This is the first amp I designed and built. It is Blameless design ( single LTP input stage). Here are the 3 pages schematics.
First page is the OPS section with SS output relay for speaker protection. I use 9 pairs of output transistors, total bias current is 0.9A ( 100mA per pair) to give the first 13W of pure class A into 8ohm. I have 0.1uF and 10uF right at the collector of all the emitter follower transistors. Together with ground and power plane, this minimize the parasitic for better stability. I use triple EF output stage to increase open loop gain ( avoid loading the VAS stage).
Attachment:
OPS Rev5 PAGE1.pdf
Page 2 is power up turn on delay and output DC detection for speaker protection
Attachment:
OPS Rev5 PAGE2.pdf
Page 3 is the IPAS section. IPS is Blameless design. I have the page number for the Power amp book by Bob Cordell labeled in different section. They are described into the book on reasoning of using the circuit. The design is very standard, the only difference here is I put ALL the bells and whistles in. I have never seen any amp on the market that put everything in. Even the high end amps like Krell and Mark Levinson leave out a lot of the features. Only thing I can think of is the more complete it is, the higher the open loop gain and the harder it is to tame and make it stable. I worked on a lot of closed loop feedback system, so I put in the time to tame the amp. I found LTSpice simulation is not accurate at all. Simulation might show a lot of phase margin, but the real amp oscillate and I have to tame it by feel. The difficulty is the transistor model is not accurate for large signal. Took me over a week to tame the amp.
Attachment:
Stuffed parts page 3.pdf
This is picture of the filter caps. I have about 2.5F of capacitors using a lot of smaller 10,000uF capacitors to lower the ESL and ESR. I have 100uF, 10uF and 0.1uF in parallel to cover full range of frequencies.
Attachment:
ADD IPS filter 1.JPG
Attachment:
Finished amp modules 3.jpg
BW of about 330KHz, slew rate of about 30V/uS. THD of 0.001%@1KHz, progressively increase to 0.0035%@20KHz at 46Vpp or 66W@4ohm or 33W@8ohm. Because I use 25V-25V power transformer, the rails are +/-34V only. This is a low power amp of only about 55W@8ohm. But it can drive low impedance. 110W@4ohm and 220W@2ohm.