Why FET instead of tube stage

[JoeCOOl]

Has anyone tried a tube stage on the front end instead of the FET?

If linearity or output impedance were a cocern you could use local feedback on one half the tube followed by a cathode follower.

Based on other threads it looks like its a 20dB stage, and I have seen at least one report that an op amp ckt used here produced similar results as the FET.

Also, why do most cloners bother with the jazz switch?

[DonMoose]

Has anyone tried a tube stage on the front end instead of the FET?

If linearity or output impedance were a cocern you could use local feedback on one half the tube followed by a cathode follower.

Based on other threads it looks like its a 20dB stage, and I have seen at least one report that an op amp ckt used here produced similar results as the FET.

Also, why do most cloners bother with the jazz switch?

I think - but am probably wrong - that a JFET is about the only thing with a higehr input impedance than a triode. Just the sort of thing you need for a Piezo or weak single-coil pickup.

[Structo]

I imagine he went the SS route because the preamplifier was an add on to later amps and he didn't have room for another tube stage.

It't mainly for piezo equipped guitars like acoustics with the under saddle piezo pickup.

Although some guys use it for low power pickups such as vintage strats have.

[David Root]

I built my first two D's with the jazz switch but never used it much. It does sound OK with the PAB on though, a bit different than the normal clean tone in Rock mode.

So I dumped the Rock/Jazz circuitry entirely on my third build, a Bluesmaster HRM, and don't miss it at all.

[Structo]

Yes, my amp is 99.999999% of the time set to "Rock".

[FUCHSAUDIO]

A tube in that location would be very noisy and prone to microphonics. A few of the high gain Marshall mods from the coast (Bradshaw did it) did this on a JCM style circuit. It was hell to find quiet enough tubes for that circuit location. Fets are quiet, consistent, and not mechanically sensitive.

[jaysg]

It't mainly for piezo equipped guitars like acoustics with the under saddle piezo pickup.

I thought it was part of the David Linley lap steel sound?

[DonMoose]

It't mainly for piezo equipped guitars like acoustics with the under saddle piezo pickup.

I thought it was part of the David Linley lap steel sound?

Musicians don't care what it's FOR, they care how it SOUNDS.

[JoeCOOl]

A tube in that location would be very noisy and prone to microphonics. A few of the high gain Marshall mods from the coast (Bradshaw did it) did this on a JCM style circuit. It was hell to find quiet enough tubes for that circuit location. Fets are quiet, consistent, and not mechanically sensitive.

Andy,

A week or two ago I played one of your ODS amps used at a local store.
it was mint and I used a Start.

I kept the master output low so I would not blast the rest of the store. I had the gain full out (is this FET?) OD section full out as well as the gain. I expected more sustain, thinking D style amps are primarily preamp distortion and output stage was just for overall level. This lead me to believe you needed the FET for better overall drive.I think I also had preamp boost switched in.

Does this sound right? It distorted but did not sing.

Clean mode and verb sounded very nice and full btw. Very nice clean, like a fine tuned twin.

Clean tone

[FUCHSAUDIO]

Not really sure. Could have been a weak tube, trimmers turned down, or were you actually IN the overdrive mode ? Since it was used, anything is possible... Not to be a wise-ass, but was the OD pull pot pulled ? Sounds off though....we usually have gobs of gain and don't need a FET to get it.

[JoeCOOl]

Is there a FET circuit in the amp? Is that what the drive is controlling?

The over drive switch was engaged definitely because I was switching between clean and lead with foot switch

The PA boost was on I believe.

Very nice amp, just thought the lead sustain was less than a pedal in front of amp and wanted more. As mentioned the master was low so I did not blast the store out.

maybe something going on with the loop?
I am not sure if this was a HRM, is there a way to tell?
50w model 2 x 6L6 TAD brand.
Amp is mint with matching cab.

For reference I use a Big Muff in front of a twin, and D clips I have heard definitely sing, at least with humbuckers on straight amp.

Would like to play it again.

Thanks for any insight.

[JoeCOOl]

Is there a FET circuit in the amp? Is that what the drive is controlling?

The over drive switch was engaged definitely because I was switching between clean and lead with foot switch

The PA boost was on I believe.

Very nice amp, just thought the lead sustain was less than a pedal in front of amp and wanted more. As mentioned the master was low so I did not blast the store out.

maybe something going on with the loop?
I am not sure if this was a HRM, is there a way to tell?
50w model 2 x 6L6 TAD brand.
Amp is mint with matching cab.

For reference I use a Big Muff in front of a twin, and D clips I have heard definitely sing, at least with humbuckers on straight amp.

Would like to play it again.

Thanks for any insight.

[FUCHSAUDIO]

If it were HRM it would (presumably) have the top hatch and the panel should say HRM. Non HRM's have ample gain, and we do not currently have a FET in the amps. If the amp was used, someone could have lowered the trimmers, it could have had a bad tube in the preamp, or something else. Tough to tell at this distance.