Fender Bassman10 - Seeking Clean Tone but distorted output

[digi001]

Hi all,

I have an old Fender Bassman 10 my friend gave me that was sitting under the stairs of an old house they cleaned out.

The cabinet had some awful toxic smell that I unfortunately could not get rid of so I stripped the head and speakers for a new cab. Seeing that a custom cabinet was around $300-400 from Webber I decided to go another route.

Now I am using the 'head only' in my recording setup to run my bass and guitars through and use the Recording Output. Sounds amazing and I've been using GuitarRig3 for Cab Simulation. (eventually will get 1 of the 10 inch speakers in a Smaller Cab and use this for recording)

Anyways my question is that the amp very easily distorts in both channels when trying to get a nice Fender Guitar Clean sound. Even with the input gain all the way down it distorts. Not major distortion but enough to screw up the sound im going for. A single note lead picked is usually fine but once I start hitting some clean chords it disorts.

I tried replacing the 12AX7 with a 12AY7 and this removes all distortion, but also seems to suck away alot of the tone.

Any suggestions?

[pdf64]

I am using the 'head only' in my recording setup to run my bass and guitars through and use the Recording Output

What's the 'recording output'?
What is connected to the amp speaker output?
The schematic has Vdc and Vac noted, so if your rig set up is ok it may be a good idea to compare measurements between your amp and the schematic http://bmamps.com/Schematics/fender/bas ... _schem.pdf

EDIT the later UL version has a recording output https://sites.google.com/site/yourtubea ... -schematic
It still needs an 8 ohm load on the speaker output!

[Stevem]

How much signal are you pumping into it from the external gear, if it's more than 350mv, than yes you will clip the preamp section dependant on how strong the preamp tube is for the channel you are playing thru.
If the amp was running thru its own outout stage and speakers it will only take a input signal level of 150mv to drive the amp to it's full output and max clipping level! If the map like you posted cleans up with a 12ay7 in it then just back down on how hard you drive the input and or use the number two input which is 3 DB down !

[digi001]

I am using the 'head only' in my recording setup to run my bass and guitars through and use the Recording Output

What's the 'recording output'?
What is connected to the amp speaker output?
The schematic has Vdc and Vac noted, so if your rig set up is ok it may be a good idea to compare measurements between your amp and the schematic http://bmamps.com/Schematics/fender/bas ... _schem.pdf

EDIT the later UL version has a recording output https://sites.google.com/site/yourtubea ... -schematic
It still needs an 8 ohm load on the speaker output!

Thanks for posting a link to the schematic!

Ok interestingly enough I am realizing this must be a uncommon version of the Fender BassMan Ten. Not sure what year? But all the other pictures I see online don't have a 'Recording Out'?

Currently I have nothing connected to the amp speaker output. (Is this ok, and can I remove the output tubes if not using?) I plan to hookup an external speaker cab if I want to mic it, otherwise most of the times I record direct and use a Cab Sim. (No phase issues)

[digi001]

How much signal are you pumping into it from the external gear, if it's more than 350mv, than yes you will clip the preamp section dependant on how strong the preamp tube is for the channel you are playing thru.
If the amp was running thru its own outout stage and speakers it will only take a input signal level of 150mv to drive the amp to it's full output and max clipping level! If the map like you posted cleans up with a 12ay7 in it then just back down on how hard you drive the input and or use the number two input which is 3 DB down !

Ok cool. Yes you are right. I didn't realize input 2 was lower gain! It seems if I back the Input Gain to about 1-2 and go into channel 2 of the normal, I get the clean sound I am looking for, all with the original 12AX7 installed!

That was easy ha.

But now to investigate something further...........

My output from 'Recording Out' is VERY low. I need to drive the preamp pretty high AND additionally add some gain in my DAW to get a useable signal. Being an unbalanced output there is some inevitable noise that gets amplified doing all this (even if going into a Transformer Balanced input preamp)

So what is going on here? I guess I need to start by finding a schematic. Haven't found anything yet though. Do the Bassman standalone Heads have this recording output section? Or does anyone know of any of the bassman series has it? Maybe it is similar?

I can post a picture later

[pdf64]

Currently I have nothing connected to the amp speaker output. (Is this ok, and can I remove the output tubes if not using?)

No that's absolutely not ok, any signal will put significant stress on the power tubes.
Unfortunately the recording out won't work without power tubes in place.

