Peavey 6505 UGLY SOUNDING

[nevetslab]

Our guitar dept sent one of our Peavey 6505 amps back to my shop, this time stated that it has Weird Breakup. It was here back in June, then with it 'popping'. I never did find that problem, while finding it sounding really dark and ugly sounding. Granted, I'm just a bass player, have two different 15" bass cabinets here in the shop (4 ohm Ampeg BXT-115HLF that I like the sound of, and some Hartke 8-ohm 15" cabinet that I don't care for it's sound character). I don't have a guitar here in the shop. I'm used to driving amps with General Radio 1382 feeding a General Radio Tone Burst Gen to yield Burst Pink Noise or Burst USASI Noise (USASI noise has a lot of midrange boost, LF roll-off relative to Pink Noise. More typical of a Guitar as far as the noise bandwidth goes).

With either one of the noise sources, this Peavey just sounds very murky and dark, though I don't hear anything outright bad about it. I do find the tone controls on the 6505 has very little range on any of the controls.

I had one of our other Peavey 6505 amps sent over, that's representative of one that sounds good to the guitar tech. It sounds just as ugly sounding as the one being objected to. I recall Enzo stating the 6505 is Identical in circuitry to the 5150. We have EVH 5150's, which are three channel amps, where each channel has it's own Lo-Mid-Hi tone controls, so not exactly the same as a 6505. Both it and the 6505 in the Lead ch have 5 cascaded 12AX7 gain stages, so it's exceptionally noisy. The 5150 sounds far better in tonality then these 6505 heads, at least to my ears.

Anyone have any good ideas on how to make these 6505's sound better?

[The Dude]

Not really an answer to your question, but FYI, there are isolated guitar tracks all over YouTube. Just search "isolated guitar". If you don't have a guitar in the shop, this is a good way to get a rough idea of how the amp sounds. Just run your PC/tablet/phone/whatever to the amp input. I often do this when burning in an amp so that I can work on something else and not have to sit around playing guitar. And, if you don't have a guitar in the shop, this may be useful.

[nevetslab]

I've been meaning to do that. I'm now waiting for the delivery of an i-Phone 15 that my wealthy nephew is sending me, so that's one task I want to do with it, once I get used to how to manipulate it and find some suitable tracks for this purpose. I might also be able to download some tracks from my band's recordings from 10 or more years ago.

[Helmholtz]

Hi nevets (or should I say Steven?),

recorded guitar is not PU signal, as it's already processed by amp and speaker,so won't do here.
Do you really consider to reengineer the 6505?

I'm a guitar player but not familiar with either amp (don't like high gain sounds).
As I quit repair work long time ago, I don't have a large collection of schematics.
But if you post the schematics of both amps, I might spot some significant difference.

Roland

[xtian]

I'm now waiting for the delivery of an i-Phone 15 that my wealthy nephew is sending me

Hooray! I'm happy you're getting a new phone!

[g1]

Any chance of getting that guitar tech over to try them out side by side? Maybe they had something going on with the set up.

[nevetslab]

Hi nevets (or should I say Steven?),

recorded guitar is not PU signal, as it's already processed by amp and speaker,so won't do here.
Do you really consider to reengineer the 6505?

I'm a guitar player but not familiar with either amp (don't like high gain sounds).
As I quit repair work long time ago, I don't have a large collection of schematics.
But if you post the schematics of both amps, I might spot some significant difference.

Roland

I've attached the 6505 Schematic I have....it's not exactly the 6505 Amp head, as it only shows a pair of 6L6GC power tubes. This one has 4 6L6GC's like the 5150.

6505_Amp Head Owners.pdf

Peavey_6505_112.pdf

Fender EVH 5150-III head.pdf

Interesting point: Recorded Guitar is not Pickup Signal, it being processed/recorded. The EVH 5150....the Eddie Van Halen amp that I guess he had something to do with the crazy noisy signal chain in these amps definitely has a sound character all its' own. I haven't heard anyone use the 6505 Head like that of the EVH 5150-III head (we have those also in our rental inventory).

When these two Peavey 6505 heads get picked up, I'll wander over to the Guitar Dept down the street/around the corner to have a listen when they're set up with a 412 cabinet each and see what they're hearing/talking about.

I can usually find issues I'm chasing using burst pink or USASI noise. I normally have this generator feeding a General Radio 1396B Tone Burst Generator, output thru an HP 353A Xfmr-coupled Step Attenuator for a very useful signal source to listen to guitar and bass amps prior to plugging my bass into them. And use it for burn-in, setting room level around 100dB SPL (moderate stage level).

