If you put new output transistors, class A/B, will tou match them?

[stocktrader200]

Sandrohv , great work there. This is what I suspected as the total bias current (700ma) should transfer seamlessly between devices.
I did not expect the high power levels to register lower distortion with mismatched outputs.

 

[sandrohv]

I would take that with a grain of salt. I think the conclusion is that matched devices don’t matter much for distortion purposes in the output stage.

 

[rsavas]

Hi Sandro,

Wonderful contribution to the community, thanks for taking the time to investigate.
I had this same discussion with Chris in another thread asking Chris to show me measurements of actual amplifiers to demonstrate his assumptions. I did not get any measurements to back his claims. I can lend him or provide him with a BC-1 prototype so he can swap transistors to verify his claims and verify against the simulations.

For Chris’s statement about Bob Cordell mostly only doing simulation, not having actual circuits built and tested, to verify the designs to match the sims, this is an incorrect statement.
I have proof that Bob does build many of his designs, his legendary MOSFET design was built before it was simulated. In Bob’s presentation of DH-220C at BAF2016, the slide set shows a picture of the hand wired prototype. The same goes for the BC-1 design in Bob’s second edition of the Power Amp Design book. I have done pcb layouts for both these designs, BC-1 and DH-220C. Bob has done exhaustive measurements on both these designs, to verify that the pcb layout versions match closely to both the simulations and the prototypes. Chris should know this because I showed the group these designs when we met at our regular Toronto group meeting at member ticknpop’s shop last time we met. If we meet again, I have the DH-220C design complete in a DH-200 chassis, ready for testing and hooked up to some speakers.

If you want Chris, we can do these tests next time we meet, you bring your bag of MJL3281/1302’s to solder in the BC-1 OPS, I’ll bring my Amber 3501 and dummy loads, I look forward to doing these tests.

Best Regards, stay healthy and safe
Rick

 

[sandrohv]

Thanks Rick! Simulation is a great platform to test theories in a very controlled and repeatable manner, and it can be done super quickly. Glad you found them useful.
Best, Sandro

 

[anatech]

Hi Rick,
I didn't say that Bob didn't build his designs. I know he builds some, but these experiments he probably does only with a simulator.

Once I get time, I'll do the output experiment using my RTX for you. It's been over a decade since I tested last time, and the results were clear at the time with BJT's. But I don't sell people on jobs to just match the outputs. I only install a set of matched outputs when I have a blown output stage. So I do have someone who wants a total amplifier rebuild with a Marantz 300DC (and a 500 - too many outputs on that one for this experiment). So I'll upgrade the amp and try the original outputs, then install a matched set and see what happens.

-Chris

 

[Bensen]

Thanks for the feedback, I'm rather happy you have the same opinion about the square wave reponse.

I just remembered I had some pictures of square wave tests done some time ago, but only with 1 pair of output devices (same circuit but different PCB).
Now we can compare the square waves done at 10kHz with a 8R//820n load.

With only 1 pair, the square wave respons is about identical, same damping but amplitude with 1 pair looks a bit bigger.

I can't quantify what I'm hearing. I have to wait until I can power up the second monoblock (I'm waiting on some copper/silver 11AWG wire for the power supply wiring), should arrive in a couple of days.

Well,

The second mono-block is running. With this one, I only used 1 pair of output devices. This to check what the difference is soundwise.

Remark, the amp with the 7 pair of output devices has burned in about 100hours currently. The one with 1 pair only a couple of houres.

1. Is there a difference between 7 pairs and 1 pair: Yes, easy to recognise
2. Difference in sound: 7 pairs = more detail, more top end. But pleasantly.
3. preference: for now the 7 pair amp is by far the better sounding one.

 

[sandrohv]

Hi Bensen, to be more engineery, can you measure or have the equipment to measure:
- Frequency response: 1W, half power, full power
- Distortion at 1k,2k,5k, 10, 20k: half power, full power
for both amps?

I am curious to what does "more detail, more top end" actually translate to.

BTW, for the seven pairs, did you just pick transistors from the same box or tried to do some matching. By now, I am convinced matching does not matter, but I am curious about what you actually end up doing.