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DIY Stompboxes => Building your own stompbox => Topic started by: aefpv on March 10, 2021, 03:56:17 PM

Title: Transistor substitute for a JHS Morning Glory (Bluesbreaker) clone.
Post by: aefpv on March 10, 2021, 03:56:17 PM
I was going to make a JHS Morning Glory clone. However, the transistor, 2N245, is out of stock at Small Bear. Do you all have any good suggestions for a substitute for this part?

Thanks
Title: Re: Transistor substitute for a JHS Morning Glory (Bluesbreaker) clone.
Post by: antonis on March 10, 2021, 04:07:23 PM
https://www.diystompboxes.com/smfforum/index.php?topic=65196.0 (https://www.diystompboxes.com/smfforum/index.php?topic=65196.0)

https://www.diystompboxes.com/smfforum/index.php?topic=109908.0 (https://www.diystompboxes.com/smfforum/index.php?topic=109908.0)
Title: Re: Transistor substitute for a JHS Morning Glory (Bluesbreaker) clone.
Post by: iainpunk on March 11, 2021, 07:47:18 AM
i had luck with replacing them with BF245 Jfets, they are somewhat easy to come by.
my local store even had some cool black and white TO-106 packages

cheers
Title: Re: Transistor substitute for a JHS Morning Glory (Bluesbreaker) clone.
Post by: duck_arse on March 11, 2021, 08:23:39 AM
I was going to make a JHS Morning Glory clone. However, the transistor, 2N245, is out of stock at Small Bear. Do you all have any good suggestions for a substitute for this part?

Thanks

BF245? 2N5457? it all had me confused for a while there. what [he ducks for cover] does the circuit diagram show?

Iain - have we seen photos of those/your jfets?
Title: Re: Transistor substitute for a JHS Morning Glory (Bluesbreaker) clone.
Post by: Mark Hammer on March 11, 2021, 09:42:35 AM
Since when does a Bluesbreaker or derivative have transistors in it?
Title: Re: Transistor substitute for a JHS Morning Glory (Bluesbreaker) clone.
Post by: antonis on March 11, 2021, 12:42:28 PM
Since when does a Bluesbreaker or derivative have transistors in it?

Since : on: Yesterday at 03:56:17 PM
Title: Re: Transistor substitute for a JHS Morning Glory (Bluesbreaker) clone.
Post by: aefpv on March 11, 2021, 01:12:27 PM
Thanks to everyone. I had seen the other posts, but Small Bear was out of all of the reasonable substitutes. I did find the part at a different store, so I think I will be in business! 

Title: Re: Transistor substitute for a JHS Morning Glory (Bluesbreaker) clone.
Post by: POTL on March 11, 2021, 01:43:42 PM
I think any Jfet transistor can be installed in this system. The gain here is small, about 3dB (if I remember correctly). When I assembled this pedal a few years ago, it seemed to me that the transistor colors the sound, although many argue that in this mode of operation, the transistor is not saturated and does not affect the sound.
Title: Re: Transistor substitute for a JHS Morning Glory (Bluesbreaker) clone.
Post by: antonis on March 11, 2021, 02:30:09 PM
Gain is about 11dB (3.66) 'cause R17 & R18 are considered in parallel..
Q1 might (or might not) be saturated, depending on previous stage output amplitude..
(which stage is an op-amp inverting configuration with a pair of high forward voltage drop diodes (2 in series) in NFB loop..)

(https://i.imgur.com/EJM9iK8.png)
Title: Re: Transistor substitute for a JHS Morning Glory (Bluesbreaker) clone.
Post by: iainpunk on March 11, 2021, 05:59:49 PM
Quote
Iain - have we seen photos of those/your f\jfets?
no, the last time i posted pictures, (mysterious double diode) they were so blurry everyone complained that they were seeing BigFoot,
ill use my other old phone to try some jfet pics, don't mind the messy soldering, its from 5 years ago.
(https://i.postimg.cc/5H9hqJ1p/2021-03-11-23-49-36-1.jpg) (https://postimg.cc/5H9hqJ1p)

cheers
Title: Re: Transistor substitute for a JHS Morning Glory (Bluesbreaker) clone.
Post by: POTL on March 12, 2021, 03:31:37 PM
Gain is about 11dB (3.66) 'cause R17 & R18 are considered in parallel..
Q1 might (or might not) be saturated, depending on previous stage output amplitude..
(which stage is an op-amp inverting configuration with a pair of high forward voltage drop diodes (2 in series) in NFB loop..)

(https://i.imgur.com/EJM9iK8.png)

11 dB are you sure? The pair of resistors R16 (22k) and R17 (12k) do not look like a high gain setting, especially due to the high impedance of R17. C14 is a bypass capacitor that overrides R17 and gives maximum gain within a certain frequency range, however R18 (12K) reduces the effect of C14 and reduces the gain. I don't understand why you decided that R17 and R18 are installed in parallel. Also, if I remember correctly, the maximum gain of the J201 is about 17dB, and the 2N5457 has a lower gain.
Title: Re: Transistor substitute for a JHS Morning Glory (Bluesbreaker) clone.
Post by: antonis on March 12, 2021, 04:45:04 PM
11 dB are you sure?

Pretty sure..!!  :icon_wink:

due to the high impedance of R17.

Resistors exhibit resistance 'cause they aren't reactive items..
(at least, for audio frequencies...)

C14 is a bypass capacitor that overrides R17 and gives maximum gain within a certain frequency range, however R18 (12K) reduces the effect of C14 and reduces the gain.
I don't understand why you decided that R17 and R18 are installed in parallel

Exactly the opposite..
C14 overrides R17 and set R18 actually AC grounded..
So we have R17 & R18 set in parallel.. :icon_wink:
(it wasn't my arbitrary decision but an elementary circuit configuration analysis - two nodes shared by two items..)

That gives as an equivalent 6k resistor hence a 3.66 gain (+11.28dB)

P.S.
Substitute short (jumper) for C14 and see what happens.. :icon_wink:

Also, if I remember correctly, the maximum gain of the J201 is about 17dB, and the 2N5457 has a lower gain.

Transistors, by their own, don't have "gain".. :icon_wink:
(their particular circuit configuration does..)
You might mean "transconductane" but this is another story 'cause it's only practically considered for grounded Source sub-tale..)