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cctsim
Silver Member
United Kingdom
418 Posts |
 Posted - 09/03/2008 : 17:47:27
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I tried this bleed fix for the SD1 today and it works like a "charm".
I thought I will post it here for the benefit of the forum. The idea is
based on the concept I found by studying the DS1 circuit.
I have used an n-channel JFET (2N5457) with measured Vp = 1.3V and IDSS = 2 mA.
Don't tried it with the J201, its max IDSS is too small, so it won't work properly.
I will post more pictures a bit later. |
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Laurie
Double Platinum Member
Canada
4854 Posts |
Posted - 09/03/2008 : 17:51:34
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quote:
Originally posted by cctsim
I tried this bleed fix for the SD1 today and it works like a "charm".
I thought I will post it here for the benefit of the forum. The idea is
based on the concept I found by studying the DS1 circuit.
I have used an n-channel JFET (2N5457) with measured Vp = 1.3V and IDSS = 2 mA.
Don't tried it with the J201, its max IDSS is too small, so it won't work properly.
I will post more pictures a bit later.
Cool! Just adds the "turn off" FET switch found on some other Boss pedals. Simple, neat.
You could also use a 2SK30 ?
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Edited by - Laurie on 09/03/2008 17:52:11 |
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MoonWatcher
Bronze Member
USA
98 Posts |
Posted - 09/03/2008 : 18:23:08
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Wow - I figured out THE EXACT SAME THING this morning!
I used a C3293 that I had laying around.
My inspiration was the Keeley article on his solution, together with Analogman's "bread crumb trail" of simply moving 1 component and 1 wire.
While Keeley tacks the JFET to C9 and cuts a track in between Q5 and C2, then adds jumpers to C2 and D7 (with an add'l 1N419 that seems to make the J201 work), I think I've come up with a more elegant solution...
I make the JFET and C2 into the equivalent of one component, which simply goes in the stock C2's place. Simply tie the JFET's S & one of C2's leads together. Bond the JFET and C2 together in a neat, compact fashion, and properly insulate the leads. The JFET's D goes in C2's hole towards the right of the pcb (looking down). The free end of the new cap goes in the other. Run a wire from the JFET's G to a 1N149, 1N4148, or 1N34A that terminates where D7's cathode is (and orient it in the same fashion). You can then heat shrink everything nice and neat, and either cable tie the add'l diode to D7, or bond it to it.
Very odd that two of us came up with this simultaneously!
Using an AVX metal film for C2 works perfectly - you can bond the JFET's "face" to the cap housing, and rig up your leads appropriately.
Not only does it work perfectly, it doesn't futz with the tonal qualities at all. |
Edited by - MoonWatcher on 09/03/2008 18:44:51 |
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cctsim
Silver Member
United Kingdom
418 Posts |
Posted - 09/03/2008 : 18:26:14
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Yes, 2SK30 is the ideal component, hard to find in Europe though.
Some useful data:
2SK30ATM
IDSS max: 6.5mA, min 0.3mA
VGS(off) max -5V, min -0.4V
2N5457
IDSS max: 5mA, min 1mA
VGS(off) max -6V, min -0.5V
The 2N5457 costs �0.10 here in UK, so you can't go wrong.
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Dingus
Silver Member
USA
472 Posts |
Posted - 09/03/2008 : 18:29:31
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| Can someone post some pictures of this mod applied? |
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cctsim
Silver Member
United Kingdom
418 Posts |
Posted - 09/03/2008 : 18:59:11
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There you go.
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cctsim
Silver Member
United Kingdom
418 Posts |
Posted - 09/03/2008 : 19:05:35
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The way I did it is to take the C2 out and put it on a small board with the JFET. I used then cables to connect to the main board (C2 and D7).
I hope it is clear from the pictures.
I was not sure how good it will be that's why I went for the separate board. There is enough space at the front anyway to accommodate for it.
I guess you can fix the whole thing on the board. My approach is mechanically also very robust. The main thing is the correct functionality, the rest is just cosmetics, not visible from the outside anyway.
