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Distortion? Poor Bass Response?

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hello all,
I had posted yesterday, that I was having distortion problems with my newly built SSE. Today I'm not so sure that it is distortion, or just really bad bass response? Highs and mids sound really pretty good, forward in the mids, but the bass is terrible, kick drums and bass lines are flabby, and broken up sounding, kind of like a blown speaker.

I put my old amp back in place, and everything is fine again. I have to assume that I have missed something or have something wrong in my SSE. Any ideas or suggestions of where I should start looking? It is wired in triode mode without feedback, speakers are 90 -91 db sensitivity.

Thanks
 
In both of your threads, you really haven't given out much information for anyone to work from.

90-91 dB, if accurate, is not that sensitive, but should be fine at reasonable volume levels.

Triode mode puts out the least power, and you haven't mentioned what tubes you are using. It makes a difference.

"Turning it up", while descriptive, is not very precise.

No pictures to try to see if something is wired wrong.

My rule of thumb is to get enough power to make 102 dB. You get 3 dB by having a second speaker, so with your speakers, 1 watt gets you 93 dB. 2 watts gets you to 96 dB. 4 watts gets you to 99 dB. 8 watts gets you to 102 dB. You can see the advantage of high sensitivity speakers ....

You might want to consider using KT88's or 6550's in Ultra Linear for your speakers.

This assumes you have adequate drive level going into the SSE. Devices ahead of the SSE may be clipping.

Other folks may have other opinions, this is my $0.02.

Win W5JAG
 
Thank you for your reply, I am using EL34 output tubes. I apologize for the lack of needed info. I am new to this, have only build a few Bottlehead kits and a couple Dynaco clones, i don't know much except to follow directions.

The preamps I have tried with it are a Bottlehead (12AU7) based, Hafler 110 and a Nikko Beta II, all of them work fine with my ST-70 and Rotel amp?

I am sure that its something I did wrong in the SSE, it just seems to have no bottom end at all, at any listening level to be honest. I was hoping there may be a common mistake that causes this.

Thanks again
 
I did get a chance to check B+ voltage today, it is 452 vdc. That seems about right, correct? I used the 6K7VG power transformer. I was thinking that I should try UL with feedback?

I know its a different animal, but with my Dynaco ST-70 Clone, there is not a huge drop in perceived power from UL to triode mode.

Thanks for your help, very much appreciated
 
I would at least try cathode feedback and ul before you give up on the combination of the sse and your speakers. I have the same power transformer and output transformers (except mine have 8 ohm secondaries). I have the same cathode resistors. My b+ has always been a bit high, typically in the 470s with el34 and 460s with kt88s (they draw more current). I'd say try cathode feedback, ul and some kt88s. It does make a difference with this amp. I have several pairs of speakers and I prefer different combinations of operating modes and tubes with each of them. I have one pair that sounds dull and a bit muddy with triode mode and el34s. Those same speakers sound much better with kt88s in ul with cathode
feedback. All of my speakers are rated between 86-89 sensitivity. They all get loud enough. I am not an expert by any means. The sse is my first tube amp. I just would hate to see you give up on it when the answer could be right in front of you. Hope this helps.
 
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Thank you for the encouragement. I am now convinced that I have simply done something wrong, installed something incorrectly, something. No way this amp can sound this bad. I did wire amp to UL with feedback, it did increase the power output, but still have the terrible low end breakup.

Also, I am positive now that its not my speakers or preamp, etc...... a friend of mine brought over his SE low watt amp (5 watt) and it sounded wonderful through my current setup.

So, I'm thinking I have overlooked something, installed an incorrect part, etc.... trouble might be finding it. The only thing that I have really checked is the B+, it measures 452 vdc

Thanks
 
Are you sure you used right HT secondaries of your power transformer?

With something like 200-0-200 (234V unloaded) your B+ is way to low and tubes are now working as they should due to different bias point.

You should use PT with 370-0-370 HT secondaries to have proper B+.
 
His meter was showing around 440 volts, I am only getting 234 volts?.....I did get a chance to check B+ voltage today, it is 452 vdc

Your readings are normal. Ty's checkout was done on an older vintage board that did not have D3 and D4. The rectifier tube is connected directly to the transformer, so he gets the same voltage readings. Your board has two additional diodes to help prevent damage to some of today's less than stellar quality rectifier tubes. This will confuse the voltmeter since it's reading half wave AC. Your 452 volt B+ indicates that the rectifier and power transformer are working fine.

