Fine tuning my new 50W #102 build

[xpc1000]

Hello everyone, this is my first post. After some months reading many posts on TAG and planning my new amp, I just finished building a 50W #102. Thanks to Erwin for the chassis and boards set.

I have stayed true to the layout/schematic component values, measuring and selecting the closest values according to the layout. Bias is adjusted to 37ma @ 465V plates (power tubes JJ 6L6GT). I Removed bright cap in master volume.

Good first impression, specially a very transparent clean channel. A little bit on the bright side for some mid-high notes, but nothing that could not be adjusted by turning down treble and switching on the mid boost. Low end is OK.

Regarding the OD channel I have two issues:
1. The OD channel is even brighter and loses a lot of low end. I did a test with my scope by playing a E2 note (82Hz) from my strat. Probe 1 at the output of V2a was detecting a frequency of 80Hz while probe 2 at the output of V2b was detecting a frequency of 160 Hz at V2b, as if the harmonics were becoming louder than the lower fundamental frequency.

2. I have to turn up the drive pot to 8-9 to start breaking up. I initially adjusted the OD trimmer entrance to 25k with respect to ground, but later on I've been increasing it to 30k aiming for earlier break up as well as more low end. V1 is a TAD 7025 WA and V2 a TAD ECC83 WA.

Is this normal or something is wrong with my build?

Xavier

[ijedouglas]

Great looking build and congrats!

I find the OD trimmer sculpts the low-end more so than just adding more distortion. Try to get your tonal balance between clean and OD with the trimmer and don't worry too much what value you arrive on.

What taper pots are you using? I just had an interesting experience with tapers. One of my amps (183) sounded WAY softer (weaker) than the others (124/102 and other commercial clones). I pretty much settled on it just being that way until I started playing around with pots and different tapers. The amp is a completely different animal now with the correct tapers. 102 has lin tapers on the OD drive and level so probably not the culprit, but take a look at your pre-amp vol and master vol pots. I believe the pots used were Fender 2-35 which is a CTS 30% taper.

[martin manning]

Taper only affects the angular position required to get a given voltage division. Using one taper vs. another might make it easier to find what you're looking for, though.

[ijedouglas]

Taper only affects the angular position required to get a given voltage division. Using one taper vs. another might make it easier to find what you're looking for, though.

Yup, but it can be incredibly confusing when one amp on 3 blows your head off and another needs to get to 6 for the same effect

[xpc1000]

Thanks for your replies!

Great looking build and congrats!

I find the OD trimmer sculpts the low-end more so than just adding more distortion. Try to get your tonal balance between clean and OD with the trimmer and don't worry too much what value you arrive on.

What taper pots are you using? I just had an interesting experience with tapers. One of my amps (183) sounded WAY softer (weaker) than the others (124/102 and other commercial clones). I pretty much settled on it just being that way until I started playing around with pots and different tapers. The amp is a completely different animal now with the correct tapers. 102 has lin tapers on the OD drive and level so probably not the culprit, but take a look at your pre-amp vol and master vol pots. I believe the pots used were Fender 2-35 which is a CTS 30% taper.

My pre-amp and master vol are both currently 1M audio taper (Alpha), while drive and level are both 100k lin. I might try first a lin taper for the pre-amp vol. Then I'll try to adjust again the trim to see if I can reach the right tone/distortion.

In case I cannot reach that point I'll probably have to think of the possibility of increasing the value of the drive and/or level pots to 250k lin.

[ijedouglas]

My pre-amp and master vol are both currently 1M audio taper (Alpha), while drive and level are both 100k lin. I might try first a lin taper for the pre-amp vol. Then I'll try to adjust again the trim to see if I can reach the right tone/distortion.

In case I cannot reach that point I'll probably have to think of the possibility of increasing the value of the drive and/or level pots to 250k lin.

The only reason I mention the taper is that it had a pretty big effect on my 183 amp. I clearly had incorrect tapers and when I spent the time sourcing the correct parts and selecting the exact values it made a big difference. I would try and stick with the stock values. If they all measure close I would look elsewhere. Remember, #102 is a pretty bright amp so that may be part of what you are experiencing.

Question: if you keep increasing the OD trimmer, do you get a better balance?

[ayan]

Thanks for your replies!

Great looking build and congrats!

I find the OD trimmer sculpts the low-end more so than just adding more distortion. Try to get your tonal balance between clean and OD with the trimmer and don't worry too much what value you arrive on.

What taper pots are you using? I just had an interesting experience with tapers. One of my amps (183) sounded WAY softer (weaker) than the others (124/102 and other commercial clones). I pretty much settled on it just being that way until I started playing around with pots and different tapers. The amp is a completely different animal now with the correct tapers. 102 has lin tapers on the OD drive and level so probably not the culprit, but take a look at your pre-amp vol and master vol pots. I believe the pots used were Fender 2-35 which is a CTS 30% taper.

My pre-amp and master vol are both currently 1M audio taper (Alpha), while drive and level are both 100k lin. I might try first a lin taper for the pre-amp vol. Then I'll try to adjust again the trim to see if I can reach the right tone/distortion.

In case I cannot reach that point I'll probably have to think of the possibility of increasing the value of the drive and/or level pots to 250k lin.

For what it's worth, I've never been fond of 250K pots in the overdrive section. Regardless of the taper of the pots you've used, with a 1K Alpha audio (about 15% taper) for the preamp volume turned halfway up, you should be able to dial in some overdrive with the 100K linear "Drive" starting at about 9 - 10 o'clock. I'm sure you will get that sorted out, though. With respect to the extra brightness in the lead channel, a really simple thing -- trued and tried -- you can try is replacing the 150K OD output resistor with a 180K one. Doesn't steal too much volume from the overdrive channel and it tames the high end slightly, but noticeably.

