In the past few weeks, I've played around with the Quickie, and installed the MQ upgrade in the S.E.X. I've come to an interesting conclusion: I seem to actually prefer choke loads over CCS, at least in the Quickie. The chokes seem to be warmer and tame my system a bit, esp. coming from digital sources. I've also noticed that the S.E.X. has lost a lot of its "warmth" and has some unwanted upper-midrange bite to it now that I've installed both the C4S boards and the new irons/caps in there, so I'm wondering if it's for the same reason. Has anybody ever choke-loaded the drivers on the S.E.X. amp, and if so, what did you use? The Quickie was easy, as the plate resistor was only 4k, which makes it easy to find a choke with a similar DCR value and not have to change anything else. I think the original plate resistors on the S.E.X., though, were 150k! What would I have to do (i.e., by changing the cathode or power supply resistors) to get a reasonable value of choke in there, and could the leftover 30H BH chokes from the big triodes work? I don't remember how many mA of current those were rated for, though, and don't remember the exact value for the driver halves of the 6DN7's.
Choke Loading the S.E.X. vs. CCS?
- Thread starter Dr. Toobz
- Start date
Grainger49
New member
You can split the plate resistor in the SEX. You could leave the 150k and put in a 4k ohm choke connected to the plate. Or shave the plate resistor a little, say a 130k and a 20k then add the 4k choke at the plate.
Could I use something like the Hammond 156C's, as in the Quickie? They are rated for 8mA current, and have a 150H inductance. I think the BH chokes I have laying around are rated for more current, but have a much lower inductance (only 30H), so I'm assuming they would defeat the purpose?
Also, what's kind of weird here is the fact that I don't mind the C4S at all when speakers are used - just headphones. On the Heresy III's, the S.E.X. is awesome. But, since I live in a condo, I do most of my listening via 'phones. I've tried Beyer DT-880's, and Grado SR-60/SR-325is on the jacks, both with resistors and without, and I hear too much "bite" and harshness (which is not found with any solid-state device I own or my Quickie - all three are actually very smooth sounding otherwise). There's also way too much gain. I'm not sure why the amp would sound brighter with the new irons and C4S boards! Bass is better, but it seems like I lost one thing to gain another....
Thanks for your advice.
Also, what's kind of weird here is the fact that I don't mind the C4S at all when speakers are used - just headphones. On the Heresy III's, the S.E.X. is awesome. But, since I live in a condo, I do most of my listening via 'phones. I've tried Beyer DT-880's, and Grado SR-60/SR-325is on the jacks, both with resistors and without, and I hear too much "bite" and harshness (which is not found with any solid-state device I own or my Quickie - all three are actually very smooth sounding otherwise). There's also way too much gain. I'm not sure why the amp would sound brighter with the new irons and C4S boards! Bass is better, but it seems like I lost one thing to gain another....
Thanks for your advice.
Paul Joppa
Moderator
Do give components - most especially iron and capacitors - plenty of time to break in before making judgements about the sound. I find most capacitors, most output transformers, and often plate chokes as well, to suffer from an unpleasant harshness of sound when first installed. It usually takes 20 to 200 hours of music going through the device before they settle down - except for teflon caps, which seem to take at least 5 times as long. I would wait for this period to be over before looking to solve this problem.
There are fairly recent threads on the problems of driving high-sensitivity, low-impedance headphones. This is probably the cause of the too-high sensitivity problem.
There are fairly recent threads on the problems of driving high-sensitivity, low-impedance headphones. This is probably the cause of the too-high sensitivity problem.
I'll definitely wait a little bit before doing anything, as you're right in that things probably have no broken in yet. I have maybe 30 hours on the new parts.
I'm still perplexed about what to do with the headphone issue. I've followed some of the threads you've mentioned, too. Even my 250 ohm Beyers don't sound as good as they should. Is there any way of reducing gain while keeping a very low output impedance? I'm thinking that's a big part of the issue, leading to an uneven frequency response, and only exacerbated by having way too much gain. Adding more series resistance wouldn't help, I would guess, and there's not another "tap" on the irons to use!
