Most of the Rotels amps RA920/93/932 and later RA 1, 2 etc are reputed to produce a lean bass anf the lack of a loudness does not arrange things. I want to modify the RA932 tone controls. I have compared some older models and found that the resistors and caps values are different, although the Variable potentiometer is 20K. Any engineers or electronic pro can tell me which of the following tone controls will produce a better bass? The first schematicsis that of my Rotel RA932 amp. The 2 others are RA840bx and RA971.
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The tone controls you show is called a 'passive' type and has very limited abilities in being able to boost and cut bass and treble. Passive means it is just added in series with the signal chain and relies on being fed a high signal level (which the opamp in front of it will do) but the actual controls are not part of the feedback loop.
A passive control can only ever cut bass and treble and so to make it appear to have boost as a well as cut the control attenuates both bass and treble significantly and then when you want more bass (or treble) it cuts these less... but it doesn't boost, it has no active gain stage.
The response should be flat with the controls centred and I suspect the 'lean' sound is simply a characteristic of the amp as I have noted that with Rotel models.
A passive control can only ever cut bass and treble and so to make it appear to have boost as a well as cut the control attenuates both bass and treble significantly and then when you want more bass (or treble) it cuts these less... but it doesn't boost, it has no active gain stage.
The response should be flat with the controls centred and I suspect the 'lean' sound is simply a characteristic of the amp as I have noted that with Rotel models.
The high end is always too shrill. Let me then put it another way....what slight modifications can I do in the treble tone control to cut some treble so as to allow make the bass appear more present?
You could try increasing the value of R517 to say 22k and at the same time increase the value C513 to lower the turnover frequency but it is all uncharted territory.
I really think your problem is more the basic character of the amp is 'harsh' and not very musical. That would be my best guess 🙂
I really think your problem is more the basic character of the amp is 'harsh' and not very musical. That would be my best guess 🙂
I had a play around with a simulation and its not good 🙁 and I don't think you will achieve what you want.
The sim (correct values) is here if anyone wants to play. I got a slightly shelving response (the top trace) but its not good and alters the whole gain set up of the amp.
The sim (correct values) is here if anyone wants to play. I got a slightly shelving response (the top trace) but its not good and alters the whole gain set up of the amp.
Thank you for your sim. Could you indicate me the right simple instructions that will allow me to learn LTspice, I m a complete noob in LTspice. In the meantime I will be thankful if you could sim the RA840BX to see whether it gives a better curve. another question what is the use of R517 and C511, they are both omitted in the BX circuit?
Have a look here:
https://www.diyaudio.com/community/...rom-beginner-to-advanced.260627/#post-4025305
And here:
https://www.diyaudio.com/community/...-2023-version-of-ltspice.394676/#post-7240021
https://www.diyaudio.com/community/...rom-beginner-to-advanced.260627/#post-4025305
And here:
https://www.diyaudio.com/community/...-2023-version-of-ltspice.394676/#post-7240021
They alter and modify the response.