Hybrid A and ODS101 nonHRM differences

[skyboltone]

Greetings Lads:
There are some differences, slight, between the scheme I was working on when building was halted back in November and what I see in 101.

1) The 4m7 switch click snuffer on the Mid Boost switch is back. Persistent feller. Are we using this now?

2) I see we are still playing with the values of series resistors at the OD 1a trim pot and the OD 2 level pot. These are easy in circuit tweeks but there is a box in the middle there with an .047-0047 cap and a 10M resistor to ground. Place before OD in network. What does that mean?

3)The parallel resistor at the presence pot has changed to 1K with the original 390 as optional. Comments?

2) The 101 scheme shows no switchable local feedback at Cl 2. Have we decided to leave it at 44M divided as shown on 101 or are some of you still satisfied with taking half of that out?

Probably more I'm forgetting.

DanH

[Bob-I]

Greetings Lads:
There are some differences, slight, between the scheme I was working on when building was halted back in November and what I see in 101.

1) The 4m7 switch click snuffer on the Mid Boost switch is back. Persistent feller. Are we using this now?

As far as I know, it never went away. I't needed unless you like that click.

2) I see we are still playing with the values of series resistors at the OD 1a trim pot and the OD 2 level pot. These are easy in circuit tweeks but there is a box in the middle there with an .047-0047 cap and a 10M resistor to ground. Place before OD in network. What does that mean?

I'm not sure what you mean by this one. The OD entrance should be pretty standard. I've never seen a 10M to ground in the OD.

3)The parallel resistor at the presence pot has changed to 1K with the original 390 as optional. Comments?

390 for sure.

2) The 101 scheme shows no switchable local feedback at Cl 2. Have we decided to leave it at 44M divided as shown on 101 or are some of you still satisfied with taking half of that out?

Your choice, I use a 22M -> .047 -> 22M switchable. You can have 22M, 44M or none on the LNFB that way.

Probably more I'm forgetting.

DanH

Perhaps a link to the schem you're refering to would help.

[skyboltone]

Perhaps a link to the schem you're refering to would help.

Sorry Bob:
This one. https://tubeamparchive.com/download/file.php?id=1178

I'm gonna start soldering next week so I can get rid of the darn dunce cap and go back to a nicer avatar.

[Normster]

1) The 4m7 switch click snuffer on the Mid Boost switch is back. Persistent feller. Are we using this now?

As Bob said, it's needed if you're using mid shift. It was removed in some other schematics that didn't use mid shift.

2) I see we are still playing with the values of series resistors at the OD 1a trim pot and the OD 2 level pot. These are easy in circuit tweeks but there is a box in the middle there with an .047-0047 cap and a 10M resistor to ground. Place before OD in network. What does that mean?

AFAIK, the OD input for the hybrid-a just uses the standard 220k into a 100k trimmer. I would start there as a baseline and just try the other versions to see if you like them.

3)The parallel resistor at the presence pot has changed to 1K with the original 390 as optional. Comments?

For 100watt amp, use a 4k7 feedback resistor with a 390R on the pot. For 50watt, use an 8k feedback resistor with a 1k on the pot.

4) The 101 scheme shows no switchable local feedback at Cl 2. Have we decided to leave it at 44M divided as shown on 101 or are some of you still satisfied with taking half of that out?

Switchable local NFB is cool, but I find it a waste of time. The 22M setting sucks the life out of the tone. The 44M setting is a lot more subtle and useable. I don't put in the switch anymore, just plate -> .05uF -> 44M (22M + 22M) -> grid.

[dogears]

Norm,

Fwiw, the 220K into 100K trimmer is indeed the baseline. However, in amps that use the higher, non 100K plate loads, the .05uf cap doesn't always work (unless it is HRM). In fact, the 220k/150k amp I saw had a .01uf there. So, what you guys are doing may not be the "norm" (lol) at all!

Also, just because an earlier 50 watter had 8k/1k on the feedback, doesn't make it "right". The later HRM 50 watter I have pics of shows even less nfb than the 4.7k/390 setup. Best to try all the options here. I tried the 8k/1k and did not prefer it at all.

