Sunn Sceptre

[phillip.lynn]

I own a Sceptre - with mid boost - and am curious about what I perceive to be an overly dark tone. I plugged it into a cheap 120w Crate 4 x 12 that a buddy had and dimed it. With an LP in the bright channel, it had this overdrive that I can only think of as 'wooly mud'. Now, I thought the drive itself was fine, but so muddy? Doesn't seem right. I'm wondering if those speakers just had the daylights beaten out of them or if I really need to have the amp serviced, as I've heard these are fairly bright amps.

[soundmasterg]

The Sunn guitar amps are bright, and have tons of low end, at the same time. Any tube amp when cranked will be more bassy than when quiet. The Sunns were pretty much hi fi amps tweaked for bass and then tweaked for guitar. As such they have a wide frequency response and much more bass and highs than many other amps.

That said, it doesn't hurt to service the amp if it has never been done. Replace all the electrolytic caps in the amp including the can cap, and then see if it is still muddy.

Greg

[phillip.lynn]

Greg, thanks for the response and input.

I bought this amp from someone on eBay who assured me it had been serviced last year, but what does that really mean, right? I planned to take it to a buddy's father who runs an electronics shop to have it gone over. I'm definitely not displeased with the amp. I don't know a thing one about tube amps or servicing them. I did buy Aspen Pittman's book and am digesting that, however. I'm gonna replace the 6550's currently in it with KT88's.

I also think that a better cabinet is in order. Never been a fan of anything Crate has offered.

Have you - or anyone else - had any experience with the NFB disconnect mod? I was toying with the idea, but loathe to actually change anything about the amp. Don't want to make a Sunn into a quasi-Sunn.

[soundmasterg]

Greg, thanks for the response and input.

I bought this amp from someone on eBay who assured me it had been serviced last year, but what does that really mean, right? I planned to take it to a buddy's father who runs an electronics shop to have it gone over. I'm definitely not displeased with the amp. I don't know a thing one about tube amps or servicing them. I did buy Aspen Pittman's book and am digesting that, however. I'm gonna replace the 6550's currently in it with KT88's.

I also think that a better cabinet is in order. Never been a fan of anything Crate has offered.

Have you - or anyone else - had any experience with the NFB disconnect mod? I was toying with the idea, but loathe to actually change anything about the amp. Don't want to make a Sunn into a quasi-Sunn.

Changing from 6550's to KT88's will make a slight difference in the sound, but either tube works fine in them. I like the JJ KT88's myself for bass applications.

If the seller said the amp was service, then it may in fact be the case. You could have a tech check it out though to make sure the correct parts were put in. I agree with you about Crate stuff...lose it as quickly as possible!..haha.

I have done the NFB disconnect mod on several Sunn amps. It will make the sound more raw and aggressive with the NFB disconnected. The amp will also be more touch responsive, will hum more, and be louder without the NFB connected. I like it better myself without it as the UL setup on Sunn amps already has it's own NFB and you don't need any more. It is easy to add a switch on the back of the amp for this feature and easy to wire up. I think most guitar players who might play these amps would appreciate it. Personally, I don't like Sunn amps for guitar, but I love them for bass.

Greg

P.S. You will get more activity and find much more info if you post in the Sunn Discussion Forum subsection.

[phillip.lynn]

Again, thanks for the information.

I was looking at the schematic for this amp and may have come up with a solution. I saw that there is a 1 meg pot for the bass control. What if I were to change that to a 500k pot? I think that might tame some of the muddiness. If I did that, would I need to change the values of anything connected to it or would that be a 'drop it right in' procedure?

[soundmasterg]

That wouldn't make a huge difference....the whole amp is voiced to give huge bass response, from the use of 6550 or KT88's to the huge transformers to the high voltages. Changing the value of that pot and/or some of the parts around it are like trying to polish a rusty fender on a car. Their bass amps were take offs from Dynaco hifi amps and their guitar amps were take offs from their bass amps. Hifi amps are designed to give a super wide frequency response with lots of lows and lots of highs, so the Sunns do this well even though their bandwidth isn't as wide as the hifi stuff. For me personally, the Sunn guitar amps are too loud, with huge bass, brittle highs and thin mids. The high voltages limit what can be done to these amps as far as voicing them to sound different. No matter what you do, it will always have huge bass and will feel hard...it is just the nature of the amp and it's design.

What kind of guitar do you use with it? Do you use pedals also? Fenders will generally do better than Gibson style guitars through these amps unless you are playing power metal stuff. P90's sound great through them....listen to old Mountain recordings for examples. For my taste though, I don't like Sunn amps for guitar personally, and there isn't much you can do to change their basic character.

Greg

[phillip.lynn]

That wouldn't make a huge difference....the whole amp is voiced to give huge bass response, from the use of 6550 or KT88's to the huge transformers to the high voltages. Changing the value of that pot and/or some of the parts around it are like trying to polish a rusty fender on a car. Their bass amps were take offs from Dynaco hifi amps and their guitar amps were take offs from their bass amps. Hifi amps are designed to give a super wide frequency response with lots of lows and lots of highs, so the Sunns do this well even though their bandwidth isn't as wide as the hifi stuff. For me personally, the Sunn guitar amps are too loud, with huge bass, brittle highs and thin mids. The high voltages limit what can be done to these amps as far as voicing them to sound different. No matter what you do, it will always have huge bass and will feel hard...it is just the nature of the amp and it's design.

What kind of guitar do you use with it? Do you use pedals also? Fenders will generally do better than Gibson style guitars through these amps unless you are playing power metal stuff. P90's sound great through them....listen to old Mountain recordings for examples. For my taste though, I don't like Sunn amps for guitar personally, and there isn't much you can do to change their basic character.

Greg

Sorry to resurrect this thread after so long! I cleared up most of the muddiness by replacing EH 7025 with Telefunken 12AX7. I saw there is a 5u4gb rectifier instead of the GZ34 specified. I am about to buy a good GZ and am wondering if I can just plug that straight in or if I will have to take it to a tech to be serviced, since changing that tube will also change the voltage (I think I'm right on that). I had posted this question on the Sunn discussion page, but they went down sometime recently. Also, what type of bias is this amp? Fixed or what? I'm wondering if I'll actually have to take it in when I change the power tubes out.

[isaac42]

Sorry to resurrect this thread after so long! I cleared up most of the muddiness by replacing EH 7025 with Telefunken 12AX7. I saw there is a 5u4gb rectifier instead of the GZ34 specified. I am about to buy a good GZ and am wondering if I can just plug that straight in or if I will have to take it to a tech to be serviced, since changing that tube will also change the voltage (I think I'm right on that). I had posted this question on the Sunn discussion page, but they went down sometime recently. Also, what type of bias is this amp? Fixed or what? I'm wondering if I'll actually have to take it in when I change the power tubes out.

Phillip, I wouldn't expect the GZ34 to make enough of a difference to require servicing. That's the rectifier the amp was originally designed for, and it's unlikely that anything was changed to accommodate the 5U4GB. Changing the power tubes is a different matter.

The Sunn discussion page is back up, at a different address: http://sunnforum.ampage.org/index.php/board,1.0.html

[soundmasterg]

Different rectifier tubes will change the bias, especially when going from a 5U4 to a GZ34. It doesn't hurt to check and could save a misbiased amp from causing problems or bad sounds.

The Sunn amps are adjustable fixed bias amps, and the bias should be checked when changing power tubes or rectifier tubes.

My 2 cents.....

Greg