Dyna Comp Transistor Equivalents

[Steve Mavronis]

What are the functional equivalents or closest thing to the specs of these transistors as used in the 76/77 MXR Dyna Comp?

SC 1849
MPS 5172

I think the later is still available, or it might be the other way around. Not sure but I need to source these soon before my build. I already have a 3080 Operational Transconductance Amplifier that I'll need too.

Thanks.

[Govmnt_Lacky]

What are the functional equivalents or closest thing to the specs of these transistors as used in the 76/77 MXR Dyna Comp?

SC 1849
MPS 5172

I think the later is still available, or it might be the other way around. Not sure but I need to source these soon before my build. I already have a 3080 Operational Transconductance Amplifier that I'll need too.

Thanks.

If the first one is 2SC1849, then a suitable replacement for BOTH of them is BC549. You are correct that the second one (MPS5172) is still available.

[Steve Mavronis]

If the first one is 2SC1849, then a suitable replacement for BOTH of them is BC549.

Hmm, not sure since I made a layout based on the original MXR factory schematic and it just calls the four of them in the drawing SC1849 and they have an EBC (NPN) arrangement.

I gave a parts list to my father and he is supposed to check a cross-reference book at his work too.

[jrod]

Hey Steve,

I got my 2SC1849's at Small Bear. www.smallbearelec.com/Detail.bok?no=493

[Mark Hammer]

Note that only two of the transistors are in the audio path.  The remainder are not, and are simly part of the sidechain.  *IF* there are any sonic properties to the 1849, it only matters i two places.

[Steve Mavronis]

Thanks for that tip Mark.

[PRR]

Device numbers often start with the number of legs minus one.

2-leg diodes start "1": 1N4007, 1N914.
3-leg transistors start "2": 2N3609 etc.
4-leg optocouplers start "3".

US makers often put the whole 2N3055 number on the part.

Japanese makers often assumed you could count and omit the leading "2". A part starting "SC..." is almost certainly "2SC..."

2SC1849 is about the cheapest part you could get in the day.

If you were fussy you could order 2SC1849-O to 2SC1849-T to specify hFE of 90-150 or 400-650. This cost more. Many-many-many circuits just do not care. They work fine if hFE is well over 50.

In the DynaComp: The two audio-path transistors are heavily constrained by feedback, their exact type does NOT matter. The main constraint on the two peak-catch transistors is not-high leakage and ~~0.6V forward drop: any not-sick Silicon transistor will work. NPN of course (the way the 3080 works, PNP peak-catches would be awkward). NOT Darlington.

If you have BC549, use it. 2N3904, 2N2222, 2N5088 will work just the same. If you have old sonar boards, blowtorch the transistors off, sort for NPN, and use them.