Bogner XTC fx loop volume and tone drop

[Setneck]

Hi!

I got quite a pi**ing-off issue with my FX loop. I am running my effects in parallel mode (if switched to series the amp squeels, also I don't like the sound of effects then as they distort a bit). I use BOSS PSM-5 Power Supply & Master Switch to engage or disconnect all the set of effects, having fx loop in XTC always on. And when I kick it the tone is fading noticeably, becoming nasally and backed-off. It seems like someone would put a blanket on my cab. The same was when the tubes were brand new, so I think it is not a matter of tubes actually.

I've heard that Bogner's loop is fixed rather for rack effects, as it works at +4dB line level. And most pedals (including mine) work at -10dB level. Mine issue is being called "parallel phasing" issue. This occurs when using an effect in the fx loop (set to parallel) that passes dry signal as well. So there are two "dry" signal streams, one going through the loop (as part of the effect signal) and one bypassing the loop. Because there will be small timing differences between the two, this will cause the sound to degrade to sound thin. The solution would be to use only effects that can be set to 100% wet. But as for now it is out of my range. Looks like I'm in a deep sh**t actually, as none of my units has such regulation. Only Level can be adjustable.

Any chance to compansate that volume loss? Any extra unit or any fx mod? Some amplifiers (not the XTC) have switchable effects loop, +4dB or -10dB. I was told that Ebtech Line Shifter can convert between line and instrument levels. Any other solutions? I wonder if the CAE Boost/Line Driver could help here, leveling the signal. But I use Seymour Duncan Pickup Booster to boost for the solos, so two boosters would be too much I think.

Sorry for kinda long post but I wanted to state my problem as clearly as it was possible. Any help would be very much apreciated.


Regards

Andy

[Setneck]

Hi!

I found two units which could help me. One is Ebtech LINE LEVEL SHIFTER http://www.ebtechaudio.com/lls-2des.html and second is polish one G-Lab Signal Adapter SA-1 http://www.glab.com.pl/sa-1_en

Could You look at it and tell me if those would solve my problem? Thanks in advance

Regards

Andy

[joey]

I was under the impression the XTC had a pot for the send level? This is essential for keeping the signal level managable for Floor units which have very limited swing capabilities. IIRC the send stage is a AC coupled cathode follower, and the return is a summing amp (or a VE stage as it is commonly referred to). If the return stage is designed for unity gain, there's your problem.... you need about 20db worth of gain to bring the signal up to the level the return stage wants to see........ If you don't want to mod the amp, maybe an mxr microamp after your FX chain might do it, it will add some noise though.

[Setneck]

I was under the impression the XTC had a pot for the send level? This is essential for keeping the signal level managable for Floor units which have very limited swing capabilities. IIRC the send stage is a AC coupled cathode follower, and the return is a summing amp (or a VE stage as it is commonly referred to). If the return stage is designed for unity gain, there's your problem

XTC has switchable loop between series and paralell which act little different. I use it in parallel mode, where there's a knob named "Mix" by which You add the effects to a dry signal, and the knob named "Master Volume", which isn't a regular MV, rather allows to match Loop on and Loop off volumes. So actually You're right that it summs up the amps signal.

It turned out that the problem of dropping volume was caused by BOSS PSM-5 unit, which was stealing part of the signal. I used to use it to engage/disangage the effects chain. It was easier for me as I often use more than one effect at the same time. So it was easier to kick two effects with the chain off and then turn it on by only one kick . But having FX loop on/off switch in Bogner footswitch I actually don't need it anymore. So I linked the effects directly with the loop and the FX Loop switch on footswitch will do the work that was previously managed by PSM-5 unit. The tone drop is present but it noticeably less heard now. I got to get used to that till I switch for rack effect unit.

If you don't want to mod the amp, maybe an mxr microamp after your FX chain might do it, it will add some noise though.

I did think about that and tried CAE/MXR Boost/Line Driver. But I also use Seymour Duncan's Pickup Booster as a clean boost for solos. Two boosts caused amp to squeel like a pig .


Best regards, Andy

[joey]

AH yes!, IMHO it may had been a better design choice to use a send level instead of the mixing level, and a return level instead of a global master with a +20db/0db return gain pad but oh well. You will notice a big difference when you finally get a line level unit

[Setneck]

Yeah, I think so too. I know that it was necessary for Bogner to choose some way of dealing with the fx loop, but I don't think it would be too hard (or it would suck THAT amount of tone) to put the button which would level the signals when using stompboxes or rack units. There's such button in Marshall 6100 and it works perfect.

