Pre 3 compared to Pre 2

[david]

Hi All,
I have my old Pre 2 with cathode follower mod back for a comparison with my Pre 3. In comparison to the Pre 2 my Pre 3 sounds a little bit light in the bass. I don't have the circuit to hand, and so can't quite see what might be causing any lightness in the bass.

Both have shunt pot mods, and the valves and all other parts in the Pre 3 are all in good order.

Any suggestions anyone? Of course, it could simply be that the Pre 2 is a little bass heavy but I have to say I prefer a bit more bass weight rather than less....
David

[bob orbell]

Hi David, I still use a CF pre, (in a pre III case) because I found the pre III a tad bright, base light it was not, it was the pre II that was very base light, I would go as far as to say the pre II was thin. Did you build it yourself ? is your power supply correct ? is the connecting cord correct ? you may have something wrong there. I know JC is going to chew my ear again for saying this, but the HT may be the wrong way round, unbilical cord connection reversed, I have seen this, and it did not pop the capacitor. BOB

[david]

Firstly, Pre 2. Mine was thin until I fitted a wonderful Mullard valve which gave a rich and thunderous sound.

My Pre 3 has Black Gate N series cathode bypass caps, Mundorf silver /gold couplers, and Shinkoh resistors. It all measured to spec on construction.
David

[david]

I think it's sorted. Seemed to be a partial short on one of the output txs. I guess it pulled down the HT on both channels, because the bass is stronger now-and the equal of the Pre 2 with Mullard. Incidentally, I would never describe my Pre 3 as bright: it is pretty neutral over the spectrum, apart from this lightness I noticed (mainly in comparing it to the Pre 2)
David

[John Caswell]

Hi David,
One thing Pre 2 suffered from was electromagnetic hum pickup from adjacent transformers so you will need to keep it well away from those sources. "Banding" the coils in copper foil helped but did not eliminate it. Pre 3 was much much better in this and other respects.

John

[Greg.]

Originally Posted by John Caswell

Hi David,
One thing Pre 2 suffered from was electromagnetic hum pickup from adjacent transformers so you will need to keep it well away from those sources. "Banding" the coils in copper foil helped but did not eliminate it. Pre 3 was much much better in this and other respects.

John

John, David has already said his Pre II was converted to cathode follower, just like mine. Your comment therefore is invalid.

I have no doubt Pre 3 is a great Pre amp. I suspect it is not the best option for David's WAD 300B PP Clone and his Pre 2 cathode follower conversion is the very best option for him. It certainly is the best for me in similar circumstances.

[John Caswell]

Greg wrote
"John, David has already said his Pre II was converted to cathode follower, just like mine. Your comment therefore is invalid."
Errrrrrrr no, my comments were made about the Pre2, as David's has been converted to a cathode follower (ie like a KLP1) it doesn't really apply, but is certainly not invalid.
And if you want to be really pedantic the cathode follower is certainly not an amplifier, it is a loss making circuit and all pretty well all the passive volume control/transformer boxes don't amplify, so therefore should not be called pre-amplifiers, although I admit that some of the passive devices have step up type outputs so could be called amplifiers in the loosest sense.

John

[pre65]

As I understand things a pre2 cathode follower is more a buffer for impedance matching.

[david]

Hi All, my Pre 2 is converted to cathode follower so hum free and yes cathode followers are essentially buffers for impedance matching. It's another topic but the Pre 3 re-design simply underlines the flawed nature of the original hum-loving Pre 2 design. Yes you could of course site the Pre 2 a long way from anything else but that type of solution helps relegate our hobby to a shed or hobby room status rather than creating a decent system for the lounge, which is why many opted for the cathode follower mod.

I'm still perplexed by the apparent better performance of the Pre 2 cathode follower compared to the Pre 3.

Lines of investigation to follow are:

1. Is there some other small fault with my Pre 3 that is reducing richness/bass response?

2. Does the Pre 2 cathode follower have a frequency response uplift in the lower registers?

3. Could the resistor /pot combo have such an effect on frequency response? I am currently using Shinkoh /Alps Blue?

Any views anyone?