Good luck!

[xpc1000]

For what it's worth, I've never been fond of 250K pots in the overdrive section. Regardless of the taper of the pots you've used, with a 1K Alpha audio (about 15% taper) for the preamp volume turned halfway up, you should be able to dial in some overdrive with the 100K linear "Drive" starting at about 9 - 10 o'clock. I'm sure you will get that sorted out, though. With respect to the extra brightness in the lead channel, a really simple thing -- trued and tried -- you can try is replacing the 150K OD output resistor with a 180K one. Doesn't steal too much volume from the overdrive channel and it tames the high end slightly, but noticeably.

Good luck!

I did the test you mentioned and only when playing a chord quite hard I started to get some distortion, but not when playing at normal levels. What I noticed while performing this test was that the brighness and the lack of low end seem to be different problems. At the mentioned level the bass notes were OK, but only when turning up Drive, the low end was disapearing while I was getting some fizz. Could this be blocking distortion?

I recorded an E2 note with my mobile phone using OD both OD and clean channels. The pre-vol was 7, drive 7, bass 4 and the od trim 30k. You will notice a "click" in the recording when switching between OD and clean.

[xpc1000]

Question: if you keep increasing the OD trimmer, do you get a better balance?

When increasing the OD trimmer I was getting a stronger distortion and what I initially detected as a lack of low end, became more apparent and more fizzy as you can hear in the recording I attached in my previous post. So now I'm quite confident that I will be able to get a good balance, but first I need to address this... Not sure if it is blocking distortion.

[ayan]

I did the test you mentioned and only when playing a chord quite hard I started to get some distortion, but not when playing at normal levels. What I noticed while performing this test was that the brighness and the lack of low end seem to be different problems. At the mentioned level the bass notes were OK, but only when turning up Drive, the low end was disapearing while I was getting some fizz. Could this be blocking distortion?

I recorded an E2 note with my mobile phone using OD both OD and clean channels. The pre-vol was 7, drive 7, bass 4 and the od trim 30k. You will notice a "click" in the recording when switching between OD and clean.

That doesn't sound like it should, reminds me of a fuzztone with a dying battery. A couple of things:

1. Preamp at 7 and Drive at 7 are settings I've never used. For what it's worth, I consider that to be a lot of gain.

2. Why is the clean sound so much louder that the OD? Where was your OD volume set for that clip?

3. Where was your global master volume set?

4. Do you have a brightness cap on the master volume? If you do, I would suggest disconnecting it ASAP and comparing the sound.

5. Is that a Strat on that clip? Sounds like there's a bit of Stratitits there.

G.

[xpc1000]

That doesn't sound like it should, reminds me of a fuzztone with a dying battery. A couple of things:

1. Preamp at 7 and Drive at 7 are settings I've never used. For what it's worth, I consider that to be a lot of gain.

2. Why is the clean sound so much louder that the OD? Where was your OD volume set for that clip?

3. Where was your global master volume set?

4. Do you have a brightness cap on the master volume? If you do, I would suggest disconnecting it ASAP and comparing the sound.

5. Is that a Strat on that clip? Sounds like there's a bit of Stratitits there.

G.

OD volume was set around 1-2, to get a similar level as the clean channel. The global master volume was also very low. IIRC around 2.

No brightness cap on the master volume, and yes, it is a Strat.

I turned up preamp and drive vol to make the problem more apparent.

Do you want me to try a different setup?

[ijedouglas]

Do you want me to try a different setup?

What happens when you turn up the master volume? I find that the sound fills out a little better once the amp is pushing some air.

What is the measured value of your V2 snubbers?

Might be the recording but it sounds like your OD level needs a little more to balance with the clean. Is that 1-2 o-clock or 1-2 on the dial? I typically have mine around 5-6 on the dial (noonish).

Strats are tough to get right. Even some of the real Dumbles I have played, I struggled to get a good tone with a strat. Have you tried an HB guitar?

[ayan]

Do you want me to try a different setup?

What happens when you turn up the master volume? I find that the sound fills out a little better once the amp is pushing some air.

What is the measured value of your V2 snubbers?

Might be the recording but it sounds like your OD level needs a little more to balance with the clean. Is that 1-2 o-clock or 1-2 on the dial? I typically have mine around 5-6 on the dial (noonish).

Strats are tough to get right. Even some of the real Dumbles I have played, I struggled to get a good tone with a strat. Have you tried an HB guitar?

Xavier, I agree with every single thing Ian says here.

[xpc1000]

Do you want me to try a different setup?

What happens when you turn up the master volume? I find that the sound fills out a little better once the amp is pushing some air.

What is the measured value of your V2 snubbers?

Might be the recording but it sounds like your OD level needs a little more to balance with the clean. Is that 1-2 o-clock or 1-2 on the dial? I typically have mine around 5-6 on the dial (noonish).

Strats are tough to get right. Even some of the real Dumbles I have played, I struggled to get a good tone with a strat. Have you tried an HB guitar?

In fact I was refering to the dial numbers. I tried to turn up the master volume and get as close as possible to your indications for the new test, but I have some limitations with my neighbours!

See below a picture of the panel so you know exactly the position of each volume.

I attached as well two samples from my HSS, one from the neck (single coil) and the othe from the bridge (humbucker)

Regarding the V2 snubbers, I will unsolder on leg to be able to measure them, so my tester doesn't allow to measure them in the circuit.

[xpc1000]

What is the measured value of your V2 snubbers?

280pF and 290pF