1) The 4m7 switch click snuffer on the Mid Boost switch is back. Persistent feller. Are we using this now?

As Bob said, it's needed if you're using mid shift. It was removed in some other schematics that didn't use mid shift.

2) I see we are still playing with the values of series resistors at the OD 1a trim pot and the OD 2 level pot. These are easy in circuit tweeks but there is a box in the middle there with an .047-0047 cap and a 10M resistor to ground. Place before OD in network. What does that mean?

AFAIK, the OD input for the hybrid-a just uses the standard 220k into a 100k trimmer. I would start there as a baseline and just try the other versions to see if you like them.

3)The parallel resistor at the presence pot has changed to 1K with the original 390 as optional. Comments?

For 100watt amp, use a 4k7 feedback resistor with a 390R on the pot. For 50watt, use an 8k feedback resistor with a 1k on the pot.

4) The 101 scheme shows no switchable local feedback at Cl 2. Have we decided to leave it at 44M divided as shown on 101 or are some of you still satisfied with taking half of that out?

Switchable local NFB is cool, but I find it a waste of time. The 22M setting sucks the life out of the tone. The 44M setting is a lot more subtle and useable. I don't put in the switch anymore, just plate -> .05uF -> 44M (22M + 22M) -> grid.

[Pete]

Also, just because an earlier 50 watter had 8k/1k on the feedback, doesn't make it "right". The later HRM 50 watter I have pics of shows even less nfb than the 4.7k/390 setup. Best to try all the options here. I tried the 8k/1k and did not prefer it at all.

I may be confused (not a first for me). 8k is less nfb than 4.7k right?
Just trying to be clear on your point. thanks

[Bob-I]

Perhaps a link to the schem you're refering to would help.

Sorry Bob:
This one. https://tubeamparchive.com/download/file.php?id=1178

I'm gonna start soldering next week so I can get rid of the darn dunce cap and go back to a nicer avatar.

Oh yea, that's a great schematic to start with. I find the .01 coupler after OD1 a little large, I prefer .0022 but these little adjustments can always be done later. FWIW I built an amp for HiGain (Jake) who drew up this schem and it sounds amazing. I had a few small mistakes 120k instead of 220k (found a mouser bag with the wrong resistors in it) so I once again learned that you need to measure every component before soldering but once he made the corrections it sounds amazing. Just a little hum issue that we'll sort out (I think the effects loop has a ground loop in it).

Stick to this one 100%, follow all the lead dress guidelines and you'll have a great start. Then let the amp speak to you and make adjustments as needed.

[Bob-I]

Also, just because an earlier 50 watter had 8k/1k on the feedback, doesn't make it "right". The later HRM 50 watter I have pics of shows even less nfb than the 4.7k/390 setup. Best to try all the options here. I tried the 8k/1k and did not prefer it at all.

I may be confused (not a first for me). 8k is less nfb than 4.7k right?
Just trying to be clear on your point. thanks

Yes, but it's the ratio between the NFB resistor and the tail resistor that matters. So 4.7k / 390 would be the same amount of NFB as 47k/3.9k. It will affect the tone so stick with the known good values.

[dogears]

I was referring to a .01 on CL2. Of course HRM amps have a .0022 on OD1. Just making sure everyone is not confused.

Perhaps a link to the schem you're refering to would help.

Sorry Bob:
This one. https://tubeamparchive.com/download/file.php?id=1178

I'm gonna start soldering next week so I can get rid of the darn dunce cap and go back to a nicer avatar.

Oh yea, that's a great schematic to start with. I find the .01 coupler after OD1 a little large, I prefer .0022 but these little adjustments can always be done later. FWIW I built an amp for HiGain (Jake) who drew up this schem and it sounds amazing. I had a few small mistakes 120k instead of 220k (found a mouser bag with the wrong resistors in it) so I once again learned that you need to measure every component before soldering but once he made the corrections it sounds amazing. Just a little hum issue that we'll sort out (I think the effects loop has a ground loop in it).

