PREAMP BYPASS

[BOOG]

I am wondering if there are any other heads out there that have a preamp bypass switch besides Ashdown RM500 / 800?

Does anyone know of any other manufacturer's/models?

Thanks for chiming in

 

[beans-on-toast]

Some preamps have an EQ bypass, there is still an input stage to boost and condition the signal from the instrument.

Many amps have a power amp input on the back.

You can plug into the power amp directly but a gain boost is often needed. Some pedals are designed to drive a power amp.

 

[Wasnex]

I am wondering if there are any other heads out there that have a preamp bypass switch besides Ashdown RM500 / 800?

Does anyone know of any other manufacturer's/models?

Thanks for chiming in

If the effects loop is placed late in the amp and has switching jacks it's basically the same thing. Plug into the Effects Return and the preamp is bypassed.

I checked out block diagrams in the the manuals for the Mesa D800 Plus and WD800, and also the Genz Benz STR900. Plugging into the Effects Return of any of these amps will bypass the preamp, and the signal is injected just before the master volume. This is a fairly common Effects Loop configuration with modern amps. So if you are interested in a specific amp, I suggest you see if it has an Effects Loop and then take a look at the manual.

 

[BOOG]

Some preamps have an EQ bypass, there is still an input stage to boost and condition the signal from the instrument.

Many amps have a power amp input on the back.

You can plug into the power amp directly but a gain boost is often needed. Some pedals are designed to drive a power amp.

If the effects loop is placed late in the amp and has switching jacks it's basically the same thing. Plug into the Effects Return and the preamp is bypassed.

I checked out block diagrams in the the manuals for the Mesa D800 Plus and WD800, and also the Genz Benz STR900. Plugging into the Effects Return of any of these amps will bypass the preamp, and the signal is injected just before the master volume. This is a fairly common Effects Loop configuration with modern amps. So if you are interested in a specific amp, I suggest you see if it has an Effects Loop and then take a look at the manual.

Thank you! Understood.

Do you know if these examples or any others have a front panel bypass switch?

 

[Wasnex]

Thank you! Understood.

Do you know if these examples or any others have a front panel bypass switch?

I don't know of any with a bypass switch on the front panel. Some amps (including the three I mentioned) have an Aux In that injects the signal at the same point as the Effects Return. You could simply turn the preamp gain down, but you will still get a small amount of circuit noise from the preamp.

Could you explain what you are trying to achieve? If you want to switch between sources, you could run an ABY box in the Effects Loop.

 

[BOOG]

I don't know of any with a bypass switch on the front panel. Some amps (including the three I mentioned) have an Aux In that injects the signal at the same point as the Effects Return. You could simply turn the preamp gain down, but you will still get a small amount of circuit noise from the preamp.

Could you explain what you are trying to achieve? If you want to switch between sources, you could run an ABY box in the Effects Loop.

Thank you
Not really trying to achieve or change anything at this point. Curiosity is all.

Originally, I was looking into how preamps effect each other when there’s more than one in the signal path because, Friday I received a GK PLEX. My goal was to be able to run that pedal pure without coloring from the Ashdown preamp.

My original concerns were that I would not be getting a clean signal through the front panel input and/or that I would get a weakened signal by using the FX Return. As this pedal/preamp business is all new to me, I did a little experimentation. Fortunately, I found both methods give favorable results. The route through the FX Return didn’t weaken the signal as much as I thought it would and the Input (gain) and Volume controls were still usable. Secondly, routing through the front panel did not color the signal if I had the EQ switch off.

So, through all of this I started thinking that in the DISTANT future I may want to get a different amp head and having that ability to plug into the front and just flip the switch or press a button to effectively bypass the onboard preamp is a really nice feature. Currently it gives me the ability to press two buttons and have the choice of GK and Ashdown sound.

 

[Wasnex]

Thank you
Not really trying to achieve or change anything at this point. Curiosity is all.

Originally, I was looking into how preamps effect each other when there’s more than one in the signal path because, Friday I received a GK PLEX. My goal was to be able to run that pedal pure without coloring from the Ashdown preamp.

My original concerns were that I would not be getting a clean signal through the front panel input and/or that I would get a weakened signal by using the FX Return. As this pedal/preamp business is all new to me, I did a little experimentation. Fortunately, I found both methods give favorable results. The route through the FX Return didn’t weaken the signal as much as I thought it would and the Input (gain) and Volume controls were still usable. Secondly, routing through the front panel did not color the signal if I had the EQ switch off.

So, through all of this I started thinking that in the DISTANT future I may want to get a different amp head and having that ability to plug into the front and just flip the switch or press a button to effectively bypass the onboard preamp is a really nice feature. Currently it gives me the ability to press two buttons and have the choice of GK and Ashdown sound.

Running an ABY switch in the Effects Loops will give you the desired functionality.

I looked at the Ashdown Rootmaster manual and I don't see a switch to bypass the preamp? I do see the EQ bypass. The amp's Effects Return has a switching jack like the other amps I mentioned.

Running through the Effects Return should not weaken the signal unless the Effects Return is both unswitched and unbuffered. An ABY switch will provide isolation between the two inputs, so the two sources should not load each other down. Of course the Sensitivity at the Input and Effects Return are very different because the preamp is intended to provide quite a bit of gain. Perhaps input impedance could also be a factor.

 

[lowfreqgeek]

Glockenklang Blue Soul has an EQ bypass switch. That's a GREAT sounding amp - in my top 3 I've ever owned (along with Trickfish BH1k and Epifani UL502).