[digi001]

Currently I have nothing connected to the amp speaker output. (Is this ok, and can I remove the output tubes if not using?)

No that's absolutely not ok, any signal will put significant stress on the power tubes.
Unfortunately the recording out won't work without power tubes in place.

So your saying:
It is not Ok to remove them?
or
It is not Ok to have no Speaker Load?

-Or Both?

[Stevem]

You should get plenty of recording signal out of that Jack if the master volume is opened up enough, get yourself two 8 ohm 25 watt resistors, wire them in parallel to a 1/4" inch Jack and unplug the amps speakers and plug in the resistor load, then you should get tons of recording signal level!
Yiu can not have no load on the output transformer nor no output tubes in the amp!

[digi001]

You should get plenty of recording signal out of that Jack if the master volume is opened up enough, get yourself two 8 ohm 25 watt resistors, wire them in parallel to a 1/4" inch Jack and unplug the amps speakers and plug in the resistor load, then you should get tons of recording signal level!
Yiu can not have no load on the output transformer nor no output tubes in the amp!

Should it be two 16 Ohm in parallel? Or how specific is it?

Original speakers are 32 Ohm each, 4 in parallel for 8 ohm total load.

[Stevem]

It will not much matter either way, but a higher load then then what is normal puts less strain on the output tubes and should still net you enough drive signal out the record Jack I woukd think!

[digi001]

Ok thanks i will try this.

It will be interesting to see if this helps with my 'recording out' level?

I think it might be related because before even seeing a schematic, I would think the 'recording out' is just some 10K-1M Resistor in Series with the Output load. So if the Output Load Resistance (no speaker present) is very High then there will be a Voltage Divider present, thus the low signal.

This makes sense?

[digi001]

Ok i found this.

https://reverb.com/item/8189-carl-s-cus ... attenuator

Pretty good price so gonna just buy it. Didn't find any power resistors laying around or at work.

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One thing to note however is that it says 50W max. Seeing that my Fender Bassman Ten is from 1980 and 75W it might get hot at full output.

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Question I have is, is the Output Level of my Fender Amp essentially controlling the Watts? If i keep the dial at 5 or Less will this limit it to under 50W?

[Stevem]

Your amps master volume controls the drive signal level to the output stage and hence the output wattage, if you get enough recording volume with the master volume open to 50 or 75% then you will not burn that up!

[pdf64]

I would think the 'recording out' is just some 10K-1M Resistor in Series with the Output load. So if the Output Load Resistance (no speaker present) is very High then there will be a Voltage Divider present, thus the low signal

The amp has a shorting speaker jack, so that with nothing plugged in, the output is shorted.
The recording out is just a ~1/10 potential divider from the speaker output.
With a proper 8 ohm load (rather than a short eg a fraction of an ohm), the signal from the recording output will be way bigger, might be too much for your system, way over 2Vrms, when 0dBU is 0.775Vrms https://www.montagar.com/~patj/db_db.htm

That box looks to be just an Lpad nicely packaged up.
The amp will likely put out over 50 watts so I suggest something with a bigger rating, as it will sound better the higher you turn the master volume.
If you want an lpad, consider something of at least 100 watts, like http://www.parts-express.com/parts-expr ... m--260-262
My experience is that a 10 watt amp can make a 15 watt lpad overheat to the point of emitting smoke.
Weber sell dummy loads, but the resistors may need heatsinking https://taweber.powweb.com/amptechtools/truload.htm
But a proper reactive load would sound better, as a tube power amp (even UL) has an output impedance that is significant in comparison to its rated load impedance. This means that the output voltage / power will tend to track the variation in speaker impedance with frequency, resulting in a treble and bass boost.
The net result being that a purely resistive load can sound flat and middy in comparison to a load that mimics a speaker's impedance - frequency characteristics.

Yes a master volume controls output wattage, but there's no correlation between the MV setting and output power, other than very trivially, such that it may well be able to put out full power at halfway or less.

[Structo]

In reference to running a tube amp without speakers attached.

Remember this, anytime, anytime! you power up a tube amp, you must have the speaker connected or a dummy speaker load (big resistor) connected.

That is pretty universal knowledge pertaining to tube power amps.

If you do run the amp without a speaker load, bad things can happen to the
power tubes and or the output transformer.