Do i need a preamp / buffer for the DRV134

[rhysh]

Hello, i am going to be using a drv134 in alex88's monoblock to convert to balanced signal. Do i need to use a buffer before the DRV134, or would i be ok giving it line level signal?

If i need to use a buffer, which one would i use? I dont really understand how buffers work.

Another question, i think i read somewhere that i cannot use a 50k pot before the DRV134, and it needs to be a stepped attenuator instead? Is this correct?

Thanks

 

[tiltedhalo]

The DRV134 can be used with out a buffer, it is actually 3 op amps in one, 3 134's to be correct, A buffer an inverted and non inverted that are cross coupled to achieve a positive and negative signal output.
Any time you use a pot at the input without capacitor couple to the op amp you will get great variations in DC at the output due to the fact you are changing the input reference to ground against the NFB loop.
Even if the op amp has DC compensation. The DC compensation is there to null out the static DC within the component.

 

[rhysh]

The DRV134 can be used with out a buffer, it is actually 3 op amps in one, 3 134's to be correct, A buffer an inverted and non inverted that are cross coupled to achieve a positive and negative signal output.
Any time you use a pot at the input without capacitor couple to the op amp you will get great variations in DC at the output due to the fact you are changing the input reference to ground against the NFB loop.
Even if the op amp has DC compensation. The DC compensation is there to null out the static DC within the component.

Thanks for the responce, what would i need to do to be able to use a pot at the input? Or can i use a stepped aut without a cap?

 

[tiltedhalo]

You simply need to put a capacitor at the input of the DRV134 after the pot, stepped or not, a stepped network will work without producing a ground reference because it simple steps the resistance on the input where as a pot will reference ground to increase or decrease signal to the input. So use a cap if you use a pot, dont if you use a step. Remember if you use a pot the you are creating a RC network and you need to pick a cap that will place the lowest corner frequency with a 50K 4.7uf should do it or you can use a good quality electrolytic jumped with a high quality poly or metal film poly.

 

[rhysh]

Thanks, would i use the cap in line, or would i jumper one leg to ground? I dont understand the best way to implement this, sorry I think it would be easier to just go the stepped route, to avoid any problems, do you think this would be the best decision?

 

[tiltedhalo]

give me a while and I will post a schematic for a stepped and pot for you using the DRV 134.

 

[rhysh]

give me a while and I will post a schematic for a stepped and pot for you using the DRV 134.

Thanks for your time and help, that will clear things up greatly for me!

 

[tiltedhalo]

Use C1 if you use a pot Don't use C1 if a stepper is used.

 

[rhysh]

Thanks,

Is it possible to use this design and just add the capacitor, or does anything else need changing?

 

[tiltedhalo]

That will work fine just add the cap at the input pin of the DRV, if you are concerned about offset between the inverted and non inverted out add a 10uf non polar caps from the outs to the sense pins, just check the docs for the DRV134.

 

[rhysh]

Thanks, i should be all set to go.