You said that I would notice a big difference getting a line level unit. So You think I am supposed to buy an Ebtech Line Level Shifter unit?


Best regards, Andy

[joey]

but I don't think it would be too hard (or it would suck THAT amount of tone) to put the button which would level the signals when using stompboxes or rack units.

Oh, It wouldn't do jack shit to the tone, and there is much better designed tube loops in general. The poor Current drive capabilities of the 12AX7 this amp uses, make it less suitable for this application.

such button in Marshall 6100 and it works perfect.

It is a very different loop. It is an opamp design, and actually a much better loop as far as clarity is concerned, you have to be careful with opamp loops. They have a very limited swing, so you have to pad the input signal from the preamp so as not to clip the opamp, I have been fairly impressed with Laney's loops too!... anyway I'm just rambling.

said that I would notice a big difference getting a line level unit. So You think I am supposed to buy an Ebtech Line Level Shifter unit?


Best regards, Andy

I mean in general, I bought a line level eventide H3000 D/SE from an old roomate, and will never go back to using instrument level stompboxes.

[Setneck]

Oh, It wouldn't do jack shit to the tone, and there is much better designed tube loops in general. The poor Current drive capabilities of the 12AX7 this amp uses, make it less suitable for this application.

There are a few issues with that XTC's loop. As I solved my tone dropping problem now I have another one. The well-known XTC issue is loud popping while changing channels or engaging the loop by footswitch. Mine amp popps very loud especially by the FX button. I wonder if the 12AT7 tube as a loop driver would solve my problem. What do you think Mate?

such button in Marshall 6100 and it works perfect.

It is a very different loop. It is an opamp design, and actually a much better loop as far as clarity is concerned, you have to be careful with opamp loops. They have a very limited swing, so you have to pad the input signal from the preamp so as not to clip the opamp, I have been fairly impressed with Laney's loops too!... anyway I'm just rambling.

Yes I know. But that loop worked perfectly for me, either with stompboxes and with GMajor which I have once tried. But I am not familiar with the "opamp", could You please explain me what does that mean?

said that I would notice a big difference getting a line level unit. So You think I am supposed to buy an Ebtech Line Level Shifter unit?

I mean in general, I bought a line level eventide H3000 D/SE from an old roomate, and will never go back to using instrument level stompboxes.

Oh well, so I might try that Ebtech unit as it is possible to buy it for 70$. Thank You very much for Your help, I really apreciate that Mate


Best Regards, Andy

[joey]

Sorry I left you hanging! The 12AT7 would be a better choice all around for the loop. It is a higher current valve, and doesn't have much less "realizable" gain than a 12ax7. In that loop it looks like a drop in replacement easy. The only thing that may affect anything is that it might drop your preamp voltages a little, because it is going to draw more current than a 12AX7, but I doubt it would be that much, or that you would hardly notice it.

The popping unfortunatley is due to other circumstances, most likely no DC ground referncing of the relay poles, or a sudden shift of DC operation

The loop in the marshal is Solid state, and what I meant by OPAmp was operational Amplifier, which is the term given to a chip. Solid state Loops, actually make more ideal loops, because you can make them transparent, so long as you control your signal level from the preamp.. which is easily done.

All that being said how do you like the XTC? I built one recently, and had to change quite a bit to get it to play nice with my setup

[Setneck]

Sorry I left you hanging! The 12AT7 would be a better choice all around for the loop. It is a higher current valve, and doesn't have much less "realizable" gain than a 12ax7. In that loop it looks like a drop in replacement easy. The only thing that may affect anything is that it might drop your preamp voltages a little, because it is going to draw more current than a 12AX7, but I doubt it would be that much, or that you would hardly notice it.

No problem with delay Mate! I actually tried 12AT7 for a loop but wasn't too impressed. Maybe because it was RFT tube, but I noticed that the effects seem to sound quite lifeless. I will give it another try if I'll grab some more other 12AT7's.

The popping unfortunatley is due to other circumstances, most likely no DC ground referncing of the relay poles, or a sudden shift of DC operation

That popping is quite annoying, especially during gigs. Do You maybe have any thoughts how to solve that problem?

All that being said how do you like the XTC? I built one recently, and had to change quite a bit to get it to play nice with my setup

Well, I must say that it is my dream amp. I has everything what I need to create the tone which I was after since I play guitar. Its smooth overdrive, that full and creamy tone makes me very happy on stage . I must admit that it is quite difficult amp to dial right, and also it is very sensitive on the tubes. I took me long time to dial and find the right setup but now I can say I'm in tone heaven. The right tubes are both essential and critical for that amp IMO.

