Biasing DSL 100

[GlamRocker]

I have read many threads on the web about setting the bias on the DSL 100 but there seems to be a varied opinion on the mV per side that should be used. Seemingly Marshall recommend 90mV per side but many users say that this is too hot and 80mV per side should be used.

Can anybody set me straight on this??

I want to get a new set of pre and power tubes for this amp cause i bought it second hand and i want to give it an overhaul before i start gigging it extensively. I want the amp to sound lively and juicy like this clip:



Any suggestions??? (I will be using a Les Paul Standard).

[surfnorthwest]

90 is not to hot. Set it to 80mV first and see how it sounds, then try is at 90.

THEORY OF OPERATION: We are setting the bias using the current method instead of cross over distortion method. The Bias PCB assembly is as follows: PR1: Bias mini-pot adjustment for pin1 which is one side of the push pull amp (two output tubes in a 100watt amp and one output tube in a 50watt amp). Pin1: Connected to the cathode of the output tube(s) which then goes through a 1 ohm resistor then to ground. Pin2: ground reference. Pin3: Same as pin1 but for the other side of the push/pull amp. PR2: Bias mini-pot adjustment for pin3, the other side of the push/pull amp.

PROCEDURE: 1. Make sure amplifier is connected to a load with the proper impedance selected. 2. Power up amplifier on STANDBY and let the circuit stabilize for a couple of minutes. 3. Locate the male three pin molex connector (CON2) with the two mini-pots (PR1 and PR2) on both ends found on the bottom of the tube bay. 4. Connect DMM (set to read mV) with alligator leads, reference common lead to center pin (pin2) on molex connector CON2 and positive lead to pin1 on CON2. 5. Take amplifier off of STANDBY with no signal, adjust mini-pot (PR1) closest to pin that the positive lead from your DMM is connected to and set it to the mV voltage that is listed in the chart below. 6. Repeat steps 4 & 5 for pin3 and until both pin1 and pin3 mV are the same.

BIAS CHART mV SETTINGS (pin1 and pin3)

DSL50 45mV
TSL60/1/2 80mV
DSL100 90mV
DSL401 1.375V
TSL100/122 90mV

[GlamRocker]

Thanks surf, i will give both values a try and see if there is any difference. I would like to have it as hot as possible without putting the valves or the amp in danger.

The tone that fella has in the clip above really excites me, hope to get in the ballpark with the LP standard and the DSL100.

Loving the 2 modes (clean and crunch) of the DSL green channel!!!

[noise5150]

I recently biased my DSL50 because I had changed the power tubes to Mesa EL34s about a year ago and I figured they probably were a little off by now. When I checked them, they were about 38/39mV so I followed Marshall's recommend settings and put them back up to 45mV. I didn't hear much of a difference. Am I missing something?

[surfnorthwest]

No, it really depends on the tubes. Many think you need to bias hot to get the most out of the amp but I disagree, you really just need to be within the range, if the stting sounds good thats really what matters.

[noise5150]

In theory, what would be the differences tonally of an amp set to 45mV vs 35mV? (based on my DSL50)

[surfnorthwest]

You would not get as much distortion.

[noise5150]

You would not get as much distortion.

Just to be clear, are you saying that if I set the amp to lets say 40mV, the amp would distort faster than if it was set for 45mV?

[surfnorthwest]

My experience is that when you bias lower it gives you gain more clean headroom, sometimes I like this. Biasing to cold though will really make your amp sound like crap.

So yes, biasing hotter will get the distortion coming up earlier on the tubes, this isn't always a good thing IMO. Some guys really bias up hot thinking their amps sound best like that, but doing so will really shorten the life of the tubes and can make your amp sound harsh. It is best to experiment with your head and the tubes you currently are using. Try the recommended setting, then back it off and try that.

[ACELUEK]

I bias my DSL100 at 85mv to keep it safe.. The bias does drift and when I had mine at 90mv it would drift up occasionally..

-- Thu Nov 24, 2011 9:51 pm --

Here are a few pictures when I was biasing mine several months ago..