TA-100 'touchy' transistor

Forum dedicated to helping people debug and troubleshoot non-functional pedals or builds. Please use an clear and informative title, indicating circuit and basic problem. Don't forget to mark the issue as fixed if this is the case.
Post Reply
User avatar
SolderGuppy
Information
Posts: 2
Joined: 05 Jan 2023, 22:02

Post by SolderGuppy »

Hey,
Just completed a 'Hundo' TA-100 clone on a board from Effects Layouts; http://effectslayouts.blogspot.com/2017 ... a-100.html using 1N34As and MP42B pnps with HFe tested around 80.

It sounds great *IF* I touch the case of Q2, otherwise it sounds quiet, farty and terrible. It isn't an intermittent issue, just works if I touch it. The other issue was the volume did not work unless I grounded pin 1. I reflowed the Q2 and vol pads but the issues persist.

Any ideas on the touchy transistor? Thanks!

User avatar
mauman
Resistor Ronker
Information
Posts: 444
Joined: 17 Jun 2017, 20:01
Location: Texas, US
Has thanked: 448 times
Been thanked: 186 times

Post by mauman »

Sounds like you have a problem with your ground. Touching the case of Q2 grounds the collector thru you, when it should be grounded thru a 10k resistor already. Pin 1 of the volume pot should already be tied to ground, so grounding it directly shouldn't make any difference. Check your ground bus.

User avatar
plush
Cap Cooler
Information
Posts: 650
Joined: 08 Dec 2015, 09:29
Location: Moscow, Evil Russia
Has thanked: 36 times
Been thanked: 175 times

Post by plush »

mauman wrote: 23 Mar 2024, 01:14 Touching the case of Q2 grounds the collector thru you
MP42B case is tied to the base, not collector.

It's either bad transistor (mp42b are little leaky shits, real 80hfe for them is very rare) or the circuit is not adopted to using mp42b (misbiased).

User avatar
RickySan
Information
Posts: 1
Joined: 23 Apr 2024, 10:40
Been thanked: 1 time

Post by RickySan »

plush wrote: 23 Mar 2024, 11:26
mauman wrote: 23 Mar 2024, 01:14 Touching the case of Q2 grounds the collector thru you
MP42B case is tied to the base, not collector.
Fun Games
It's either bad transistor (mp42b are little leaky shits, real 80hfe for them is very rare) or the circuit is not adopted to using mp42b (misbiased).
:shock: :shock: :shock: It turns out it was mounted like that 8) 8)

User avatar
rabblepowered
Information
Posts: 2
Joined: 13 May 2024, 02:25

Post by rabblepowered »

plush wrote: 23 Mar 2024, 11:26
mauman wrote: 23 Mar 2024, 01:14 Touching the case of Q2 grounds the collector thru you
MP42B case is tied to the base, not collector.

It's either bad transistor (mp42b are little leaky shits, real 80hfe for them is very rare) or the circuit is not adopted to using mp42b (misbiased).only up
So what type of transistor does that circuit accept?

User avatar
plush
Cap Cooler
Information
Posts: 650
Joined: 08 Dec 2015, 09:29
Location: Moscow, Evil Russia
Has thanked: 36 times
Been thanked: 175 times

Post by plush »

rabblepowered wrote: 13 May 2024, 02:32
plush wrote: 23 Mar 2024, 11:26
mauman wrote: 23 Mar 2024, 01:14 Touching the case of Q2 grounds the collector thru you
MP42B case is tied to the base, not collector.

It's either bad transistor (mp42b are little leaky shits, real 80hfe for them is very rare) or the circuit is not adopted to using mp42b (misbiased).only up
So what type of transistor does that circuit accept?
It was designed to use ac128

Post Reply