that R31 on the schematic should be 680ohm-5W, yet mine is measuring 660kOhms.

I'm using a Fluke multimeter, and other resistors are bang on.

Just wondering if this is a typo on the schematics, or if it's the wrong resistor, the resistor is burning out, and what affect that could have on the amp?

If I should replace the resistor, any specific type?

Thanks,

Curtis
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Les Paul Lover
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Re: AD30TC channel 2 68k ohm resistor

Post by Les Paul Lover » Mon Aug 14, 2017 11:32 am

That's a huge variance!!!!!
Ant

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Previous Orange Gear: Orange AD30TC Combo, AD15, Tiny Terror

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Re: AD30TC channel 2 68k ohm resistor

Post by Farrerdale Records » Tue Aug 15, 2017 1:05 am

It is! I'm inclined to believe it's supposed to be 680 Ohm, as that's what on both the schematic and the board.

Any indication as to what is a good replacement? Lots of variables, but I'm guessing I should be getting a 460V rated, though 18AWG leads seem too big for the board, aren't they?
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Jondog
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Re: AD30TC channel 2 68k ohm resistor

Post by Jondog » Tue Aug 15, 2017 1:08 am

Farrerdale Records wrote:
Mon Aug 14, 2017 4:11 am
So this weekend I had a couple cracks at updating the caps, all seems good, some patience was required but it looks good.

I haven't started it up yet, was doing some other basic checks and I found that R31 on the schematic should be 680ohm-5W, yet mine is measuring 660kOhms.

I'm using a Fluke multimeter, and other resistors are bang on.

Just wondering if this is a typo on the schematics, or if it's the wrong resistor, the resistor is burning out, and what affect that could have on the amp?

If I should replace the resistor, any specific type?

Thanks,

Curtis
It should definitly be 680 ohms. Re-check with your meter. If that resistor burns out, you will have no power to the preamp. It shouldnt burn out. You just need a 5 watt resistor.
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Re: AD30TC channel 2 68k ohm resistor

Post by fiveightandten » Thu Aug 17, 2017 1:14 am

Are you sure it's not reading .660K? It seems like a coincidence that it's failed and the numbers would work out like that.

If you do need to replace it, Mouser.com has an exact replacement.

http://www.mouser.com/ProductDetail/IRC ... qx7Um28%3d
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Re: AD30TC channel 2 68k ohm resistor

Post by Farrerdale Records » Wed Aug 30, 2017 2:28 am

Well, that's embarrassing, turns out it was just reading .670k, well at least I have a spare now...

Last step - for this and other projects where there are exposed solder joints that should be covered, which is better application:

http://www.mroelectronics.com/mro/produ ... oduct=1682

or

http://www.mroelectronics.com/mro/produ ... oduct=1701

Thanks!
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fiveightandten
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Re: AD30TC channel 2 68k ohm resistor

Post by fiveightandten » Wed Aug 30, 2017 3:12 am

Farrerdale Records wrote:
Wed Aug 30, 2017 2:28 am
Well, that's embarrassing, turns out it was just reading .670k, well at least I have a spare now...

Last step - for this and other projects where there are exposed solder joints that should be covered, which is better application:

http://www.mroelectronics.com/mro/produ ... oduct=1682

or

http://www.mroelectronics.com/mro/produ ... oduct=1701

Thanks!
Why do you feel you need to cover exposed solder joints?
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