THETA GEN 5A OUTPUT GAIN CHANGE MOD

Pardon the long post that follows. Different volume settings in a preamp cause the source impedence to change coming out of the volume control, and therefore affect the character of the sound. If you are using unusually low or high settings then the sound will be more aggressive or laid-back (respectively) than the designer intended. The designer will usually have designed for greatest linearity of this volume to line-driver stage when the volume control is between say 10 o'clock and 2 o'clock. This effect is usually lessened with a ladder-resistor volume control because each step can be optimised (within reason). The problem is greatest with conventional volume pots, both because the sweet spot is narrower and because the channel balance at low volume settings is often poor (depends on the quality of the pot of course). The other advantage of lowering the output on the Thetas is if you are using a stepped attenuator (eg. Placette) and you find you cannot get fine enough volume adjustment. For example, many have complained with items like the Placette being quite loud after only say six clicks up on the volume control, and even the first click being too loud for background music. I have had the volume reduced on my Theta DAC, but had it done by the importer and so cannot advise you exactly what was done. But the modification is a standard one and Theta has pre-printed instructions for it. Phone Theta while you have the unit open in front of you so that you can confirm to them precisely what board you have inside your DAC. The other issue to keep in mind is that in most cases there is just one analogue stage in a DAC. Therefore there is not an opportunity to pad a signal down between two analogue stages (as there often is in a preamp). Therefore adjusting the output of a DAC will often be done by altering the resistor in a feedback loop. Naturally, the result will be to change the sound of the DAC. For example, if this is how the mod is done in the Gen Va (and it was done this way in earlier Theta DACs), then lowering the volume will be achieved by increasing the feedback around the device that provides the analogue output drive stage. This will tend to reduce distortion and make the sound a bit more analytical. You may like the change, or you may find it makes the sound too reticent for your tastes. Obviously Theta will have tailored the sound of the analogue stage to sound best (in their opinion) at its current high output. Personally, I marginally preferred the sound after the mod - how much was due to the preamp operating in its best range, and how much was due to more feedback in the Theta's analogue stage, I don't know. If you have problems with Theta, then a clever technician will probably be able to analyse the output stage in the Theta for you and supply some added feedback. But without a full schematic you might find that the technician will just not wish to take the risk that the stage goes unstable.

Rrlibv, I agree. I reckon that people have got the wrong components in their system if they feel the insertion of a preamp improves it. The biggest problem is usually inability of a DAC to drive a power amp, but you do not have such a problem with components like the Theta. Your solution of putting a passive attenuator in the amp is a viable solution to get the best resolution and natural harmonic textures, but will risk some compromise in dynamics. This is because the output impedence from your attenuator will be higher than is ideal to drive the amp's input stage. What saves this from being a serious problem is that the output of the attenuator will be driving very short cables. But it all depends on the amp. Some amps sound best with some padding down at their inputs (my tube monoblocks being a case in point - it has two inputs, one of which is padded down, and the reduction in distortion is significant in the context of my system - this being due to the vanishingly low output impedence of the previous stage and the relatively high input impedence of my amps). Presumably this is what you are finding too.