Just finished a 102 build, some questions

[beasleybodyshop]

Hello everyone, I just finished building a 50W 102 from fender bassman iron. I have stayed true to the layout/schematic component values, used 6PS caps and mostly RN65 metal films throughout. As per the layout document, i adjusted the OD trimmer entrance to roughly 25K with respect to ground, and adjusted the PI trimmer so the that PI output AC voltage is the same on both sides. Preamp plates are 201/200 for V1, 210/217 for V2. PI plates are both right at 300 volts. Bias is adjusted to 30ma @ 460V plates.

My first impression is woah, this amp is bright. Even with my Les Paul. Clean tone is great, very articulate to my ear. OD channel sounds a little harsh to my ear. overdrive has a bit of a ragged edge to it, has anyone experienced this? Any remedies for this? Any any remedies to tame the brightness ? Thanks Everyone. Mark Fowler and Jelle Welagen have been big influences on me building this 102, big thanks goes out to them for inspiration and everyone else on TAG that has been patient with me over the last few years.

[norburybrook]

What speaker are you using? My recently build 50w #102 isn't bright , in fact I have the bright switch on unusually.

I've used the same orange drops and RN65's but I used quite a lot of NOS Piher resistors.


I don't have a bright cap on the master, do you, and if so what value?



Marcus

[ayan]

All of these amps are arguably "bright." These are things that I believe make your particular build brighter:

1. You use the Dale resistors, which are metal film, everywhere. Dumble used Koa (or something similiar to them), which are also metal film, everywhere in some early 90s HRM amps that featured NTE Mylar caps, etc. However, in the amps that I've seen Dumble use the RN65s resistors, he only used them on the plates; he favored other metal film types for the cathodes, sometimes carbon film and some times metal film for the slope, and carbon film just about everywhere else. The choice of resistors will affect the sound, and the RN65s that Dumble used are not the same current production ones you can buy from Mouser. Those newer RN65s look nice, though, and I've used them as well.

2. If you don't use the amp with a Dumbleator or equivalent, the amps get brighter real quickly. But, there's something to the brightness of the amp that's very cool for live playing, provided it doesn't sound harsh in OD mode.

3. You apparently have the 68pF master volume brightness cap. I used to use an HF taper in my amps until I was able to get the amps to sound good without the HF taper control (i.e., component choice and orienting the coupling caps properly, which you have already done). In my case, it was a .001uF cap and a 1 Meg trimmer to ground; note that Dumble apparently used a .01uF with a trimmer, which is bound to seem to "add bass"-- although it won't -- whereas the .001uF cap will only dial out the very top end and it will sound honky and unnatural if you use too much of it. Anyway, after I tried the 68pF master brightness cap, I loved what it did to the clean sound, but I was forced to put the HF trim control back in my amps; I dial it back to about 350K on the trimmer. The sound of the amp's OD with the HT trim and the 68pF master brightness cap, for the master settings I use, is brighter than the amp without the 68pF cap and without the HF trim control. A different choice of shielded cable for the OD section might balance things a little better, but generally speaking, I would say that you need to dump some highs to ground on the OD if you use a 68pF brightness cap. Something else you can do is increase the value of the OD's output resistor (normally 150K), but doing so will mess with the available OD volume from the amp. You could try a 250K pot for the OD volume, instead of 100K, and select an output resistor (instead of 150K) that will get you the amount of highs you want. If you start with no resistor, that is equivalent to 150K fixed plus a 100K pot. So you can the add a 10K, 24K, 47K, etc., until you get the sound you want Using the larger pot will preserve plenty of volume in OD mode. The standard fix, 180K resistor and 100K pot, compromises the OD volume already for my taste.

Hope the above helps you try to tame the beast a bit. Cheers,

Gil

Hello everyone, I just finished building a 50W 102 from fender bassman iron. I have stayed true to the layout/schematic component values, used 6PS caps and mostly RN65 metal films throughout. As per the layout document, i adjusted the OD trimmer entrance to roughly 25K with respect to ground, and adjusted the PI trimmer so the that PI output AC voltage is the same on both sides. Preamp plates are 201/200 for V1, 210/217 for V2. PI plates are both right at 300 volts. Bias is adjusted to 30ma @ 460V plates.

My first impression is woah, this amp is bright. Even with my Les Paul. Clean tone is great, very articulate to my ear. OD channel sounds a little harsh to my ear. overdrive has a bit of a ragged edge to it, has anyone experienced this? Any remedies for this? Any any remedies to tame the brightness ? Thanks Everyone. Mark Fowler and Jelle Welagen have been big influences on me building this 102, big thanks goes out to them for inspiration and everyone else on TAG that has been patient with me over the last few years.

[jelle]

What preamptubes are you using?

Also, the real 102 is a bright amp, and needs a Dumbleator and tuned cables to do what it does.

[beasleybodyshop]

Jelle, I'm using JJ preamp and power tubes.