For your purpose, I'd go with something that has a parallel effects return and use the external pre into that. I do that on occasion with the Trickfish, and I've done that for years with the blendable return on my SWR Bass 350. Sometimes different flavors of amps are nice to have, though it's more of a studio thing for me, in which case I don't often go to that kind of trouble.

 

[BOOG]

Glockenklang Blue Soul has an EQ bypass switch. That's a GREAT sounding amp - in my top 3 I've ever owned (along with Trickfish BH1k and Epifani UL502).

For your purpose, I'd go with something that has a parallel effects return and use the external pre into that. I do that on occasion with the Trickfish, and I've done that for years with the blendable return on my SWR Bass 350. Sometimes different flavors of amps are nice to have, though it's more of a studio thing for me, in which case I don't often go to that kind of trouble.

Wow, cool! Three companies I rarely think of. Gonna have to look into glockenklang further

 

[SteveBassJr]

Before I decided to go with a power amp, I bypassed my amps pre amp/ eq section on my Aguilar th 500 and ag700 by using The effects return. If your gk plex has enough power it will feed your amps power section. I eventually went with a clean power amp because I love my tube pre amp more.

 

[BOOG]

Before I decided to go with a power amp, I bypassed my amps pre amp/ eq section on my Aguilar th 500 and ag700 by using The effects return. If your gk plex has enough power it will feed your amps power section. I eventually went with a clean power amp because I love my tube pre amp more.

Yeah, I really love the RM500 but the GK sound is nice to have.

 

[Downunderwonder]

If the effects loop is placed late in the amp and has switching jacks it's basically the same thing. Plug into the Effects Return and the preamp is bypassed.

I checked out block diagrams in the the manuals for the Mesa D800 Plus and WD800, and also the Genz Benz STR900. Plugging into the Effects Return of any of these amps will bypass the preamp, and the signal is injected just before the master volume. This is a fairly common Effects Loop configuration with modern amps. So if you are interested in a specific amp, I suggest you see if it has an Effects Loop and then take a look at the manual.

Not really the same unless the preamp adds no gain up to the fx loop. I don't know of any like that.

Vintage Trace can all bypass the EQ after the initial gain stage.

 

[Wasnex]

Not really the same unless the preamp adds no gain up to the fx loop. I don't know of any like that.

The OP asked about amps with a front panel preamp bypass switch. This functionality is built into the Effects Return. This is what I meant by my statement..."it's the same thing." FYI, I don't know of any amps that have a front panel preamp bypass switch.

If you plug into the front end of the amp and bypass the EQ, the sensitivity will be different than if you plug into the Effects Return and bypass the preamp. I mentioned this in post #7.

 

[Downunderwonder]

The OP asked about amps with a front panel preamp bypass switch. This functionality is built into the Effects Return. This is what I meant by my statement..."it's the same thing." FYI, I don't know of any amps that have a front panel preamp bypass switch.

If you plug into the front end of the amp and bypass the EQ, the sensitivity will be different than if you plug into the Effects Return and bypass the preamp. I mentioned this in post #7.

Trace vintage do exactly that.

 

[BOOG]

I really appreciate all the help and insight. You guys are great!
@Wasnex @Downunderwonder @lowfreqgeek @SteveBass5 @beans-on-toast

 

[Jay Corwin]

I bypass mine and any backline rigs I use by going into the effects return with my preamp/pedal set.

On older heads with graphic EQ's (Hartke comes to mind), you could often switch the graphic on/off.

 

[agedhorse]

Switching out the eq is different than bypassing the preamp. The preamp also supplies the gain necessary to drive the power amp.
As far as bypassable eq, it's not a very common feature, or one used by many people. There's a parametric eq bypass footswitch function on the WD-800 for example, but it doesn't bypass the remaining eq/voicing of the amp.

 

[BOOG]

Switching out the eq is different than bypassing the preamp. The preamp also supplies the gain necessary to drive the power amp.
As far as bypassable eq, it's not a very common feature, or one used by many people. There's a parametric eq bypass footswitch function on the WD-800 for example, but it doesn't bypass the remaining eq/voicing of the amp.

Thank you.

Are there any publications or sites you can recommend for helping to learn all these different signal paths and configurations? I am trying to get a clearer picture in my head of what is happening with the signal path and what that does to the sound qualities and how different paths would effect the strength of signal and audible quality.

I'm at work and can't look at the components right now but as I can recall,,,

plex- OUTPUT---SEND---RETURN---INPUT (1/4" X 4 on the top of the unit)

With that, I am curious what are the results using output vs. send to the RM500 input or fx return?

 

[agedhorse]

Good question. I don't know of any resources, but spending time with a variety of owner's manuals and block diagrams is a good start.

 

[beans-on-toast]

Here is another example of a preamp with a front panel EQ bypass switch. It's a B-15 preamp and DI. It looks well executed but a schematic is not provided.

TONECRAFT AUDIO


Some studio equipment offers a bypass feature. Everything in the signal chain can affect the tone. The idea is, by bypassing stages, the amp can deliver better tone.

The bypass design is complicated. To do this properly, the EQ stage needs to be switched out at each end and replaced with a direct connection. An EQ can have gain makeup stages as well as an impedance adjustment stage. So it isn't as simple as bypassing the tone circuits. There could be other stages around the EQ circuit that should remain in the signal path.