A key to dream tone was for me Telefunken smooth plate in V1, which gives an amp clean input and detailed character (I would say that the amp with TFK smooth plates sounds very "noble" and "classy"), Tungsram ECC83 in V2 which gives an amp agression and that sweet round crunch and NOS Tesla E83CC goldpins for PI, which is very quiet and neutral tube, not colouring the sound in any way. As it's not as high gain tube, it gives the powertubes that cool clean kick. Perfect!!

The only thing I am struggling with using XTC is huge amount of squeeling when using B1 pre-eq and boost locked on. But most likely it's because of using LP with hot pickups.


Regards, Andy

[joey]

Well, I must say that it is my dream amp. I has everything what I need to create the tone which I was after since I play guitar. Its smooth overdrive, that full and creamy tone makes me very happy on stage . I must admit that it is quite difficult amp to dial right, and also it is very sensitive on the tubes. I took me long time to dial and find the right setup but now I can say I'm in tone heaven. The right tubes are both essential and critical for that amp IMO.

A key to dream tone was for me Telefunken smooth plate in V1, which gives an amp clean input and detailed character (I would say that the amp with TFK smooth plates sounds very "noble" and "classy"), Tungsram ECC83 in V2 which gives an amp agression and that sweet round crunch and NOS Tesla E83CC goldpins for PI, which is very quiet and neutral tube, not colouring the sound in any way. As it's not as high gain tube, it gives the powertubes that cool clean kick. Perfect!!

The only thing I am struggling with using XTC is huge amount of squeeling when using B1 pre-eq and boost locked on. But most likely it's because of using LP with hot pickups.


Regards, Andy

The cabinet I was using was a V30 Legacy cabinet, so that might have been part of it. i don't really care for V30's myself. I guess i just found the stock tone a little too woody, and warm/fuzzy. I ended up modding it to a circuit I had been working on in order to make it Cleaner and more refined in the overdrive channel. i added gain in the stages, played with voltages, and took out the '2004 update" for something else. I thought it gave the amp a kinda ugly sound (I had it switchable). I also changed the excursion. I found the medium setting kinda useless, and instead made the tight the medium, the loose I kept as is, and changed the tight to super tight.

mine is as silent as death, even dimed with a tube screamer in front, no more hissy than most high gain amps without a boost, but again it was a home brew so I could use my grounding scheme, and layout, Which probably had to do with the difference in tone too. Do you still have problems with the B1 even when you jockey the tubes around? You might have some slightly microphonic tubes.

[Setneck]

The cabinet I was using was a V30 Legacy cabinet, so that might have been part of it. i don't really care for V30's myself.

Well, I must say that I have similar thoughts about that speakers. People really enjoy them, and I find them quite fine when playing myself. But in my band's mix they sounded too backed off. You see, XTC is rather dark-voiced amp, so linked with V30's it's too dark to '80-'90 rock/metal IMO. Maybe it's the way I am setting up my Ecstasy but the 75's (which I actually hated when playing Marshall DSL and 6100 ) seem to suit better my needs and tastes.

I guess i just found the stock tone a little too woody, and warm/fuzzy. I ended up modding it to a circuit I had been working on in order to make it Cleaner and more refined in the overdrive channel. I added gain in the stages, played with voltages, and took out the '2004 update" for something else.

Well, I really like XTC's tone in general, however my amp is slightly modified . My tech installed Dagnall 2668 OT taken from vintage JCM800 and also a mod which allows me to choose from three different voicings on Red Channel - pre2004, post2004 and mod known as "Cameron Mod". I use mainly pre2004 setting as it gives the amp the most open tone. Now we plan to modify pre-eq B2 settings on both overdrive channels to give it more usable gain.

Wouldn't be a problem for You if You'd write me a few words (here or by PM) what have You done to the circuit in case of adding gain to stages and making the amp more open?

mine is as silent as death, even dimed with a tube screamer in front, no more hissy than most high gain amps without a boost, but again it was a home brew so I could use my grounding scheme, and layout, Which probably had to do with the difference in tone too.

Mine is hissing a lot but it isn't a problem for me actually. I struggle more with popping while changing channels or engaging the loop and also with squeeling.

Do you still have problems with the B1 even when you jockey the tubes around? You might have some slightly microphonic tubes.

