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.
Layout or Schematic with Stability Mods?
I've been lurking here for months hoping that you'll post an Eagle or Kicad layout with all the stability mods you listed for the UT. So...do you have a layout you could share on this thread? If not, maybe just a schematic with the mods?
I've been lurking here for months hoping that you'll post an Eagle or Kicad layout with all the stability mods you listed for the UT. So...do you have a layout you could share on this thread? If not, maybe just a schematic with the mods?
I don't have any mods at this time, other than the diode fix in the simulation thread.
I hope that others will post their mods in their own threads since I'm trying to keep
this as close to stock as possible - for now.
I hope that others will post their mods in their own threads since I'm trying to keep
this as close to stock as possible - for now.
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
I have a feeling that this would also apply to the UT:
https://www.diyaudio.com/community/...rossover-p3a-of-rod-elliot-as-example.402148/
https://www.diyaudio.com/community/...rossover-p3a-of-rod-elliot-as-example.402148/
My first build was a crystal radio with the coil wrapped on a TP tube... I built a Heathkit amp with my dad somewhere about '68 or '69. He built the receiver. We worked at the kitchen table... Then, I started building speakers for my friends and work colleagues. I built some for myself, too. My first one used an Allied 8 inch 2-way coax speaker. Later I made 12 inch EV three-way speakers, The mid was actually a whizzer cone. I made many more after that- a JBL L200 look-alike, but with an Altec 811b and an 18 inch EV woofer, and an EV tweeter (forgot the number). The biggest thing I did was Klipschorn copies- really demanding cutting on the table saw. I used a 15" EV woofer, and many variations of midrange horn and tweeter over the years trying to get the sound just right. Finally, I settled on a big horn with a 1" Selenium driver and an expensive Selenium tweeter. I rebuilt VOX amplifiers and cabinets for decades. I still have about 11 or 12 in the studio. Looking back, it really was fun to take an old beat-up amp and restore it to near-new.
Back in 1973 I built a pair of Tiger amps when I was in EE at university. I designed a small circuit to sit in the base bias loop to better bias the power transistors. I never had an issue with these amps, even playing them outside for a block party. I tuned the circuits in the EE test lab. Marantz and McIntosh used to do demo testing of amplifiers if you brought them to a local stereo shop. Both of the companies were floored at how low the distortion was- I still have the old data plots in my files. McIntosh measured 87W and 85W output into 8 Ohms. Distortion was measured at 0.008% in one amp and about 0.01% in the other. I used them up to about 5 years ago. The only major change was to recap about every 10 years or so. Time to sell them on, I think.
Back in 1973 I built a pair of Tiger amps when I was in EE at university. I designed a small circuit to sit in the base bias loop to better bias the power transistors. I never had an issue with these amps, even playing them outside for a block party. I tuned the circuits in the EE test lab. Marantz and McIntosh used to do demo testing of amplifiers if you brought them to a local stereo shop. Both of the companies were floored at how low the distortion was- I still have the old data plots in my files. McIntosh measured 87W and 85W output into 8 Ohms. Distortion was measured at 0.008% in one amp and about 0.01% in the other. I used them up to about 5 years ago. The only major change was to recap about every 10 years or so. Time to sell them on, I think.