Amplifier output stages

[drummerman]

 

[drummerman]

Transistor amplifiers are almost exclusively direct coupled. Lower cost, less invasive and better control of speakers are usually the reason.

There is a noteable exception; Musical Fidelity is using transformer coupled design in one of their high power design, apparently with little detriment to performance (measurements are superb as is usually the case with the brand).

MacIntosh is another one though their 'Autoformers' design differs as it has only a single winding (rather than split primary and secondary). It does not provide isolation.

Are there any technical reasons as to why transformer coupling in solid state amplifers should be used and if so, why it has not been adopted more widely?

regards

 

[busb]

Low end f response for starters.

 

[drummerman]

Interesting. Why is that?

regards

 

[drummerman]

I didn't mean to kill this stone dead and I do, to some extend, understand the implications/difficulties and reasons not to use transformers but my question was more why such a design could be a positive? - MF seemed to think so and Macintosh, to some extend, does too.

In both cases, harmonics, both even and uneven are vanishinly low. Much lower than many Tube amplifiers and as low as many good direct coupled designs. I initially thought that this perhaps would introduce 2nd and so forth order distortion to mimic certain thermionic designs but on paper, that does not seem to be the case ... ?

regards

 

[andyjm]

Google 'impedance matching of amplifier outputs' and there is a wealth of information about the advantages of using transformers in amplifiers. The negatives generally outweigh these advantages however. For a transformer to have decent LF response it needs to be big. This creates cost and weight issues, and for a stereo amp you need two of them. Transformer coupling is widely used at higher frequencies where size isn't such an issue, but at LF it is hardly used anymore - except in valve amps where there isn't much alternative.

 

[drummerman]

Google 'impedance matching of amplifier outputs' and there is a wealth of information about the advantages of using transformers in amplifiers. The negatives generally outweigh these advantages however. For a transformer to have decent LF response it needs to be big. This creates cost and weight issues, and for a stereo amp you need two of them. Transformer coupling is widely used at higher frequencies where size isn't such an issue, but at LF it is hardly used anymore - except in valve amps where there isn't much alternative.

Where is transformer coupling still used widely (at higher frequencies) in Solid State?

regards

 

[Mooly]

Digital (SPDIF) outputs are often transformer fed via a special HF "pulse" transformer to give a balanced isolated feed. For that application its a perfect solution.

For solid state audio there is just no reason to use them... at least not in engineering terms... but someone somewhere will think they can get better (read different due to distortion) sonics from using them.

 

[andyjm]

Google 'impedance matching of amplifier outputs' and there is a wealth of information about the advantages of using transformers in amplifiers. The negatives generally outweigh these advantages however. For a transformer to have decent LF response it needs to be big. This creates cost and weight issues, and for a stereo amp you need two of them. Transformer coupling is widely used at higher frequencies where size isn't such an issue, but at LF it is hardly used anymore - except in valve amps where there isn't much alternative.

Where is transformer coupling still used widely (at higher frequencies) in Solid State?

regards

Transformers are widely used in data transmission, ethernet, ADSL use transformers to balance input and output lines. Your TV, radio and satbox all use signal transformers for coupling and matching. In the audio world, SPDIF is often transformer coupled.