Gil, thanks for your comments. When you say adding a HF taper, where are you inserting this into the circuit specifically?

[Smokebreak]

Not to speak for Gil, but I believe traditionally it's hung off the ratio/OD level control. I've used 2n and 1M pot to great effect, granted not on a 102.
He explains it here : https://tubeamparchive.com/viewtopic.ph ... eble+bleed

[ayan]

Check out the thread Smoke pointed you to for a diagram of it. Increasing the output resistor method may be the preferred way to go for some, as it may squash the signal a little less than dumping highs to ground via a cap. As Jelle said, 102 is supposed to be a pretty bright amp; I've never played it, but got to hear it a bunch of times and yes, it is bright. Don't know if the amp has been modified after RF ditched his rack with Dumbleator, etc., I suspect it has not. I have used my amps without the rack and while brighter, the clean sound is just fine; the overdrive is definitely more aggressive, but not brighter than a Marshall Plexi, for example. Perfectly fine if you put a pedal in front of it, for example, like RF does these days.

G.

Jelle, I'm using JJ preamp and power tubes.

Gil, thanks for your comments. When you say adding a HF taper, where are you inserting this into the circuit specifically?

[Charlie Wilson]

Hello, one thing that I did in my amp to tame the high end a little was to use a 100k drive pot that measured a bit high (about 120k). I have been playing around with the HF taper and I prefer just a straight cap 100-200pf to ground rather than the larger .02-.001uf. The larger caps strip to much sparkle out of the OD for my taste regardless of the resistance. I posted this before but I find that the HF taper also rolls some highs off of the clean and I am not sure why.
CW

[Pacosipulami]

Hi, I mostly add a simple cut off filter (250k pot and 2.2 or 3.3nF cap) behind the OD stages to tame the highs a bit down. Works pretty good! I make this a switchable mod along with some other tweaks on non-HRM designs. Pretty nice results as I can tell you. Other thing would be a small capacitor between the plates of the PI - note, this would affect the clean channel too.

My experience regarding higher vs. lower value potentiometers on the OD circuit is a small tonal shift torwards more focus and less low end when using lower (aka 100k lin) potentiometer instead of 250k pots. All IMO

cheers
P

[Structo]

I think I have a 15pf bright cap on my Master.

But I run the master pot up around 1:00, so it may not be doing much.

I control the overall volume of the rig with the Dumbleator output pot.

I do have a HF trimmer and I set it where it just takes the high fizzyness off, that can sometimes be a nuisance.

When I first built it I had problems with too much low end.

Probably because the cab sits in a corner of the room with a pair of EV 12L's.

Oh and I have 250K OD pots.

[ayan]

If you haven't already, you may want to try something larger than that. I started with 15pF after inspecting 124, then moved up to 30pF, then 47pF... and I didn't like that, it was too harsh, so I stayed at 30pF for years. Finally, when the 102 fever broke, I tried 68pF and it was perfect... and I like to set my master where the 68 can really be felt.

G.

I think I have a 15pf bright cap on my Master.

But I run the master pot up around 1:00, so it may not be doing much.

I control the overall volume of the rig with the Dumbleator output pot.

I do have a HF trimmer and I set it where it just takes the high fizzyness off, that can sometimes be a nuisance.

When I first built it I had problems with too much low end.

Probably because the cab sits in a corner of the room with a pair of EV 12L's.

Oh and I have 250K OD pots.

[aflynt]

I've found the #102 circuit works best with a D'lator in it's stock form, though the clean can be a bit dull for some people once the OD is smoothed out. The bright on clean mod works well for balancing that out.

Assuming you don't have a D'Lator, some easy things you might try are lowering the V1 and V2 plate voltages by increasing the V2 PS dropper and / or lifting the bright cap. Also, raising the bias current will generally lower the preamp voltages and soften things a bit, so that would be even easier to try.

I personally find the master bright cap to be a PITA if you're not going to just leave the master at a fixed setting. The amp becomes a tonal moving target with different playing volumes. I like what it does in conjunction with the D'Lator in the stock circuit, though. I had the same problem with the loop network filter but in reverse... and the HF taper too (changing OD gain would take me out of the sweet spot), but I fixed that with this circuit:

https://tubeamparchive.com/download/file.php?id=39706

So far, the above (in combination with low plates) is my favorite fix for the bright OD / dull clean issue.

-Aaron

[brewdude]

Is that a dual ganged 100k pot for the level control?

[aflynt]

Is that a dual ganged 100k pot for the level control?

Yeah. Dual 100k pot. One side standard OD Level, other side wired as HF taper in reverse. As you turn up the gain you get more highs dumped to ground. The 68k is a minimum taper setting. So at full gain the HF taper is 68k => .001uF => ground. At minimum gain it's 168k => .001uF => ground. I found that range is about right with low plates to keep the overall timbre of the amp balanced between clean and OD at various gain levels.

-Aaron

[Smokebreak]

That's a fantastic use of a dual-gang!