Funny thing is that the Universal Tiger DOES have a built in power transistor short protector, hidden in plain sight.
You have 50 ohm in series with each power transistor base.
Q7 has R12 and R15 in parallel; same thing with Q8 and R14//R16.
I built tons of these in my early days for grueling MI amplification, they survived stage conditions very well.
I sparked a screwdriver across output terminals with no fear (after the initial tests).
Being an inveterate tinkerer, reduced resistor values "to see what happens", amp worked as before on a regular load but died instantly on shorts.
Given the era, it was an acceptable short protection, since almost everywhere else standard was simple *current* limiting, not sophisticated VI limiting.
"125W"???b No way José (unless you fed it from a regulated bench supply) but a very honest 100W into 4 ohm.
An Ampeg BT15 FET+Bipolar preamp (straight from Jack Darr´s book) driving this loud and robust amp (you should have seen the competition
) was one of my first successful commercial products.
You have 50 ohm in series with each power transistor base.
Q7 has R12 and R15 in parallel; same thing with Q8 and R14//R16.
I built tons of these in my early days for grueling MI amplification, they survived stage conditions very well.
I sparked a screwdriver across output terminals with no fear (after the initial tests).
Being an inveterate tinkerer, reduced resistor values "to see what happens", amp worked as before on a regular load but died instantly on shorts.
Given the era, it was an acceptable short protection, since almost everywhere else standard was simple *current* limiting, not sophisticated VI limiting.
"125W"???b No way José (unless you fed it from a regulated bench supply) but a very honest 100W into 4 ohm.
An Ampeg BT15 FET+Bipolar preamp (straight from Jack Darr´s book) driving this loud and robust amp (you should have seen the competition
) was one of my first successful commercial products.Tiger
Easy to stop these oscillating.
1] Add emitter degeneration resistors to the diff amp of about 470 ohm.
2] Remove C8 which is in parallel with R7
3] Add a Miller compensation capacitor C-B of Q3 (47-100pF)
4] Remove the idiotic bias network and put in a CFP type with the NPN attached to either Q5 or Q6. If R21 goes faulty = puff of smoke!
5] Put in 10 ohm base stoppers on Q5 and Q6
6] Put in 1.5 ohm base stoppers on the output devices Q7 and Q8.
7] To remove DC offset change R7 to 10K and R8 to 715 ohm 1%
8] Change the input resistor arrangement so that R2 is before R1. Why attenuate and then re amplifiy? Change R2 to 10K and change R1 to 1K.
9] The Zoebel must be across the speaker terminals NOT on the PCB.
10] Remove C10.
11] Remove C11 and C12.
Re ground. R2, C1, C2 must have their own ground isolated ON THE PCB by a 10 ohm resistor from the noisy ground which is R12, R14, C6 and C7
Then the noisy ground is returned to the main T-ground with it's own wire and the quiet ground (R2, C1, C2) is then also returned to the T-ground.
I did many of these with these mods and each has worked well.
Steve Mantz
Zed Audio
Los Angeles.
Easy to stop these oscillating.
1] Add emitter degeneration resistors to the diff amp of about 470 ohm.
2] Remove C8 which is in parallel with R7
3] Add a Miller compensation capacitor C-B of Q3 (47-100pF)
4] Remove the idiotic bias network and put in a CFP type with the NPN attached to either Q5 or Q6. If R21 goes faulty = puff of smoke!
5] Put in 10 ohm base stoppers on Q5 and Q6
6] Put in 1.5 ohm base stoppers on the output devices Q7 and Q8.
7] To remove DC offset change R7 to 10K and R8 to 715 ohm 1%
8] Change the input resistor arrangement so that R2 is before R1. Why attenuate and then re amplifiy? Change R2 to 10K and change R1 to 1K.
9] The Zoebel must be across the speaker terminals NOT on the PCB.
10] Remove C10.
11] Remove C11 and C12.
Re ground. R2, C1, C2 must have their own ground isolated ON THE PCB by a 10 ohm resistor from the noisy ground which is R12, R14, C6 and C7
Then the noisy ground is returned to the main T-ground with it's own wire and the quiet ground (R2, C1, C2) is then also returned to the T-ground.
I did many of these with these mods and each has worked well.
Steve Mantz
Zed Audio
Los Angeles.
One reason that I stopped working on this was that I did not find consistent results from
two samples of the UT mono block amps. The second one did not oscillate at all. Here is
another thread to discuss possible differences:
https://www.diyaudio.com/forums/sol...versal-tiger-inconsistencies.html#post6479814
two samples of the UT mono block amps. The second one did not oscillate at all. Here is
another thread to discuss possible differences:
https://www.diyaudio.com/forums/sol...versal-tiger-inconsistencies.html#post6479814