GenRad 1382 Noise Spectrum.pdf

Do I really consider re-enginering these 6505 amps? Not really, unless there's some mod's folks have done to get them to not sound so ugly. I did have a passing thought changing the output stage to use EL34's instead of 6L6GC's, but doubt that would really buy me anything.

[Helmholtz]

Ok, there's a major difference between the amps.
The 6505 uses a weakish cathodyne PI while the 5150 has a solid Marshall-style LTPI (which IMO makes them completely different amps).
A cathodyne can work fine with EL34s, EL84s and 6V6s, but it's not well suited for 6L6s requiring a significantly larger grid signal (~120Vpp).
Means that the PI will struggle to drive the power tubes to full output without being overdriven.
It is known that a cathodyne produces a nasty distortion sound when overdriven (or with power tube grid conduction).
In his book about guitar preamps Merlin addresses both effects and recommends countermeasures.

[Pedro Vecino]

The 6505 and the 5150 heads are identical. The schematic shown is for a 6505 combo (a different circuit). Itīs not valid as a reference.
The 6505 barely has a clean sound as it is a more crunch focused and the clean mode is a compromise. The center of the amplifier is the lead channel. With the gain at 4 and the EQ at half, some emphasis on controlling resonance and timely adjustment of presence is a distortion machine. And it has a higher noise level than other amplifiers.
All of this can be somewhat disconcerting if there is no prior familiarization with it.

Itīs not common to find problems in the preamplifier except potentiometers and buttons in poor condition in older units or a preamp tube that does not work well. Itīs possible to find some open screen grid resistor in power tubes, with which the power stage loses symmetry. Factory bias setting is pretty low too.

[Helmholtz]

The 6505 and the 5150 heads are identical.

Interesting, but if they're identical, how could they sound that different?
Do you think both 6505s have issues?

@nevetslab: Did you measure power output?

[Pedro Vecino]

I think there is some confusion with the nomenclatures. Peavey 5150 and 6505 heads are electrically identical. Peavey 5150 II and 6505+ heads are also identical to each other but different from the previous ones (two channels with independent equalization).
EVH 5150 is the Fender version but with three channels. More similar to the Peavey 5150 II and 6505+. They have lighter bass profiles prior to the distortion process and sound less coarse, with more articulation and better prepared for low tunings.

I had understood that both 6505 units sounded equally bad, but I understand that this may be a product of amplifiers being very oriented towards extreme sounds. I wouldn't be able to identify anything unusual about them without having a guitar in my hands.

I had one of our other Peavey 6505 amps sent over, that's representative of one that sounds good to the guitar tech. It sounds just as ugly sounding as the one being objected to.

[nevetslab]

Interesting, but if they're identical, how could they sound that different?
Do you think both 6505s have issues?

@nevetslab: Did you measure power output?

NO, I didn't make any power output measurements. I only took them up to where it sounded like it was clipping. Didn't even have analyzer/scope on it. Did this evaluation sonically, as I normally do before I move them to the test bench. Checked my service notes from 6/30/23, when it came in before, with complaint of it popping. I did run it somewhat hard (8 ohm load), 105dB SPL @ 20 ft in my shop, which is about where it topped off going into distortion, but I didn't even take any power consumption readings. I was looking for the gross problem that was stated before moving it to the test bench and pulling the chassis from the cabinet.

This amp that was sent here last week sounds the same as the 'good one' that came here earlier this week for comparison.

I will get a chance to hear these with a 412 cabinet and guitar player ripping on both of them, so hopefully I'll hear what's going on that I have yet to hear in the shop.

[nevetslab]

[QUOTE=Pedro Vecino;n987465]The 6505 and the 5150 heads are identical. The schematic shown is for a 6505 combo (a different circuit). Itīs not valid as a reference. /QUOTE]

That was the only schematic I have for the 6505, and yes, I do know it's not the same (only pair of 6L6GC's and no doubt a different power supply & output Xfmr).

So, I CAN use the 5150 schematic for this model 6505 Head that I have (looks just like the one on the front page of the User manual). Thanks.

I found the schematic for this amp, I believe. Attached below.

Peavey_5150_(EVH_120,_2-92)_Schematics.pdf

[g1]

Attached is 6505 120 Head preamp schematic, with actual 6505 designation

[nevetslab]

Attached is 6505 120 Head preamp schematic, with actual 6505 designation

Interesting that the Output Stage and power supply stage primary sch missing, along with the PCB layouts. But yes, the rest looks (at a glance) like the 5150-EVH_120) circuit.

Thanks g1!