Verify that the 5 volt windings go to the rectifier tube (side of board), and the 6.3 volt windings go to the output tubes (back of board). Swapping these will cause distortion.

It's difficult to determine the source of your distortion without some more information. You chose 4 ohm OPT's, are your speakers 4 ohm? Are they wired correctly red to B+, Blue to tube plate? Measure the voltage at the output tube's cathode (connect the meter across the large white resistor next to each tube) That is the best indicator of proper operation in the output tubes.

Post some pictures of your board and the wiring to it so we can look for any obvious errors. DC voltage readings on the 12AT7 pins would help too.

It is possible that your amp is working properly. Try CFB, UL mode, and both. Some speakers need the lower output impedance afforded by CFB or the extra headroom of UL.


I did not install D1 or D2 at all, was this a mistake? I also have installed a choke, Edcor CXC100-5H-200mA, could this cause a problem? I did not install R1

No these are correct. I assume that you are using an Edcor power transformer. What transformer are you using.

You have three different threads asking the same questions with bits of information in each one. Please keep them all in this one so I don't have to read 3 different ones to piece together all the clues as to what might be wrong.
 
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I am using the Allied 6K7VG power transformer. I am sure that the 5 volt tap and the 6.3 tap are connected correctly. I have taken the board back out to double / triple check my work, all resistors, capacitors and semiconductors are, I believe installed correctly. I've looked at all solder joints for proper "wetting", cold joints etc.... all looks good to me.

I will get it put back together, take the readings you suggested, take a couple pictures and post my findings.
I do not feel as positive about the OPT hook up, I will pay extra attention to that this time.
I bought 4 0hm OPT's because I am in the process of putting together a 4 ohm MTM speaker, currently running 8 ohm speakers.

George, sorry about the scattered threads, I appreciate everyone's help very much.
 
Ok, I have some more measurements, next I hope to get a few pictures. I will first say that I installed R17 & R27 (560 ohms) thinking of using EL34's, but the amp actually sounds much better with KT88's in place, although the power transformer seems to get a little warm.

12AT7
Pin 1: 222 v
Pin 3: 2.07 v
Pin 4: 6.4 v
Pin 5: 6.4 v
Pin 6: 216 v
Pin 8: 1.98 v
Pins 2,7 and 9 was not sure how or what to check? ( i'm very much a novice)

Measurement across R17: 47.0 v
R27: 44.9 v, I could easily have calculated this wrong, but with a 560 ohm cathode resistor, the above readings are 84 mA and 80 mA of current, correct?

B+ is 446

I have used the Allied 6K7VG transformer, I looked at the tubes and application chart, it appears the 560 ohm cathode resistor could be used on both EL34 and KT88 tubes with B+ at 446 volts, but something tells me this is not optimal for KT88?

I mentioned above that with EL34's my amp does not sound good, worse with the Svetlana some better with JJ's, but the sound really improves when I install the EH KT88's.

I have a few 12AT7 tubes, a couple older RCA and a new JJ, the JJ has a little hum, does't sound great, the RCA seem fine. I'm not sure what the measurements of the 12AT7 should be?

I am currently wired in UL with feedback. Balance of the amp seems to be just a little heavy on the left output.

I appreciate any help or advice very much,
Thanks
 
Thanks, I do have an old set of Boston Acoustic towers that are 4 ohm, they aren't great speakers, but they have the same bass distortion. Like I said, much much better with KT88's, so I think that I'm close, hopefully just overlooking something.

It may just have been a mistake to buy 4 ohm OPT's? I have some Scan Speak drivers and tweeters, my plan was to build MTM speakers with them, 4 ohm
 
91db, the are a TMM tower


I would say moderate volume, not trying to make my ears bleed or anything


Music, a lot of different taste, Pink Floyd to The Clash, The Band, Bowie, Al Dimeola, Mozart.............I listen to a pretty wide variety, not to much hard rock or country


I will get some pictures posted in the next day or two, maybe someone will see an obvious mistake that I have made?


Thanks to everyone for your help
 
Beginner here but I think the KT88 works better than an EL34 into lowish OT primary resistances which suggests maybe you have the screen (UL) rather than plate hooked up for Triode mode?

Using an 8 ohm speaker on a 4 ohm tap would give you lower distortion and less power (higher OT resistance; hope I got that right).
 
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