I'm still perplexed about what to do with the headphone issue. I've followed some of the threads you've mentioned, too. Even my 250 ohm Beyers don't sound as good as they should. Is there any way of reducing gain while keeping a very low output impedance? I'm thinking that's a big part of the issue, leading to an uneven frequency response, and only exacerbated by having way too much gain. Adding more series resistance wouldn't help, I would guess, and there's not another "tap" on the irons to use!
audiblesoundwave
New member
Hi Dr. Toobz,
Not sure this would help on your gain issue! I started one thread on this issue a while back. There are two suggestions (from PJ and PB) toward the end of the following thread.
http://www.bottlehead.com/smf/index.php/topic,323.0.html
I was considering to implement PB's suggestion on installing one DPDT switch. However, after I installed the Dale 23 step attenuator, I found that the new attenuator has so much better control. I did not have to install the DPDT switch for reducing the gain for the headphone connection anymore.
http://www.bottlehead.com/smf/index.php/topic,406.0.html
Good luck,
Milton
Not sure this would help on your gain issue! I started one thread on this issue a while back. There are two suggestions (from PJ and PB) toward the end of the following thread.
http://www.bottlehead.com/smf/index.php/topic,323.0.html
I was considering to implement PB's suggestion on installing one DPDT switch. However, after I installed the Dale 23 step attenuator, I found that the new attenuator has so much better control. I did not have to install the DPDT switch for reducing the gain for the headphone connection anymore.
http://www.bottlehead.com/smf/index.php/topic,406.0.html
Good luck,
Milton
Milton,
Adding resistors is the approach I thought I'd have to take, though it seems like adding more series resistance leads to worse sound with low impedance phones like the Grados (even my Beyers don't sound completely "right" unless the output impedance is very low). Wouldn't adding more resistance increase the output impedance seen by the headphones?
It's too bad there's not a good way to take the outputs right after the parafeed caps and do some sort of OTL type arrangement - the plate impedance is way too high on the 6DN7's (over 2k), and lord knows what the sound would be like, even though there would be more than enough power, despite the impedance mismatch. If the triodes were more amenable to that, I could see having a switch before the OPT's that either a) allowed output through the irons (for speakers) or b) cut them out of the circuit and activated an OTL headphone jack. Dream on, I suppose!
6EM7's have a lower plate impedance of 880 ohms, but I still would have no idea of how to get down to something lower (i.e., 32) without an OPT in the path.
Adding resistors is the approach I thought I'd have to take, though it seems like adding more series resistance leads to worse sound with low impedance phones like the Grados (even my Beyers don't sound completely "right" unless the output impedance is very low). Wouldn't adding more resistance increase the output impedance seen by the headphones?
It's too bad there's not a good way to take the outputs right after the parafeed caps and do some sort of OTL type arrangement - the plate impedance is way too high on the 6DN7's (over 2k), and lord knows what the sound would be like, even though there would be more than enough power, despite the impedance mismatch. If the triodes were more amenable to that, I could see having a switch before the OPT's that either a) allowed output through the irons (for speakers) or b) cut them out of the circuit and activated an OTL headphone jack. Dream on, I suppose!
6EM7's have a lower plate impedance of 880 ohms, but I still would have no idea of how to get down to something lower (i.e., 32) without an OPT in the path.
Dr. Toobz said:Milton,
Adding resistors is the approach I thought I'd have to take, though it seems like adding more series resistance leads to worse sound with low impedance phones like the Grados (even my Beyers don't sound completely "right" unless the output impedance is very low). Wouldn't adding more resistance increase the output impedance seen by the headphones?
It's too bad there's not a good way to take the outputs right after the parafeed caps and do some sort of OTL type arrangement - the plate impedance is way too high on the 6DN7's (over 2k), and lord knows what the sound would be like, even though there would be more than enough power, despite the impedance mismatch. If the triodes were more amenable to that, I could see having a switch before the OPT's that either a) allowed output through the irons (for speakers) or b) cut them out of the circuit and activated an OTL headphone jack. Dream on, I suppose!
Adding series resistance at the input has zero effect on the output impedance of the headphone amp. If your SEX amp is too sensitive, this series resistance at the input is a great way to get more range out of your volume control.
