Better than the Keeley Mod!-Modifying The Boss DS-1

A forum devoted to mod, tips and suggestions for upgrading and rehousing your VERY CHEAP commercial stompbox to near boutique excellence.
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Billybob2134
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Post by Billybob2134 »

There are all kinds of DS-1 mods out there and some are better than others. I've tried several and replaced all caps, the IC, etc...but it always falls short because of the overcompressed sound that plagues Boss distortion and OD pedals. I hit my low E string to hear the bass and when the stock DS-1 is engaged it cuts off so much low end it is ridiculous! This is why an old MIJ DS-1 is surprising because it is very open and warm. The reason is the diodes. The 1S2476 diodes clip at higher voltage in the circuit than the stock diodes in the new DS-1s or common diodes like the 1N4002. That is what opens up the tone to be very good. The 1S2476 diodes aren't in production anymore, but you can get a hold of older ones or try two diodes in series for each of the two clipping diodes to achieve the same result.
I modified a DS-1 and did put the 1S2476 diodes in as well. You can hear it in the link below:


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ChopSauce
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Post by ChopSauce »

Well, I understand that this thread is pretty old but it still is well referenced by search engines, especially as the only one "dealing" with just the clipping diodes D4 & D5, so, here I am posting.

I'm only interested in the "stock" MIJ mod by Brett Miller but don't feel much like paying 20++ EUR for Mouser shipping fees (plus VAT, plus outside EU transaction fees) for almost just two 1N4150 diodes, and wonder:

Firstly, why the foward voltage for the 1N4148 reads as 1V on the datasheets if it is only 0.65V?

Secondly, how about - for example - 1N400x diodes, or is the 1V foward voltage mentionned on the datasheet over-estimated, too?

Thirdly, is anyone aware of some other substitution that would be more easily available (in extenso: from some online european distributor)?

Thanks for your consideration, anyway!

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mauman
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Post by mauman »

Hope this helps:
1. The forward voltage of a diode is dependent on the current, increasing with higher current in a nonlinear way. The datasheet on the Fairchild 4448 (which is a closer-tolerance 4148) specifies a forward voltage of 0.62V to 0.72V @ a current of 5 mA, rising to 1.0V @ 100 mA. The Fairchild 1N400x datasheet specifies Vf of 1.1 V @ 1 A. When I measure a 4001 @ 1 mA, I get around 0.6V.
2. Same as 1.
3. A possible substitute for a 1N4150 (Si small-signal diode with a datasheet Vf of 0.54 to 0.62 @ 1 mA) would be the 1N400x series, I measure those to be right in that range. Their Vf is slightly lower than 1N4148 and they should be widely available.

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ChopSauce
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Post by ChopSauce »

Thank you very much. Your explanations helped a lot: now I know what to look at!

So, looking at the datasheets, the forward current at 3-400mA of the stock 1N4148 (if I'm not mistaking) seems to match the recommended ~1V & now I really don't understand the rationales for changing them... :?

I must have been missing something else ... :scratch:

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mauman
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Post by mauman »

The differences are in the voltage vs. current curves, it's hard to characterize a diode at one or two points. When the curves are close, it's likely they will sound similar, although not guaranteed. Some people say they can hear differences in similar diodes, others say they can't. There are some sample curves and related discussions at viewtopic.php?p=267968 and viewtopic.php?p=268015

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ChopSauce
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Post by ChopSauce »

That should be something indirectly related to the absolute forward voltage, yes - even though this is what I was suggested by reading the document.

Afterwards, I could read some comments along the lines you mentionned, so thanks again for pointing me in what seems to be the right direction.

I could find some 1N4150 in a german shop also, so I'll buy a few, with the hope that they are not cheap repro/counterfeit ones ... :?

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ppluis0
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Post by ppluis0 »

Hi ChopSauce,

Perhaps you can experiment adding a small resistor in series with each diode in order to modify the action of these components.

Take a look at the diagram and the discussion in the following thread:
viewtopic.php?t=29864

Cheers,
Jose

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ChopSauce
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Post by ChopSauce »

That's interesting. Thanks for the link... :thumbsup

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