Stick to this one 100%, follow all the lead dress guidelines and you'll have a great start. Then let the amp speak to you and make adjustments as needed.

[Normster]

I understand the ratio thing, but I thought the ratio included the presence pot since that's really the tail to ground. IOW, 390R over 2k is 326R.

If I'm doing the calcs correctly, 4k7/390R gives a gain reduction of -7.2 dB off the 4 Ohm tap on a 100 watt amp. However, with the same values on a 50 watt amp, the gain reduction is only -5.7 dB. (That may be a good thing.) Using the 8K/1K setup, the gain reduction is -6.4 dB. I suppose you could also run the 4k7/390R from the 8 Ohm tap on a 50 watt amp which would give you a -7.2 dB gain reduction as on the 100 watt amp. However, I tend to like less NFB rather than more. I think it makes the amp more responsive and I like the added harmonics.

[Normster]

Yes, but it's the ratio between the NFB resistor and the tail resistor that matters. So 4.7k / 390 would be the same amount of NFB as 47k/3.9k. It will affect the tone so stick with the known good values.

Good point, Bob. Same amount of feedback, but different bias for the PI since it's also part of the LTP. Best not to mess with the values too much unless you're prepared to also mess with the bias and tail resistors.

[HiGain]

If you guys think the schematic should be updated in any way, please let me know. I just put together what's been worked out here by the forum members.

Bob built a fantastic nonHRM amp for me using the ODS101 schem. I've been doing very minor tweaks, heavily informed by Scott.

One thing I've found is that the mid switch and PAB for the nonHRM are not that great. Again, no new news.

One cool mod for the mid switch is 330p treble cap/.01 midcap vs 270p/.02 mid cap. These are values floated around this place for a while, especially by Scott. Use a 330p on the board and a .002 cap on the switch, while switching in a parallel .01 for the mid cap.

I'm not sure what to do with the PAB yet. Maybe reduce the 22M resistors on the swtich.... or perhaps bypass the tonestack a little with a resistor and cap... All ideas welcome!

Norm: great news about the LFB switch. I have 44M in there now and was wondering wheter to install a switch. I guess I won't!

Jake

[Pete]

What results/sound/effects are you experincing with the PAB? Using all combinations of settings gives many good sound variations with my amp (non HRM). PAB with OD as well as without OD is very usable. Also, after much experimenting I prefer the Mid boost (.002mf+390pf) over a deep switch, although I usually don't use it. YMMV

If you guys think the schematic should be updated in any way, please let me know. I just put together what's been worked out here by the forum members.

Bob built a fantastic nonHRM amp for me using the ODS101 schem. I've been doing very minor tweaks, heavily informed by Scott.

One thing I've found is that the mid switch and PAB for the nonHRM are not that great. Again, no new news.

One cool mod for the mid switch is 330p treble cap/.01 midcap vs 270p/.02 mid cap. These are values floated around this place for a while, especially by Scott. Use a 330p on the board and a .002 cap on the switch, while switching in a parallel .01 for the mid cap.

I'm not sure what to do with the PAB yet. Maybe reduce the 22M resistors on the swtich.... or perhaps bypass the tonestack a little with a resistor and cap... All ideas welcome!

Norm: great news about the LFB switch. I have 44M in there now and was wondering wheter to install a switch. I guess I won't!

Jake

[HiGain]

What results/sound/effects are you experincing with the PAB? Using all combinations of settings gives many good sound variations with my amp (non HRM). PAB with OD as well as without OD is very usable. Also, after much experimenting I prefer the Mid boost (.002mf+390pf) over a deep switch, although I usually don't use it. YMMV

hmmm.. To answer this fairly I'll have to go back and listen more.

But, with 4 6L6 tubes and the schematic based on the ODS101nonHRM, it just puts the mid-emphasis in the wrong place. Very middy, and too far away from the highs and lows. But, I need to double check, as I am going from memory. Interesting-- I also do not like the .002 for the treble cap!! This amp likes 270P and about 320p (as Scott has said).

Based on your comments, I'll go back and listen again. I also don't like the deep switch much.

Jake