If you took the output off the plate of the 6DN7, you would have incredibly high output impedance, incredibly high voltage, lots of noise, etc. etc. Besides, OTL requires a series capacitor of usually 100+uf per channel. Try replacing your parafeed cap with a sloggy electrolytic like that and you will understand why we don't sell OTL amps (they are vastly less expensive to make, however).
You can also try the 4 ohm speaker taps.
-Paul
Caucasian Blackplate said:Dr. Toobz said:Milton,
Adding resistors is the approach I thought I'd have to take, though it seems like adding more series resistance leads to worse sound with low impedance phones like the Grados (even my Beyers don't sound completely "right" unless the output impedance is very low). Wouldn't adding more resistance increase the output impedance seen by the headphones?
It's too bad there's not a good way to take the outputs right after the parafeed caps and do some sort of OTL type arrangement - the plate impedance is way too high on the 6DN7's (over 2k), and lord knows what the sound would be like, even though there would be more than enough power, despite the impedance mismatch. If the triodes were more amenable to that, I could see having a switch before the OPT's that either a) allowed output through the irons (for speakers) or b) cut them out of the circuit and activated an OTL headphone jack. Dream on, I suppose!
Adding series resistance at the input has zero effect on the output impedance of the headphone amp. If your SEX amp is too sensitive, this series resistance at the input is a great way to get more range out of your volume control.
If you took the output off the plate of the 6DN7, you would have incredibly high output impedance, incredibly high voltage, lots of noise, etc. etc. Besides, OTL requires a series capacitor of usually 100+uf per channel. Try replacing your parafeed cap with a sloggy electrolytic like that and you will understand why we don't sell OTL amps (they are vastly less expensive to make, however).
You can also try the 4 ohm speaker taps.
-Paul
For some reason, I kept thinking about adding resistors to the headphone jack vs. the input. My bad! Padding the input actually makes sense, though - in fact, since I don't want to lose sensitivity/gain with my speakers, I could probably rig up a switch to decrease the input signal with some resistance when using headphones (and switch it off for speakers).
100uF cap in the path of the audio signal? Yuck. Too bad OTL is so hard to do well - transformers seem to impart their own signature on the signal, which isn't always a good thing. Of course, neither is paralleling 18 output tubes - I'd imagine smearing would be an issue?
I have no 4-ohm taps anymore, since the MQ irons are in there. I think listening to SS for most of my life primed me to expect a certain sound or tightness in the bass that is hard to attain with tubes, esp. SET. After all, SS amps have tons of current and an average output impedance of what, .1 ohm? Maybe my next project should be a triode (or triode-strapped pentode) PP/UL amp with a little bit of global NFB to dry up/tighten the sound for when I really want to "rock." Or perhaps a switch to activate NFB.
I know I'm probably going to ask something that's taboo here, but is there a way to add a tiny bit of NFB to the S.E.X. circuit, say 6dB? I'd assume you'd have to take the speaker output from the primary on the OPT to the input of the driver cathode, correct? But what value of resistor/cap combo between them is the question. Again, maybe I could rig up a switch to compare the two modes - NFB vs. no NFB - and maybe it would help with lowering the output impedance (and gain) a little bit.
Paul Joppa
Moderator
There was a big thread a while back, but we seem not to have turned it up yet. The idea is to install some kind of L-pad between the SEX speaker output and the headphones. Even an 8 ohm adjustable L-pad from a speaker crossover would work, since the SEX is perfectly capable of driving an 8 ohm load. This would attenuate the output, while providing a phone output whose impedance is significantly less than 8 ohms, i.e. pretty good damping for 32 ohm cans.
Try this: short out the 120 ohm resistance so the headphones are connected directly to the output transformer, turn the volume control all the way down, and listen. If you don't hear any noise then the SEX amp itself is quiet enough to directly drive your headphones, and you can attenuate the input to get a suitable volume control range. If you do hear noise that is obtrusive (obviously nothing is completely silent) then you need to attenuate the SEX output before it gets to the phones.