Best Regards
cctsim |
Edited by - cctsim on 09/03/2008 19:16:15 |
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Dingus
Silver Member
USA
472 Posts |
Posted - 09/03/2008 : 21:08:25
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| Thanks cctsim! |
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starr36
Platinum Member
Canada
1172 Posts |
Posted - 09/04/2008 : 17:02:56
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| Sorry for my ignorance, but what was bleeding to be needed a fixing? How common is this problem with SD-1s and is there a certain version prone to this? |
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cctsim
Silver Member
United Kingdom
418 Posts |
Posted - 09/04/2008 : 19:53:35
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When the pedal is in bypass mode you can still hear the distorted sound.
This is referred to as "bleeding" through and it happens if you have the Drive set past 9.
Most of SD1s have this problem by design, in some cases is less audible depending on the pinch-off voltage of the Q1 JFET.
I have found this quite annoying especially if you play clean and loud. But it's gone now for good. |
Edited by - cctsim on 09/04/2008 19:54:57 |
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Laurie
Double Platinum Member
Canada
4854 Posts |
Posted - 09/04/2008 : 20:07:10
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quote:
Originally posted by cctsim
Yes, 2SK30 is the ideal component, hard to find in Europe though.
Some useful data:
2SK30ATM
IDSS max: 6.5mA, min 0.3mA
VGS(off) max -5V, min -0.4V
2N5457
IDSS max: 5mA, min 1mA
VGS(off) max -6V, min -0.5V
The 2N5457 costs �0.10 here in UK, so you can't go wrong.
There was a seller on ebay called "the thai shop etc" who was selling K30's in lots of 20 for about US$10 shipped. I bought some a while ago expecting them to be out of spec and nasty, but they are fine.
Just checked on ebay and the Thai ones aren't there any more, but there is at least one seller in hong Kong:
http://cgi.ebay.ca/20-TOSHIBA-2SK30A-K30A-N-Channel-VHF-RF-AMP-MOSFET-NEW_W0QQitemZ220276803632QQihZ012QQcategoryZ4666QQssPageNameZWDVWQQrdZ1QQcmdZViewItem
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cctsim
Silver Member
United Kingdom
418 Posts |
Posted - 09/04/2008 : 20:15:56
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I have managed today to put the small board directly above C2. Here are some pics.
This looks more elegant and it's also more robust. I have left one leg of C2 and the Drain of the JFET
a bit longer so that the small board can be mechanically fixed.
Best Regards
cctsim |
Edited by - cctsim on 09/04/2008 22:54:30 |
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cctsim
Silver Member
United Kingdom
418 Posts |
Posted - 09/04/2008 : 23:01:05
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Thanks for the ebay link Laurie, I will definitely order a batch.
Optically at least, they look like the real thing.
Best Regards
cctsim |
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starr36
Platinum Member
Canada
1172 Posts |
Posted - 09/04/2008 : 23:03:43
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| Excellent work. IN hindsight, one never really wants to solder like this without first being sure it works (not that this is that complicated, with only two components) so using the leads the first time around was good for saving the traces on the main board. Great work. |
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MoonWatcher
Bronze Member
USA
98 Posts |
Posted - 09/04/2008 : 23:04:26
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Nice job!
Thanks for the 2N5457 suggestion - I went to order the SK's, and they're 40 cents each! The 2N's are about a dime a piece.
If one's in a pinch, the MPF102 from Rat Shack looks like it might work (spec's seem to indicate that it would).
When I get my 2N's, I will try to post some pics of one fastened to an AVX. I don't need the perfboard at all, but it's hard to explain how I've done it without pics. |
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cctsim
Silver Member
United Kingdom
418 Posts |
Posted - 09/04/2008 : 23:26:43
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The first approach with the long wires worked just fine, and some will say if it ain't broken...
But as it happens, I have some free time during lunch breaks.
As MoonWatcher suggested, It can be done without the perfboard for sure,
but the wire to D7 will put some unnecessary strain on the Gate electrode of the JFET.
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Topic |
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One component SD1 Bleed fix