Well, I haven't yet a chance to crank the amp after I swapped tubes to NOS as I used to use all chinese in the preamp. Now I have selected Telefunken in V1, it's quieter and less gainy than chinese, so I hope it'll help. The amp actually seem to be quieter (especially with Tesla in PI position), but You know - bedroom level can tell You nothing actually in that matter . I am thinking also about screening the V1 with a cover, maybe that would help with squeeling. We'll see

Regards, Andy

[joey]

Well, I really like XTC's tone in general, however my amp is slightly modified . My tech installed Dagnall 2668 OT taken from vintage JCM800 and also a mod which allows me to choose from three different voicings on Red Channel - pre2004, post2004 and mod known as "Cameron Mod". I use mainly pre2004 setting as it gives the amp the most open tone. Now we plan to modify pre-eq B2 settings on both overdrive channels to give it more usable gain.

These are my thoughts on the mods, I tried both.

2004 = .22uf/2.7K to ground partial bypass on 3rd stage rk. gives a ton of gain but I thought is sounded too ice picky

Cameron = 1uf/10K to ground partial bypass. Fatter sounding, and more subtle, but a little loose

pre b2 is an easy fix, although if you set your gain levels high, they are really shunted out of the circuit. but here are a couple of mods: If you like the tone then you can reduce it's effect by putting a 47K resistor in series with the b2 cap. Each channel doesn't have it's own, so this will change it for both the red and the blue. if you want a different shelving frequency altogether, you can replace it with a different value .001uf or .0022uf.

I ended up using an Ariel OT from an older Laney, Damn fine Iron

Wouldn't be a problem for You if You'd write me a few words (here or by PM) what have You done to the circuit in case of adding gain to stages and making the amp more open?

Mine is always a work in progress. Still not quite where I want it, but I can give you some advice to get you closer to a more open tone if you want. There will be comprimises though. Here is an easy mod that will open the amp up a bit. There is a 15K 5W resistor in the dropping string right before the PI. If you replace it with a 10K, you will notice the OD channel will become much more open, the only drawback is that the blue channel will feel less compressive, because of the increased headroom. you can play around with this to get a good compromise. there are many ways to skin a cat.

[Setneck]

These are my thoughts on the mods, I tried both.

2004 = .22uf/2.7K to ground partial bypass on 3rd stage rk. gives a ton of gain but I thought is sounded too ice picky

Cameron = 1uf/10K to ground partial bypass. Fatter sounding, and more subtle, but a little loose

Well, I find Cameron very nice, but You're right that it's kinda loose. As I use L Excursion it becomes too loose actually . But if I'd be able to use B1 + Cameron that would rule, but unfortunately the amp squeels like hell with that settings .
As I find factory 2004 mod completely useless I think about modding that position of my selectable mod which allows me to choose "Factory mod" to the specs which would give me more open sound, less compression and some liquid drive. Unfortunately I am completely not familiar with all those values, caps, resistors etc. . Any tips here?

pre b2 is an easy fix, although if you set your gain levels high, they are really shunted out of the circuit. but here are a couple of mods: If you like the tone then you can reduce it's effect by putting a 47K resistor in series with the b2 cap. Each channel doesn't have it's own, so this will change it for both the red and the blue. if you want a different shelving frequency altogether, you can replace it with a different value .001uf or .0022uf.

I actually would like B2 to be something inbetween the B1 and B2, let's say about 3/5 of B1's drive and character. Now B2 has to little usable gain, even with Cameron Mod, and also it has not enough sustain.

Well, as I've said - I'm quite happy in general with the overall XTC's character. Those mods I'm after are actually done in case of making the tone a little bit personal and usable in certain situation. I am certainly not into reworking entire circuit, as it is designed very well.

Could You write a few words about that adding a gain You've written before?


Best regards, Andy

[joey]

of my selectable mod which allows me to choose "Factory mod" to the specs which would give me more open sound, less compression and some liquid drive. Unfortunately I am completely not familiar with all those values, caps, resistors etc. . Any tips here?

Thats a little difficult, and depends on how much work you want done on the amp. My suggestion would be that you can wire in another switch to switch a 33K 5w resistor in parallel with the 15K dropping resistor I mentioned earlier, but that does involve more work. If you wanted a boost, something in between the cameron and the 2004, you could try an array of different combinations. .68uf/6.8K will work

as for b2, try a .0015uf

Well, as I've said - I'm quite happy in general with the overall XTC's character. Those mods I'm after are actually done in case of making the tone a little bit personal and usable in certain situation. I am certainly not into reworking entire circuit, as it is designed very well.

Could You write a few words about that adding a gain You've written before?


Best regards, Andy

The problem is that what I did Involved reworking most of the circuit to get everything to interact well. Try that 10K-12K dropping resistor I mentioned earlier. It is easily reversable.