Per the IHF standard, the 120 ohms resistor provides that attenuation for low impedance phones. The problem is many modern phones are designed to work with iPods (low voltage, low impedance) without regard to whether they work well with the IHF standard - manufacturers are ignoring the standard so it's becoming obsolete. You can use an 8 ohm loudspeaker L-pad (the kind used to adjust tweeter level in a two-way system, for instance) or a wirewound pot, of say 10 to 50 ohms, to find out how much attenuation is needed to get the phones quiet. That will reduce the system gain, but also the system headroom, so you don't want to attenuate more than necessary here. Once you've found the required level of attenuation, you can keep the L-pad or substitute another with the same attenuation but made of fixed resistors, and possibly a different input impedance.
After that experiment, if the amp is still too sensitive then you'll want to install some more attenuation at the amp's input. That includes the case where the straight output is quiet enough, but the volume control setting is too low for a useful range. The series resistor of 33K to 470K that PB (Caucasian Blackplate) described is appropriate for this function.
We've been looking at the idea of very small, inexpensive, passive kits - just a Sweetest Whispers in a box, or a baffle step corrector, etc. I'll see if I can come up with something suitable for these headphone sensitivity-optimization experiments. Headphones cover wider ranges of sensitivity and impedance every day it seems, and it's getting quite frustrating!
Try this: short out the 120 ohm resistance so the headphones are connected directly to the output transformer, turn the volume control all the way down, and listen. If you don't hear any noise then the SEX amp itself is quiet enough to directly drive your headphones, and you can attenuate the input to get a suitable volume control range. If you do hear noise that is obtrusive (obviously nothing is completely silent) then you need to attenuate the SEX output before it gets to the phones.
Per the IHF standard, the 120 ohms resistor provides that attenuation for low impedance phones. The problem is many modern phones are designed to work with iPods (low voltage, low impedance) without regard to whether they work well with the IHF standard - manufacturers are ignoring the standard so it's becoming obsolete. You can use an 8 ohm loudspeaker L-pad (the kind used to adjust tweeter level in a two-way system, for instance) or a wirewound pot, of say 10 to 50 ohms, to find out how much attenuation is needed to get the phones quiet. That will reduce the system gain, but also the system headroom, so you don't want to attenuate more than necessary here. Once you've found the required level of attenuation, you can keep the L-pad or substitute another with the same attenuation but made of fixed resistors, and possibly a different input impedance.
After that experiment, if the amp is still too sensitive then you'll want to install some more attenuation at the amp's input. That includes the case where the straight output is quiet enough, but the volume control setting is too low for a useful range. The series resistor of 33K to 470K that PB (Caucasian Blackplate) described is appropriate for this function.
We've been looking at the idea of very small, inexpensive, passive kits - just a Sweetest Whispers in a box, or a baffle step corrector, etc. I'll see if I can come up with something suitable for these headphone sensitivity-optimization experiments. Headphones cover wider ranges of sensitivity and impedance every day it seems, and it's getting quite frustrating!
Long story made short - the Grados are going bye-bye. I have no problems with sound, impedance, loading, etc when listening to my Klipsch speakers - the S.E.X. Seduction and Quickie combo is perfect. I bought some SR-325is cans because I used to have the older ones and enjoyed them, but that was on a warm-sounding solid-state amp that probably benefited from the treble boost. My Beyers are perfect, except that they have wimpy bass. However, the bass weakness is far more forgivable than the shouty, loud sounds coming from the Grados. So, they're going back to the store. Problem solved, and no further mods needed! (Though I may try the 6EM7 mod anyway - a lower output impedance couldn't hurt with speakers).
Too bad I can't get the airy, detailed sound of the Beyers with a bit more bass. I thought about the HD650, but I've always heard Senns are veiled sounding.....
Too bad I can't get the airy, detailed sound of the Beyers with a bit more bass. I thought about the HD650, but I've always heard Senns are veiled sounding.....
Hmm, perhaps it is time to consider just a tiny bit of global feedback... If you have a spare trim pot and a really cheap test speaker, you could probably do this by ear...
I have neither. What value range would the trim pot have to cover? Also, for global feedback, would I be taking the signal from the output parafeed cap (i.e., right before the autoformer) back to the cathode of the driver triode, with the trim pot (or fixed resistor) in between?
